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Management of sub-transmission and distribution system in power utilities


Overall energy loss reduction
The investment to be made to upgrade the distribution system can be meaningful only if simultaneous steps are taken to render the power utility financially viable. It is very well understood that capital expenditure on technical improvement or system augmentation/up-gradation alone can not be financially justified merely because it will improve quality and reliability of power supply and benefit customer. Ultimately, consumers individually or as a group have to pay for the services delivered. The most common causes for the commercial losses i.e. loss of revenue to the utility arising out of energy consumed but not paid for are: due to faulty /tampered metered supplies, due to illegal connections, due to power delivery at flat rate to the subsidised category of consumers.

Now, it is unfortunate but true that to day there is not even a correct assessment of the quantum of the total Energy losses i.e. commercial plus technical losses prevailing in a sub-transmission and distribution system of say, a distribution circle or a discom. It is now imperative and a strategic need to establish Energy accounting system for assessment of the commercial (unaccounted) losses in the given system on continuous basis. For proper energy accounting, implementation of an energy metering plan which will ensure generation of accurate metering data at strategic points i.e. at points where energy is input into the system or its part will be the first step. Review of the existing metering practice in the utility and replacement of defective meters plus calibration check of working meters will be taken up on priority. Thereafter, the following steps can be adopted for achieving a reduction of energy losses and an improvement in realisation of revenue in the short-term:
  • Energy balance is to be prepared from the Billed energy input and the actual energy input from the energy meters.
Ideally, energy audit should be carried out over smaller area so that the areas suffering from high-energy losses can be localized. This would however require providing a very large number of energy input meters at strategic points and check meters. While it would certainly be desirable and justifiable to install check meters for high value consumers, installing energy meters on all distribution feeders (at 11 kV) in 33/11kV substations should be a considered as a minimum investment by the utilities and distribution companies for protecting the revenue earning. Energy losses in Pockets known to be having high losses could also be checked by additionally installing energy meters on the distribution transformers feeding these high loss pockets.
  • Estimate the total energy losses from the above. Segregate the technical and commercial losses by computing the technical losses from the results of the network analysis. Once feeder-wise energy losses are established, feeders having high-energy losses should be further investigated for localizing pockets of high-energy losses by installing energy meters after distribution transformers.
  • After performing spatial analysis of the commercial losses to identify high loss areas or consumer category responsible for the loss, implement appropriate energy metering and billing in these areas. In some cases, use of certain technological measures like aerial bunched cables LT lines in theft prone areas and conversion of LT into HT lines i.e. less LT are suggested for reduction of the commercial losses.
  • Computerised billing of energy sales in a pilot area could be taken up to investigate the scope of loss reduction.
  • Simultaneously to the above, prepare a plan for liquidation of revenue arrears from the data/information collected during the energy audit and study of the Billed-energy data and the accounting information. The existing billing and revenue realisation system should be also evaluated for improvement of revenue collection efficiency. Implementation of on-line payment system in a pilot area in the short term could pave the way for offering the system to a larger number of consumers.
The medium and long-term plan would introduce higher levels of automation and remote-monitoring systems, as by then the utility could have started benefiting from the short-term plans in controlling the energy losses and increasing revenues. Gradual introduction of electronic energy meters to replace the outdated electro-mechanical energy meters will be inevitable as then it would permit monitoring. Installation of Computerised customer billing, payment collection, customer complaint registering system and continuous loss monitoring are the key to efficient and financially strong utility.

The above approach is by no means sufficient to eliminate the commercial losses totally. As long as the energy consumed is not being charged to the consumer in accordance with the actual cost of energy being delivered the losses will remain. Issues of tariff cross-subsidisation and rationalisation of the tariff, legislative and legal issues and issues relating to the surveillance and vigilance for revenue protection still remain inadequately addressed.

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