ECONOMICS OF UPGRADING SWER
DISTRIBUTION SYSTEMS
Nasser Hosseinzadeh1 and John Rattray2
1. Swinburne University of Technology, Hawthorn, Vic 3122, Australia
2. Central Queensland University, Australia
Abstract- This paper reports on the various means by which
Single Wire Earth Return (SWER) distribution systems may be
upgraded, comparing the various limits that are associated with
each method and the economic costs of its deployment. An
existing overloaded SWER system, Mistake Creek North in
Central Queensland - Australia, has been used as a concrete
example. Conclusions are drawn about the appropriateness of
each method and recommendations are made.
Keywords: SWER; Single Wire Earth Return; Electrical
Power Distribution Systems; Rural Electrification
I.
INTRODUCTION
Single Wire Earth Return (SWER) distribution systems
provide electricity to rural areas from the central network where it wouldn’t otherwise be economic- by using a
combination of light-weight, high-tensile conductors and an
isolating transformer so that the earth itself forms the return
path. The choice of conductor minimises the number of poles
required (about 50% of the number for normal aluminium
conductors) and the single wire means no cross arms, narrower
easements, and lighter poles. This provides a substantial
saving over traditional single phase on longer lines that covers
more than the additional cost of the transformer and the higher
losses in the high tensile conductor [1].
SWER distribution systems have long been recognised as
the most cost effective way of distributing electricity over long
distances to sparsely populated areas. A good introduction to
this technology can be found in [2]. The World Bank has been
encouraging the expansion of simple systems for rural
electrification to reduce the cost of the grid extension [3].
Although the utilisation of SWER initiated in New Zealand
followed by Australia, other nations have used this technology
for supplying their rural areas, too [4].
Within the Australian context, SWER networks are widely
used with a total length estimated at over 190,000 km. The
first SWER line in Queensland was built in 1959, and
following a State government drive (the RESS program) to
increase rural electrification, rapidly expanded in the 1970’s
and early 1980’s. Today, little new SWER is being built as
coverage of the easily accessible rural areas is nearly
complete; consequently the bulk of SWER lines are between
25 and 49 years old. After about 30 years of approximately 3%
compound growth, many are now reaching or exceeding their
original design limits. This growth is compounded by the
recent wide spread deployment of affordable air conditioners
and equipment such as faxes and computers, which are
sensitive to poor quality supply.
As the loads on these networks have increased, the problem
of increased losses and voltage drop at high loads is now a
common problem. On the other hand, at the off-peak times
increased level of voltage due to line charging is observed.
With the recent increased demand for high power electrical
appliances, the increased load on SWER networks makes it
difficult to maintain good voltage regulation without utilising
methods to improve the network performance [5].
Traditional upgrades are expensive on a per customer basis
often exceeding $25,000 per customer (in rural areas) or
$10,000 per km. However, modern power electronics and
control systems offer alternatives albeit at the cost of added
complexity and points of network failure [6].
The total installed length of SWER within Ergon Energy
Corporation in Queensland is approximately 64,000 km with
26,000 customers spread over 865 schemes, making up 5% of
Ergon’s business by customer numbers and 9% by asset base.
The average customer consumes approximately 9 MWh per
annum which is about 20% more than the average urban
customer consumption [7].
This paper reviews how various technologies can be used to
effectively upgrade SWER lines as they reach the limits of
their current capacity. In order to substantiate generalities, an
actual SWER line was chosen against which to evaluate the
various upgrade options. The study has concentrated on
modelling Mistake Creek North SWER line, which is typical
of many of the more heavily loaded lines within Ergon’s
distribution area. The study has been conducted using the PSSSINCAL modelling tool produced by Siemens.
II.
MISTAKE CREEK NORTH SWER
Mistake Creek is located near the small rural town of
Clermont in Central Queensland. Built in 1987, it was
originally designed for an After Diversity Maximum Demand
(ADMD) of 200kVA. It has been upgraded over time to
400kVA by the addition of a second 200 kVA isolating
transformer and a single phase voltage regulator. The currently
estimated maximum ADMD of 380 kVA occurred in 2004;
subsequent peak loads being depressed because of the drought
conditions occurring over much of the local countryside. The
climate of the area is typical of Central Queensland with hot
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TABLE I
MISTAKE CREEK SWER CUSTOMER DEMAND GROWTH
2007
Peak
2009
(2004)
2011
2013
2015
2018
Peak kW
285
345
360
380
400
420
440
Avg kW
115
137
145
150
160
167
176
Min kW
71
86
90
95
100
105
113
Peak kVA
336
404
424
445
468
492
530
% of installed
kVA
30
35.9
37.7
39.6
41.6
43.7
47.1
The kVA figure assumes a power factor of 0.85 and the
percent of installed kVA is calculated on a base of 1.125 MVA
distribution transformers, which supply the SWER line. Note
also that these figures represent summed customer demand. To
derive the demand at the isolating transformers, a load flow
must be run to calculate system losses, charging currents, etc.
Figure 1 shows the estimated future demand.
Figure 1. Mistake Creek North estimated future demand
The power losses of this SWER line are shown in Figure 2.
Existing Network Losses
100
25%
90
80
20%
70
60
kW
summers (an average of 60 days in excess of 35oC) and cool
winter nights. The area receives considerable sunlight, but
little wind with average wind speeds between 10 and 11 km/h.
The load on the SWER consists of 68 customers and 123
metering points with a total of 1.1 million kWh recorded
consumption in 2007. Of this, the top 6 customers used 30%
of the energy and the bottom 32 customers 7.7%. Residential
loads (including residential component of farms) made up
84% of the load by usage and 55% by number of connections,
with the remaining connections consisting of small
commercial and off-peak farms. Off-peak tariffs made up 15%
of the load by usage and 31% by number of connections.
The loads on the SWER system are both larger in size and
smaller in number than on the average distribution feeder.
This means that individual customer actions have a larger
impact on the total demand on the SWER line expressed as a
percentage than is the case for loads on a normal distribution
feeder. In terms of the shape of the load duration curve, this is
mainly governed by the degree of co-incidence of loads which
in turn depends on the statistical correlation between loads and
external factors such as temperature and time of day with the
stronger the correlation, the more ‘peaky’ the curve. SWER
loads are likely to be less strongly correlated than the feeder,
as they contain more loads such as pumping that do not
depend on external factors. The currently accepted average
growth rate per customer over the whole state is 3% per
annum; however, given that the area is in the middle of a
significant drought and suffering some depopulation, the
average load growth on this SWER line has been arbitrarily
reduced to 2.5% for the purpose of this study.
The consumption peaked in 2004 at an estimated 345 kW
and since then has been reducing slightly, probably due to the
drought and cooler summers. The peak demand has been
estimated by summing the non-controlled tariffs and adding in
1/3 of the time of day tariffs (excluding night-only usage) to
reflect the uncertainty of the actual peak load time. This was
reduced to a daily consumption, of which 40% was assumed to
occur as a peak half hour load. The actual 2004 peak value
was assumed to be the maximum potential demand in 2007,
which was then projected forward at a steady 2.5% growth
over the period of the study. The Average value was
calculated as 40% of the peak and the low as 25% of the peak.
The result is shown in table I.
15%
50
40
10%
30
20
5%
10
0
0
50
100
150
200
250
300
350
400
0%
450
Customer Load kW
Line Losses
Total Losses
Percentage of Load
Figure 2. Power losses of the existing network at Mistake Creek North
III. MODELLING
Mistake Creek North SWER was modelled using PSSSINCAL software package by isolating the system from the
rest of the network at the isolating transformers and adding an
infinite bus to supply the required power at 1 per unit. Loads
were assumed to be proportional to the size of the distribution
transformers and uniformly at 0.85 lagging power factor. This
treats the distribution transformer losses and the change in
power factor caused by the transformer inductance as customer
loads.
It also ignores any voltage drop between the
distribution transformer and the customer connection point.
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In order to evaluate the impact that changes to the SWER
network has on the rest of the feeder, a second model was
constructed of the Capella feeder. In this model the lines were
pared down to a single branch connecting the Mistake Creek
SWER with the zone substation and replacing the other SWER
lines on this line with single loads. Loads on the Cappella
branch were replaced by a single load at the point that it
branched off from the line.
IV. SWER LIMITS
SWER systems typically have slightly different limits than
do standard distribution feeders. These limits are evaluated for
the existing system and then for each of the upgrade
technologies.
A. Voltage Variation
The regulatory limits at the customers connection point is
240 V ± 7%. Allowing for the nominal output voltage of the
distribution transformer being 250 V and a drop of between 0
and 1% between the transformer and the connection point,
gives an allowable range of 1.027 and 0.907 pu at the
distribution transformers. As the voltage limits apply to the
customer connection point, but the study models the system at
the distribution transformer, adjustments were made to the
model to ensure that the regulatory limits are met.
B. Isolating Transformers
The two isolating transformers have a combined rating of
400 kVA, the assumption being that they are matched closely
enough to evenly share the load.
As for any transformer, power ratings are limited by the
temperature rise caused by heat generated through losses.
SWER isolating transformers tend to be a little less affected by
short term over rating as they are pole mounted and are
therefore more exposed to cooling from the prevailing wind.
However, SWER lines also tend to be in the hotter parts of
Queensland and therefore the winds tend to be warmer.
Note that there is no regulatory requirement for redundancy
in the supply of electricity to SWER lines and therefore the
limit is the combined throughput of both transformers.
C. Isolating Transformers Current
As all of the SWER line current flows through the isolating
transformer earth, a voltage rise occurs between the ground
and the case of the transformer due to the impedance of the
earth connection. Ergon Energy has found that this impedance
is typically in the order of 2 Ω in the dry sandy soils typical to
Central Queensland. They also limit the voltage between the
case and the ground to 20 V meaning a maximum of 10 Amps
per earth. In the case of Mistake Creek having two earth
connections (one per transformer) this means a limit of 20
Amps to the line current.
D. Fault Currents
As SWER systems use very lossy conductors, fault currents
are typically quite low, compounded by the faults themselves
typically having high impedances – e.g. a line dropping over a
bush or tree branch. These faults cannot be detected by
measuring the presence of an earth current (as is common on
balanced three phase systems). Therefore, the safe design of
the line often requires additional protection to be added and
the line to be segmented. For the purposes of this study, these
limits will be mentioned only in passing, except where
particularly relevant, e.g. distributed generators.
E. Impact of SWER on the System
As SWER lines appear to the rest of the network as large
loads across two phases and as they are highly variable in size,
a large SWER system has a considerable impact on the phase
voltages in the rest of the network. The problem is
compounded when multiple systems are on the same feeder as
the variability of the loads may make it impossible to balance
the system. For example, a feeder which is balanced when
SWER A is at a peak will be unbalanced when SWER B is
peaking and A is back to average. Consequently, the
traditional distribution feeder analysis assuming a balanced
system with loads of constant power factor is of doubtful
accuracy when applied to lines in which SWER systems form
a considerable part of the load.
V. TRADITIONAL IMPROVEMENTS OF SWER NETWORKS
A. Upgrade of Isolating Transformers
There are two limits that are impacted by the arrangement of
the isolating transformers:
1) The capacity of the transformers;
2) The voltage rise between the transformers and earth.
To relieve the capacity issues, three solutions are apparent:
1) Upgrading the two transformers from 200kVA units to
say twin 300 or 350 kVA units;
2) Changing the twin units for a larger single unit;
3) Add a third 200 kVA transformer in parallel with the
two existing transformers.
The preferred option will depend on details of the site and
the availability of equipment including spares in case of
failure. Adding a third 200 kVA transformer is the most likely
option if the engineering difficulties of additional land and
matching the existing units can be overcome. In all cases,
however, the earth mat must be improved or extended which
will add considerable additional expense. The installation of a
new isolating transformer and earth mat is currently estimated
as costing in the vicinity of $100,000.
B. Upgrade of Distribution Transformers
By changing the customers distribution transformer to a
tapped transformer up to an additional 5% may be gained to
the bottom voltage. However, the maximum allowable
voltage also drops by 5% as the voltage variation cannot be
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greater than 14% and the taps are fixed. On this SWER, all
customers at low loadings have a voltage in the order of 1.0 to
1.01 pu. This limits the maximum additional boost to 2.5% to
avoid breaking the voltage range at the top end at times of
light loads. Costs have been estimated at around $8,000 per
replacement transformer with a per unit reduction if multiple
transformers closely located are being replaced.
C. Additional Regulators
Adding additional single-phase voltage regulators to
troublesome parts of the line looks attractive as the installed
cost is in the order of $40,000 and multiple clients are assisted.
However, there is a major technical and regulatory problem
when multiple voltage regulators are placed on the same line
caused by the delay between a change in the voltage and the
subsequent tap change to control the voltage. The following
scenario illustrates this point:
1) A line with three regulators is at or near maximum
demand – a typical hot summer day and all voltage
regulators are consequently on maximum tap;
2) A lightning strike occurs on the line and one of the
automatic reclosing relays cuts off a substantial part of
the load;
3) The total boost on the line from the three voltage
regulators all at +10% results in a voltage of 1.33 pu;
due to the light load and the Ferranti effect there is little
or no voltage drop over the length of the line to
compensate for the rise from the regulators. Therefore
the entire voltage of 1.33 or 319 V appears at the
connection point and through to the customer
switchboard of any customers still connected following
the final voltage regulator.
D. Upgrade of Lines
Another traditional solution is to replace lines with heavy
currents with conductors of lower resistance; therefore,
reducing voltage drops and losses.
Costs for this type of work for the case study have been
estimated at $20,000/km. Therefore, the total cost over 40 km
is around $800,000.
E. Convert to Duplex
This represents a major upgrade in the size of the SWER
system with a potential near doubling of capacity. As such, it
represents a major investment in a limited number of
customers and, given the uncertainties around continued load
growth, there is a major risk of having stranded assets in the
future. Technically duplex SWER systems consist of two
single independent SWER systems. They are isolated from
the feeder in one of two ways depending on the major
constraint that is being addressed:
1) If the earth current is a limiting factor, then the two
SWER lines are constructed with a feed from the same
two phases, but with reverse polarity (180 degrees
apart). The earth point is the middle point between
these two and the earth current represents the difference
in demand. Therefore, one can have a combined total of
800 kVA on the SWER with zero voltage rise at the
earth point if the loads are evenly split over both
systems. However, this load appears on only the two
phases and represents a considerable imbalance.
2) If the impact on the feeder is the limiting factor, then all
three phases are used as a source and the phase
difference between the two SWER systems is 120
degrees. In this case the load is more balanced on the
feeder with it being split approximately 25%, 50% and
25% over the three phases.
In terms of construction, the second system is normally built
on separate poles and is therefore free to take whatever path
the designer regards as best to pick upload and minimise costs.
Ergon energy has estimated an approximate cost of $2 million
for this upgrade, consisting of around 70 km of new line,
additional isolating transformers, voltage regulators and
changing connections from the old line as appropriate. This
scenario, therefore, represents the base solution against which
all others should be measured.
VI. IMPROVEMENT OF SWER NETWORKS USING NEW
TECHNOLOGIES
A. Low Voltage Regulators
Low Voltage Regulators (LVR’s) are power conditioning
units designed to supply power at a settable constant voltage
and at unity power factor within a broad range of input
voltages and power factors. Within the SWER context they
are likely to be used to:
1) Support low voltage levels at a customer supply point
where other methods of support are unavailable or too
expensive;
2) Reduce voltage variation at a customer supply point to
fall within ±7%;
3) Improve power quality by removing peaks and sags.
They have some limitations such as:
1) As the units are owned by the utility, they will be
typically installed on the distribution transformer pole.
They will therefore not help customers with excessive
voltage drops between the meters and customer loads.
2) On a fault, they fail to a pass-through mode and the
customer is supplied with power at the network voltage.
Depending on the reliability of the units, there may be a
decrease in system reliability to a customer.
They will modify power demand by:
1) The conversion of constant impedance loads to constant
power loads, which is likely to reduce demand in times
of light demand and increase it in times of high
demand. The size of this effect will vary dynamically
with the supply voltage and also the types of loads
installed on the system.
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B. Switched Reactors
Traditionally shunt reactors have been added to the line to
control the Ferranti effect of high voltages at the end of the
line at light loads by adding inductance to the line. However,
being fixed, they continue to add inductance at heavy loads
and significantly worsen the low voltage constraint.
A switched reactor topology was proposed by [8]. A
prototype was designed and installed on Ergon Energy SWER
line of Stanage Bay. Ergon energy is studying the conversion
of the fixed reactors into dynamic elements that switch in and
out depending on the voltage level.
While a number of
different control strategies are possible, this study reflects a
low-cost approach by which the existing seven reactors are
replaced with new controlled ones of the same size.
The expected cost of the units is in the order of $6,000 on a
replacement basis, assuming that multiple units are being
replaced at the same time. However, as the units are not yet
commercially available this could vary considerably in either
direction.
C. Distributed Support
Distributed support means a series of highly distributed
generators (negative loads) scattered throughout the network
effectively connecting to the SWER line at the distribution
transformers. The expectation is that these loads are customer
owned and managed albeit with potentially substantial Ergon
Energy subsidies or help.
These negative loads may be:
•
Photovoltaic panels
•
Battery storage systems
•
Small (< 5 kW) generators
•
Or any other load support technology.
Costs vary considerably depending on what subsidies the
owner of the equipment is entitled to and the particular balance
chosen between running costs and capital costs. The simplest
and most widely available system are grid connected PV
panels which are in the order of $10,000 a kW installed for
multiple units and about $14,000 a kW for single lots. On our
case study this comes to about $250,000 in direct costs.
D. Point Support
Point support represents equipment of an order bigger than
distributed support loads and the same order as the total ‘near
by’ load – typically in the order of 25kW. Examples of this
would be a large number of PV panels associated with a
school installation, a diesel generator next to a road station, or
a large flow battery in a small hamlet.
The major electrical differences with distributed support are:
•
The size of the installation, 25 kW+ as compared with 1-2
kW.
•
The location of the installation. They can be placed where
in the network they will provide most support as
compared with distributed support, which sits at the
individual premises of people who wish to have it.
Costs vary by the type of unit ranging from low capital costs
and higher running costs of diesel units to moderate capital
costs and low running costs of flow batteries.
E. Load Management
Load management is the generic term given to those
techniques and technologies by which the nature of the
electrical load is changed to better match the capabilities of the
supply infrastructure. It comes in two broad flavours: Load
reduction through which the size of the load is reduced; and
load shifting through which demand is time-shifted to periods
when the line is more capable of supporting it.
Some examples of load management are using off-peak
tariffs to control the supply of electricity, usage of replacement
energy such as using sun to heat water and changing electric
stoves to gas ovens, and load reduction techniques such as roof
insulation and painting with reflective paint, changing to low
energy lighting, etc. The major issue with these techniques is
the degree of customer assistance required to implement them.
VII. IMPACT ON VOLTAGE REGULATION
Figure 3 shows the impact of various options of improving
the SWER network on voltage regulation.
Comparision of Voltage Regulation
90
80
Number of customers < 0.9
2) Decrease the demand for reactive power through
motors.
3) Increase the demand for active power by removing
current supply constraints caused by the poor quality of
supply offered on many SWER lines.
Installed costs are expected to be in the order of $5,000 per
unit, depending on the distance from base and the number
being installed at any one time, i.e. traveling time will have a
significant impact on actual costs in a SWER context.
70
60
50
40
30
20
10
0
250
275
300
325
350
375
400
425
Customer load kW
Switched Reactors
Point Support 25 kW
PointSupport 50 kW
Distributed Support 22 kW
Line Upgrade
Existing network
2nd Regulator
LVR
Figure 3. Comparison of the impact on voltage regulation of various
techniques to improve SWER network operation
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450
VIII.
FINANCIAL COMPARISON
A. Evaluation of Losses
The price of electricity varies by time of day and season,
with a large random element reflecting the availability of
supply. Because of this random element in pricing and due to
the variability in SWER demand, losses will be valued by
calculating annual volume by average cost. To get a feeling
for the value of losses, an average customer load of 140 kW
has approximately 17% loss (expressed as a percentage of load
from the energy delivered to the Supply Point). Applying this
average figure to the annual metered consumption in 2007 of
1,127 MWh gives an estimated loss of 191,000 kWh. At an
average wholesale price of 4.5 cents per kWh this corresponds
to a value of approximately $8,500.
Therefore, loss reduction or increase can have a significant
impact on the overall cost of SWER upgrades and needs to be
taken into account. This will be calculated by increasing the
total number of MWh consumed each year by the annual
growth percentage and recalculating the average loss
percentage as the system moves into higher loss bands. A
constant value of 4.5c per kWh will then be applied.
B. Impact of Consumer Service Obligation
Ergon Energy is required by the Queensland State
government to supply all non-contestable loads at a standard
tariff irrespective of the actual cost of supply. In order to
compensate Ergon Energy for the losses involved in a
transparent way, an agreement has been reached called the
Consumer Service Obligation (CSO). The details of CSO are
confidential. The CSO agreement effectively insulates Ergon
Energy from changes in the cost of supplying rural customers.
However, as Ergon’s shareholder, the State government is also
the payer of the net CSO loss; thus, there is considerable
wisdom in minimising these costs. Consequently, the value of
system losses and the return on assets have been included in
the NPV calculations. This effectively views the value of the
network from the view of the State government.
C. Summary of Cost Comparison
A period of 10 years has been chosen for the financial
analysis for the following reasons.
1) Given the substantial issues of climate change, drought,
water usage, rural depopulation, fuel prices and
technological change, it is unlikely that any growth
scenario will be within cooee of the actual figures much
past this period.
2) A number of the options examined are unproven and
therefore commercially meaningful statements on
equipment life are difficult to believe. This implies that
maintenance costs have a large degree of risk attached
to them.
The three options for the improvement of SWER network
considered in this section are:
Option one. Converting the SWER to a duplex system.
The SWER is converted in year one at a cost of $2 million.
Option two. Converting the shunt reactors to switched
reactors plus Point Support.
The hardware upgrades consist of:
•
Switched reactors plus Point Support in year 1
•
Additional isolating transformer in year 6
•
Upgrade / refurbishment of point support in year 7
•
LVR’s added to difficult customers in year 8
Option three. As for option two, but also reducing demand
by 10% in year 1.
The delay that this causes effectively moves the requirement
for the LVR’s to outside of the study period and shifts the
point support and isolating transformer upgrades back by three
years.
Table 2 shows the comparison of costs for these options.
TABLE 2
COMPARISON OF COSTS FOR THREE OPTIONS OF IMPROVING SWER
NETWORKS
Duplex
Switched
Reactors +
Point Support
Option 2 +
Demand
Management
Total discounted
equipment costs
-2,000,000
-265,411
-197,107
Total discounted
return on Assets
1,040,065
104,313
68,523
Additional Losses
0
-9,588
-13,798
-25,658
-19,277
PS Maintenance
Discounted book
value of residual
assets
528,745
70,007
71,513
Total NPV cost
-431,190
-100,679
-90,147
The following remarks are in order with regard to Table 2.
1) The ‘total discounted return on assets’ is the cost of the
upgrade recovered in the study period from the users of
electricity in the broader community at Ergon Energy’s
standard rate. For an efficient system this should be as
small as possible.
2) The loss adjustment represents an estimate of the value
of the ‘additional system losses’ caused by the upgrade
and illustrates the sensitivity of this analysis to the price
of power. If wholesale prices rise, so will this cost.
3) The importance of the ‘discounted book value of
residual assets’ is that it illustrates the size of the assets
at risk through shifts in demand or technological
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redundancy. As can be seen duplexing the SWER
leaves a substantially higher volume at risk.
4) The losses of the duplex SWER system are assumed to
be the same as for the existing system; as although the
total length of line has been substantially increased the
current on that line has decreased but probably not to
the point where the losses start to rise as a percentage.
5) The cost difference between options two and three
represent how much could be spent on the load
management and still be ahead.
As can be seen, the variations in the NPV of the three
options is considerable and certainly of sufficient size for
Ergon Energy to take seriously both ‘load management
techniques’ and the ‘new technology’ potentially available on
SWER systems.
IX. CONCLUSIONS
This paper has reported on the various means by which
Single Wire Earth Return (SWER) distribution systems may
be upgraded. The conclusions of this study in regard to the
upgrade options for a case study, Mistake Creek SWER, are:
•
•
•
ACKNOWLEDGMENT
Ergon Energy Corporation sponsored this project. The
authors would like to thank Mr. Jon Turner of Ergon Energy
for his support to this project.
REFERENCES
[1]
[2]
[3]
[4]
The economically viable upgrade path for this SWER is to
upgrade separately the constraints caused by voltage drops
and transformer limits. In particular, voltage limitations
are best dealt with through a combination of two
experimental options: switched reactors and point support
of the network.
While little is known about the potential size of savings
through load management, it would appear after making
some reasonable assumptions that this is likely to be the
second or third most economic method to upgrading the
SWER. However, two substantial problems remain to be
solved: 1) the lack of load diversity on SWER suggests
that existing ripple control tariffs will not be particularly
effective; 2) the high peak power costs suffered by Ergon
Energy aligns with the low benefits accruing to the
consumer of existing load management techniques.
•
Of the traditional methods, the cheapest option is to add a
high-voltage regulator to the network if one is not already
present. However, more than two on the network is likely
to cause over-voltage problems and will significantly
complicate the placement of fault protection.
•
The other traditional upgrade options of either converting
the SWER line to a duplex or re-conductoring the line are
either very expensive or just expensive and not very
effective, respectively.
•
Low Voltage Regulators (LVR’s) if put into widespread
use for relieving voltage constraints will most probably
exacerbate network problems on both the SWER and its
feeder. However, they do have a limited use for attacking
localised problems that are otherwise unsolvable
economically.
Open-delta high-voltage regulators are unlikely to be
suitable for use on feeders that have large SWER lines, as
they do not independently compensate individual phases.
With the lack of diversity on SWER systems, these can
become significantly unbalanced and, therefore, limit the
degree of boost available to well below the maximum
capacity of the individual transformers.
[5]
[6]
[7]
[8]
L. Mandeno, “Rural Power Supply Especially in Back Country Areas”,
Proceedings of the New Zealand Institute of Engineers, Vol 33, 1947,
Ferguson and Osborn Printers, Wellington, pp 234-271.
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W.
Holland,
“SWER,
How
does
it
work?”,
http://www.ruralpower.org/swer_003_what_is.htm, viewed Sept. 2008,
or
“Single-Wire
Earth
Return”,
Wikipedia,
http://en.wikipedia.org/wiki/Single_wire_earth_return.
National Rural Electric Cooperative Association, “Reducing the cost of
grid extension for rural electrification”, February 2000,
http://www.worldbank.org/html/fpd/esmap/pdfs, Accessed July 2005.
T. R. Brooking, N. Janse van Rensburg, R. J. Fourie, “The Improved
Utilization of Existing Rural Networks with the use of Intermediate
Voltage and Single Wire earth Return Systems”, Proceedings of the
IEEE AFRICON ’92 Conference, pp 228-234.
A. Loveday and J. Turner, “Remedial treatment of voltage unbalance on
three-phase distribution feeders caused by supply to large SWER
systems”, Distribution Conference, Adelaide, November 2003, Paper
No. 138.
N. Hosseinzadeh, P. Wolfs, S. Senini, D. Seyoum, J. Turner and A.
Loveday, “A proposal to investigate the problems of three-phase
distribution feeders supplying power to SWER systems”, Proceedings of
Australian University Power Engineering Conference (AUPEC), 26-29
September 2004, Brisbane, Australia.
J. Turner, “Delivery Service Improvements Across Ergon Energy’s
Single Wire Earth Return (SWER) Network”, Internal Ergon Energy
document, 2005
P. J. Wolfs, N. Hosseinzadeh, S. T. Senini, “Capacity Enhancement for
Aging Single Wire Earth Return Distribution Systems”, IEEE Power
Engineering Society Annual General Meeting, Tampa Florida, 24-28
June 2007.
Nasser Hosseinzadeh (IEEE-M’86) is currently with
Swinburne University of Technology, Melbourne,
Australia. Earlier, he had worked as a senior lecturer at
Central Queensland University in Australia, as a lecturer
at Monash University Malaysia and as an assistant
professor at Shiraz University. His special fields of
interest include power system analysis and planning,
power system stability, application of intelligent systems
in engineering, power distribution networks and engineering education.
Dr. Hosseinzadeh is a registered member of Engineers Australia, a member of
IEEE and also is on the Australian Panel APC1 System Development and
Economics of CIGRE.
John Rattray is a recent graduate of Central Queensland
University, Australia.
2008 Australasian Universities Power Engineering Conference (AUPEC'08)
Authorized licensed use limited to: SWINBURNE UNIV OF TECHNOLOGY. Downloaded on January 3, 2010 at 18:41 from IEEE Xplore. Restrictions apply.
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