Condition assessment of 500/150 kV power transformer based on condition based maintenance

Maintenance on high Voltage/Extra High Voltage equipment can be divided into preventive maintenance and corrective maintenance. Mostly, the cost for doing a corrective maintenance is much higher than the preventive maintenance, beside of when an equipment break down, it will cause another problem such as customer dissatisfaction. These reasons bring the consequence to any electricity utility like PLN P3B Jawa and Bali to do a reliable preventive maintenance. There are two types of preventive maintenance, e.g. scheduled maintenance and condition based maintenance. For years, most of the maintenance methods were done under scheduled maintenance (oil replacement, shutdown inspection/measurement, etc), but this method is less cost-efficient and less reliable on preventing the failure. The time interval in scheduled maintenance is based on the statistical data, which usually came from the factory recommendation (with some safety factor) or based on PLN P3B Jawa Bali experience, while the time interval in condition based maintenance is based upon the degradation of some parameters of the equipment. So, the knowledge of condition degradation on an equipment is important in condition based maintenance. This paper will present about condition assessment on power transformer as a part of condition based maintenance process. The causal method based on FMEA and FMECA of power transformer will be discussed first to get the information about critical component and the suitable monitoring needed at sub system levels. The next part will explain about how to compile the maintenance data into a management report which mainly giving the information whether the power transformer is in good/deteriorated or already in bad condition. The data presented here are based on 500/150 kV power transformer in P3B Jawa Bali.