While the transformer is energized, visual Inspections are performed to look for cleanliness, cracked insulators and bushings, condition of paint, oil levels, oil leaks, oil/winding temperature gauges, nitrogen pressures, relay targets, condition of grounds, etc. Further, using the latest, state-of-the-art infrared thermographic equipment, trained technicians are able to locate hot spots, poor connections, defective surge arresters, etc. This inspection is fast, accurate and practical, while being recommended by ANSI/NFPA 70B.
Using an ultrasonic detector, technicians can identify improperly shaped medium and high voltage connections, defective insulation, bushings, and surge arresters - all likely causes of excessive corona. Measuring specific combustible gas levels in transformer oil is a good way to predict transformer problems. Technicians take oil samples for analysis and engineers compare the results to historical records of recent test results as precursors of internal problems such as arcing, corona and overheating.
While the transformer is de-energized and disconnected, insulation tests such as Doble power factor testing and insulation/winding resistance testing are performed, along with diagnostic tests such as turns ratio testing. The internals of open or ventilated transformers are visually inspection when de-energized. Since the core and coils of these units are subject to contamination by air flowing through the transformer, maintenance includes cleaning the internal parts. Also, since the voltage impulse levels for dry-type transformers are usually lower than for liquid filled transformers, surge arrestors are often installed either inside the transformer case or immediately adjacent to it.
Whenever de-energized maintenance is performed on the transformer, the arrestors should be inspected, cleaned and tested. Covers are removed and the transformers and transformers' bushings are cleaned and inspected. Additionally, fans, cooling louvers, enclosures, and cable compartments are cleaned and inspected. This inspection includes checking for signs of tracking and corona, loose blocking, wedges, etc.
Back to Maintenance Services
