Procedure for Conducting An Energy Audit

The various steps in the methodology for conducting a detailed energy audit for an industry may be outlined as follows:

1. Gathering and collating information in a specially designed, “Energy Systems Questionnaire” format, for the industry under study. (A format of the questionnaire is given in an Appendix to this unit.)

2. Inter- and intra-industry comparison of the collected data.

3. Assessment of present efficiency index for energy consumption in the industry/process.

4. In-depth study of plant operations, equipment and systems for a general review of the energy systems to assess the operational efficiency and potential for economising.

5. Evaluation of the detailed recommendations for energy saving/conservation,

6. Formulation of detailed action plans/strategies in consultation with plant management for implementation of the identified energy saving measures.

7. Training operating personnel in the specifics of energy conservation to enable them to implement the recommendations and also to monitor the progress on a periodic basis.

Let us now study how this methodology can be applied to the power distribution systems. You have studied in Units 1 and 2 that in the process of supplying electricity to consumers, energy losses occur on account of technical and commercial reasons. The technical losses are due to energy dissipation in the conductors and the equipment used for transmission and distribution of power. Commercial losses are caused due to pilferage of energy, defective meters, meter reading errors and energy not accounted for(Table).

Energy Losses in the Power Distribution System

In an energy audit of a power distribution system, the energy losses are to be computed for each element of the network on the basis of actual energy sent out and actual consumption as recorded by the meters installed on both sides of the element .It may not be possible to conduct energy audit for the entire power system of a utility in one go. This could be due to financial, organizational and logistical constraints. Hence it may have to be conducted in stages. A compact area ofmthe power system would have to be identified and energy audit studies taken up. We now describe briefly the procedure to determine technical and commercial losses for an 11 kV feeder.Procedure to Determine Technical Losses on the 11 kV Feeder Technical losses on the 11 kV feeder are assessed by conducting load flow analysis of the individual 11 kV feeder including distribution transformer and LT distribution losses.We consider the steady state model to find technical losses and take the loads to be of constant impedance.

1. Assessing Load Factor (LF) and Loss Load Factor (LLF)

a) Copper losses of all transformers = Copper loss of each transformer capacity wise in kWh x Numbers of transformers capacity wise in the feeder

b) LF = Energy input to the transformr= Energy input to the transformer/(Peak load of the transforme r during the month × number of hours the transformer is in service during the month)

c) LLF = 0.3 (LF) + 0.7 (LF) 2

d) Energy input to the transformer =((Energy sent out on the 11kV feeder from SS −Energy losses in the 11 kV feeder) × Capacity of the transformer)/Total transforme r capacities in the feeder
 

2. Distribution Transformer Losses

a) No-load losses, i.e., iron losses:

No-load losses in kWh of one distribution transformer = No load loss of transformer in kW x number of hours the transformer was
in service during the month

b) Load losses, i.e., copper losses:Copper losses in kWh = Copper loss of each transformer capacity wise in kW x (Actual load / Full load) 2 x number of hours the transformer capacity wise was in service during the month x LLF

3. Calculation of LT Line and Network Losses

a) The losses of LT network of each capacity transformer are computed by averaging the losses of the LT network of all similar capacity
transformers.

b) The computed average losses of LT network radiating from each capacity transformer are extrapolated for assessing the total energy
losses of LT network on the feeder.

4. 11 kV Feeder Loss

The monthly energy losses in the feeder should be computed by extrapolating the daily energy loss proportional to the energy sent out in the feeder, for all feeders for all the months in the audit period.

5. Energy losses in loose jump connections, short circuit and earth faults on the lines, service mains and energy meters are assumed to
be:

a) 1% of the total energy sent out through the 11 kV line from the substation, for the 11 kV lines of 20 km and more, and
b) 0.5% of the total energy sent out through the 11 kV line from the substation, for the 11 kV lines of less than 20 km.

The total technical loss in the 11 kV feeder is the sum of the various losses described above.
Total Technical Loss on the 11KV Feeder
This is equal to the sum of

1. 11 kV line losses,

2. Distribution transformer (no load and load) losses,

3. LT network losses, and

4. Energy losses in loose jump connections, service mains and energy meters.

Energy losses in the feeder = Energy input to the 11 kV feeder − Energy sales

Determining Commercial Losses

The commercial losses are assessed by deducting technical losses from the total losses of the feeder, i.e., the difference between energy sent out and the energy sold. Thus,

Commercial loss in the feeder = Energy loss − Technical loss

The following activities are undertaken to record these losses:

The meter reading schedules of meter readers are revised and made coterminous with distribution transformers. On that day, the distribution transformer meter is also read and comparison is made between distribution transformer meter reading and sum total of consumption recorded in all other consumer meters coming under that distribution transformer. The difference is noted. If the losses are found to be high, action is initiated toFi trace the installation causing losses.It is very difficult to get a very accurate picture of these losses due to the following reasons:

• the energy meters provided on 11 kV feeders are of class 1 / class 0.5 accuracy, whereas at consumer installations the meters are of Class 2 accuracy;

• all the energy consumed is not recorded due to illegal tapping, theft, pilferage etc.;

• the sending end readings are taken on a particular day whereas the readings for consumers are taken in a staggered manner;

• the meter readings of some consumers are not taken due to locked premises/ defective meters;

• meters are not reading at light load;

• meters are not recording within prescribed accuracy limits; and

•assessment of consumption in respect of un-metered consumers is missing.

Determining Technical Losses

Proper and accurate meters, meter reading, meter testing and calibration,billing and collection systems are essential for effective and accurate energy accounting and audit. The meters for energy accounting and audit are termed as system meters which basically are meters at S/S, outgoing feeders, distribution transformers, etc. The role of meters for energy accounting and audit, i.e., system meters is to arrive at operating and performance parameters, energy accounting and energy audit. System meters are generally not used for measuring energy for commercial purposes, and hence need not cater to any tariff structure.

Conducting an effective energy audit will be possible only through a perfect mechanism where the required facilities are available.

You may like to pause here and consolidate the ideas presented so far.

Audits will usually culminate in an energy audit report that must be easily readable and digestible by both technical and non-technical audiences.

We now briefly describe what the energy audit report should contain.