Software guided safe loading of transformers and its economics

Abstract

The life duration of a transformer depends to a high degree on extraordinary events, such as over voltages, short-circuits in the system. emergency loading and harmonic loading. The application of a load m excess of nameplate rating and or ambient temperature higher than the designed ambient involves a degree of risk-. and accelerated ageing. initially a study was carried out by the author on the usage of distribution -transformers by the private customers. The study involved the measurement of load pattern at 15-minute intervals for two to three days. Then the required transformer capacity as per I EC - 3 54: Loading guide for oil immersed power transformers [ 1] was compared against installed capacity. One common feature observed was that the installed capacity at all the places was much more than required. No customer was aware of the possibility of loading a transformer above nameplate rating provided it is under loaded for a part of the day. This realised the importance of developing a user friendly computer software l2,3] to help transformer users to get the maximum utilisation of transformers. The economic cost involved with improper selection of transformer capacity is another aspect, which have not been realised by most ... users. The usefulness of analysing the transformer options available for a user with their economic evaluations is another area covered in this study. The increased use of electronic loads such as computers and adjustable-speed-drive motors in light industrial. commercial and residential loads has' created a need to apply the harmonic loading practices to liquid filled distribution transformer s below the small and medium power rating . It is quite common for the harmonic factor of the current to exceed 0.05 per unit, which is the limit specified for usual service conditions. It is also well known that higher harmonic content in the current causes higher eddy current loss in winding conductors and structural parts linked by the transformer leakage field and, consequently, higher operating temperatures. The harmonic loading condition in Sri Lankan scenario and it s significance on transformer performance is therefore considered part of the study.