Energy Measurement

Preparation of an effective energy account will be possible only if:

1.    Meters are installed on both sides of every element of the network as indicated.

2.    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 although the accuracy class of the meters at consumer installations must be Class 2.

3.    Energy meter readings are taken at the sending end and at all the consumer installations concurrently.

4.    Same accuracy class meters are installed both for measuring energy input to the system and energy sales.

5.    Electronic trivector meters along with data logging facilities are provided on the 11 kV feeders/secondary sides of distribution transformers to record load curve that facilitates assessment of load factors and loss load factors.

The data to be registered at the 11 kV meter level involves:

• 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 might be 15 or 30 minutes.

You might not be familiar along with the terms kVA and kVAr.

• kVA is the product of kilovolts and amperes. It is also known as the apparent power.
• kVAr is the reactive power, i.e., the portion of apparent power which does no work. This power must be supplied to all reactive loads, for example, magnetic equipment, transformers, motors, etc.

Energy measurement at several points informs you about the losses among 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, defective, non-working, un-metered supply, etc. should be documented for taking corrective measures.

A sample format for computation of losses is given in below Table:

                                Table: Sample Format for Computation of Losses for System Elements