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40130017-TDC 02-24226
ENERGY SAVING IN INDUSTRIAL DISTRIBUTION
TRANSFORMERS
May 2002
Authors:
W.T.J. Hulshorst
J.F. Groeman
KEMA
Copyright © KEMA Nederland B.V. Arnhem, the Netherlands. All rights reserved.
This document contains proprietary information that shall not be transmitted to any third party without written consent
by or on behalf of KEMA Nederland B.V. The same applies to file copying, wholly or partially.
ECI and KEMA Nederland B.V. and/or its associated companies disclaim liability for any direct, indirect, consequential or incidental damages that may result from the use of the information or data, or form the inability to use the information or data.
KEMA report reference 40130017-TDC 02-24226A
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TABLE OF CONTENTS
MANAGEMENT SUMMARY ......................................................................................................4
1.
1.1
1.2
1.3
INTRODUCTION .................................................................................................................5
Background .......................................................................................................................5
Project objective and scope ............................................................................................6
Methodology ......................................................................................................................6
2.
2.1
2.2
2.3
2.4
2.5
2.6
2.7
INDUSTRIAL ELECTRICITY SUPPLY IN EUROPE..........................................................7
Energy consumption by industry sector ........................................................................7
Transformer population in industry ................................................................................8
Large office buildings .................................................................................................... 10
Data hotels ...................................................................................................................... 10
Failure statistics of transformers in the field .............................................................. 11
Costs of electricity for industry in Europe .................................................................. 11
Environmental issues .................................................................................................... 12
3.
3.1
3.2
3.3
LOSSES IN TRANSFORMERS ....................................................................................... 14
No Load losses .............................................................................................................. 14
Load losses .................................................................................................................... 15
Extra losses due to harmonics ..................................................................................... 16
3.3.1
3.3.2
3.3.3
3.3.4
Harmonic components of the transformer load .................................................................................... 16
Extra losses due to harmonics ............................................................................................................ 17
Characterisation of non-linear transformer load: K-factor (US practice) ............................................... 18
HD538 Transformer derating due to harmonics: Factor K (Europe) ..................................................... 19
3.4 Thermal ageing of transformers ................................................................................... 21
3.5 Loss evaluation .............................................................................................................. 22
3.6 CO2 reduction and emission trading............................................................................ 24
4.
4.1
4.2
4.3
TYPICAL INDUSTRIAL TRANSFORMER DATA ........................................................... 25
HD standard data for distribution transformers up to 2500 kVA .............................. 25
Data for oil-immersed transformers between 100 and 1600 kVA ............................. 28
Data for transformers between 1000 and 4000 kVA ................................................... 29
5. CASE STUDIES ............................................................................................................... 31
5.1 Case study 1: a large company in the iron-steel sector ............................................ 31
5.1.1
5.1.2
Iron-steel: a big consumer of electricity ............................................................................................... 31
Conclusion .......................................................................................................................................... 33
5.2 Case study 2: A large company in the non-ferrous metals sector ........................... 34
5.2.1
5.2.2
Non-ferrous metal sector: replacing older transformers ....................................................................... 34
Conclusion .......................................................................................................................................... 35
5.3 Case study 3: a paper and pulp company ................................................................... 36
5.3.1
5.3.2
Paper industry: energy savings based on practice .............................................................................. 36
Conclusion .......................................................................................................................................... 37
5.4 Case study 4: a chemical industrial enterprise .......................................................... 38
5.4.1
5.4.2
Chemical industry: energy savings by placing energy efficient transformers ........................................ 38
Conclusion .......................................................................................................................................... 39
5.5 Case study 5: a large data hotel start-up .................................................................... 40
5.5.1
5.5.2
5.5.3
5.5.4
5.6
5.7
5.8
5.9
Data hotels: a quickly growing sector .................................................................................................. 40
Evaluation of more efficient transformers with the same rating ............................................................ 41
Evaluation of smaller transformers ...................................................................................................... 42
Conclusion .......................................................................................................................................... 43
Case study 6: An office building .................................................................................. 43
Case study 7: Reliability and availability..................................................................... 44
CO2 emission trading .................................................................................................... 46
Sensitivity of the input parameters .............................................................................. 46
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5.10 Total energy saving potential by efficient transformers in the industrial sector .... 50
6. CONCLUSIONS AND RECOMMENDATIONS ............................................................... 52
6.1 Conclusions ................................................................................................................... 52
6.1.1
6.1.2
6.1.3
6.1.4
Transformer population ....................................................................................................................... 52
Transformer purchasing policies ......................................................................................................... 53
Loss evaluation, including the effects of harmonic pollution ................................................................. 53
Energy saving potential ....................................................................................................................... 53
6.2 Recommendations ......................................................................................................... 54
6.2.1
6.2.2
6.2.3
6.2.4
Purchasing policies and promotion...................................................................................................... 54
Standardisation: HD428 and 538 ........................................................................................................ 54
Savings potential of special transformers and high-voltage motors...................................................... 55
Optimised system voltage in industrial networks ................................................................................. 55
REFERENCES ........................................................................................................................ 57
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MANAGEMENT SUMMARY
Industrial companies account for approximately 1000 TWh/a or half the total electricity consumption in Europe. The total European population of industrial distribution transformers is
estimated to be 100.000-150.000 units, totalling to 100-150 GVA installed, total losses being
almost 10 TWh/a.
A study has been performed to explore the potential for energy savings and CO 2 emission reduction in industries and offices by using energy-efficient distribution transformers. Based on
interviews with representatives from several large Dutch industrial companies, the population
was roughly characterised and case studies have been carried out.
Comparing distribution transformers in industry to those in (public) utilities, some salient differences are present:
 industrial transformers sizes are typically 1000-4000 kVA, contrary to the public transformers which are in the range 50 – 1000 kVA
 the average load of an industrial transformer is relatively high (30 – 100% of the rated
loading)
 the newest transformers in industry are often dry-type instead of oil-immersed. Losses in
these dry-type transformers are relatively high
 high levels of harmonic pollution of the load current frequently occur (this causes extra
losses and a higher risk of extra ageing)
 the transformer population is relatively young (up to 30 years).
Despite several favourable exceptions, industrial purchasing policies are relatively unfavourable for application of energy-efficient transformers, the purchase price being a dominant factor
over loss evaluation.
The case studies carried out show that there is a considerable potential for energy saving in
industrial distribution transformers.. When ordering a new transformer, industries should pay
attention to the loss evaluation, since they can save a lot of money, energy and CO 2 emissions during the lifetime: the extra investment costs of energy-efficient transformers can be
earned back. This savings potential is fully economically feasible.
On the other hand, neglecting the loss evaluation criteria will almost certainly lead to a wrong
investment (the cost of transformer losses will more than offset the lower purchase price of an
inefficient transformer).
If, as is often the case in industries and office buildings, the transformer load current contains
harmonic distortion, e.g. by computers or power electronic drives, transformer losses increase
as does the savings potential of energy-efficient transformers.
Two activities are proposed to improve the use of energy-efficient distribution transformers in
industry:
 promoting the importance to use loss evaluation, i.e. to use the (simple) loss evaluation
formula when specifying and evaluating transformers
 adapting the international distribution transformer standards to include the transformer
population in industry and to reduce the allowed loss levels.
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1.
INTRODUCTION
1.1
Background
40130017-TDC 02-24226
A study carried out in 1999 by the European Copper Institute has revealed that the scope for
energy savings and CO2 reduction through the use of energy-efficient distribution transformers in the EU is substantial [1]. The savings potential is estimated at approximately 22
TWh/year, worth EUR 1,2 bn at 1999 prices, mainly for oil-filled distribution transformers in
“public” electricity networks. The savings potential can be achieved by application of energyefficient transformers, the extra investment cost of which is earned back by the energy savings.
In the European project mentioned, the focus was not directed to large industries and large
office buildings, which obtain their electricity from the public medium and high voltage networks. However, much electricity used by those industries is consumed at low-voltage level –
the conversion to low-voltage is performed by privately owned distribution transformers.
Some differences between these privately owned distribution transformers and their public
counterparts are:
 The load pattern, often constant load
 The insulation medium, in many cases transformers are of the dry type for fire safety
 Harmonic components in the loading current
Especially related to the latter, these transformers are close to the end-use, and could suffer
from significant harmonic loads in IT-intensive facilities. Harmonic loads cause extra heating
in conductors, but especially in transformers. This heating effect causes circuit breakers to
trip, neutral and phase conductors to heat up to critical flash over temperatures, and premature failure of motors and transformers. This is costly in terms of downtime, loss of production,
repair and possible replacement.
In many cases, in the private sector, little attention is paid to energy losses in e.g. transformers.
Energy-efficient transformers may be more robust against harmonics, and provide more flexibility for future load-growth over the 30 years of transformer lifetime operation.
Medium and large industrial electricity user account for over half the Dutch electricity use. In
order to estimate the savings potential, it has been proposed to investigate the potential for
applying energy-efficient transformers for following industrial sectors:
 Metal
 Non-metallic minerals
 Chemical & petro-chemical
 Paper
 Data hotels
 Large offices (above 10 000 m 2).
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1.2
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Project objective and scope
The project objective was to carry out six technical/economic case studies to estimate the energy saving potential for different industrial sectors by economic application of energy-efficient
distribution transformers (copper-wound, dry type or oil-cooled). Description and quantification, where possible, of the soft benefits resulting from efficient transformers (increased reliability, possibility for future load growth, robustness against harmonics) was another objective
of the study.
1.3
Methodology
The study was based on interviews with several Dutch enterprises to collect data on the energy use and generation pattern, the transformers applied, energy costs and investment evaluation criteria. The aim was to collect sufficient data for at least one representative transformer type for each industrial sector.
From these data, KEMA has estimated loss evaluation values and assessed the benefits of
changing from a standard dry type distribution transformer (based on CENELEC HD538) to
an energy-efficient transformer. A dry transformer was designated energy-efficient at a loss
level 20% below HD538 levels, an oil-cooled transformer at HD428 – CC’ loss level. For users
which already use oil-cooled transformers, a DD’ level with further reduced losses have been
evaluated. Pauwels Trafo Belgium has contributed typical transformer data for the transformers mentioned, based on HD538 required and reduced loss values. For HD428 range transformers, data from the previously mentioned study [1] have been used.
The benefits have been expressed in terms of net present value, internal rate of return, energy savings and CO2 emission reduction. Based on extrapolation, the European potential for
energy savings and CO2 reduction has been roughly estimated. For CO 2 emissions, each
kWh saving was associated with 0,4 kg CO2 reduction, which is the average European value.
Two other cases to be considered have been low emissions (0,3 kg CO 2 / kWh) and high
emissions (0,6 kg CO2 / kWh). The impact of emission trading on the transformer investment
decision has been evaluated at € 10/tonne and € 33/tonne.
Finally, a simple spreadsheet model has been developed for dissemination, allowing users to
evaluate individual transformer investment decisions by input of: load loss, no-load loss, load
pattern, transformer price, electricity tariff, and to evaluate their energy & emission savings
potential.
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2.
INDUSTRIAL ELECTRICITY SUPPLY IN EUROPE
2.1
Energy consumption by industry sector
Industry forms a sector that accounts for almost half the final electricity consumption in Europe. The figure below shows OECD electricity consumption data for 1997.
Misc
2%
Network losses
8%
Commercial/public
22%
Machinery
4%
Food/tobacco
4%
Non-metallic minerals
3%
Non-ferrous metals
Industry
3%
44%
Chemical,
petrochemical
7%
Iron/steel
5%
Paper, pulp & print
5%
Misc. Ind.
9%
Residential
28%
Figure 2.1 Final electricity consumption (and network losses) for the European OECD countries 19971
Industry sector
INDUSTRY, of which:
Iron and steel
Chemical/petrochemical
Non-ferrous metals
Non-metallic minerals
Machinery
Food/tobacco
Paper, pulp and print
Other industry
TRANSPORT
COMMERCIAL AND PUBLIC SERVICES
RESIDENTIAL
OTHER SECTORS
FINAL CONSUMPTION
Electricity consumption (TWh)
1044
131
195
88
76
99
95
127
235
70
570
719
62
2464
Source: Energy statistics of OECD countries 1996-1997, IEA, Paris, 1999
Includes following countries: Austria, Belgium, Czech Republic, Denmark, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Poland, Portugal, Spain, Sweden, Switzerland, Turkey and the UK.
NON-OECD Europe: Albania, Bosnia-Herzegovina, Bulgaria, Croatia, Cyprus, Former Yugoslav Republic of Macedonia, Gibraltar, Malta, Romania, Slovak Republic, Slovenia, Federal
Republic of Yugoslavia.
1
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Although large industries and large office buildings obtain their electricity from the public medium- and high-voltage networks, most electricity used by those industries is consumed at
low-voltage level – the conversion to low-voltage level is performed by privately owned distribution transformers. Often the transformers placed at industry or commercial offices are similar transformers as the distribution transformers in the public electricity supply system.
Distribution transformer losses in industry are estimated to account for 1-2% of total final electricity consumption in Europe. As these losses occur in privately owned networks, these losses are not shown in the statistics as network losses!
Private generation represents less than 10% of total capacity in the EU. However on-site
generation of electricity for non-utility systems is growing rapidly, frequently using gas as fuel.
Overall, it is estimated that private generation could reach 20% of total capacity in the near future. Growth is being assisted by a number of special factors, including the development of
renewable and combined heat and power technology, improved economics for gas-based
generation, the liberation of tariff controls, and deregulation of electricity supply.
2.2
Transformer population in industry
According to [1], electricity utilities are estimated to own and operate about 70% of the total
population of distribution transformers in the EU. Transformer ownership outside the utility
sector is shared between the non-utility electricity supply systems and the medium sized customers for electricity.
The population of distribution transformers installed in European electricity utility and private
sector networks is estimated to be about four million units. Statistical records are poor, however, particularly for privately owned installations.
Non-utility distribution transformers account for about 30% of the total population, but a much
higher proportion, possibly almost 50%, of the total installed capacity. This is because nonutility transformers have a higher rating than the transformers at the utility (see figure 2.2).
Some differences between these privately owned distribution transformers and their public
counterparts are2:
 larger transformers: as the load relatively concentrated on a small area, the transformers
are often larger in size than distribution transformers in residential areas, even urban areas: the latter normally range from 50 to 1000 kVA, industrial transformers often range
from 1000 to 4000 kVA, see figure 2.2.
These differences are deducted from KEMA’s experience and information from the interviews.
2
40130017-TDC 02-24226
70%
60%
50%
40%
30%
20%
10%
0%
00
40
50
31
00
25
00
16
00
10
0
63
0
40
0
25
16
10
0
Utility
Industry
0
Relative population
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Size
Note: transformers with intermediate sizes are attributed to the next higher size
Figure 2.2 Relative transformer population in the Netherlands (estimate KEMA)







the low-voltage system: the low-voltage side of transformers up to 1600 kVA is usually at
420 V (sometimes 690 V). For transformers above 1600 kVA the low-voltage side is at
420 V or 690 V. Some industries use 3 or 6 kV, but they find it hard or expensive to get
new components at this voltage, and new installations will be built for a voltage of 10 kV
or 690 V
the average load. As the load can be predicted better in an industrial process than in a
public supply system, the transformer rating often is well tailored to the peak load. The interviewed industries have an average transformer load between 30 and 65% of the installed ratings, peak loads up to 100% for several hours sometimes occurring. Compared
to the average loading of a transformer in the public network, typically 10-30%, the loading of ‘industrial’ transformers is relatively high
the large loads, which are often equipped with their own transformer, e.g. drives
the load pattern. The electricity consumed by industry keeps pace with economic activities. Almost each industry is working 24 hours a day and 7 days a week. This means the
load pattern is often constant.
the insulating medium: contrary to transformers in public networks, which usually apply
oil-filled transformers, industrial transformers are often of the dry type for fire safety or due
to bad experiences with oil-filled transformers3. In some cases, the higher civil engineering costs for civil works regarding fire safety of oil-filled transformers are said to offset the
higher price of the dry-type transformer
harmonics: industrial transformers are close to the end-use, and could suffer from significant harmonic loads in IT-intensive facilities. See section 3.3
industrial transformers with a range up to 1600 kVA are the same as those used by the
utilities. Since 1970, there is an increasing use of variable speed drives (AC or DC) in the
industry. Therefore the industries have some special transformers (3 windings) or transformers with different impedance or phase sequences. These special transformers are
outside the scope of this report.
Transformers in industry seem to be relatively new compared to those at utilities. In the indusThe oil in some older transformers contained very toxic components (e.g. PCBs) and had to
be replaced)
3
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try and some large older office buildings only few transformers are older than 30 years. Since
1980 some industrial companies started to use dry-type transformers instead of oil transformers.
While utilities generally rely on their own engineering staff to set standards for performance,
including energy efficiency, private sector electricity supply systems are often designed with
outside assistance. The pattern in Europe varies widely. In some countries, this work is undertaken mainly by firms of management contractors, or the design staff of a major electrical
contractor. Elsewhere, independent professional consulting engineers are responsible for design and project management.
In many cases, little or no attention is paid to energy losses in transformers.
This may be due to the fact that the electrical infrastructure is not a core business of the owner and the electrical infrastructure is often realised on a turnkey, lumped-sum basis. This may
make the specification and costs of transformers invisible to the future owner. Because the
industry itself is not the customer ordering the transformer, the properties of the transformer
are often unknown.
Industries are reported to show less interest in longer-term problems, and demand more rapid
paybacks, than the public sector network. A great difference between the industry and utilities
is the payback period. The required payback period in industry may be between 1 and 5
years.
2.3
Large office buildings
The load pattern for an office building is low (< 20%) in the weekend, and is higher for the
working days (between 20% for the night hours up to 80% at the office times). The transformers used at an office building are between 250 kVA and 1000 kVA (almost the same range as
the utilities).
Until the 60s, in a typical office few electrical devices were present, typically an electric typewriter, a calculator and of course incandescent lights. These devices are known to be linear
loads: the current waveform is the same as the voltage waveform. Later, the fluorescent
lamps were introduced. Since the mid-80s, there has been a proliferation of electronic equipment in the offices. Today, in a typical office there is a minimum of personal computers, telephone systems, copier machines, fax machines and laser printers. All of these new loads are
non-linear.
2.4
Data hotels
Power supply designs for data processing rooms tend to be much more oversized compared
to designs for general office areas or typical building wire systems where harmonic currents
from electronic loads (like personal computers and terminals) have caused problems or public
networks. Data hotels have a very large specific load (W/m2); they also have a high share of
non-linear loads. Dimensioning is done with large margins, to be reliable and to anticipate
(high) growth expectations. The consequence is that the actual loading is low compared to
the nameplate rating. A survey [2] of computer power systems showed that the majority is op-
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40130017-TDC 02-24226
erated at less than half of their rated capacities. The transformers used for the data hotels are
between 250 kVA and 1600 kVA.
2.5
Failure statistics of transformers in the field
Only limited information is available about the transformer failure pattern in Europe. Several
studies have been undertaken, but the results are rather inconclusive. A 1983 survey [1]
based on 47,000 transformer-years of service in 13 European countries estimated the meanlifetime-between-failures (MLBF) of installed transformers to be 50 years, and showed design
defects, manufacturing problems and material defects to be the main causes of failure. The
same project identified windings and terminals to be the components most likely to cause failure in service. Failures in coils using jointed conductors, built in earlier years, have caused
some problems.
Next to MLBF values, some information about the mean-time-between-failures (MTBF) was
found. The table below shows some data that were collected during the present study.
Table 2.2
Reliability of distribution transformers in Europe
Situation, source
Number
Total units in Annual transformer
of failed operation
faults
units
Distribution
transformers,
0,2% per year, i.e.
source [1]
one in 500 transformers
Average figure in one Dutch
0,25%
industrial company interviewed
Distribution transformers in 87
117297
0,0742%, i.e.
Dutch networks, year 2000
1 in 1350 trans[12]
formers
Remark
Oil transformers
Dry-type
transformers, high load,
harmonic distortion
Oil transformers
From the table it can be seen, that distribution transformers are very reliable components.
The industrial company cited suggests a somewhat lower reliability (although, strictly spoken,
the population is too small to draw statistically significant conclusions). This may be explained
by differences of transformer types (dry vs. oil), the higher load, harmonic distortion or a combination of these factors. It should be noted that these figures are not suitable to draw conclusions on which type of transformer (dry or oil) is better.
2.6
Costs of electricity for industry in Europe
The rates for electricity depends on the industry sector and the country. In general, a company with a higher electricity consumption benefits a lower electricity rate. Table 2.3 shows the
average electricity price for captive customers (i.e. smaller customers that may not yet choose
their electricity supplier) in the Netherlands.
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Table 2.3 Average electricity prices in the Netherlands (exc. regulatory energy tax and vat)
Customer category
Small consumers
Of which households
Large consumers (offices, datahotels)
Of which industry
Source: EnergieNed
Electricity price (Euro/kWh) in 2000
0,095
0,104
0,082
0,064
The values given above are just indicative of the average price. There are differences between the electricity prices between the industry sectors.
Figure 2.3 gives a comparison of the average electricity prices for some European countries.
Comparison of european electricity prices for industry
Euro/MWh
100
80
60
40
20
Ita
ly
G
re
ec
Fi e
nl
a
Sw nd
ed
e
Ire n
la
nd
Un
it e
Sp
d
Ki ain
n
Lu gd
xe om
m
bo
u
Po rg
rtu
g
Th
Fr al
e
Ne an
th ce
er
la
nd
Au s
s
G tria
er
m
a
Be ny
lg
i
De um
nm
ar
k
0
Figure 2.3 Electricity prices in Europe (source EnergieNed [6])
2.7
Environmental issues
Carbon dioxide (CO2) is believed to significantly reinforce to the greenhouse effect, which
may lead to a change in the global climate. The annual emission of CO 2 in the Netherlands is
about 181 million tonnes, almost half of which is due to energy consumption. This includes
combustion of gas by energy consumers and combustion of fuels in electric power stations.
Figure 2.4 gives the emission of CO2 per sector.
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40130017-TDC 02-24226
Emission of carbon dioxide in the Netherlands (181.009
thousand tonnes per year)
12%
15%
road traffic
3%
14%
6%
other transport
oil refineries
industry
energy sector
26%
24%
households
other
Figure 2.4 CO2 emissions in the Netherlands
Source EnergieNed
In the Netherlands the government and industry have adopted an Environmental Action Plan
in 1991 with the objective of reducing by the year 2000 CO 2 emissions. On one hand the Environmental Action Plan stimulates energy conservation in homes, commerce and industry;
while on the other hand the measures focus on more efficient energy production techniques
(cogeneration) and the use of sustainable sources of energy.
In Europe, each kWh end-use of electricity is associated with 0,4 kg CO2 emission, on the average. The emission rates vary from one country to another, in fact even from one power station to another, depending on the plant efficiency, and the fuel mix. The country average
emission rates range from 0,3 to 0,6 kg per kWh in Europe.
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3.
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LOSSES IN TRANSFORMERS
A power transformer normally consists of a pair of windings, primary (HV) and secondary
(LV), linked by a magnetic circuit or core. When an alternating voltage is applied to one of
these windings, generally the HV winding, a small current will flow which sets up an alternating magnetic flux in the core. This alternating flux, linked to both windings, induces a voltage
in each of them. The current which is flowing is the situation that both windings are not loaded, is the magnetising current.
This chapter describes the losses in transformers as provided by the J&P transformer book
[11].
3.1
No Load losses
An unloaded transformer experiences losses. The magnetising current is required to take the
core through the alternating cycles of flux at a rate determined by system frequency (50 Hz).
In doing so energy is dissipated. This loss is known as the core loss, no load loss or iron loss.
The core loss is present whenever the transformer is energised. Thus they represent a constant and therefore significant energy drain on any electrical system. In addition, the alternating fluxes generate also alternating forces in the iron core and hence noise.
The core loss is made up of two components: the first one, the hysteresis loss, is proportional
to the frequency and dependent on the area of the hysteresis loop in the B-H diagram, and
therefore characteristic of the material and a function of the peak flux density. The second
component is the eddy current loss that is dependent on the square of the frequency, the
square of the thickness of the material and the resistivity.
Minimising hysteresis losses therefore implies application of a material having a minimum area of hysteresis loops, while minimising eddy current loss is achieved by building up the core
from a laminate of thin strips and high resistivity.
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3.2
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Load losses
The load loss of a transformer is that part of the losses generated by the load current and
which varies with the square of the load current. This falls into three categories:
 Resistive loss within the winding conductors and leads
 Eddy current loss in the winding conductors
 Eddy current loss in the tanks and structural steelwork.
The latter two categories are also referred to as “extra losses”.
Resistive loss follows Ohm’s law and can be decreased by reducing the number of winding
turns, by increasing the cross-sectional area of the turn conductor, or by a combination of
both. However, reducing the number of turns requires an increase of the flux i.e. an increase
in the core cross-section, which increases the iron weight and iron loss. So a trade-off has to
between made between the load loss and the no-load loss.
Eddy currents arise from the fact that not all the flux produced by one winding links to the other winding. This flux leakage also leads to the short-circuit reactance or impedance of a transformer. In the past, this reactance was simply considered an imperfection arising from the unavoidable existence of leakage flux. Nowadays, the transformer impedance is a valuable tool
for the system designer to determine system fault levels to meet economic limitations of the
connected plant.
The path of eddy currents in winding conductors is complex. The magnitude of this leakage
flux depends on the geometry and construction of the transformer. The effect of leakage flux
within the transformer windings results in the presence of radial and axial flux changes at any
given point in space and any moment in time. These induce voltages which cause currents to
flow perpendicular to the fluxes which lead to losses. The magnitude of these currents can be
reduced by increasing the resistance of the path through which they flow, and this can be effected by reducing the total cross-sectional area of the winding conductor, or by subdividing
this conductor into a large number of strands insulated from each other (in the same way as
laminating the core steel reduces eddy-current losses in the core). However, the former alternative increases the overall winding resistance and thereby the resistive losses. Conversely, if
the overall conductor cross-section is increased with the object of reducing resistive losses,
one of the results is an increase of the eddy current losses. This can only be offset by a reduction in strand cross-section and an increase in the total number of strands. It is costly to
wind a large number of conductors in parallel and so a manufacturer will wish to limit the total
number of strands in parallel. Also, the extra insulation resulting from the increased number of
strands results into a poorer winding space factor. It will be evident that in a transformer having a low reactance, winding eddy currents are less of a problem than one with high reactance.
On very high currents (>1000 A) fluxes generated at the main leads can give rise of eddy current losses in the tank adjacent to these. Due to the leakage flux there are also eddy-current
losses in tanks and internal structural steelwork.
– Page 16 of 57 –
3.3
Extra losses due to harmonics
3.3.1
Harmonic components of the transformer load
40130017-TDC 02-24226
In the last few years, there has been a growing concern about harmonic distortion and the effects of harmonics in the power systems. The distribution grid is designed to carry the fundamental 50 Hz frequency. Almost all industries have non-linear loads. Non-linear loads generate high levels of harmonic currents. Typical non-linear loads include:
 computers
 UPS systems
 variable speed drives
 inverters.
The non-linear load at the industries is a major difference in circumstances between transformers placed at the industries and utilities.
The harmonic currents cause higher losses in the transformer and therefore a higher temperature, which will affect the lifetime of the transformers. The extra losses depend on the harmonic spectrum of the load current.
The triple harmonics (3rd, 9th, 15th, etc.) are the major cause of heat because the phase currents add in the neutral conductor. The magnitude of the harmonic current produced by the
triples can approach twice the phase current. This causes the neutral conductor to overheat
because neutral conductors were historically designed for the same current as the phase
conductors.
Transformers are configured with a delta-wye connection to reduce the effects of harmonics.
The triple harmonics are trapped and circulate in the delta primary of the transformer. Thus
the harmonic content reflected back to the source (the medium-voltage network) is reduced.
The circulating harmonics in the delta connected winding of the transformer create heat because of their higher frequencies.
Next to problems with the triple harmonics a transformer feeding a converter or inverter can
also have problems with other harmonics. The typical harmonics (h) in a semiconductor
bridge can be calculated by using the formula:
h=pxk 1
Where p is the pulse number of the bridge (6, 12) and k is an integer equal to 1, 2 …, n.
For a 6 pulse bridges the typical harmonics are: 5, 7, 11, 13, 17, 19, 23, 25 etc.
For a 12 pulse bridges the typical harmonics are: 11, 13, 23, 25 etc.
Due to the harmonic currents in the transformer load at industries and the higher loading profile it is reasonable to expect that these transformers will have a lower lifetime. Harmonics are
responsible for a higher load loss in the transformer and therefore a higher hot spot temperature in the transformer, which reduces the lifetime of a transformer.
According to IEC 61378-1: “it is necessary that the harmonics spectrum of current at rated
load be specified by the purchaser prior to the time of placing the order. In the absence of
specific information, a harmonic spectrum can be derived according to 3.6.2 of IEC 60146-1-2
[10]”.
– Page 17 of 57 –
40130017-TDC 02-24226
IEC 60146-1-2 says: “at an early stage of the design the following formulae may be used
when only the convertor size is known by its transformer rating”. The harmonic current can be
calculated as:
I hl 
I 1L
1, 2
 5
 h 
 h
Where:
IhL is the harmonic current
h is the harmonic number
I1L is the fundamental current
The fundamental current is given by:
I 1l 
S
U 3
Where:
S is the power of the transformer
U is the line voltage
Notes:
1
The formula for IhL is approximate, especially for large values of the angle of delay of
control in rectifier operation for converters.
2
Depending on the DC load circuit inductance, the direct current ripple may increase
the 5th harmonic current by 0,3 p.u. or more
3
Other uncharacteristic harmonics may remain due to supply voltage unbalance which
prevents the expected cancellation.
For this study it’s presumed that the harmonics in the current can be calculated according the
given formula. For the 5th harmonic it’s presumed that this current is increased by 0,1 p.u.
3.3.2
Extra losses due to harmonics
The extra losses arise as follows.
Higher frequency components in the load current (harmonics) cause extra losses because
harmonics do not fully penetrate the conductor. They travel on the outer edge of the conductor. This is called skin effect. When skin effect occurs, the effective cross sectional area of the
conductor decreases; increasing the resistance and the I2R losses, which in turn heats up the
conductors and anything connected to them.
Harmonic currents increase also the eddy current losses in transformers as described in [3].
The eddy current losses are of most concern when harmonics are present, because they increase approximately with the square of the frequency. The no-load losses are transformer
core losses, which are affected by harmonics only in relation to voltage distortion, not current
distortion. Consequently, the increase in no-load losses due to harmonics is usually negligible. Harmonic currents however, very significantly affect load losses.
– Page 18 of 57 –
40130017-TDC 02-24226
As described earlier, load losses consist primarily of resistive (or I 2R or ‘copper’) losses and
extra (eddy current) losses. Due to harmonics, not only the eddy current losses but also the
resistive losses increase. By definition, however, the loss increase due to the presence of
harmonics is usually also designated as “extra losses”, see figure 3.1.
Extra loss
Load loss
Resisitive loss
Extra loss due to
harmonics
Conventional load
loss excl harmonics
No load loss
Unloaded Rated load
Actual load
Actual load
(excl harmonics) (incl harmonics)
Figure 3.1 Extra losses due to harmonics
There are several approaches to account for the increased losses caused by harmonics in selecting a transformer. The first one, devised by transformer manufacturers in conjunction with
Underwriters Laboratories in the United States, is to calculate a factor for the increase in eddy
current loss; this is known as ‘K-Factor’. The second method is to estimate by how much a
standard dry-transformer should be de-rated so that the total loss on harmonic load does not
exceed the fundamental design loss; this is known as ‘factor K’. The ‘factor K’ method (used
in Europe) is described in the Harmonisation document HD 538.3.S1. A third way to calculate
the influence of harmonics is described in the IEC 61378-1 “Transformers for industrial applications”.
3.3.3
Characterisation of non-linear transformer load: K-factor (US practice)
In US practice, where dry-type transformers are often used, the K-factor is the ratio of eddy
current losses when driving non-linear and linear loads:
h
K   I h2 h 2
1
The higher the K-factor the greater the harmonics present, hence the more harmonic current
the transformer must be designed to survive.
K=1
K=4
K = 13
K = 20
Resistance heating, motors, distribution transformers
Welders, induction heaters, Fluorescent lighting
Telecommunications equipment
Mainframe computers, variable speed drives, desktop computers
– Page 19 of 57 –
3.3.4
40130017-TDC 02-24226
HD538 Transformer derating due to harmonics: Factor K (Europe)
In Europe, the transformer de-rating factor is calculated according the formula in HD
538.3.S1. The factor K is given by:
2

e  I h  n  N  q  I n
K  1 
   n 
 1  e  I  n  2   I 1




2




0,5
Where
e=
the eddy current loss as the fundamental frequency divided by the loss due to a DC
current equal to the RMS value of the sinusoidal current, both at reference temperature.
n=
the harmonic order
I=
the RMS value of the sinusoidal current including all harmonics given by:
 n N
2
I    I n  
 n 1

0,5
n  N  I
 I 1    n
 n 1  I 1



2



0,5
In =
I1 =
q=
the magnitude of the nth harmonic
the magnitude of the fundamental current
exponential constant that is dependent on the type of winding and frequency. Typical
values are 1,7 for transformers with round rectangular cross section conductors in
both windings and 1,5 for those with foil low voltage windings.
3.3.5
Method according to IEC 61378-1
IEC 61378-1 deals with the specification, design and testing of power transformers and reactors, which are intended for integration within semiconductor convertor plants; it is not designed for industrial or public distribution of AC power in general.
The scope of this standard is limited to applications of power converters, of any power rating,
for local distribution, at moderate rated convertor voltage, generally for industrial applications
and typically with a highest voltage for equipment not exceeding 36 kV.
The convertor transformers covered by this standard may be of the oil immersed or dry-type
design. The oil-immersed transformers are required to comply with IEC 60076, and with IEC
60726 for dry-type transformers.
As described, the load losses in transformers are subdivided into loss as measured with DC
(I2R loss) and, in addition, eddy current loss in windings and connections, and stray losses in
conductive structural parts of the transformer. For this study its presumed that for the dry
transformer there are only extra losses due to eddy losses in the windings. For oil transformers it is presumed there are extra losses due to eddy losses in the windings, connections and
stray losses in construction parts (e.g. tank wall).
– Page 20 of 57 –
40130017-TDC 02-24226
In normal service, the convertor transformer load current is non-sinusoidal hence, when transformed into a Fourier series; it shows a considerable amount of harmonics. This nonsinusoidal current raises the eddy loss and stray flux loss, and significantly increases the total
loss calculated or measured with purely sinusoidal current.
A correction to the higher loss value at rated; non-sinusoidal convertor load is required for the
thermal rating of the transformer, and for the correct calculation of the loss and efficiency of
the transformer.
The total RMS value of the current IL with harmonic content can be calculated according to:
n
I L2   I h2
1
Where IL is the RMS value of the non-sinusoidal current of the transformer and h is the harmonic order number and therefore I h is the RMS value of the harmonic current, having order
number h.
The eddy current losses PWE in the windings are equal to:
I
  PW Eh  PW E1    h
1
1  I1
n
PW E
n
2

  h 2

With PWE is the winding eddy loss at current IL. I1 represents the RMS value of the fundamental current, at rated load.
For oil transformers where the low-voltage windings have high rated currents, in the range of
a few kA, the internal high current connections require a separate analysis of the additional
eddy current loss. The calculation of these losses (P CE) is almost identical to the eddy current
losses in the winding, except that the enhancement factor for the harmonic number now is not
equal to 2 but 0,8.
n
PCE   PCEh
1
I
 PCE1    h
1  I1
n
2

  h 0,8

The stray losses in construction parts can be calculated the same way:
n
PSE   PSEh
1
I
 PSE1    h
1  I1
n
2

  h 0,8

The total load loss of a transformer without harmonics (fundamental) equals:
PT1 = PDC1 + PEXTRA1 = PDC1 + PWE1 + PCE1+ PSE1
If the same transformer is used in a grid with harmonics the total load loss equals:
I
PT  PDC1   L
 I1
2
 n I

  PW E1     h
 1  I1


2
 n I
 2 
 h  PCE1  PSE1      h

 1  I1



2
 0,8 
 h



The above formula can be used for oil- and dry type transformers. As mentioned before for
the dry type transformer PCE1 and PSE1 are both assumed to be zero.
– Page 21 of 57 –
40130017-TDC 02-24226
During testing of the transformer at the manufacturer, PT1 and PEXTRA1 are measured at 50 Hz.
Establishing of the PWE1, PCE1 and PSE1 can be done by the manufacturer, since they exactly
know the design and construction of the transformer. It is also possible by measuring transformer losses both at DC, at the standard sinusoidal 50 Hz current and at a frequency other
than 50 Hz. Combining these three measurements, it is possible to establish the eddy current
losses in the windings and in the structural parts.
3.4
Thermal ageing of transformers
Since harmonics introduce extra losses and therefore extra heat dissipation in transformers,
harmonics may have a great influence on the lifetime of the transformer. The effect is usually
expressed in terms of loss of lifetime or lifetime consumption. Based on IEC 60354 (oilimmersed transformers) and IEC 60905 (dry type transformers) it is possible to estimate the
loss of lifetime due to harmonics. The calculation models provided in these standards are
based on the hottest part in the winding. This hot-spot temperature is used for evaluation of a
relative value for the rate of thermal ageing. The parameters and formulas as given in the
both standards are used in this study to establish the hot spot in the transformers and the lifetime consumption when the transformers are loaded with harmonic current.
The actual lifetime of a transformer depends to a high degree on extraordinary events, such
as overvoltages, short-circuits in the system and emergency overloading. In this study we only take into account the hot-spot temperature in the winding, caused by harmonics in the current.
The consequence of a higher hot-spot temperature in the winding, caused by harmonics will
be a risk of premature failure. This risk may be of an immediate short-term character or come
from the cumulative deterioration of the transformer over many years.
Oil –immersed transformers
For oil-immersed transformers designed in accordance with IEC 60076, the relative rate of
thermal ageing is taken to be equal to unity for a hot-spot temperature of 98 oC, which corresponds to operation at an ambient temperature of 20 oC and a hot-spot temperature rise of 78
K. The relative ageing rate as a function of the hot-spot temperature θh is defined as:
V = (ageing rate at θh / ageing rate at 98 oC) =
2 ( h 98) / 6
So for oil-immersed transformers the relative ageing doubles every increment of approximately 6 K. If the load and ambient temperature are constant during a period, the relative loss of
life (L) is equal to L = V x t, t being the period under consideration. A value equal above 1
means that the loss of life greater is than “normal” expectation.
In this report the maximum allowable hot spot temperature for oil immersed transformers is
taken as 140 oC.
Dry-type transformers
For dry-type transformers designed in accordance with IEC 60726 the daily use of life due to
thermal effects is calculated at an ambient temperature of 20 oC. The parameter θc (Hot spot
temperature in the winding) is used to calculate normal lifetime consumption. For dry-type
transformers, the relative ageing doubles every increment of approximately 10 K.
– Page 22 of 57 –
40130017-TDC 02-24226
In this report the maximum allowable hot spot temperature for dry type transformers is taken
as 190 oC.
3.5
Loss evaluation
The total owning cost of a transformer consists of several components, including the purchase price, the value of energy losses, maintenance and repair costs over the lifetime, and
decommissioning cost. The purchase price and the energy losses are the two key factors for
comparison of the different transformers.
In the industry it is very common that transformers are part of a turn key project. The contractor is often interested in a transformer with a low purchase price. However the user/owner of
the transformer aims at buying the cheapest transformer, i.e. with the lowest total owning
cost, which complies with the requirements for a given application. Losses, installation,
maintenance, repair and decommissioning costs are seldom taken into account by the contractor when choosing between transformers.
When comparing two transformers with different purchase prices and/or different losses, one
must take into account that the purchase price is paid at the moment of purchase, while the
cost of losses come into effect during the lifetime of the transformer. Usually the costs are
converted to the moment of purchase by assigning capital values. When transformers are
compared with respect to energy losses, the process is called loss evaluation.
In the basic loss evaluation process, three transformer figures are needed:
 purchase price
 load loss
 no-load loss.
For the specified load loss of a transformer, the purchaser can assign a cost figure per kW of
loss representing the capitalised value (net present value) of the load losses over the lifetime
of the transformer or a shorter time scale e.g. 5 or 10 years. This cost figure is based on the
expected transformer load over time and the average cost per kWh.
Similarly, for the no-load loss of a transformer, the purchaser can assign a cost figure per kW
of no-load loss representing the capitalised value of the no-load losses. This cost figure is also based on the average cost per kWh and the interest rate chosen by the purchaser. As
nearly all transformers are connected to the grid for 100% of the time, and the no-load losses
are independent on the load, the load curve is not relevant. The average cost per kWh will
tend to be lower than for the load losses, as the latter will tend to coincide with peak loads, at
which time energy is very expensive.
If high capitalisation values for losses are chosen, transformers with low losses but with higher investment cost tend to be favoured. If however capitalisation values are set to zero, a purchaser effectively eliminates energy loss evaluation from the purchase decision, which favours the cheapest transformer.
Thus, the capitalised cost (CC) of a transformer can be expressed as the sum of the purchase
price (Ct), the cost of no-load losses and the cost of the load losses, or as a formula:
– Page 23 of 57 –
40130017-TDC 02-24226
CC = Ct + A x Po + B x Pk
where A represents the assigned cost of no-load losses per watt, Po the value of the no-load
losses per watt, B the assigned cost of load losses per watt and Pk the value of the load losses per watt. This formula can also be found in HD428 and HD538.
Po and Pk are transformer properties. A and B are properties that depend on the expected
loading of the transformer and energy prices.
The choice of the factors A and B is difficult, as often the future loading of the transformer is
not known. If the load grows over time, the growth rate must be known. Also, the applicable
kWh price over the lifetime must be forecast. A tricky task! Finally, the interest rate and the
economic lifetime may be difficult to choose. In practice, therefore, there is a lot of guesstimation in determining A and B factors, A ending up between less than 1 and 6 EUR/W and B
ending up between 0,2 and 5 EUR/W.
For this report, we provide a relatively simple method for determining the A and B factor for
small transformers. The total cost over the lifetime of a transformer depends on a lot of figures. We only look at the costs of purchaser price and the price of the losses during the lifetime. This method is not entirely correct, but gives an indication of the factor A and B for the
industry and is therefore better than disregarding the costs of loss during lifetime at all. A and
B are calculated as follows:
A
(1  i) n  1

 8760 (no-load loss capitalisation)
i  (1  i) n C kW h
and
I
(1  i ) n  1
B
 C kW h  8760   l
n
i  (1  i )
 Ir
2

 (load loss capitalisation)

where:
i
n
CkWh
8760
IL
Ir
= interest rate [%/year]
= lifetime [years]
= kWh price [EUR/kWh]
= number of hours in a year [h/year]
= loading current [A]
= rated current [A]
These formulae assume that energy prices and the loading are constant over the transformer
life.
Usually, the loss evaluation figures A and B are submitted to the transformer manufacturers in
the request for quotation. They can in turn start the complicated process of transformer design, to obtain a transformer design which performs best using the same formula. The result
of this open process should be the cheapest transformer, i.e. with the lowest total owning
cost, optimised for a given application. Drawbacks of this process are, as mentioned, its extreme complexity and the uncertainty of the purchaser with the exact load profiles of the transformers and energy prices in the future. Tariff structures are very complex.
For large transformers, above a few MVA, the cost of losses are so high, that transformers
– Page 24 of 57 –
40130017-TDC 02-24226
are custom-built, tailored to the loss evaluation figures specified in the request for quotation
for a specific project.
For distribution transformers, often bought by large batches, the process is undertaken infrequently, e.g. once every 5 years. This yields an optimum transformer design, which is then
kept for several years until energy prices or load profiles have changed dramatically. In fact
the loss levels established in HD428, HD538 and national standards reflect established practice of preferred designs with respect to loss evaluation values.
3.6
CO2 reduction and emission trading
Benefits of energy saving are not only the avoidance of energy cost, but also the avoidance of
CO2 emission and a contribution to the reduction of global warming. Usually, the CO 2 emission associated to the use of electricity is assumed to be 0,4 kg CO 2 per kWh of electricity
used. The CO2 emission depends on the average share of fossil fuels in the fuel mix of power
plants, and values between 0,3 and 0,6 kg/kWh are used for different countries in Europe.
Presently, CO2 emission is free, but emission limits are underway. To allow for economic optimisation, emission-trading schemes are under discussion, and by that time, CO2 emission
rights will have a price. The price will depend on actual market conditions. The price for CO 2
emissions will add to the cost of energy. For this study, prices of EUR 10 and EUR 33 per
tonne of CO2 will be considered4.
The extra cost of energy are equal to the CO2 emission per kWh times the price of the emission. For the variants for CO2 emission and emission cost, following variants arise for the extra cost of energy due to the emission cost:
Table 3.1 Extra cost of energy due to emission cost, expressed as EUR/MWh
CO2 emission (depending on fuel mix of power plants)
Emission cost
EUR 10/tonne
EUR 33/tonne
0,3 kg/kWh
3 EUR/MWh
9,9 EUR/MWh
0,4 kg/kWh
4 EUR/MWh
13,2 EUR/MWh
0,6 kg/kWh
6 EUR/MWh
19,8 EUR/MWh
The extra cost of energy can vary between 3 and about 20 EUR/MWh.
These prices may seem high, but could become reality in the near future. If the legislation
becomes implemented, the price ceiling will be the penalty for producing too much emission.
As described in [13] the European Parliament has proposed a penalty of about EUR 50,= per
tonne CO2 in 2005, rising to even EUR 100,= in 2008.
4
– Page 25 of 57 –
4.
40130017-TDC 02-24226
TYPICAL INDUSTRIAL TRANSFORMER DATA
Distribution transformers as used in the industry, are normally considered to be the same
transformers which provide the transformation from medium-voltage to low-voltage in public
distribution networks. In Europe this is 420 V phase to phase, but for the industry 690 V
phase to phase is also a common value.
Distribution transformers are usually made in a different factory from larger transformers.
There are many more manufacturers that build small transformers than those at the larger
end of the scale. The industry is very competitive, and as a result the main consideration in
the design of the active part is to achieve the best use of materials and to minimise costs.
4.1
HD standard data for distribution transformers up to 2500 kVA
Most of the characteristics of industrial transformers are specified in national or international
product standards for distribution transformers. Generally, the purpose of standards is to facilitate the exchange of products in both home and overseas markets, and to improve the product quality, health, safety and the environment. International standards are also of importance
in reduction trade barriers. The application of standards can be legally required, or by specific
reference in the purchase contract.
For distribution transformers purchased in the European Union, three levels of standards are
applicable:
 World-wide standards (ISO, IEC)
 European standards and regulations (EN, HD)
 National standards (e.g. NBN, BSI, NF, DIN, NEN, UNE, OTEL).
European Harmonisation Documents (HD) are initiated if there is a need for a European
standard. The draft HD is a compilation of the different national standards on the subject. The
HD is finalised by eliminating as many national differences as possible. When a harmonisation Document has been issued, conflicting national standards have to be withdrawn within a
specified period of time, or modified to be compatible with the HD. Usually, the HD is the predecessor of an European standard (EN), which must be adopted as a national standard in the
EU member countries. Thus, purchase orders which refer to national standards are compatible with European standards (EN) and/or harmonisation documents (HD).
Among the many international standards for distribution transformers, two main European
Harmonisation Documents specify energy efficiency levels:
 HD 428: Three phase oil-immersed distribution transformers 50 Hz, from 50 to 2500 kVA
with highest voltage for equipment not exceeding 36 kV.
 HD 538: Three phase dry-type distribution transformers 50 Hz, from 100 to 2500 kVA,
with highest voltage for equipment not exceeding 36 kV.
For the industrial transformers there are also other world-wide standards. These standards
are IEC 61378-1: Transformers for industrial applications, and if the transformer is loaded with
a non-linear (converter) load IEC 60146-1-2: Semiconductor convertors, general requirements
and line commutated converters.
– Page 26 of 57 –
40130017-TDC 02-24226
Figure 4.4 gives the limits for load losses for some important types of oil-filled and dry-type
distribution transformers according to HD428.1 and HD538.1 for the preferred rated power
range of the transformers. For oil-filled distribution transformers, the HD allows a choice of
energy efficiency levels, A, B and C. The no-load losses (iron losses) for the same range of
transformers are given below. For oil-filled distribution transformers, the HD offers a choice
between three efficiency levels, A’, B’ and C’. (Figure 4.1)
Figure 4.1 Distribution Transformer Loss Standards
RATED
POWER
kVA
50
100
160
250
400
630
/4%1)
630 /6%
1000
1600
2500
4000
Notes
Load Losses
OIL-FILLED (HD428)
DRY TYPE
UP TO 24kV2)
(HD538)
LIST A
LIST B
LIST C
12kV PRIMARY 3)
W
W
W
W
1100
1350
875
N/A
1750
2150
1475
2000
2350
3100
2000
2700
3250
4200
2750
3500
4600
6000
3850
4900
6500
8400
5400
7300
6750
10500
17000
26500
N/A
1.
2.
3.
8700
13000
20000
32000
N/A
5600
9500
14000
22000
N/A
7600
10000
14000
21000
N/A
No-Load Losses
OIL-FILLED (HD428)
DRY TYPE
UP TO 24kV2)
(HD538)
LIST A’ LIST B’ LIST C’ 12kV PRIMARY 3)
W
W
W
W
190
145
125
N/A
320
260
210
440
460
375
300
610
650
530
425
820
930
750
610
1150
1300
1030
860
1500
1200
1700
2600
3800
N/A
940
1400
2200
3200
N/A
800
1100
1700
2500
N/A
1370
2000
2800
4300
N/A
The short-circuit impedance of the transformers is 4% or 6%, in most cases. This technical parameter is of
importance to a utility for designing and dimensioning the low-voltage network fed by the transformer.
Transformers with the same rated power but with different short-circuit impedance have a different construction and therefore slightly different losses. For HD428 / HD538 compliant distribution transformers, the
preferred values for the short-circuit impedance are 4% for transformers up to and including 630kVA, and
6% for transformers of 630kVA and above.
For 36kV transformers, different values apply.
For 24 and 36kV transformers, different values apply.
Source: European Harmonisation Documents
HD428 therefore allows customers to choose between three levels of no-load losses and
three levels of load losses. In principle, there are a total of 9 possible combinations, ranging
from the lowest efficiency, (B-A’), to the highest, (C-C’), which may be regarded as providing
a high practical standard of energy efficiency for a distribution transformer.
HD428 defines five preferred combinations of these losses. These combinations are shown
below in Table 4.2, where the combination A-A’ is chosen as the base case (shown as a bold
line – the percentages refer to this combination).
– Page 27 of 57 –
40130017-TDC 02-24226
Table 4.2
lower losses
Load losses
B
(+20..30%)
A
(base)
C
(-15..20%)
No-load losses
A’
(base)
B’
(-15..25%)
C’
(-35%)
There is a significant difference in total no-load and load losses between A-A’ and C-C’ distribution transformers, approximately 1.5 kW for a 630 kVA unit.
HD428.1 (part 1: general requirements and requirements for transformers with highest voltage for equipment not exceeding 24 kV) as well as other HD sections also contain phrases
such as “(…) in the case of established practice in the market (…) the transformers can be
requested and, by consequence, offered, with losses differing from the tabled losses”, which
indicates some freedom to national or local deviations.
As stated before, HD428 and HD538 represent a compilation and/or compromise on the various old standards which were used in European countries. It appears to be rather unambitious in terms of the loss levels set, and by allowing capitalisation formulas to be used. The
standard HD 538 specifies only one level of losses.
Both standards seem to be tailored to public utility applications, but they could easily become
much more applicable for industry by:
 extending the rated power range to 4000 kVA transformers
 adding 690 V as a secondary voltage for the higher power range (1600-4000 kVA)
 differentiating preferred loss levels for HD538 transformers.
Distribution transformers built according to HD428 and HD538 have a limited number of preferred values for rated power (50, 100, 160, 250, 400, 630, 1000, 1600 and 2500kVA). Intermediate values are also allowed. The two key figures for energy efficiency, the load losses
and the no-load losses, are specified for each rated power.
The interviews do not provide enough data for concise statements on the population in a specific sector in the industry. In the companies interviewed, often the preferred ratings from the
HD documents are found, but also many transformers with ratings of 850, 1250, 3000 or 3150
kVA.
This suggests that the range of preferred values for rated power according the HD 428 and
HD 538 could be extended. The extension should be up to 4000 kVA rated power, and should
follow a geometric series. In order to reduce losses due to mismatch between transformer
– Page 28 of 57 –
40130017-TDC 02-24226
and load, the rating for transformers >630 kVA should become more fine (R10 geometric series instead of R5 series), all the more since the load can often be predicted more exactly,
which allows a better match between transformer and load. Table 4.3 gives the proposed (extended) range of preferred transformer ratings.
Table 4.3 proposed (extended) range of preferred transformer ratings
Present range in Proposed range Proposed secondHD428/538
HD 428/538
ary voltages
50
50
420 V
100
100
420 V
160
160
420 V
250
250
420 V
400
400
420 V
(500)
420 V
630
630
420 V
800
420 V
1000
1000
420 V
1250
420 V
1600
1600
420 V
2000
420 V
2500
2500
420 V, 690 V
3150
420 V, 690 V
4000
420 V, 690 V
4.2
Data for oil-immersed transformers between 100 and 1600 kVA
Table 4.4 shows the data for oil-immersed transformers as given in [1]. Since the industries
use transformers with higher ratings this table should be extensive with higher transformer
ratings as given in chapter 4.3.
Table 4.4 data for transformers used in the utilities
RATING
kVA
100
400
1600
HV
kV
20
10
20
LV
V
400
400
690
LOSS-LEVEL
HD428
A-A'
C-C'
ACA-A'
A-A' C-C'
C-C'
ACA-A' A-A'
C-C' C-C'
ACAMDT AMDT
AMDT AMDT
AMDT AMDT
210
60
60
930
930
610
610
150
160 2.600 2.600 1.700 1.700
380
420
NO-LOAD LOSSES
W
320
LOAD LOSSES
W
1.750
1.475
1.750
1.475
4.600
4.600
3.850
3.850
4.600
3.850 14.000 14.000 17.000 17.000 17.000 14.000
TOTAL MASS
kg
520
650
740
770
1.190
1.200
1.300
1.400
1.590
1.750
3.300
3.240
3.370
3.680
4.310
4.550
CORE MASS
kg
150
220
220
225
435
440
450
540
570
600
1.100
1.210
1.200
1.460
1.400
1.550
FLUX DENSITY
T
1,83
1,45
1,35
1,35
1,83
1,84
1,65
1,6
1,35
1,35
1,84
1,84
1,7
1,6
1,35
1,35
CONDUCTOR MA- Cu/Al
TERIAL
WINDING MASS
kg
CURRENT DENSITY A/mm2
Cu
Cu
Cu
Cu
Cu
Al
Cu
Al
Cu
Cu
Cu
Al
Cu
Al
Cu
Cu
85
115
130
155
203
145
350
220
360
450
505
295
725
465
1.120
2,9
2,3
2,35
2
2,9
1,55
2,1
1,1
2,3
1,85
3,65
2
2,75
1,4
2,45
1.225
2,1
HEIGHT
mm
1.300
1.300
1.300
1.300
1.330
1.420
1.350
1.550
1.400
1.400
1.890
1.820
1.860
2.000
1.870
1.900
LENGTH
mm
890
830
1.050
1.100
1.320
1.100
1.010
1.130
1.340
1.240
1.820
2.000
1.710
1.850
1.770
1.770
WIDTH
mm
600
560
620
620
800
840
800
780
770
800
1.180
1.280
1.100
1.020
1.320
1.200
EFFICIENCY (*)
%
97,94
98,32
98,19
98,46
98,62
98,62
98,89
98,89
98,81
99,00
98,78
98,78
99,02
99,02
98,91
99,10
– Page 29 of 57 –
SOUND POWER
dB(A)
57
36
UNIT COST
UNIT COST
Euro
2538
2800
%
90,7
100
59
59
61
68
3456
3567
4385
123,5
127,5
93,2
40130017-TDC 02-24226
56
58
4286
4881
4705
91,1
103,7
100
68
68
68
72
63
63
6373
6797
9692
9251 10307 10119
15050 15531
135,5
144,5
95,8
91,4
148,7
101,9
100
76
76
153,5
Source: [1]
4.3
Data for transformers between 1000 and 4000 kVA
As mentioned before, the industries have transformers with higher ratings than those used in
the distribution grid of the utilities. Pauwels Trafo calculated different types of transformers
with power between 1000 and 4000 kVA for industrial use.
Table 4.5 shows the calculated values for 16 transformers. As can seen there are 4 different
transformers chosen with power of 1000, 1600, 2500 and 4000 kVA. The information is based
on oil-immersed transformers and dry-type transformers. For each type of transformer there is
made a calculation with the losses according (or in range) with the HD 428 or HD 538 and
losses with 15% reduction. This is reduction is done to investigate the transformers if they are
loaded typical industrial loading (i.e. loading with harmonics). It should be noted that the values given in table 4.5, are rough indications and can only be used for indication!
Table 4.5 calculated losses for industry transformers
Typical Industry Transformer Parameters
rating
kVA
1000
1600
2500
HV
kV
10
10
10
10
LV
V
420
420
420
420
Uk
%
LOSS-LEVEL
6
Oil CC' Oil DD' Dry base
6
Dry Low Oil CC' Oil DD' Dry base
8
Dry Low Oil CC' Oil DD' Dry base
4000
8
Dry Low Oil CC' Oil DD' Dry base
Dry Low
NO-LOAD LOSSES
W
1100
935
2000
1735
1700
1445
2800
2670
2500
2125
4300
4130
3800
3230
7000
5540
LOAD LOSSES 75 ºC
W
9500
8075
8600
7270
14000 11900
10000
9350
22000 18700
18000
14930
34000 28900
27000
26630
TOTAL MASS
kg
2715
3157
2530
2800
3900
4210
3840
3900
4925
6065
5350
5410
8885
10108
7660
7710
HEIGHT
mm
1890
1800
1560
1620
2090
2090
1830
1820
1925
1915
2040
2130
2485
2415
2470
2410
LENGTE
mm
1500
1540
1710
1690
1875
1795
1920
1840
2360
2370
2160
1980
2545
2545
2310
2360
WIDTH
mm
950
1800
940
940
1155
2090
940
940
1235
2370
1230
1230
1375
2545
1230
1230
T HS (F)
K
65
65
100
100
65
65
100
100
65
65
100
100
65
65
100
100
T LS (H)
K
65
65
100
100
65
65
100
100
65
65
100
100
65
65
100
100
SOUND POWER
dB(A)
56
51
68
61
68
57
70
67
69
59
74
73
72
60
80
77
EFFICIENCY (*)
%
98,94
99,10
98,94
99,10
99,02
99,17
99,20
99,25
99,02
99,17
99,11
99,24
99,06
99,20
99,15
99,20
UNIT COST
Euro
8007
10353
10074
11108
10865 12832
14451
14990
13670 17887
17951
19073
24987 29402
25527
27494
UNIT COST
%
100
129
126
139
133
138
131
140
102
110
100
118
100
131
100
118
(*) at full load and cos phi = 1
Source Pauwels
Based on the provided information one can conclude that in general dry-type transformers are
having a higher purchase price than oil-immersed transformers. There is also a big difference
in the losses and dimensioning.
Since harmonics do have a great influence on the extra losses, Pauwels also calculated the
following values for the extra losses (as a percentage of the total load losses at 50 Hz). These
losses have been subdivided in:
 extra losses in the winding (expressed as percentage of the total load losses at 50 Hz).
These losses are designated as PWE
 extra losses in structural parts, tank walls etc. and in the internal high current connections
(expressed as percentage of the total load losses at 50 Hz). For dry type transformers,
these losses are negligible. These losses are designated as PSE and PCE
Table 4.6 Extra losses in the winding and structural parts
1000 kVA
1600 kVA
In wind- Other
In wind- Other
2500 kVA
In wind- Other
4000 kVA
In wind- Other
– Page 30 of 57 –
Oil CC’ HD 428
Oil DD’ HD 428
Dry type HD538
Dry type low
losses
Source Pauwels
ing
PWE
6%
6%
6%
6%
PSE +
PCE
5%
5%
–
–
ing
PWE
9%
9%
9%
9%
PSE +
PCE
13 %
13 %
–
–
40130017-TDC 02-24226
ing
PWE
11%
11%
11%
11%
PSE +
PCE
14 %
14 %
–
–
ing
PWE
13%
13%
13%
13%
As can seen from the data in table 4.6, there is a large difference between the extra losses of
a oil- or dry type transformer in the range from 1 MVA up to 4 MVA.
It should be noted that, in order to make the difference clear between a dry and oil transformer, Pauwels based the calculations on a foil LV winding for both transformer types and for all
transformer ratings. Therefore the extra losses of the 2500 kVA and the 4000 kVA transformers are relatively high. To lower these extra losses, it is possible to use another (not a foil) LV
winding configuration. However this will increase the purchase price. Next to this, the transformer supplier should take care of the axial forces during short circuit.
PSE +
PCE
28 %
28 %
–
–
– Page 31 of 57 –
5.
40130017-TDC 02-24226
CASE STUDIES
This chapter describes some typical examples (based on the practice) about using energyefficient transformers. For these case studies, typical data collected during interviews were
used, completed with KEMA estimates. All cases refer to Dutch industrial companies.
5.1
Case study 1: a large company in the iron-steel sector
As shown in chapter 2 the iron and steel industry is one of the industry sectors with the highest electricity consumption in Europe. This case describes the possible energy saving for a
steel plant in the Netherlands by using energy efficient transformers.
5.1.1
Iron-steel: a big consumer of electricity
In this case study we are considering a company in the iron-steel industry with average electricity loading of 400 MW. About 60 MW of the loading is used at higher voltages (mainly highvoltage motors) and are therefore not distributed by distribution transformers. The electricity
consumption is relatively constant during 24 hours a day, 7 days a week.
The transformer rating is between 800 kVA and 4800 kVA. There are about 400 transformers.
200 transformers (50%) are 1250 kVA; 25% of the transformers 1600 kVA and 25% other ratings. Almost all transformers are dry-type transformers because of problems in the past with
PCB in oil. Most of the transformers have been (re)placed between 1982 and 1990. The losses of the existing transformer are almost identical as the losses given in the HD538.
The company usually buys transformers separately (i.e. not in large turnkey contracts). The
loss evaluation used for small transformers is given as EUR 2,27/W (no load losses) and EUR
1,63/W (load losses). These values are regarded as outdated now. In the following cases we
evaluate the energy saving between the HD538 dry-transformers and the low loss dry transformers for the ratings 1250 and 1600 kVA compared with the actual present transformers.
1250 kVA transformer
The table below shows the input data for the case study. Also shown are the economic loss
evaluation factors resulting from the input data.
Table 5.1 input data 1250 kV transformer
Transformer size
1250 kVA dry-type
Transformer load
65% (constant load, 24/24h) with 6 pulse harmonics
Economic lifetime
10 years
Interest rate
7%
Energy price
EUR 40/MWh
Harmonic spectrum
1
3
5
7
9 11 13 15 17 19
%
100 0
29
11
0
6
5
0
3
3
A (no-load loss evalua- EUR 2,46 /W
tion)
B (load loss evaluation)
EUR 1,04 /W
21
0
23
2
25
2
– Page 32 of 57 –
40130017-TDC 02-24226
As can be seen, the actual no-load loss evaluation (A) and load loss evaluation (B) are different from the calculated loss evaluation factors. The load loss evaluation used by the company
seems rather high, the actual no-load loss evaluation rather low.
Because of the loss evaluation factors in the past, the actually placed transformers have relatively low losses and it is not cost-effective to replace the existing transformers with new
transformers with lower losses. However if an existing transformers failed or a new transformer would be needed, it would be very attractive to use transformers with low losses. The key
output data are given in table 5.2 for the situation with harmonic loading.
Table 5.2 outcome 1250 kVA transformer
Unit
Transformer rating
Rated no-load loss
Rated load loss
Total annual losses
CO2 emission @ 0,4 kg/kWh
Purchase price
Present value no-load loss
Present value load loss
Capitalised costs
Pay back (years)
Internal rate of return
kVA
W
W
kWh/a
ton/a
EUR
EUR
EUR
EUR
Dry
transformer
1250
2400
13568
71241
28,5
12250
5907
14108
32265
Dry transformer,
low losses
1250
2200
11712
62618
25,0
13000
5414
12178
30592
Difference
-200
-1856
-8623
-3,5
750
-493
-1930
-1673
2,2
45%
Although the dry transformer with low losses has a price that is about 6% higher than the dry
transformer according the HD 538, it is clear that the low loss transformer in fact is the most
economical transformer. The payback time (2,2 years) is far smaller than the economic lifetime of 10 years. Even without evaluating the CO2 emission values, the dry transformer with
the lowest loss is the cheapest dry transformer during the lifetime.
1600 kVA transformer
Table 5.3 shows the input data for the case study. Also shown are the economic loss evaluation factors resulting from the input data.
Table 5.3 input data 1600 kV transformer
Transformer size
1600 kVA dry-type
Transformer load
65% (constant load, 24/24h) with 6 pulse harmonics
Economic lifetime
10 year
Interest rate
7%
Energy price
EUR 40/MWh
Harmonic spectrum
1
3
5
7
9 11 13 15 17 19
%
100
0
29 11 0
6
5
0
3
3
A (no-load loss evaluation) EUR 2,46 /W
B (load loss evaluation)
EUR 1,04 /W
21
0
23
2
As seen at the 1250 kVA transformer, the actual no-load loss evaluation (A) and load loss
evaluation (B) are different than the calculated loss evaluation factors. Because of the loss
evaluation factors in the past, the actually installed transformers have relatively low losses
25
2
– Page 33 of 57 –
40130017-TDC 02-24226
and it is not cost-effective to replace the existing transformers with new transformers with
lower losses. However if an existing transformer failed or the industry were growing, it would
be very attractive to use transformers with low losses.
The key output data are given in table 5.4 for the situation with harmonic loading.
Table 5.4 outcome 1600 kVA transformer
Unit
Dry
transformer
Transformer rating
kVA
1600
Rated no-load loss
W
2800
Rated load loss
W
15207
Total annual losses
kWh/a
80809
CO2 emission @ 0,4 ton/a
32,3
kg/kWh
Purchase price
EUR
14451
Present value no-load EUR
6891
loss
Present value load loss
EUR
15812
Capitalised costs
EUR
37154
Pay Back (years)
Internal rate of return
Dry transformer, low
losses
1600
2670
14218
76012
30,4
Difference
-130
-989
-4797
-1,9
14990
6571
539
-320
14784
36345
-1028
-809
2,8
34%
Although the dry transformer with low losses has a price that is 4% higher than the dry transformer according the HD 538, it is clear that the low loss transformer in fact is the most economical transformer. Even without evaluating the CO 2 emission values, the dry transformer
with the lowest loss is the cheapest dry transformer during the lifetime (pay back period 2,8
years). It is clear that this transformer is more attractive if the emissions levels are taken in
account.
5.1.2
Conclusion
Since this company is familiar with (and uses) loss evaluation for small transformers, the
transformers are already rather efficient and replacing all existing dry type transformers with a
transformer with low losses is not economical. However if a transformer fails, or if there are
new transformers needed, it is economical to buy dry-type transformers with low losses compared with the existing transformers and HD 538 transformers. The payback period for energy
efficient transformers is even smaller than 3 years.
Based on a European average value of 0,4 kg/kWh CO 2 emission, the annual energy saving
for the 1250 kVA transformer is about 3,5 tonne. The annual energy saving for the 1600 kVA
transformer is about 1,9 tonne. For all other small transformers it is presumed that the energy
and CO2 emission saving can be taken as the average saving of the 1250 and 1600 kVA
transformer. Table 5.5 gives the potential annual energy and CO2 emission saving for this
company, if all transformers were replaced.
– Page 34 of 57 –
Table 5.5 annual savings potential
Transformer
Total
Energy saving
size
number [MWh/a]
1250 kVA
200
1724,6
1600 kVA
100
479,7
Other
100
734,8
Total
400
40130017-TDC 02-24226
CO2 emission saving
[tonnes/a]
700
190
300
2939,1
1190
The average annual energy consumption of this company is about 3,5 TWh. This means a
reduction of 0,084% which equals an annual cost saving of EUR 117564,= (exclusive CO 2
emission saving).
5.2
Case study 2: A large company in the non-ferrous metals sector
Almost 3% of the electricity consumption in Europe is used by the non-ferrous metals sector.
However, only a small share of this electricity passes a distribution transformer, as much electricity is used for e.g. electrolysis.
5.2.1
Non-ferrous metal sector: replacing older transformers
For this case study we are considering a company in the Netherlands, with an electricity loading of about 190 MW. Almost 180 MW of the loading is used at higher voltages (electrolysis)
and therefore not distributed by distribution transformers. This load is present during 24 hours
a day and 7 days a week. The remaining electricity consumption varies between 10 MW between 07.00 and 17.00 h, and 8 MW during the night hours.
There are 25 transformers installed, with ratings between 500 kVA and 1250 kVA. Half of the
transformers have a size of 1000 kVA. Three new dry type transformers were installed in
1999, and 1 oil transformer in 1987. All other 1000 kVA transformers are old transformers and
installed between 1965 and 1970. The losses for these older transformers are:
 No load loss
: 1900 W
 Load loss
: 10250 W.
During working hours the average loading of these transformers is about 45%, during the
night hours the average loading is about 35%. In the following cases we evaluate the energy
saving between the existing 1000 kVA transformers and the 1000 kVA low loss transformers.
Since the latest transformers are dry type transformers and the older transformers are oilimmersed transformers, the differences between these two transformers are calculated.
1000 kVA transformer
The table below shows the input data for the case study. Also shown are the economic loss
evaluation factors resulting from the input data.
Table 5.6 input data 1000 kVA transformer
Transformer size
1000 kVA oil-type
Transformer load
45% during 10/24 hours; 35% during 14/24 hours
– Page 35 of 57 –
Economic lifetime
Interest rate
Energy price
Harmonic spectrum
A (no-load loss evaluation)
B (load loss evaluation)
40130017-TDC 02-24226
5 years
7%
EUR 40/MWh
No harmonic load is considered
EUR 1,44 /W
EUR 0,24 /W
Since the evaluation of the load loss (B) is relative low, it is not economical to replace the older transformers with a transformer with lower losses. Even when the CO2 emission values are
taken into account, it is not economical to replace.
When this plant buys new transformers, the key output data are given in the table below for
the situation with harmonic loading and the lowest CO2 emission values.
Table 5.7 outcome 1000 kVA transformer
Unit
Dry HD 538
transformer
Transformer rating
kVA
1000
Rated no-load loss
W
2000
Rated load loss
W
8600
Total annual losses
kWh/a
30336
CO2 emission @ 0,4 ton/a
12,1
kg/kWh
Purchase price
EUR
10074
Present value no-load EUR
2873
loss
Present value load loss
EUR
2102
Capitalised costs
EUR
15049
Pay back (years)
Internal rate of return
Oil C-C’
transformer
1000
1100
9500
23793
9,5
Difference
-900
900
-6543
-2,6
8007
1580
-2067
-1293
2322
11909
220
-3140
N/A
N/A
The internal rate of return can not be calculated since the difference between the purchase
price and the differences between the annual losses are both negative. This makes clear that
the oil transformer should be preferred, since the purchase price is lower and annual losses
are also lower. The difference between these transformers will even be more, if the CO 2
emission values and/or losses due to harmonics are taken into account
5.2.2
Conclusion
Although there are some older transformers (1965) in this plant, it is not recommended to replace the existing transformers. As long as these transformers do their job properly, no action
should be taken.
The latest transformers placed at this plant are all dry-type transformers. The given calculation shows however that if new transformers should be placed the oil-immersed transformers
should preferred (looking at the transformer types used in the case study).
Based at a European average value of 0,4 kg/kWh CO 2 emission, the annual energy saving
– Page 36 of 57 –
40130017-TDC 02-24226
between the 1000 kVA oil and dry type transformer is about 2,6 tonne. For all other small
transformers it is presumed that the energy and CO 2 emission saving can be taken as the average saving of the 1000 kVA transformer. Table 5.7 gives the annual energy and CO 2 emission saving potential for this company by placing oil immersed transformers instead of dry
type transformers
Table 5.8 annual savings potential
Transformer
Total
Energy saving [MWh]
size
number
1000 kVA
12
78,5
Other
13
85,1
Total
25
CO2 emission saving [tonnes]
164
31,2
33,8
65
The average annual electricity consumption of this company is about 1,66 million kWh. This
means a reduction of 0,0099% which equals an annual cost saving of EUR 6560,= (exclusive
CO2 emission saving). The reason for the relative small reduction is because the most of the
electricity consumption does not pass a distribution transformers but is used by the electrolysis equipment.
5.3
Case study 3: a paper and pulp company
This case study shows an example (based on practice) of a paper and pulp plant which in the
past (1978) bought transformers with normal losses (at that time) and for another process
(1986) bought transformers with low losses (even nowadays these losses are very low).
5.3.1
Paper industry: energy savings based on practice
This paper and pulp plant has two paper mills. The first mill was build in 1978, the second mill
in 1986. The peak electricity loading is about 110 MW. The loading at higher voltage is about
72 MW (High voltage motors). About 12 MW of this loading is consumed during 24 hours a
day, 7 days a week (Paper mill), and presumed is that the other 60 MW loading is consumed
between 21.00 u and 06.00 u for the making of pulp.
There are 52 transformers, with ratings between 1000 kVA and 3150 kVA. The latest 6 transformers (placed in 1997) are dry-type transformers, all other transformers are oil transformers.
Most of the transformers (28) are 3150 kVA transformers with a LV of 690 V. The average
loading of these transformers is about 65%, some of them with 6 pulse drives.
Since the lifetime of a paper mill is several decades, this company applies since 1986 an
evaluation of the losses of transformers and the purchase price over a lifetime of 20 years.
However, this method is not based on the given loss evaluation method.
The transformer losses for the transformers placed in 1986 are even lower than the D-D’
transformers as given in this report. The losses of the transformers placed in 1978 are almost
identical to the losses of the C-C’ transformers. To evaluate the differences between the two
transformers, it is presumed that the purchase price of the 1978 transformers nowadays
equals the C-C’ transformer and the 1986 transformer equals a D-D’ 4000 kVA transformer,
– Page 37 of 57 –
40130017-TDC 02-24226
however actual losses of this transformer are even lower than the given D-D’ transformer.
3150 kVA transformer
This calculation will show the differences in losses between the 1978 and 1986 transformers
(3150 kVA). Table 5.9 gives the input data as used for this evaluation:
Table 5.9 input data 3150 kVA transformer
Transformer size
3150 kVA oil-type
Transformer load
65% during 24/24 hours with 6 pulse harmonics
Economic lifetime
20 years
Interest rate
7%
Energy price
EUR 40/MWh
Harmonic spectrum
6 pulse according to IEC 146-1-1
A (no-load loss evaluation) EUR 3,71 /W
B (load loss evaluation)
EUR 1,57 /W
Since the economic lifetime is long, the no-load and load loss evaluation are relative high.
Obviously, it is not cost-effective to replace the existing 3150 kVA transformers (build in 1978)
with D-D’ transformers.
The key output data between the 1978 and 1986 transformers are given in the table below,
including harmonics and with the lowest CO2 emission values.
Table 5.10 Outcome 3150 kVA transformer
Unit
Oil
1978
transformer
Transformer rating
kVA
3150
Rated no-load loss
W
2870
Rated load loss
W
24500
Total annual losses
kWh/a
181908
CO2
emission
@
0,4 ton/a
72,8
kg/kWh
Purchase price
EUR
19329
Present value no-load loss
EUR
10654
Present value load loss
EUR
66432
Capitalised costs
EUR
96415
Pay back (years)
Internal rate of return
Oil 1986
Transformer
3150
3150
16800
135092
54,0
24987
11693
45553
82233
Difference
-280
-7700
-46816
-18,8
5658
1039
-20879
-14182
3,0
33%
Although the purchase price of the 1978 transformer is about 30% more expensive, over a life
time of 20 years, the 1986 transformer is most cost effective (even without evaluating the CO 2
emission values).
Thanks to the lower annual losses of the 1986 transformer, this company saves about 46816
kWh/year per 3150 kVA transformer.
5.3.2
Conclusion
Although there are some older transformers (1978) in this plant, it is not recommended to re-
– Page 38 of 57 –
40130017-TDC 02-24226
place the existing transformers. As long as these transformers do their job properly, no action
should be taken. There are 18 transformers (3150 kVA) from about 1986 with very low losses.
By calculation of the difference between the 1978 and 1986 transformers it is possible to give
an estimation of the energy and emission savings by using energy efficient transformers.
Based at an European average value of 0,4 kg/kWh CO2 emission the annual energy saving
between the 3150 kVA oil type transformer is about 18,8 tonne. Table 5.11 gives the annual
energy and CO2 emission saving for this company by placing oil immersed 1986 transformers
instead of 1978 transformers (C-C’).
Table 5.11 annual savings potential
Transformer
Total
Energy
saving
size
number [MWh/a]
3150 kVA
18
842,7
CO2
emission
[tonnes/a]
338,4
saving
Due to the use of energy efficient transformers (3150 kVA) this company already saves about
843 MWh per year. If we are considering the other transformers placed at this plant (16 x
2500 kVA; 5 x 1600 kVA; 7 x 1000 kVA and some other small transformers) the total potential of energy saving could be about 1250 MWh, which equals a CO2 emission of 500 tonnes.
The average annual electricity consumption of this company is about 600 Million kWh. This
means a reduction of 0,14% which equals an annual cost saving of EUR 33.700,= (exclusive
CO2 emission saving). Due to the fact that most electricity consumption is caused by the HV
motors, this reduction looks relative small compared with the total electricity use.
5.4
Case study 4: a chemical industrial enterprise
Differences between plants in this sector are enormous. However, despite differences in the
processes, the electrical installations are often similar. Often this industry uses electrolysis for
the process and/or HV motors. Depending on the process, high reliability requirements cause
a lot of redundancy in the electrical installation. Because of this redundancy the average loading of transformers is often not higher than 40%.
Since there are some differences between the industrial plants, we have taken a fictitious
case based on several chemical plants. The average loading is assumed to be 110 MW.
About 40 MW is used by HV motors or electrolysis.
The loading is 24 hours a day, 7 days a week. The loading is not linear (AC 12 pulse drives).
A typical transformer for this kind of industry is a 1250 kVA transformer (60 out of 71 transformers). The other transformers have a ratings of 630, 1000 and 1600 kVA.
5.4.1
Chemical industry: energy savings by placing energy efficient transformers
In this case we compare an 1250 kVA dry type transformer with losses in the range of the HD
538 and a 1250 kVA dry type transformer with low losses.
1250 kVA
– Page 39 of 57 –
40130017-TDC 02-24226
This calculation is based on a loading of 40%. Table 5.12 gives the input data as used for this
evaluation:
Table 5.12 input data transformers
Transformer size
1250 kVA dry-type
Transformer load
40% 24/24 hours
Economic lifetime
5 year
Interest rate
7%
Energy price
EUR 50/MWh
Harmonic spectrum
No harmonics
A (no-load loss evaluation) EUR 1,80 / W
B (load loss evaluation)
EUR 0,29 / W
The key output data between the two transformers are given in table 5.13 (without harmonics
and without the CO2 emission values).
Table 5.13 Outcome 1250 kVA transformer
Unit
HD
538
transformer
Transformer rating
kVA
1250
Rated no-load loss
W
2400
Rated load loss
W
9500
Total annual losses
kWh/a
34339
CO2
emission
@
0,4 ton/a
13,8
kg/kWh
Purchase price
EUR
12250
Present value no-load loss
EUR
4310
Present value load loss
EUR
2730
Capitalised costs
EUR
19712
Pay back (years)
Internal rate of return
Low loss
Transformer
1250
2200
8200
30765
12,3
13000
3951
2356
19686
Difference
-200
-1300
-3574
-1,5
750
-359
-374
-17
4,2
6%
5.4.2
Conclusion
As can be seen from table 5.13, the differences between the two 1250 kVA transformers are
small. Even a small variation of one of the input variables can influence the decision which
transformer is more economical. This shows that the input parameters are very sensitive for
the decision to buy low loss transformers or regular transformers. However estimating these
parameters can save a lot of energy loss and money (see also chapter 5.10). Still the pay
back period for the transformer with the low losses is lower than the economic life time (4,2
respectively 5,0 years).
Based at a European average value of 0,4 kg/kWh CO 2 emission the annual energy saving
between the 1250 kVA dry type transformer is about 1,5 tonne. Table 5.14 gives the annual
energy and CO2 emission saving for this company due to placing dry type transformers with
lower losses.
Table 5.14 annual savings potential
Transformer
Total
Energy saving [MWh]
CO2 emission saving [tonnes]
– Page 40 of 57 –
size
1250 kVA
number
60
214,4
40130017-TDC 02-24226
85,8
Due to the use of energy efficient transformers this company saves about 214 MWh per year.
If we are considering the other 11 transformers placed at this site, the total potential of energy
saving could be about 254 MWh, which equals a CO 2 emission reduction of 101 tonnes/year.
The average annual electricity consumption of this company is about 964 Million kWh. This
means a reduction of 0,026% which equals an annual cost saving of EUR 12700,= (exclusive
CO2 emission saving). Due to the fact that most electricity consumption is caused by the HV
motors or electrolysis, this reduction is relatively small compared with the total electricity use.
5.5
Case study 5: a large data hotel start-up
5.5.1
Data hotels: a quickly growing sector
Within the time scope of the project, it was not possible to arrange an interview with a representative of this sector. Based on KEMA’s experience, however, sufficient data was available
to set up a typical case study.
Within a short time, data hotels have become notorious for applying for huge connections at
network companies, sometimes in the order of 100 MW or more, i.e. comparable to heavy industry. The rated power of the network connection is, as with any customer, based on growth
expectations, the annual growth expectation for data hotels often being in the double or triple
figures. The cited power ratings are extrapolations of the growth rates for a few years.
The result of this approach often is an electrical power supply installation that is overdimensioned to a very large extent. The loading of transformers may be as low as 5-10%.
Caused by the power supply of computers, datahotels have a lot of harmonics in their loading.
The spectrum used for this case study is similar to the harmonic spectrum of the office building (case 6). However it contains more third harmonics.
The economic lifetime will be very short, e.g. one year only. Table 5.15 shows the input data
for the case study. Also shown are the economic loss evaluation factors resulting from the input data.
Table 5.15 input data transformers
Transformer size
1600 kVA dry-type
Transformer load
25% (constant load, 24/24h), initial loading
70% (constant load, 24/24h), end of year 1
Economic lifetime
1 year
Interest rate
7% (not very relevant in view of the economic lifetime)
Energy price
EUR 60/MWh
Harmonic spectrum
1
3
5
7
9 11 13 15 17 19 21
%
100 59 41 23 0
6
5
0
3
2
0
A (no-load loss evaluation) EUR 0,52 /W (initial loading)
EUR 0,52 /W (end of year 1)
23
1
25
1
– Page 41 of 57 –
B (load loss evaluation)
40130017-TDC 02-24226
EUR 0,03 /W (initial loading)
EUR 0,24 /W (end of year 1)
Since the loading is low and the economic lifetime is short, one could ask if the relatively large
transformers are an optimal choice and if it is cost effective to have a transformer with a lower
power rating. Based on the following figures it is possible to estimate if a 1600 kVA transformer is economically the best chosen transformer. Also, it is estimated if energy-efficient
transformers are also economically efficient.
5.5.2
Evaluation of more efficient transformers with the same rating
Table 5.16 shows the results for a more efficient transformer.
Table 5.16 Outcome 1600 kVA transformer (initial loading)
Unit
Dry
trans- Dry transformer
former
Low losses
Transformer rating
kVA
1600
1600
Rated no-load loss
W
2800
2670
Rated load loss
W
10000
9350
Total annual losses
kWh/a
38428
36385
CO2
emission
@
0,4 ton/a
15,3
14,5
kg/kWh
Purchase price
EUR
14451
14990
Present value no-load loss
EUR
1444
1377
Present value load loss
EUR
818
765
Capitalised costs
EUR
16714
17132
Pay back (years)
Internal rate of return
Difference
-130
-650
-2043
-0,8
539
-67
-53
418
N/A.
-76%
Since the economical lifetime is very short (1 year) and the loading is low, it is clear that the
purchase price of the transformer is the most dominant part in the capitalisation of the costs.
In fact, the cheapest transformer is not a dry type transformer but an oil-immersed C-C’ one,
having total capitalised costs of about Euro 12951,= (including harmonics).
At the end of year 1, when the loading has increased from 25% to 70%, following results are
obtained (see table 5.17).
Table 5.17 Outcome 1600 kVA transformer (end of year 1)
Unit
Dry
trans- Dry transformer
former
Low losses
Transformer rating
kVA
1600
1600
Rated no-load loss
W
2800
2670
Rated load loss
W
10000
9350
Total annual losses
kWh/a
133501
125279
CO2
emission
@
0,4 ton/a
53,5
50,1
kg/kWh
Purchase price
EUR
14451
14990
Present value no-load loss
EUR
1444
1378
Difference
-130
-650
-8222
-3,4
539
-66
– Page 42 of 57 –
Present value load loss
Capitalised costs
Pay back (years)
Internal rate of return
EUR
EUR
6416
22311
40130017-TDC 02-24226
5999
22366
-417
55
N/A.
-4%
Even at this relatively high load and much higher losses, the purchase price is still dominant.
Energy efficiency does not pay off in this case either. Again, the cheapest transformer is an
oil-immersed C-C’ one, having total capitalised costs of Euro 21225,= (including harmonics).
Although this transformer is only loaded with 70%, due to the harmonics the loss of life at the
end of the year is about 5. If we presume a lifetime about 30 years, this means the actual life
time is shorted to 30 / 5 = 6 years. Since the economical lifetime is taken as one year, the reduction in technical life time is no problem as long as the hot spot temperature is below the
maximum levels.
5.5.3
Evaluation of smaller transformers
Since the loading is low and the economic lifetime is short, one could ask, why one would
choose for a 1600 kVA transformer. Instead of the 1600 kVA transformer it is possible to use
a 1000 kVA transformer. The loading of the 1000 kVA transformer will initially be 40%. Table
5.18 gives the calculation for the 1000 kVA transformer.
Table 5.18 Outcome 1000 kVA transformer (initial loading)
Unit
Dry
trans- Dry transformer
former
smaller size
Transformer rating
kVA
1600
1000
Rated no-load loss
W
2800
2000
Rated load loss
W
10000
8600
Total annual losses
kWh/a
38428
48121
CO2
emission
@
0,4 ton/a
15,3
19,2
kg/kWh
Purchase price
EUR
14451
10074
Present value no-load loss
EUR
1444
1032
Present value load loss
EUR
818
1802
Capitalised costs
EUR
16714
12907
Pay back (years)
Internal rate of return
Difference
-800
-1400
9693
3,9
-4377
-412
984
-3807
N/A.
-86%
In fact, changing to a smaller transformer seems very attractive: the purchase costs are much
lower, and the much higher (+25%) energy losses will not offset the lower purchase costs:
capitalised cost saving is approximately 25%.
The internal rate of returns has turned negative, which is due to the initial cost advantage and
the later periodic extra cost. Financially speaking, the smaller transformer is a good investment!
The influence of harmonics will reduce the technical lifetime of the 1000 kVA transformer, but
this should not be critical, as the economical lifetime is only 1 year.
Obviously, if this company would exist more than one year, it would regret the short sight of
the initial investment. Also, if the expected load growth would occur, the transformer would
– Page 43 of 57 –
40130017-TDC 02-24226
become overloaded very quickly.
5.5.4
Conclusion
For this company, the predominant condition is the short economic scope. Hence, all investments can be viewed in light of initial cost only. In this case, only the setting of minimum energy loss levels in standards forms the limit to buying cheap and inefficient equipment.
This somewhat unsatisfactory outcome of the case study is mitigated in another business
model, in which the transformer is owned by e.g. the utility. Utilities are used to long planning
scopes of their infrastructure and, as they may move equipment along their infrastructure as
needed, will probably optimise the transformers with respect to losses as they can be sure the
transformer will be employed anywhere during its lifetime.
A scope for annual energy saving and CO2 reduction can not be given in this case.
5.6
Case study 6: An office building
In a lot of older office buildings there are transformers that are as old as the building. Due to
the enormous growth of non-linear loading in office buildings, it is known that in the past there
were serious problems with harmonics.
One could ask, if the used transformers are capable to take care of these harmonics, since
they were not always designed for a non-linear loading. This case study is based on an actual
failure caused by non-linear loading in an office building.
The given office building was placed in the sixties and on each floor there are two transformers of 400 kVA, each feeding half a floor. The last decennium there is a certain growth of
computers. The power supplies of each computer and monitor are causing harmonics. Based
on measurements it is found that the harmonics in the current are according to table 5.19.
Table 5.19 input data transformers
Transformer size
400 kVA oil-immersed transformer (1965)
Transformer load
40% (constant load, 10/24h), during office time
20% (constant load, 14/24h)
Economic lifetime
10 year
Interest rate
6%
Energy price
EUR 70/MWh
Harmonic spectrum
1
3
5
7
9 11 13 15 17
%
100 59 41 23 0
6
5
0
3
A (no-load loss evaluation) EUR 4,51 /W
B (load loss evaluation)
EUR 0,34 /W
19
2
21
0
23
1
The no-load loss of the older 400 kVA oil-immersed transformer is Pn = 710 W and the load
loss Pk = 3925 W (based on figures in 1966/1967). The eddy current loss for the windings is
presumed to be 4%, while the other eddy current losses are also presumed to be 4%. Although these losses are relatively high, it is not economical to replace these older transform-
25
1
– Page 44 of 57 –
40130017-TDC 02-24226
ers with new transformers.
Since the no-load loss evaluation (A) is high, one could ask if it is cost effective to place new
transformers with amorphous cores if one of the existing transformers failed. Table 5.20
shows the outcome for an amorphous core compared with a C-C’ oil transformer.
Table 5.20 Outcome 400 kVA transformer (initial loading)
Unit
C-C’
Oil Amorphous
transformer transformer
Transformer rating
kVA
400
400
Rated no-load loss
W
610
160
Rated load loss
W
3850
3850
Total annual losses
kWh/a
10528
6586
CO2
emission
@
0,4 ton/a
4,2
2,6
kg/kWh
Purchase price
EUR
4874
6787
Present value no-load loss
EUR
2753
722
Present value load loss
EUR
2671
2671
Capitalised costs
EUR
10298
10180
Pay back (years)
Internal rate of return
Difference
-450
0
-3942
-1,6
1913
-2031
0
-118
6,9
6%
As can be seen, the transformer with the amorphous core reduces the losses and can be cost
effective. The total energy and emission savings between the existing and amorphous transformer are given in table 5.21.
Table 5.21 Annual savings
Transformer
Total
size
number
400 kVA
24
Energy saving [MWh]
CO2 emission saving [tonnes]
94,6
37,8
Since the average use of electricity per year equals almost 12,5 Million kWh, this means a
energy saving of about 0,76%.
5.7
Case study 7: Reliability and availability
A lot of industries (e.g. chemical) are interested in a reliable power supply, as an unforeseen
interruption of the power supply may have severe consequences. First there is the economical damage if there is a shutdown, which leads to loss of production until the process has restarted. But also there can be damage of the installation. Next to the direct damage, long outages may cause pollution and human safety problems.
To reduce the risks of an outage, it is possible to have two transformers in redundancy. This
means if one transformer fails, the other transformer will carry the full load, and there will be
no interruption of the power and/or shutdown of the factory.
For this case study, the economical cost when an unforeseen outage occurs is a necessary
input figure. The costs of outages are very hard to determine, for this given situation it is pre-
– Page 45 of 57 –
40130017-TDC 02-24226
sumed that outage of the electricity will cause a shutdown of the factory, whereby each hour
outage is equal to Euro 10.000,=.
The MTBF (mean time between failure) for a transformer is presumed to be 40 years. The
MTTR (mean time to repair) or time to replace a failed transformer is 8 hours. This means that
the average outage frequency equals 0,025 per year and the average outage duration equals
12 minutes per year. If there is redundancy the average outage frequency equals 1,14*10 -6
per year, while the average outage duration equals 2,7*10 -4 minutes per year. This means the
chance that both parallel transformers having a failure at the same time is very small compared to the outage of one transformer.
The choice for the designer to use one transformer (2500 kVA) or two transformers (1600
kVA) can now be quantified. Presuming the load is 1500 kVA; the 2500 kVA transformer loading is 60%, while the loading of the 1600 kVA transformer is 47% when both transformers are
in parallel. Based on the transformer data shown in chapter 4, the total annual losses for both
options are given in table 5.22.
Table 5.22 electricity losses over a year
2500 kVA Transformer
Oil C-C’
No load kWh/yr.
21900
Load kWh/yr.
69379
Total kWh/yr.
91279
2x 1600 kVA Transformer
Oil C-C’
No load kWh/yr.
29784
Load kWh/yr.
54182
Total kWh/yr.
83966
Oil D-D’
18615
58972
77587
Oil D-D’
25316
46054
71370
Dry HD 538
37668
56765
94433
Dry HD 538
49056
38702
87758
Dry Low loss
36179
47083
83262
Dry Low loss
46778
36186
82964
If the economic life time is estimated at 10 years, and the electricity price Euro 70,= per MWh,
the following costs are expected in these 10 years (see table 5.23).
Table 5.23 Costs over 10 years.
2500 kVA Transformer
Purchase price [Euro]
Cost of no load [Euro]
Cost of load [Euro]
Cost of outage [Euro]
Total cost [Euro]
2x 1600 kVA Transformer
Purchase price [Euro]
Cost of no load [Euro]
Cost of load [Euro]
Cost of outage [Euro]
Total cost [Euro]
Oil C-C’
24897
15330
48565
20000
108792
Oil C-C’
27340
20849
37927
<1
86117
Oil D-D’
29402
13030
41280
20000
103712
Oil D-D’
35774
17721
32238
<1
85734
Dry HD 538
25527
26368
39736
20000
111631
Dry HD 538
35902
34339
27091
<1
97333
Dry Low loss
27494
25325
32958
20000
105777
Dry Low loss
38146
32745
25330
<1
96222
From table 5.23 it can be seen that the costs of outage are having influence on the total costs
over 10 years. If the costs of outage are neglected, the designer would probably have chosen
for a single 2500 kVA oil-transformer type D-D’ or a dry transformer with lower losses than
given in the HD 428.
– Page 46 of 57 –
40130017-TDC 02-24226
However if the average costs of an outage are taken in account, the designer will probably
order two 1600 kVA transformers. However, the two 1600 kVA transformers will also need an
installation more than the 2500 kVA transformer, which is not taken in account in this case
study. Nevertheless, it is clear that redundancy of transformers is preferred anyway for situations were shutdown of a process causes pollution or safety risks.
5.8
CO2 emission trading
In all above given cases the influence of CO 2 emissions was not evaluated. Throughout the
world it is clear that CO2 emissions and trading can not be omitted in the future. To allow for
economic optimisation, emission trading schemes are under discussion, and by that time,
CO2 emission rights will have a price. The price for CO 2 emission will add to the cost of electricity. The extra costs are shown in table 3.1 (chapter 3.6).
Considering these extra costs for case study 4 table 5.24 gives the payback time, IRR and
capitalised costs for different CO2 emissions and costs.
Table 5.24 Evaluation with cost for CO2 emissions
Costs
Eur 0/tonne
Eur 10/tonne
Eur 33/tonne
Eur 50/tonne
0,3 kg/kWh
Pay back
IRR
4,2
6%
4
8%
3,5
13%
3,2
17%
CC
-17
26
128
203
CO2 emission
0,4 kg/kWh
Pay back
IRR
4,2
6%
3,9
9%
3,3
15%
3
20%
CC
-17
41
176
276
Pay back
4,2
3,7
3
2,6
0,6 kg/kWh
IRR
6%
10%
20%
26%
CC
-17
250
273
423
This example shows that if the cost per tonne CO2 emission is high, it is cost effective to
choose the transformer with the low losses. If there is a cost evaluation considered for the
CO2 emission, a higher CO2 emission (kg/kWh) makes it more attractive to choose a transformer with low losses.
5.9
Sensitivity of the input parameters
As discussed in chapter 5.4, the input parameter can have a great influence on the results.
Establishing the right values is very difficult, since a lot of circumstances during the lifetime of
the transformer can (and will) change. By variation of the input parameters it is possible to establish which parameters are the most important for making a right decision. This chapter
shows an example for making an accurate decision between two 1250 kVA dry type transformers (one with losses according the HD 538; one with lower losses). Table 5.25 shows the
parameters that are changed and how much they are changed. The middle values shown
form the base case.
Table 5.25 Parameter variation
Harmonic loading
Electricity price (Eur/MWh)
CO2 emissions (kg/kWh)
Low
Medium
(base case)
High
No harmonic loading
40
0,3
12 pulse loading
60
0,4
6 pulse loading
80
0,6
– Page 47 of 57 –
CO2 costs (Eur/tonne)
Loading profile (%)
Economic lifetime (years)
Interest (%)
Purchase price (%)
40130017-TDC 02-24226
0
20
1
5
80
10
40
5
7
100
33
60
10
9
120
For each situation, the payback period, IRR and capitalised costs are calculated. Table 5.26
and figure 5.1 shows the results for the pay back period in years.
Table 5.26 Parameter sensitivity on the payback period
Parameter
Parameter variation
L
M
H
Unit
Harmonic spectrum
Electricity price
CO2 emissions
CO2 costs
Loading profile
Economic lifetime
Interest
Purchase price
None
12 pulse
6 pulse
EUR/MWh
40
60
80
kg/kWh
0,3
0,4
0,6
EUR/tonne
0
10
33
%
20
40
60
years
1
5
10
%
5
7
9
%
80
100
120
Payback time (years)
L
M
H
3,3
4,5
3,2
3,3
5,2
3,1
3,1
2,5
3,1
3,1
3,1
3,1
3,1
3,1
3,1
3,1
2,7
2,4
3,0
2,7
1,9
3,1
3,1
3,7
Purchase price
Interest
Economic life time
Loading
CO2 value
CO2 emission
Electricity price
Harmonics
0
1
2
3
4
5
6
years
Figure 5.1 Parameter sensitivity on the payback period
At the average values, the payback period is 3,1 year. As can be seen, the loading profile and
electricity price have the most influence on the pay back period. The influence of all other parameters is smaller. By definition, interest and economic lifetime do not have an influence on
the payback period at all. This example clearly shows that it makes more sense to determine
the expected loading of the transformer than just looking at the purchase price of the trans-
– Page 48 of 57 –
40130017-TDC 02-24226
former. In this example it also makes more sense to focus on the electricity price than on the
purchase price of the transformers.
It can also been seen that in this example the transformer with the low losses always has an
acceptable pay back period. This means that, even when a parameter is not correctly specified, the transformer with the low loss is the best choice, however the pay back time will
change.
Figure 5.2 and table 5.27 show the results for the IRR parameters, where the parameters are
changed as shown in table 5.25.
Table 5.27 Parameter sensitivity on the IRR
Parameter
Parameter variation
L
M
H
Unit
Harmonic spectrum
Electricity price
CO2 emissions
CO2 costs
Loading profile
Economic lifetime
Interest
Purchase price
None
12 pulse
6 pulse
EUR/MWh
40
60
80
kg/kWh
0,3
0,4
0,6
EUR/tonne
0
10
33
%
20
40
60
years
1
5
10
%
5
7
9
%
80
100
120
IRR (%)
L
M
H
16%
3%
17%
15%
-1%
-68%
18%
29%
18%
18%
18%
18%
18%
18%
18%
18%
25%
31%
20%
24%
45%
30%
18%
11%
60
80
100
Purchase price
Interest
Economic life time
Loading
CO2 value
CO2 emission
Electricity price
Harmonics
-100
-80
-60
-40
-20
0
20
40
Percentage
Fig. 5.2 Parameter sensitivity on the IRR
As can be seen in figure 5.2 the most important parameter based on the IRR method, is the
expected economic lifetime. Contrary to the method based on the payback time, a different
economic lifetime or loading pattern can mean a different choice of the transformer (negative
– Page 49 of 57 –
40130017-TDC 02-24226
IRR). Although its influence is smaller, a low electricity price can give a low IRR value (3%).
This means that for an interest rate higher than 3%, the transformer with the low losses is not
economical. The purchase price is only the fourth dominant factor.
This example shows that determining a (too) short economic lifetime of the transformer will
cost the industry money. Although the numbers from this example are not applicable for every
situation, the method itself is and it is strange that a lot of industries do not take in account the
economic life time when deciding which transformer should be used, and are only interested
in the lowest purchase price of the transformer.
Figure 5.3 and table 5.28 show the results when the capitalisation formula is used. A negative
value means it is useful to choose for the transformer with the low losses. When the result is
positive, the transformer with the losses according the HD 538 should be used.
Table 5.28 Parameter sensitivity on the capitalised cost
Parameter
Parameter variation
L
M
H
Unit
Harmonic spectrum
Electricity price
CO2 emissions
CO2 costs
Loading profile
Economic lifetime
Interest
Purchase price
None
12 pulse
6 pulse
EUR/MWh
40
60
80
kg/kWh
0,3
0,4
0,6
EUR/tonne
0
10
33
%
20
40
60
years
1
5
10
%
5
7
9
%
80
100
120
Capitalised cost (Euro)
L
M
H
-188
71
-222
-176
158
525
-292
-387
-237
-237
-237
-237
-237
-237
-237
-237
-392
-546
-268
-379
-896
-941
-186
-87
500
750
Purchase price
Interest
Economic life time
Loading
CO2 value
CO2 emission
Electricity price
Harmonics
-1500
-1250
-1000
-750
-500
-250
0
EURO
Figure 5.3 Parameter sensitivity on the capitalisation formula
250
– Page 50 of 57 –
40130017-TDC 02-24226
Again, it is clear that most attention should be given to the used economic lifetime, loading
pattern and electricity price. Disregarding these values will certainly have a great influence on
deciding which transformer should be used and could give a wrong optimised transformer.
Again the influence of the purchase price of the transformer is relatively small.
5.10
Total energy saving potential by efficient transformers in the industrial sector
In this section, a rough estimate is made for the total European energy savings potential by
application of energy-efficient distribution transformers in industry.
Since the load conditions of distribution transformers and ordering procedures are different
even within an industry sector, it is not possible to determine one or more transformers which
could be typical for the transformer population in a given industry sector. The estimate for Europe therefore will have to be very global.
A complicating factor is that distribution transformers do not distribute all electricity consumed
by the industries. Depending on the sector of industry, there are HV motors, large drives with
dedicated transformers and/or electrolysis processes which are having a large share in the total electricity consumption. Therefore it is very hard to estimate the exact share of electricity
consumption that is distributed by distribution transformers. Even between two companies in
the same industry sector, there are differences.
If we presume the above given cases per sector to be representative for the sector, the annual saving of electricity in Europe can be estimated based on the values given in chapter 2.
Table 5.30 estimated electricity saving, based on the case studies
Industry sector
INDUSTRY, of which:
Iron and steel
Chemical/petrochemical
Non-ferrous metals
Non-metallic minerals
Machinery
Food/tobacco
Paper, pulp and print
Other industry
COMMERCIAL AND PUBLIC SERVICES
FINAL SAVINGS approximately
Electricity saving (GWh)
650,6
0,084% * 131G = 110,3
0,026% * 195G = 50,7
0,01% * 88G = 8,8
0,06% * 76G = 45,6
0,06% * 99G = 59,4
0,06% * 95G = 57,0
0,14% * 127G = 177,8
0,06% * 235G = 141,0
0,76% * 570G = 4332
5000
This means a total electricity saving of about 0,3%. This equals a saving of 2 million tonnes
CO2, which is about 0,6% of the total European aim for reduction of CO 2 until 2012.
Of course, the extrapolation of six cases gives rather unreliable results. Therefore, another
approach is chosen to estimate the order of magnitude of the energy savings.
The industries interviewed for this project employ distribution transformers with relatively low
losses. It seems reasonable that the average energy efficiency of distribution transformers
– Page 51 of 57 –
40130017-TDC 02-24226
across Europe is lower than in the companies considered. The average losses are estimated
at 1,5% of the energy transmitted. For privately owned transformers, an energy savings potential of 0,5% is assumed, i.e. approximately one-third of the losses in these distribution
transformers. This results in table 5.31.
Table 5.31 estimated annual electricity saving in private distribution transformers
Economical sector
INDUSTRY, of which:
via distribution transformers
not via distribution transformers
COMMERCIAL AND PUBLIC SERVICES
TOTAL
Electrici- Losses in disty con- tribution transsumption
formers
(TWh)
(TWh)
Savings potential (TWh)
1000
500
500
600
7,5
7,5
2,5
2,5
9
3
1700
16,5
5,5
Privately owned transformer offer a savings potential of approximately 5,5 TWh/year, if all distribution transformers would be replaced by energy-efficient transformers. The associated
CO2 emission reduction would amount to 2,2 million tonnes/year, or 0,65% of the 340 Mton
emission reduction target of the European Union for 2012.
– Page 52 of 57 –
40130017-TDC 02-24226
6.
CONCLUSIONS AND RECOMMENDATIONS
6.1
Conclusions
The industrial sector is a large energy user, covering nearly half of the electricity use or 1000
TWh annually in Europe. Although these enterprises obtain their electricity from the public
medium and high voltage networks, much electricity is consumed at low-voltage level – the
conversion to low-voltage is performed by privately owned distribution transformers.
A preliminary investigation by interviews with representatives several large Dutch industrial
companies and case studies has been carried out to obtain an insight into the energy saving
potential in industry through the use of energy-efficient distribution transformers.
6.1.1
Transformer population
The population of distribution transformers in industrial enterprises and large office buildings
shows some salient differences with their counterparts in the public electricity networks:
 industrial transformer sizes are typically 1000–4000 kVA, contrary to the public transformers which are in the range 50–1000 kVA
 the secondary voltage for larger transformers is regularly 690 V instead of 420 V
 the average load of industrial transformers is relatively high (30-100% or rated load)
 the newest transformers are often dry-type transformers instead of oil-cooled ones
 high levels of harmonic pollution of the load current frequently occur (extra losses, risk of
extra ageing)
 a relatively young transformer population (up to 30 years).
The total European population of industrial transformers is estimated to be 100.000-150.000
units, with total installed power of approximately 100-150 GVA.
Based on the HD 538, HD 428 and the interviews the following differences are observed
when comparing a dry- to an oil-cooled transformers:
 The purchase price of dry transformers is higher than the purchase price of oil-immersed
transformers.
 The no-load losses of a dry transformer are higher, due to their bigger dimensions
 The load losses however, are at full load lower compared to oil-immersed transformers.
 Harmonic pollution of the load causes less heating and ageing the dry transformer less
than the oil-immersed transformer. However, due to epoxy the heat emission of the drytransformer is less than the oil-immersed transformer.
 Dry-type transformers are considered better provided against fire5
 Dry-type transformers do not need an oil-spilling container.
As a rule of thumb, for a lower loading profile, the oil-immersed transformers are cost effective, sometimes even with an amorphous core, however if the load is growing and/or significant harmonic pollution is present, the dry-type transformers are more cost effective.
If the losses given in the HD 538 and HD428 are not taken in account, but are based on the
based on the loss evaluation ( A and B factors), it is possible to buy transformers with even a
It should be noted that there are special ranges of oils (O, K and L) for better fire protection
of oil-immersed transformers.
5
– Page 53 of 57 –
40130017-TDC 02-24226
higher energy efficiency than the D-D’ range. This is irrespective of the type of transformer.
6.1.2
Transformer purchasing policies
In case of turnkey contracting of entire installations, little control is exerted on the loss levels
of transformers purchased. If loss levels are considered, payback times often are very short.
Also, energy prices are often very low due to large purchase volumes. These factors are relatively unfavourable for the application of energy-efficient transformers.
Some industrial companies are aware of the energy savings by using transformers with low
losses. These industries typically do not buy their transformers in a large turnkey contract but
separately. An excellent illustration of this practice is one of the interviewed companies which
has been applying quite energy-efficient transformers in 1986 as described in case 5.3. The
used transformers are cost-effective and even more energy efficient than the losses of the DD’ transformer as given in this report! Transformer standards apparently are not very demanding regarding energy efficiency.
Almost every interviewed company has placed dry type transformers, or is considering to
place dry type transformers instead of oil immersed transformers. Comparing the losses of a
dry type transformer with an oil-immersed transformer and the purchase price, this is remarkable. The losses of a dry type transformer are very high compared with the oil-immersed
transformers. In other words, the efforts to lower the losses of an oil transformer in the last
decades are wept out by using dry type transformers with higher losses.
6.1.3
Loss evaluation, including the effects of harmonic pollution
Special attention has been paid to the effect of harmonic pollution. Harmonics create extra
losses and therefore a temperature rise, which has a negative influence of the lifetime of
transformers. The influence of harmonics on the transformer is for the dry transformer less
than the oil-immersed transformer. In the case studies, the increase of energy losses due to
harmonics was significant (over 30%), while the lifetime reduction was rather limited.
Transformer loss evaluation with A and B factors (according to HD 428 and 538) is applied in
some cases, but this method neglects the influence of higher harmonics: differences up to
30% may occur.
In fact, the loss evaluation method with the A and B factors is not well applicable if significant
harmonic distortion is present. One of the complications is that in the presence of harmonics,
A and B, as presently defined, become dependent on the transformer construction, so can not
be used anymore to compare different transformers in a simple way.
6.1.4
Energy saving potential
The case studies showed that, although there are some older (oil) transformers used in the
industry, it is normally not cost effective to replace these transformers with new ones with
lower losses, an exception being the situation where very old (<1970), inefficient transformers
are applied.
For new transformers, energy-efficient designs are often attractive, provided a “reasonable”
payback time (5-7 years) for the increased investment is allowed.
– Page 54 of 57 –
40130017-TDC 02-24226
The energy savings potential by application of energy-efficient transformers differs significantly from company to company. A rough estimate of the European potential is 5,5 TWh/a for Europe, equivalent to CO2 emission savings of 2,2 million tonnes/year, or 0,65% of the 340 Mton
target for Europe in the year 2012.
Because of the long life span of distribution transformers, market penetration of energyefficient transformers in the private sector will only be achieved gradually.
6.2
Recommendations
6.2.1
Purchasing policies and promotion
One of the main problems to improve the use of energy efficient transformers is the ignorance
of electricity consumers for buying and using energy efficient transformers. Since a lot of
transformers are bought as part of turnkey projects, there is a little (or sometimes no) attention for the losses of transformers. Low attention for the evaluation costs will result into an inefficient transformer during the complete lifetime. Therefore the purchaser should be aware of
the loss evaluation formula at the moment of ordering the transformer. A problem here is the
estimation of these evaluation factors by the purchaser. A good estimation of these factors
can save the environment, electricity and costs over a long period of time.
The awareness of the purchaser for the no load and load loss evaluation factors should be
the way to promote energy efficient transformers.
6.2.2

Standardisation: HD428 and 538
The transformers as given in the HD 428 and HD 538 are based on distribution transformers in the utilities. The industry uses similar transformers, but there is a difference in
rating of the used transformers for utilities and industries, so it is proposed to extend and
refine the range to make it suitable for the industry. The extension should be up to 4000
kVA rated power, and the rating should become more fine as the load can often be better
predicted, which allows a better match between transformer and load. Table 6.1 gives the
proposed (extended) range of preferred transformer ratings.
Table 6.1 proposed (extended) range of preferred transformer ratings
Present range in Proposed range Proposed secondHD428/538
HD 428/538
ary voltages
50
50
420 V
100
100
420 V
160
160
420 V
250
250
420 V
400
400
420 V
(500)
420 V
630
630
420 V
800
420 V
1000
1000
420 V
1250
420 V
1600
1600
420 V
2000
420 V
– Page 55 of 57 –
2500


2500
3150
4000
40130017-TDC 02-24226
420 V, 690 V
420 V, 690 V
420 V, 690 V
Attention should be paid to the influence of harmonics in the HD 428 or HD 538. The use
of the economic evaluation factors A and B needs adaptation in order to correctly represent the influence of harmonics. It is proposed to develop a simple system for this.
HD 428 contains three lists for no-load and load loss levels. Following modifications are
proposed (and similar modifications for HD 538):
 List C-C’ should be the preferred series.
 The list with higher no-load loss levels (A’ and B’) should be removed. It is proposed
to add a list D’ for reduced no-load losses (15% less no-load losses than list C’) and
E’ for strongly reduced no-load losses (70% less no-load losses than list C’, i.e.
amorphous cores).
 The list for the highest load loss levels (B) should be removed, too. The load loss level A (15-20% higher than level C) will be justified in some cases of very light loading.
It is recommended to add a list D for reduced load losses (15% less load losses than
list C) and a list E for further reduced load losses (30% less load losses than list C)
6.2.3
Savings potential of special transformers and high-voltage motors
Although the using of energy saving transformers can be cost effective and saves energy, a
lot of electricity consumed in the industries is at a higher voltage rating than 420 or 690 V. A
lot of energy is consumed by HV motors or equipment for electrolysis.
The most widespread high-voltage load in industrial networks is the high-voltage motor, with
rated voltages up to several kV and powers in the megawatt range. It might be worthwhile to
investigate the scope for energy savings by application of energy efficient high-voltage motors.
Electrolysis is often used in chemical and non-ferrous metal industry, which in Europe are responsible for about 27% of the total electricity consumption. For electrolysis a converter transformer in combination with a rectifier is used to produce a low DC voltage. The rectifier produces high levels of harmonic pollution in the load current. Filtering of these harmonics is very
limited due to the high cost of filtering in such high-power installations. Therefore the harmonic loading and the extra losses in the converter transformers may be expected to be very high.
It is recommended to assess the potential for energy savings by application of energy efficient
converter transformers.
6.2.4
Optimised system voltage in industrial networks
Some industrial companies use 3 and 6 kV networks and installations, in order to feed large
motors. Networks of these voltages have following drawbacks:
 components for these voltages are ‘specials’ (so expensive)
 safety regulations are very stringent for 3 and 6 kV networks, which are formally considered ‘high voltage’. 690 V installations are still ‘low voltage’, requiring less qualified personnel.
– Page 56 of 57 –
40130017-TDC 02-24226
Since a lot of electrical equipment is standardised for 420, 690 V or 10 kV, it is proposed to
investigate if it would be cost effective to replace existing 3 and 6 kV installations with a 690 V
or 10 kV installation [14].
– Page 57 of 57 –
533565406
2001-10-23
REFERENCES
[1]
The scope for energy saving in the EU through the use of energy-efficient electricity
distribution transformers, European Copper Institute, December 1999.
[2]
Quick scan: Power demand of ICT companies, KEMA TDP-01-16731, January
2001 on behalf of NWN (now NUON), (in Dutch, confidential).
[3]
Harmonics, Transformers and K-Factors, Copper development Association, CDA
publication 144, September 2000.
[4]
Loading guide for dry-type power transformers, IEC 60905.
[5]
Loading guide for oil immersed transformers, IEC 60354.
[6]
Energy in the Netherlands, EnergieNed 2000.
[7]
Dry-type power transformers, IEC 60726.
[8]
Power transformers, IEC 60076.
[9]
Transformers for industrial applications, IEC 61378-1.
[10]
Semiconductor convertors, general requirements and line commutated convertors
part 1-2: Aplication guide, IEC 146-1-2.
[11]
J & P Transformer book, twelfth edition 1998, Martin J. Heathcote.
[12]
Availability of the power supply system in the Netherlands – Report for systems
from 0,4 kV to 150 kV in 2000; KEMA report (G.A. Bloemhof, W.T.J. Hulshorst),
reference 40110014-TDP 01-21151A d.d. Aug 23, 2001.
[13]
Boete van 50 Euro voor ton teveel kooldioxide; http:www.energiemanagement.net
(in Dutch).
[14]
Use of 690 V for LV industrial distribution network to save capital cost and improve
network efficiency, P.F.Lionetto, R.Brambilla, P.Vezzani and E.Picatoste, CIRED
2001