Increasing the life cycle of existing grids to avoid high replacement costs of new systems By S.R.Sethi Member Delhi Electricity Regulatory Commission

Power system is a seamless system from generator to consumer. Transmission system and sub-transmission is the integral part of the system. Cost of transmission system is almost 50% of that of generating system. Though as per depreciation norms, generating system and transmission system have the same life but in actual practice, transmission system is not replaced but only augmented/components replaced with the latest technology such as circuit breakers, CT,CVT, & PTs.

3 The equipment which is required to be upgraded for increasing the life cycle of the transmission system are as follows: Earthing system to be re-inforced depending upon the erosion effect and to take into account the increased fault level in the system. Circuit breakers which were conventionally oil circuit breakers were replaced with Minimum oil, Air blast and now replacement with SF6 breakers which are maintenance free.

CT, CVT and PTs are to be replaced depending upon various requirements of the fault level, Metering and aging of the equipment. Aging of the equipments where paper insulation is immersed in oil are viz. (a) Power transformer, (b) Current transformer, (c) CVT and PTs.

5 Checking of the Tan delta value of such equipment yield the health of the equipment. Infra red scanning of the switch yard on monthly basis helps to detect in incipient fault in such equipments apart from hot spot on connectors of the switch yard.

6 Thermo graph of Transformer during heat run test compared with field measurement is quite indicative of incipient faults. Life of transformers can be enhanced by carrying out the nitrogen cycling for removal of water and restoring the health of paper and wood insulation periodically at an interval of say ten years or as per diagnostic tests. Replacement of insulating oil (need based) would also enhance the life of the transformers.

7 Control cables are one of the major source of problems after the insulation becomes brittle and replacement of cables is not an easy job in an existing sub-station. Replacement of Electro mechanism relays/static relays with numerical relays conforming to IC along with automation of the sub-station based upon bay control unit system would reduce control cables requirement.

Bay control units are installed in each of the bay where the relays are also provided in the outdoor kiosk, Co axial or Optical fiber cable is brought to the control room for operations of the sub-station equipment. Even remote operation of the sub-station from master stations could be achieved. These are not only cost effective but are necessary for upgrading the life of the existing sub stations.

Painting of structures and proper upkeep of the civil works can increase the life of the sub-station. Increasing Power carrying capacity of Transmission and Sub transmission lines with the aluminum alloy conductors, it is possible to use the same Towers with higher current carrying capacity conductors for optimum utilization.

Right of way for new lines within the urban areas are extremely difficult and most of the Transmission projects get delayed due to right of way problems. Right of way problems in cross country poses problems of environmental clearance and the wrath of the land owners for laying up the new towers which nevertheless reduces the value of the land. Incidentally, Electricity Act does not provide any compensation for the right of way of the transmission lines.

Since cities in India were not planned in the manner they have developed over a period of time, space for sub stations is becoming non-existent and wherever available is at prohibitive costs. Thus increasing the life of existing substations and upgrading equipment with the latest technology is the only solution in such Metro cities and towns. Cost of refurbishment could be a fraction of cost of new sub-station and is thus an optimal solution.

Indoor substations and underground substations is the future of Transmission and Distribution Sub-stations. As per the provisions of Electricity Rules installation of Oil Type Transformers below first basement is not permitted. Solutions need to be found out for installation of Oil Type Transformers. One solution could be to put the GIS Sub Station underground while the Transformers could be installed on the ground level to take care of the requirements of the IE rules for safety.

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