Condition Monitoring of Transformer
Transformer is static electrical equipment. As it has no moving parts, wear & tear due to friction doesn’t occur in it. But different electrical, chemical stresses and stresses due to the environment affects the condition of the transformer.
While thinking of CM of any equipment it is necessary to learn about the failure modes of that equipment. The major failure modes of transformers are Short Circuited Windings, Insufficient Oil Level, Contaminated Oil, Tracking at Bushings/Arresters/Insulators, Arcing/ corona/ Contact Resistances at cable – Insulator Joints, Choked Breather, Choked Radiator, Overheated Oil, Rusted Main Tank, Leaks from Conservator Assembly etc.
Online CM of Transformer is done with Thermography, Ultrasound Analysis and Oil Analysis. Above all, failure modes can be monitored closely with these inspection methods. The Oil Analysis includes DGA – Dissolved Gas Analysis, NAS Oil Analysis & Particle Counting. The tracking, arcing, corona at HT bushings & bushing – cable Joints can be detected by Ultrasound Inspection & Thermography. The Loose connection of cables & other joints can be detected with Thermography.
Offline condition monitoring of Transformer winding – Online CM may not cover faults with the winding & core properly. Therefore, offline condition monitoring is necessary at least once a year, Preferably half-yearly. Surge Comparison Testing, Offline Partial Discharge Testing, HV Testing, Winding Resistance Testing, PI Testing are the offline CM methods.
Real Time Condition Monitoring of Transformer techniques are at the development stage and are not going beyond Winding Temperature, Oil temperature and Current/Voltage monitoring. But it is possible to club manual & real time CM methods together to improve the CM of Transformer.
