Browsing by Author "Perera, KBMI"

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item: Thesis-Abstract
Condition monitoring of power transformers using frequency response analysis
Tilakeratne, RP; Lucas, JR; Perera, KBMI
Power transformers are the most expensive and important equipment of a high voltage power system. Therefore it is essential to have a suitable and effective condition monitoring system to assess the conditions of power transformers well in advance to maintain the reliability of the power system by averting unexpected expensive failures. Conventional condition .monitoring techniques do not conclusively indicate mechanical conditions of the transformer such as winding movement, loss ·of clamping pressure, disc movements etc. which can take place during handling and transport, short circuit forces, faults in the power system network near the transformer or a high voltage stress which affects inductance or capacitance. This project thesis deals with Frequency Response' Analysis technique for condition monitoring of power transformers, which is suitable for detecting the deformation of transformer windings. A mathematical model for obtaining frequency response characteristics has been developed for 'a typical transformer, and the effect of variation of parameters on frequency response has been examined. Case studies based on frequency response tests on typical 31.5 MVA, 132/33 kV grid transformers have been presented. Case studies reveal that any mechanical deformation in the transformer winding is clearly reflected in the frequency response characteristics. The frequency response characteristics obtained in the field for different aged power transformers are found to be somewhat similar in nature to those obtained analytically using ladder network equivalent circuit.
item: Thesis-Abstract
Software guided safe loading of transformers and its economics
Perera, KBMI; Lucas, JR
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.