Abstract:
The substation is serving a load demand of a geographical defined area. When load demand of the area is increased, substation modification is required. The substation planner is having two alternatives, . either existing facilities may be over loaded or extra facilities may be added earlier before load growth. Since transformer is a costly piece of equipment in a substation, transformer loading, maintenance and reliability should be studied carefully, so that maximum benefit is derived from the investment on the transformer.
Transformer loading limits are mainly due to thermal limits. In practice, these limits are not experienced most of the time and ambient temperature conditions are less most of the period. So there is always a margin available to overload the transformer. When overloading is done proper maintenance is required and health of the transformer can be estimated by conducting tests recommended by manufacturers and users„
Optimal transformer loading has to be decided after quantifying and analysing the cost structure for the available alternative. The costs involved are -capital cost of the transformer, repair and replacezent cost, maintenance and testing cost, failure cost, ,energy loss cost, interest on capital, depreciation and salvage value.- The mathematical optimization technique i.e., Dynamic programming is used for making decision at each stage (year). Finally the optimal transformer loading policy, for a given example, is found to be 110% of the name plate rating.
