Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008
A Novel Method for Estimation of HT and LT
Feeder Losses in Distribution System
P. Chandra Sekar, R.S. Shivakumara Aradhya and M.M.Babu Narayanan
Abstract: Losses in distribution system play a major role in
the economic viability of power system operation. Efforts toMa
estimate distribution losses by suitable metering are very limited
in our country. Practical experience in one of the distribution
companies show that reliability of load survey type energy meters
used to record energy input to HT and LT distribution feeders is
poor and the scenario may not be much different in many other
distribution companies. Effort is made in this paper to estimate
the total energy loss in three types of distribution feeders, namely,
urban, industrial and rural with data as collected by utilities to
highlight the need for deriving common time duration (data time
synchronization) for the collected data at different schedules by
different agencies to be used for loss estimation.
Simple method is proposed to estimate the energy input to
HT and LT feeders where the meters are not functional. With the
estimated energies and time synchronization of data, the estimated
total HT and LT losses are found to be much different and appear
reasonable.
Many distribution companies are adopting the approach of
“100% metering and Total Energy Audit” to curb the
commercial loss. While load flow analysis is universally used
for technical loss estimation, the commercial loss is obtained by
subtracting technical loss from the total loss. However, the
estimation of total loss pose the same difficulty attributed to the
estimation of commercial loss mentioned above. Hence, there is
a need for formulating and standardizing the procedure for total
loss estimation, which in turn facilitates estimation of
commercial loss with reasonable accuracy. The new procedure
shall take into account all major constraints experienced in
collection of the necessary field data for total loss estimation. A
schematic of a typical distribution is shown in fig 1.
LT feeder
400 V
It is also found that the new method is effective only if the
number of defective meters is limited within a certain range.
LT
feeder
400 V
HT feeder
33 KV
I. INTRODUCTION
11 KV
400 V
Distribution reforms have been implemented by many
electricity supply utilities to improve their performance and
achieve economic self sustenance. In this regard, one aspect
which still bothers the distribution companies is the distribution
system losses which are found to be very high in the range of
18-62%[1] compared to the existing levels in developed
countries. Hence loss reduction is seen as one of the primary
means of achieving commercial performance improvement of
distribution companies.
The need for reducing excessive
distribution losses, in the Indian power sector is now being
recognized as one of the key requirements for restoring
financial viability of the distribution companies.
LT feeder
400 V
LT feeder
Metering point
Fig 1: Schematic diagram of Distribution feeder
II. PROCEDURE FOR TOTAL LOSS ESTIMATION
The total energy loss in a distribution feeder is in general
defined as the difference between the energy input and energy
supplied (billed). The following expressions are true:
Total energy loss = Loss in HT feeder + Loss in LT
kWh
Where,
The distribution system losses have two components,
namely, technical and commercial, together called “total
distribution loss”. Technical loss [2] is amenable to reasoning
and fairly accurate estimation. Hence could be controlled with
some financial investment, the returns on which could be
predicted. Contrary to this, commercial loss is mainly governed
by non-technical issues like theft, lack of metering and non
timely replacement of faulty meters which make its
quantification difficult.
feeder,
Loss in HT feeder = Energy input to HT feeder - (energy sent
out on LT feeders + billed energy of HT
consumers), kWh
and,
Loss in LT feeder = Energy input to LT feeder – billed energy
of LT consumers, kWh
P.Chandhra Sekhar is with Central Power Research Institute, 9480619140,
pcs@cpri.in
R.S. Shiva Kumara Aradhya is with Central Power Research Institute,
9448282334, aradya@cpri.in
M.M.Babu Narayanan is with Central Power Research Institute, 9448282321,
babu @cpri.in
From the above, it is evident that the total loss estimation
requires accurate measurement of energy input to the HT (11
kV) and associated LT (440 V) feeders, feeder wise
450
Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008
consumption of energy by HT and LT consumers, all
recorded simultaneously for the same period of time. The
estimated losses will be dependable only if all the energy
meters are in good working condition. In reality, certain
percentage of meters at LT feeder and LT consumer may be
non-functional [3] due to some reason or the other. While there
is no standard procedure followed by distribution companies to
account for the unread energy input to the LT feeders, for HT
and LT consumers’ average consumption based on the previous
few month’s consumption is considered for billing. The same
data is also considered for loss estimation. As exact meter
reading date and time is not generally recorded by distribution
companies, the conventional method does not account for the
non-simultaneous reading of the energy meters and assumes
that the data is gathered for the same duration and hence
suitable for loss estimation.
distribution companies as per their schedule is also formulated
to suit different class of consumers.
III. CONSTRAINTS IN
PRESENT PRACTICE
B. Estimation of total energy consumed by consumers on LT
feeder where some consumer meters could not be read
Field experience of the authors in gathering the energy
and consumer consumption data shows that in most cases,
appreciable percentage of meters, mainly at the sending end of
the LT feeders located at the secondary of the Distribution
Transformers (DTR) and consumer meters would be faulty at
any given point of time. In addition, though arrangements are
available to record the HT and LT feeder inputs simultaneously,
by use of Load Survey type of electronic energy meters, the
individual HT and LT consumer consumption supplied by these
feeders are collected by different agencies at their own
schedule, often convenient for billing. Adding to the
complexity is the fact that it is not the practice of distribution
companies to collect and record the individual consumer
consumption feeder wise. It is also observed that the set date
and time in the HT and LT feeder meters are non-synchronized
either due to not taking care while commissioning or not setting
it correctly after replacing the drained batteries providing power
supply to the memory unit. Hence correlation between the
energy input and consumption in a particular feeder for a fixed
duration of time is not possible. Obviously the losses estimated
using this data would be erroneous.
There are some cases where individual LT consumption
could not be read using spot billing machine due to various
reasons for the period considered for loss estimation. In such
cases, the average LT consumption per KVA rating of a
distribution transformer is calculated by considering the data of
successfully down loaded DT meters and their LT
consumption, wherever both are available. The LT
consumption corresponding to a transformer where some
consumer meters could not be read is calculated by multiplying
the average LT consumption per KVA with the KVA rating of
the transformer under consideration.
A. Estimation of energy supplied to the LT feeders with nonfunctional DTR energy meters
1.
For a HT feeder under consideration, from the energy
recorded by the healthy DTR meters, the average
energy sent out per KVA rating of the transformers
per hour are calculated separately for different ratings
of the transformers in the feeder.
2.
The estimates for the energy sent out by transformers
having non-functional
energy meters are obtained
by multiplying the transformer KVA rating by
respective average consumption per hour.
C. Estimation of energy Consumed by
Agricultural pump sets
un metered
LT Agricultural feeder consists of mix of agriculture and
rural domestic consumers. Energy supply is restricted to a few
hours per day to suit agricultural consumers. Some of the
distribution companies do not provide energy meters to
agricultural pump sets as the energy is to be supplied free as per
the policies of the government. Hence the consumption is to be
derived from one time measurement of the load current and
average time for which the energy is supplied.
IV. THE NOVEL PROCEDURE
As none of the constraints mentioned in the previous
section could be readily overcome, in order to bring some
acceptability to the estimated losses, procedures have been
formulated for reasonable estimation of (a) energy supplied to
the LT feeders with non-functional DTR energy meters, (b)
total energy consumed by consumers on LT feeder where some
consumer meters could not be read and (c) energy consumed by
agricultural pump sets which are not metered.
Collection of field information showed that power supply
is restricted to an average duration of 5½ hours/day to
agricultural pump sets. An average power factor of 0.85 for the
pump sets is found to be a reasonably good assumption.
Therefore,
Consumption of an agricultural Pump set
Procedure for indirect time synchronization between HT
feeder input, LT feeder input , HT consumer consumption data
and LT consumer consumption data for the data collected by
= ¥3 VLIL CosɎ * Nh*Nm , Wh / month
Where,
451
Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008
VL= line voltage
IL = line current
CosɎ = power factor
Nh = No. of hours of power supply per day
Nm = Period considered for loss calculation, days
c.
The total DTR consumption (LT feeder input) is calculated
by adding Normalized Distribution transformer
consumption and projected normalized Distribution
transformer consumption.
Total DTR Consumption =
D. Procedure for Indirect time synchronization of feeder inputs
and consumer data
Normalized consumptio n Pr ojectedNor malizedDTR consumptio n
Feeder loss estimation requires time synchronized energy
data for HT feeder input, LT feeder energy input and HT and
LT consumer consumption. This aspect will be presented in
detail while discussing field data collection for this work.
2 .Time Synchronization at Consumer level
In most of these estimates, a common time frame (average
duration) is to be evolved for all the measured and estimated
quantities. The experience of reading load survey data from HT
feeder meter, DTR meter, HT consumer and LT consumers is a
time consuming process. On an average, it requires about 30
minutes to download a HT feeder meter, 48 hrs for DTR
meters, 8 hrs for reading HT consumers data and about week to
10 days to record all LT consumers consumption data. While
reading, the HT feeder meter and DTR meters, called CMRI
instrument is used .The data read by CMRI contains starting
and ending time of the data recording in addition to the energy
supplied.
a. Urban feeder
The procedure varies based on the category of the consumers in
the feeder. The following procedures are proposed for each category
In the case of urban feeders, LT consumer monthly billing
data is available but time of reading is not available. However,
it is a general practice that the meter reading is done from 08.00
Hrs to 12.00 Hrs in the morning and again from 14.00 Hrs to
18.00 Hrs in the afternoon on any scheduled meter reading day.
Therefore, the total duration is eight hours for billing per day
i.e. 480 minutes in two parts of 240 minutes. The no. of meters
corresponding to a distribution transformer (LT feeder) read
during morning half of the day and also during the afternoon
half are obtained from the billing section of the distribution
company. Similar information is collected for the whole period
of meter reading for that month for all the LT feeders. Average
time of successive meter reading is computed separately for the
meters read in the morning half and in the afternoon by
dividing 240 minutes by the number of meters read during that
time. These are calculated for every meter read for both initial
reading and final reading after one month. The difference
between the initial and final average time for individual
consumer meters gives reasonably accurate duration for which
the energy is supplied. From this, average energy consumed
per hour is calculated by dividing the billed energy by the
average time duration obtained as above.
In order to arrive at a common time frame for data
synchronization the average of the reading times of the feeder
meter and DTR meters is taken as this provides some authentic
information on time.
Average Duration (Hrs):
FeederMeterrecording duration SumofDTRme tersrecord ingduratio n
1 No.ofDTRs
1. Indirect time synchronization
Between HT, LT feeder and HT consumer data
The individual consumer consumption is then
normalized to the time duration arrived for LT feeder input in
Section D by multiplying the average energy consumed per
hour with the time interval considered for LT feeder input in
hours. The sum of all such normalized consumptions for a
particular LT feeder will be the time synchronized LT
consumption which is to be considered for loss estimation.
a. Normalization of HT & LT feeder energy input for feeder
with functional meters
Normalized HT or LT feeder input Energy =
b. Industrial feeders
Re cordedFeederInputEnergyxAverageDuration
Actualrecordedduration(hrs )
LT consumption reading, date and time are noted down
manually for individual LT consumers in the case of Industrial
feeder and procedures similar to that described in section D are
followed.
b. Projected Normalized Energy of Non-functional
Energy (DTR) Meters is calculated as
c. Agricultural feeders
There is no requirement for specific procedure in the case
of agriculture consumers as the time considered for estimating
the consumption in section C it self is average time. However,
EstimatedE nergyasper D u AverageDur ationinHrs
452
Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008
agriculture feeder also has domestic (rural) consumers whose
consumption is normalized using procedure in section D.
Feeder
d. HT Consumers
Urban
Industrial
Agricultural
The HT consumer billing data collected from Private agencies
with the permission of concerned utility officials .The data is
normalized using procedure in section D.
Urban
Industrial
Agricultural
51
24
39
20
76.47
83.33
15.2
55
21
38.18
3-7-06
19-8-06
7-8-06
21-9-06
840
840
Energy
input to
the feeder
(kWh)
1650835
789288
7-7-06
12-8-06
864
642054
The Table 3 and Table 4 shows details of measurement dates
and energy input to feeders.
Three typical 11 kV feeders are chosen representing the
three common types of consumers, namely, urban, industrial
and agricultural. The details of these feeders are given in Table
1.
Lengt
h
of
11 kV
feeder
(km)
5.39
7.10
Duration
(Hours)
Table 2: Details of energy input to HT feeders
V. DISTRIBUTION FEEDERS CONSIDERED FOR THE
LOSS ESTIMATION
Type
of
feeder
Date of meter reading
First
Second
HT
Feeder
Distribution transformers and
DTR meters in the feeder
Total
Working % of
meters meters
Working
(No.)
(No.)
meters
Urban
Industrial
Agricultural
Date of meter reading
First
Second
Average
Duration
(Hours)
16days
3rd July 2007
to 19th July
2007
6th Sep07
3rd Aug to 19th
Aug 07
13th Oct 07
1 day
Rural
Consumer
Agricultural
consumer
4July 07 to
17July 07
10th to 11th Aug
07
14 days
2 days
Table 3: Details of dates of measurements of energy input
to LT feeders
Table 1: Details of distribution feeders chosen
for the study
It could be observed from the feeder data that the
agricultural feeder is the longest and is evident that being rural
feeder, may have received less attention in provide metering.
VI. COLLECTION OF ENERGY INPUT AND
CONSUMPTION INFORMATION
HT
Feeder
Total energy input to LT feeders for the duration
given in Table 3
(kWh)
Measured for
Estimated for
Total
LT feeders with LT feeders with
working meters
faulty meters
Urban
Industrial
Agricultural
746867
770729.9
129074
NA
875941
770729.9
132331.9
480146.6
612478.5
Table 4: Total energy input to LT feeders
A. Energy input to HT and LT feeders
B. HT and LT consumer energy consumption
Electronic Trivector meters provided at the input to HT
(sending end of the 11 kV feeders) and LT (output of
distribution transformers) feeders record among other data,
energy supplied by the feeder at every half hour interval along
with date and time stamp for each data recorded. The energy
meter memory in most cases is adequate to store the data for
minimum period of 36 days. The stored data is downloaded into
Common Meter Reading Instruments (CMRI) at site in on line
mode at the end of a month.
All distribution companies generally read HT and LT
consumer meters once a month except for agricultural (rural)
feeder, whose meters are read once in two months. The LT
consumer meters are read geographical area wise and not feeder
wise by private agencies that are hired by the utility. These
results in the LT consumer meters belonging to a LT feeder
read on different days and at different time contrary to the
requirement of simultaneous reading for loss estimation. The
LT consumer data is either read and recorded manually or
keyed into a hand held Spot Billing Machines. The HT
consumers’ meters are read by the HT billing section of
Distribution Company using the CMRI.
The content of the CMRI are transferred to a personal
computer using the software of the meter manufacturer for
storing and further analysis. Table 2 shows the energy input to
the HT feeder as recorded by CMRI.
The urban feeder chosen for the study supplied 3185
nos.of LT consumers and 11 nos. of HT consumers. The
reading was completed in 16 days during the period 3rd to 19th
453
Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008
August 2006. The HT consumer meters were read in one day on
31st August 2006.
From the results, it is seen that the % loss of urban feeder is
higher than Industrial feeder and Agricultural feeder .In
contrast, the % losses in normal practice are more in
Agricultural feeder than urban and industrial feeder.
The industrial feeder supplied 25 LT consumers and 12
industrial consumers at HT level. The initial LT and HT
consumption readings were taken in one day on 6th September
2006 and the second reading was taken again in one day on 13th
October 2006. The readings were taken on 6th September
between 12.00 Hrs and 17.00 Hrs and on 13th October it was
from 16.00 Hrs to 19.00 Hrs.
B. Results from Proposed Method
The % losses at HT level, LT level and total losses are shown in
Table 6 for the same feeder and with modified procedure.
There were 132 irrigation pump sets and 1570 rural
domestic consumers in the rural feeder, all supplied at LT
voltage level. In this distribution company the supply for
irrigation pump sets are not metered. Hence the line currents of
all the 132 irrigation Pump sets were measured on 10th and 11th
August 2006 to assess the energy consumed.
Sr.No
1
2
3
VII. CALCULATION OF HT & LT LOSSES
Sr.No
The data is normalized as per procedure given in clause
4.4 at HT level as well as at LT Level. The total losses are
calculated using this data at HT level by subtracting the sum of
the energy output of DTRs from the energy input to the HT
feeder. The percentage losses are calculated by dividing the
total losses by Input energy.
1
2
3
Sr.No
Similarly, Total LT Losses with Normalization of date
and time: (Input Energy to LT feeder with normalization dataConsumer consumption with normalized data)
1
2
3
VIII. RESULTS & DISCUSSION
3.06%
8.38%
12.37%
% losses
1.21%
13.811%
15.021%
% losses
5.76%
9.66%
14.87%
In this case, as observed from the results, the % loss in urban
feeder is considerably lower compared with the loss estimated
with conventional method.
The % losses at HT level, LT level and total losses are shown in
Table 5 for the three classes of feeder considered.
URBAN FEEDER
Category of
Loss
loss
(kwh)
1
HT Level
102272.48
2
LT Level
197849.2
3
Total losses
300121.63
INDUSTRIAL FEEDER
Sr.No
Category of
Loss
loss
(kwh)
1
HT Level
18558.1
2
LT Level
7392.9
3
Total losses
25951
RURAL/AGRICULTURE FEEDER
Sr.No
Category of
Loss
loss
(kwh)
1
HT Level
37415.59
2
LT Level
71099.20
3
Total losses
108514.79
% losses
Table 6: Results from Novel Method
A. Result from Conventional Method
Sr.No
URBAN FEEDER
Category
Losses
of loss
(kwh)
HT Level
49050.935
LT Level
90186.95
Total
139237.88
losses
INDUSTRIAL FEEDER
Category
Losses
of loss
(kwh)
HT Level
9173.7
LT Level
5860.31
Total
15034.01
losses
RURAL FEEDER
Category
Losses
of loss
(kwh)
HT Level
37533.02
LT Level
59263.02
Total
96796.04
losses
C. Comparison of Results from the Two Methods
The various percentage losses estimated with data received
from utility is compared with that obtained with normalized
data with proper date and time in Table 7.
% Loss
6.2%
18.425%
25.52%
The results clearly indicate that the loss estimated
without normalization of data is in general higher.
% Loss
Sr.
No.
( 2.35%)
( 14.02%)
(16.37%)
1
2
3
% Loss
( 5.76)
(11.61)
(16.70)
Sr.
No.
Table 5: Results from Conventional Method
454
URBAN FEEDER
Difference
in
loss (kwh)
HT Level
53221.905
LT Level
107662.25
Total losses 160883.745
INDUSTRIAL FEEDER
Voltage
Difference
Level
In
Loss
(kwh)
Voltage
Level
Difference
in % Loss
(3.14%)
(10.045%)
(13.15%)
Difference
in % Loss
Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008
1
2
3
Sr.
No.
1
2
3
In Industrial feeder, the difference in percentage of losses at HT
level is 1.14 where as the difference at LT level is 0.209 and the
overall difference is 1.349 .The consumption (two sets) readings were
taken in the month of Aug, 06 and Sep, 06 within one day at HT level
as well as at LT level. The time interval of meter reading at HT level is
two days and the time interval of meter reading for LT consumers is
just six hours, hence the difference between the losses estimated with
normal practice and with proposed new method is very less.
HT Level
9384.4
(1.14%)
LT Level
1532.5 9
(0.209%)
Total losses 10916.99
(1.349%)
RURAL/AGRICULTURE FEEDER
Voltage
Difference
Difference
Level
InLoss
in % Loss
(kwh)
HT Level
-117.43
(0%)
LT Level
11836.18
(1.95%)
Total losses 11718.7478
(1.83%)
In rural/agriculture feeder, difference in % losses at HT level is
zero (actually a negative value, but within the error limit of energy
meter used at DTRs), where as, the difference at LT level is 1.95. The
overall difference in percentage losses for two methods is 1.83%.
Table 7: Difference in Results from the two methods
It is observed that in urban feeder , the difference in
percentage losses at HT level is 3.14, where as, the difference at
LT level is 10.045 . The overall difference is 13.15 which are
high. The % error at HT level is less than at LT level because
the Load survey data was downloaded for feeder and
Distribution transformers within a day i.e. on 3rd July, 2006 for
one set of readings and on 7th Aug, 2006 for second set of
readings after one month at LT level of urban feeder .It has
taken 16 days to complete all the LT consumers meter reading
both on july ,06 and aug,06.Hence it is evident that the loss
estimate without normalization of data results in higher
estimate for LT loss .
However in the case of rural feeder in addition to non metering of
agriculture pump sets, a large number of DTR meters were found
defective (34 out of 55 DTR meters).Hence, there is a possibility that
the estimated consumption of agricultural loads and LT consumption
on the same feeder could be inaccurate and these renders the
comparison difficult and no meaningful conclusion can be drawn.
Hence , the new novel method also could pose some limitation if large
no. of DTR meters are not working .It is observed that with about 80%
of DTR meters working in a feeder, the new method is useful for
meaningful estimation as shown for urban and industrial feeder in this
paper .
IX . CONCLUSIONS
X. ACKNOWLEDGEMENT
1.
Estimation of HT & LT losses for urban, industrial and
rural feeder was attempted by collecting field data on
consumption & supply.
2.
Loss estimation was carried out with data received from
field as followed by utilities.
3.
Time synchronization of data was found to be a major
source of error in the estimated losses
4.
A new method was proposed for normalization of field
data to arrive accurate loss estimation
The authors wish to thank management of CPRI for
granting permission to publish this paper .The authors are also
thankful to Smt.J.Sri Devi, E.O.IV and S.Shyamsundar, EO IV of
Power System Division of CPRI for their help during the field work
and the authors also thank Prof.Atmanand for his valuable inputs in
the dissertation .
XI. REFERENCES
1. www.powermin.nic.in
5. It is concluded that normalization or time synchronization
of data is highly essential for accurate loss estimation
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is influenced by the number of non available
DTR/Consumer meter reading and possibly these
could
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metered faulty
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simple.
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7. The new method proposed here can be employed by the
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455
Losses in SPDCL using a novel Method, A dissertation
Submitted in Partial fulfillment of the requirements for the
award of PGDEM at MDI, Gurgaon.