In last unit, you have learnt that energy accounting in the electricity sector involves evolving procedures and checks to account for energy fromg enerating stations down to the consumer level. The various steps in the energy accounting procedure are:
•measurement of the available energy (the energy input);
•measurement of the energy consumed; and estimating the energy lost, the revenue realised and the commercial losses.
The deficit in the cost of energy available at the meter and the billing collections give an estimate of the AT&C losses.
Table shows how a typical town area could be divided for the purposes of energy accounting.
•measurement of the available energy (the energy input);
•measurement of the energy consumed; and estimating the energy lost, the revenue realised and the commercial losses.
The deficit in the cost of energy available at the meter and the billing collections give an estimate of the AT&C losses.
Table shows how a typical town area could be divided for the purposes of energy accounting.
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| The Town Level Grid to Consumer Supply and the Administrative Setup from the JE to CE Level |
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| Organisational Structure and Areas of Responsibility for Energy Accounting |
We shall discuss in a while how the technical and commercial losses can be segregated.
For distribution utilities, the focus of energy accounting should be on grid substations where sub-transmission systems (66/33/11kV) take off generally as a radial system to supply power to consumers at different voltage levels. Note that feeders emanate from each substation towards the customers. The feeders at 11kV are taken to the load centre and terminated into a distribution transformer (DTR). The customers are connected at 220 V from the secondary of the distribution transformer.
In order to implement the energy accounting procedure successfully, utilities should adopt a bottom-up rather than a top-down approach to energy accounting. The reason is very simple. The first view of the loss can be obtained by monitoring the energy input to a particular feeder and the amount of energy bill collected. Thus feeder becomes the focal point and must, therefore, be the first point of check and measure. Each Junior Engineer should be entrusted with the responsibility of covering one or more 11 kV feeder(s), which could be feeding a number of consumers. S/he should be responsible to account for the energy received by the feeder and billing of consumers connected to it.
The following steps could be taken at the feeder level for energy accounting:
measure the energy received at the feeder;
list the customers billed;
record the revenue from bills;
compute the difference in billing and collections from customers; and
obtain the difference in input energy cost at the feeder level and the total revenue realised from collections.
In the next step, energy accounting could be done for the set of feeders at the substation level and then for the group of substations at circle level and finally for the town area. The hierarchy in this distribution could be matched with the administrative hierarchy for the purpose of accounting as shown in Fig.
Responsibility could be fixed for the higher levels like EE Level, SE Level and CE Level. The exercise would involve establishment of an energy measurement system and preparation of energy balance related to the different responsibility areas. It would also require the segregation of technical and commercial losses. Let us now look at these aspects.
Energy Measurement
Preparation of an effective energy account will be possible only if: Meters are installed on both sides of each element of the network as indicated in Fig.Accurate energy meters are installed in all the consumer installations. The accuracy class of the 11 kV feeders must be Class 1 / Class 0.5 while the accuracy class of the meters at consumer installations must be Class 2.Energy meter readings are taken at the sending end and at all the consumer installations simultaneously.Similar accuracy class meters are installed both for measuring energy input to the system and energy sales.Electronic trivector meters with data logging facilities are provided on the 11 kV feeders/secondary side of distribution transformers to record load curve which facilitates assessment of load factors and loss load factors.The data to be registered at the 11 kV meter level includes:
• 3 phase energy;
• kW of all the phases at peak kVA interval;
• kVAr of all the three phases at peak kVA of interval;
• phase voltages of each phase with respect to neutral; and
• power down time in minutes during the interval.
The time interval may be 15 or 30 minutes.
You may not be familiar with the terms kVA and kVAr.
• kVA is the product of kilovolts and amperes. It is also called the apparent power.
• kVAr is the reactive power, i.e., the portion of apparent power that does no work. This power must be supplied to all reactive loads, for example,transformers, motors, magnetic equipment, etc.Energy measurement at various points informs you about the losses between those points.
All meters should be regularly tested and calibrated as the efficacy of the data for energy accounting would largely depend on the quality of meters employed in the system. Network metering and consumer metering system should be reviewed regularly. Working, non-working, defective, un-metered supply, etc.should be documented for taking corrective measures.
For distribution utilities, the focus of energy accounting should be on grid substations where sub-transmission systems (66/33/11kV) take off generally as a radial system to supply power to consumers at different voltage levels. Note that feeders emanate from each substation towards the customers. The feeders at 11kV are taken to the load centre and terminated into a distribution transformer (DTR). The customers are connected at 220 V from the secondary of the distribution transformer.
In order to implement the energy accounting procedure successfully, utilities should adopt a bottom-up rather than a top-down approach to energy accounting. The reason is very simple. The first view of the loss can be obtained by monitoring the energy input to a particular feeder and the amount of energy bill collected. Thus feeder becomes the focal point and must, therefore, be the first point of check and measure. Each Junior Engineer should be entrusted with the responsibility of covering one or more 11 kV feeder(s), which could be feeding a number of consumers. S/he should be responsible to account for the energy received by the feeder and billing of consumers connected to it.
The following steps could be taken at the feeder level for energy accounting:
measure the energy received at the feeder;
list the customers billed;
record the revenue from bills;
compute the difference in billing and collections from customers; and
obtain the difference in input energy cost at the feeder level and the total revenue realised from collections.
In the next step, energy accounting could be done for the set of feeders at the substation level and then for the group of substations at circle level and finally for the town area. The hierarchy in this distribution could be matched with the administrative hierarchy for the purpose of accounting as shown in Fig.
Responsibility could be fixed for the higher levels like EE Level, SE Level and CE Level. The exercise would involve establishment of an energy measurement system and preparation of energy balance related to the different responsibility areas. It would also require the segregation of technical and commercial losses. Let us now look at these aspects.
Energy Measurement
Preparation of an effective energy account will be possible only if: Meters are installed on both sides of each element of the network as indicated in Fig.Accurate energy meters are installed in all the consumer installations. The accuracy class of the 11 kV feeders must be Class 1 / Class 0.5 while the accuracy class of the meters at consumer installations must be Class 2.Energy meter readings are taken at the sending end and at all the consumer installations simultaneously.Similar accuracy class meters are installed both for measuring energy input to the system and energy sales.Electronic trivector meters with data logging facilities are provided on the 11 kV feeders/secondary side of distribution transformers to record load curve which facilitates assessment of load factors and loss load factors.The data to be registered at the 11 kV meter level includes:
• 3 phase energy;
• kW of all the phases at peak kVA interval;
• kVAr of all the three phases at peak kVA of interval;
• phase voltages of each phase with respect to neutral; and
• power down time in minutes during the interval.
The time interval may be 15 or 30 minutes.
You may not be familiar with the terms kVA and kVAr.
• kVA is the product of kilovolts and amperes. It is also called the apparent power.
• kVAr is the reactive power, i.e., the portion of apparent power that does no work. This power must be supplied to all reactive loads, for example,transformers, motors, magnetic equipment, etc.Energy measurement at various points informs you about the losses between those points.
All meters should be regularly tested and calibrated as the efficacy of the data for energy accounting would largely depend on the quality of meters employed in the system. Network metering and consumer metering system should be reviewed regularly. Working, non-working, defective, un-metered supply, etc.should be documented for taking corrective measures.
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| Sample Format for Computation of Losses for System Elements |
Preparation of Energy Balance
An energy balance is a set of relationships accounting for all the energy that is produced and consumed. It matches inputs and outputs in a system over a given time period (Fig.).
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| Energy Balance Matches Energy Input with Energy Output in a System |
The system could be the entire country or a limited area or even a process in a factory. An energy balance is usually made with reference to a year, though it can also be made for consecutive years to show variations over time.Energy balances are used to quantify the energy used or produced by a system.These are usually constructed from two sides:
1) from end-uses back to total primary energy consumption, and
2) from resource extraction to primary energy supply.
The basic equation of an energy balance is:
Source + Import = Export + Variation of stock + Use + Loss + Statistical differences
In this equation,
sources are local primary energy sources;
imports are energy sources which come from outside the area under consideration (e.g., the country, region, village, etc.);
exports go to other areas (countries, regions, etc.);
variation of stock is reduction of stock (wood, oil) and storage;
use can be specified sector-wise or by energy form or by end-use. This includes use of fuels for non-energy purposes;
losses can be technical and administrative;
statistical difference is included to balance for inaccuracies in supply and demand, for example, due to evaluation of losses. These statistical differences can sometimes be as high as 10%.
We need to quantify all these quantities while preparing the energy balance for energy accounting. An important part of preparing an energy balance is the construction of an energy chain to trace the flows of energy within an economy or system, starting from the primary source(s) of supply through the processes of conversion, transformation and transportation, to final/delivered energy and
finishing with end-use .
All too frequently, energy balances are constructed in terms of primary energy without taking into account conversions or transformations. This can lead to incorrect conclusions. The most common example is electricity,which is a secondary form of energy. Electricity is usually included in a primary energy balance on the basis of the amount of fossil fuel needed to produce it.Or, when electricity is generated from hydro, renewable energy resources or nuclear energy, an energy equivalent or heat content is used.However, it is not simply a matter of taking a conversion of one single fuel to another, since the conversion efficiency varies with the primary energy source.1) from end-uses back to total primary energy consumption, and
2) from resource extraction to primary energy supply.
The basic equation of an energy balance is:
Source + Import = Export + Variation of stock + Use + Loss + Statistical differences
In this equation,
sources are local primary energy sources;
imports are energy sources which come from outside the area under consideration (e.g., the country, region, village, etc.);
exports go to other areas (countries, regions, etc.);
variation of stock is reduction of stock (wood, oil) and storage;
use can be specified sector-wise or by energy form or by end-use. This includes use of fuels for non-energy purposes;
losses can be technical and administrative;
statistical difference is included to balance for inaccuracies in supply and demand, for example, due to evaluation of losses. These statistical differences can sometimes be as high as 10%.
We need to quantify all these quantities while preparing the energy balance for energy accounting. An important part of preparing an energy balance is the construction of an energy chain to trace the flows of energy within an economy or system, starting from the primary source(s) of supply through the processes of conversion, transformation and transportation, to final/delivered energy and
finishing with end-use .
For example, for hydro it is around 90%, whereas for coal it is around 40%.The amount of energy required to produce electricity should reflect these differences. For example, it would take at least twice the amount of energy to produce one unit of electricity if coal were used instead of hydro.An energy balance should include the accounting of commercial energy, non-commercial energy, non-energy products, and energy imports and exports.
We now briefly explain what is involved in this.Commercial Energy: It should be clearly specified which energy forms are included in commercial and non-commercial energy categories.Non-commercial Energy: Non-commercial energy usually includes biomass (woody and agricultural residues) and animate energy . Despite their important contribution to the energy supply, particularly in rural areas, these sources do not usually appear in national energy balances. They are difficult to quantify physically since they are traded and used in non-standard units. Their flows are not monitored since they fall outside the purview of the monetised economy.A few countries now include agricultural processing residues, such as bagasse and rice husk, in their energy balances.
Non-energy Products: These include products from primary energy carriers such as petrochemicals from crude oil, coal and natural gas and should be listed separately Energy Imports and Exports: These include imports, exports, storage,stock changes, transformation (conversion of one fuel to another, for example, coal to coke), distribution and conversion losses as well as self consumption by the energy industry (if relevant). These must be included while constructing an energy balance for the Energy Accounting System.
Energy balances provide overviews, and constitute basic energy planning tools for analysing the current and projected energy situation. The overviews aid sustainable resource management, indicating options for energy saving, or for policies of energy pricing and redistribution, etc.Having explained the concept of energy balance, we would like to discuss the measurement and separation of technical and commercial losses.
How to Measure and Separate the Technical and Commercial Losses
The separation of commercial loss from the total technical and commercial loss involves comparison of the losses as measured by ‘Energy Accounting’with the losses as estimated by network simulation studies. For an 11 kV feeder, the procedure can be outlined as follows:
Undertake energy accounting for the particular 11 kV feeder. The difference of energy input measured at feeder end and the recorded
consumption is the total loss:
Total loss = (Energy input measured at feeder end) − (Recorded consumption)
Using modern distribution system analysis software, carry out a simulation study for the load flow for different loading conditions during the Energy Accounting period.
The difference of total loss and the loss obtained from simulation studies (technical loss) is an indication of the non-technical loss in each distribution feeder:
Non-technical loss = Total loss − Loss obtained from simulation studies (technical loss)
This accounting and analysis would enable segregation of technical and non- technical losses in the system and help in drawing up strategies for achieving results on both the fronts. It is also essential to identify network elements with high technical losses.
Identification of Elements with High Technical Losses
The technical losses computed for each element of the network from load flow studies are to be compared with reasonable level of losses for that element.The reasonable level of losses in various segments of the system have been set out by the Committee of experts/ Central Electricity Authority in the“Guidelines for Development of Sub-transmission and Distribution System” for conditions prevailing in the country. These are given in Table.
How to Measure and Separate the Technical and Commercial Losses
The separation of commercial loss from the total technical and commercial loss involves comparison of the losses as measured by ‘Energy Accounting’with the losses as estimated by network simulation studies. For an 11 kV feeder, the procedure can be outlined as follows:
Undertake energy accounting for the particular 11 kV feeder. The difference of energy input measured at feeder end and the recorded
consumption is the total loss:
Total loss = (Energy input measured at feeder end) − (Recorded consumption)
Using modern distribution system analysis software, carry out a simulation study for the load flow for different loading conditions during the Energy Accounting period.
The difference of total loss and the loss obtained from simulation studies (technical loss) is an indication of the non-technical loss in each distribution feeder:
Non-technical loss = Total loss − Loss obtained from simulation studies (technical loss)
This accounting and analysis would enable segregation of technical and non- technical losses in the system and help in drawing up strategies for achieving results on both the fronts. It is also essential to identify network elements with high technical losses.
Identification of Elements with High Technical Losses
The technical losses computed for each element of the network from load flow studies are to be compared with reasonable level of losses for that element.The reasonable level of losses in various segments of the system have been set out by the Committee of experts/ Central Electricity Authority in the“Guidelines for Development of Sub-transmission and Distribution System” for conditions prevailing in the country. These are given in Table.
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| Level of Power Losses in Various Segments of the System |
Estimation of losses in LT network may be done initially for a sample network emanating from representative distribution transformers covering different categories of consumers and load density. With full computerisation of the database, it would be feasible to cover the whole LT system as per needs.After going through this section, it must have become amply clear to you that proper ‘Energy Accounting’ is a must for identifying the technical and commercial losses, separating them and also identifying the ‘culprit’ feeder.
We now discuss special cases and the precautions required in taking energy measurements.
Special Cases and Cautions in Measurements
Here, we discuss special cases that may arise in the Sub-transmission and Distribution systems.
Case of Feeders Crossing Boundaries
In the Sub-Transmission and Distribution systems in a responsibility area,some feeders may cross the boundaries and feed the loads (either in part or in full) of other areas also. Such inter-area exchanges should be avoided at 11 kV level by network reconfiguration and administrative/jurisdictional adjustments.
In cases where such network restructuring is not feasible or economical,additional energy meters could be placed at appropriate locations. Or else, relevant data on energy transfers/billed consumption could be exchanged between the units to avoid complication of accounting.The network within the unit at Division/Sub-Division/feeder level may also be reconfigured so as to minimise the Inter-Division/Sub-Division/feeder exchange of energy so that there is no dilution of responsibility in actual practice.
Measurements and Corrections
The following practices would enhance the reliability and correctness of energy accounting:well defined procedures for reading of the energy meters (on 11 kV feeders) not having data logging facilities, and consumer meters.simple procedures to correct for non-simultaneous reading of consumer meters and billing cycles;accounting for un-metered consumption, till such time as 100% consumer metering is in place. For this purpose, data derived from sample metering at selected distribution transformers and sample surveys of consumption of various categories of consumers on a system wide basis would be required.
Scientific sampling techniques should be adopted for getting optimum results.The size of the sample and the actual location of the meters to be installedshould be based on a detailed analysis of the consumers’ profile, identification of regional factors and other parameters having an impact on consumption.
For example, in the case of agricultural consumers, the parameters would be cropping pattern, ground water profile, irrigation practices, agro-climatic factors, etc. For domestic and commercial consumers, the parameters could be based on income levels, sanctioned/connected load, etc. In the case of street lighting, the season-wise sample survey, hours of supply and number of working light points, etc., should be considered. With the analysis of data from such surveys, the energy consumption of un-metered consumers could be worked out on a reasonable basis. Accordingly, a reasonably reliable figure of energy losses for each feeder could be derived.
We now discuss special cases and the precautions required in taking energy measurements.
Special Cases and Cautions in Measurements
Here, we discuss special cases that may arise in the Sub-transmission and Distribution systems.
Case of Feeders Crossing Boundaries
In the Sub-Transmission and Distribution systems in a responsibility area,some feeders may cross the boundaries and feed the loads (either in part or in full) of other areas also. Such inter-area exchanges should be avoided at 11 kV level by network reconfiguration and administrative/jurisdictional adjustments.
In cases where such network restructuring is not feasible or economical,additional energy meters could be placed at appropriate locations. Or else, relevant data on energy transfers/billed consumption could be exchanged between the units to avoid complication of accounting.The network within the unit at Division/Sub-Division/feeder level may also be reconfigured so as to minimise the Inter-Division/Sub-Division/feeder exchange of energy so that there is no dilution of responsibility in actual practice.
Measurements and Corrections
The following practices would enhance the reliability and correctness of energy accounting:well defined procedures for reading of the energy meters (on 11 kV feeders) not having data logging facilities, and consumer meters.simple procedures to correct for non-simultaneous reading of consumer meters and billing cycles;accounting for un-metered consumption, till such time as 100% consumer metering is in place. For this purpose, data derived from sample metering at selected distribution transformers and sample surveys of consumption of various categories of consumers on a system wide basis would be required.
Scientific sampling techniques should be adopted for getting optimum results.The size of the sample and the actual location of the meters to be installedshould be based on a detailed analysis of the consumers’ profile, identification of regional factors and other parameters having an impact on consumption.
For example, in the case of agricultural consumers, the parameters would be cropping pattern, ground water profile, irrigation practices, agro-climatic factors, etc. For domestic and commercial consumers, the parameters could be based on income levels, sanctioned/connected load, etc. In the case of street lighting, the season-wise sample survey, hours of supply and number of working light points, etc., should be considered. With the analysis of data from such surveys, the energy consumption of un-metered consumers could be worked out on a reasonable basis. Accordingly, a reasonably reliable figure of energy losses for each feeder could be derived.
Even after achieving 100% metering of consumers, it would be necessary to have metering of some selected distribution transformers, serving different categories of load to provide a reference point for checking the energy balance. The data from consumer level metering and sample survey data should be utilized to firm up consumption of each class of consumer and derive validated data. The sample metering data would enable the utility to establish norms of consumption. The utility would also be able to investigate any deviations from normal consumption and their causes and reasons. The overall check would also be possible by adopting the population of each class of consumer and applying the sample data for estimation of consumption to validate T&D losses.Finally, we would like to present the major obstacles to energy accounting by utilities and give some suggestions about how to overcome them.
Overcoming the Problems in Energy Accounting
Lack of meters, inadequate workforce, insufficient numbers of computers are some of the issues that need to be dealt with by the utility management in order to implement energy accounting. In addition, there is the problem of corruption and inefficiency of the workforce of the utility, which is largely responsible for insufficient revenue realization. The technical problem of time parallax in data collection also needs to be addressed.
Overcoming the Problems in Energy Accounting
Lack of meters, inadequate workforce, insufficient numbers of computers are some of the issues that need to be dealt with by the utility management in order to implement energy accounting. In addition, there is the problem of corruption and inefficiency of the workforce of the utility, which is largely responsible for insufficient revenue realization. The technical problem of time parallax in data collection also needs to be addressed.
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| Some Problems in Energy Accounting |
In Table, we give some suggestions for taking care of these problems.Obviously, it is for the management of the power utilities to take action along these lines for effective implementation of the energy accounting procedure.
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| Role of the Management in Overcoming the Problems in Energy Accounting |
We now acquaint you with certain technological requirements and advances in the energy accounting procedure that should be adopted by utilities to reduce their losses.
So good explained by them
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