Glossary of Terms

Billing Efficiency

Billing efficiency is an indicator of proportion of energy that has been billed (includes both metered and unmetered sales) to consumers w.r.t. energy supplied to an area. Billing Efficiency can be computed using formula provided below:-

Billing Efficiency = Total Energy Billed to Consumers (kWh) / Total Energy Input (kWh)

Collection Efficiency

All the consumers are billed on the basis of energy consumed by them which is obtained from meter reading and assessment of unmetered energy of consumers. The billed amount is computed on the basis of tariff fixed by regulatory commission for applicable customer category.
However, there are quite a few consumers who have tendency to default in their payments for various reasons. Thus utility is not able to recover entire amount billed by it, resulting in commercial losses.
Collection efficiency is an indicator of proportion of amount that has been collectedfrom consumers w.r.t. amount billed to them. Collection efficiency can be computed using formula provided below:-

Collection Efficiency = Revenue Collected (In Rupees)* / Billed Amount (In Rupees)

*The revenue collected shall exclude the arrears. Collection efficiency to be capped at 100%.

AT&C Losses

The aggregate technical and commercial losses shall be measured using formula mentioned below:-

AT&C Losses = {1 - (Billing Efficiency X Collection Efficiency)} X 100

The concept of Aggregate Technical & Commercial losses provides a realistic picture of loss situation in the context it is measured. It is combination of energy loss (Technical loss + Theft + inefficiency in billing)& commercial loss (Default in payment + inefficiency in collection).

SAIDI/SAIFI

System Average Interruption Duration Index (SAIDI) is commonly used as a reliability indicator for electric power utilities. SAIDI is the average outage duration for each customer served, and in 11 KV feeder system in the town level, SAIDI may be calculated as follows

Where Ui is the duration of interruption of the ith feeder and Ni is the number of customers in that feeder. NT and is the total number of customers served in all feeders of the town.
SAIDI is measured in units of time, in minutes or hours.

SAIFI= (Total No Of customers interrupted)/(Total No. Of Customers served) Assuming all customers connected with the feeder gets interrupted for each feeder failure,

Where is the no. of failure in the ith feeder and Ni is the number of customers in that feeder. NT and is the total number of customers served in all feeders of the town.

SAIFI is measured in units of no of interruptions per customer.

Average Billing Rate (ABR):

Total Amount Billed / Total Energy Billed

Feeder Severity Index (FSI)

FSI Indicates comparative severity of Impact of a feeder in a Discom in respect of AT&C losses. It is derived from Billing Efficiency, Collection Efficiency, Average Billing Rate and weightage of feeder in terms of Input Energy.

Coal Average Criticality Index

The value signifies the average coal criticality position in a financial year which is derived by dividing total number of critical days in terms of non availability of coal with number of stations remained critical.