TNB experience in condition assessment and life management of distribution power transformers

Tenaga Nasional Berhad (TNB), an electric utility company in Malaysia has embarked on condition assessment and life management program for 707 units of in-service oil immersed free breathing distribution power transformers with on-load tap changer. The program consists of threetiered approach. The first tier involved transformer population screening by means of on-line diagnostic techniques through assessment of the insulating oil, physical, thermal and operating performance. The second tier focused on off-line diagnostic testing on few identified transformers from the fleet using basic electrical testing techniques. The third tier involved more advanced diagnostic techniques namely frequency response analysis and partial discharge test. Results of the condition assessment on individual transformer were analyzed and transformer health index was formulated to provide engineering solutions and asset management direction.