A: We are seeing this situation with our clients more often. RESA is unique in the fact that our transformer service team has substantial experience repairing, testing, drying, and servicing transformers up to 500 KV primary voltage. This capability coupled with our ability to staff restricted service date outages with capable breaker testing technicians to perform testing, cubicle cleaning, and MCC bucket maintenance, truly sets us apart from other regional service contractors.
A: At this voltage, we assume that the transformer tank is rated to withstand full vacuum. RESA can drain the unit and repair any leaks by re-gasketing any leaking pressure relief devices, bushings, radiators, pumps etc. Then we place the unit under full vacuum and simultaneously circulate 10-15% of the nameplate volume of oil to heat the internals. Elevated heat helps release moisture from the paper. The vacuum line includes a liquid nitrogen cold trap which accumulates moisture removed from the paper. Over several days of treatment, you would gradually see the amount of moisture removed decrease, thus indicating insulation dryness. We then refill the unit under vacuum and electrically test the unit when it cools. This is the most effective means to quickly dry out insulation for vacuum rated transformers.
A: RESA can review your most recent oil test reports, discuss your unit priorities, and offer to staff the project with one or more repair teams to perform the required services during the limited duration outage. We can perform oil processing services while certain transformers remain in service. We can also perform oil processing services before the actual outage takes place, and leave the specific outage date for unit repairs. After the plant is back online, we can continue to perform energized oil processing services such as degassing, dehydration, re-inhibiting, hot oil reclamation, etc. to complete your maintenance requirements in one trip. With limited outage projects like this, please keep us in mind to assist you or your local contractor with breaker inspection and testing services as well.
A: Yes, we can! We have experienced crews and oil processing apparatus in the Midwest, Southeast and West Coast. We can perform turnkey initial inspection, transformer assembly, oil storage and fluid testing, vacuum dry out and vacuum filling, and complete OEM required electrical testing, including SFRA. If you have another contractor scheduled to perform the mechanical assembly portion of the work, we would be pleased to perform the oil processing and vacuum services along with the final electrical testing if they cannot perform these tasks on a turnkey basis. We have assembled and repaired existing transformers in the 230-345-500 KV range.
A: No. HI-POT testing is a destructive test that could lead to cable insulation failure. We recommend doing a VLF or combination VLF and TAN DELTA test to determine the cable’s condition. The combination VLF and TAN DELTA test results actually give a condition assessment of the cable and allow for trending in your preventative maintenance program.
A: NETA recommends cleaning and testing 480V breakers every 12-24 months depending on criticality, environment and load.
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