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Sunday, September 11, 2011

Current Transformer Nameplate Data (Part 2)

I have posed before the commonly data on a current transformer nameplate. Listed below are the data and its brief description:

IEEE C57.12.90-2006 Test Code for Liquid-Immersed Transformers (series 1)

I have obtained a photocopy of the IEEE Standard C57.12.90-2006 Test Code for Liquid-Immersed Distribution, Power and Regulating Transformers. I am posting part by part of the standard and the posts will serve as my reference notes.

Winding Resistance Testing for Power Transformer

Measurement of winding resistanceThe purpose of testing the winding resistance is to detect and confirm faults in the transformer winding.  The standard criteria being used before is that the standard deviation of three readings must not exceed 0.5. However, the new IEEE standard C57.12.90, there is no specific requirements for the resistance but will serve as reference for future testing.

Transformer Ratio Test and Phase Displacement Check

In the measurement of power transformer voltage ratio, the different taps of the tap changer are tested compared to the nameplate rating. If the testing is from high voltage side and low voltage side, then each tap position is tested against its nameplate rating. Each tap position has corresponding nameplate tap voltage and ratio. During the testing, the measured ratio and its corresponding error are determined.

Sunday, September 4, 2011

Emergency Shutdown of 50 MVA Transformer due to Oil Leak at the Base of Ground-Connection Terminals for Transformer Active Parts (Core Clamps and Core Laminations)

Our power transformer in our substation has been plagued by various oil leak problems. Considering that the transformer is still 15 years old, it is still considered at its peak performance. But some of its parts had failed already on which the insulating oil inside had found its way to leak. This article is about another weak part of the power transformer that may be a probable source of oil leak.