TxMonitor^® successfully completed verification of distribution transformer protection system works on 6 transformers manufactured in 2009 for a coal mine located in Western Region of NSW. Works involved testing to verify the functional operation of Winding Temperature Indicators (WTI) and Oil Temperature Indicators (OTI).

Take home message

Transformers operate in tough environments always exposed to the elements. New transformers need to be inspected, maintained and commissioned properly. This case study highlights the importance of regular routine maintenance by competent, trained professionals.

Specific works included

• Measurement of transformer winding temperature CT using a Omicron CT Analyzer
• DC resistance
• CT turns ratio
• Polarity
• Knee point voltage
• Measurement of CT insulation resistance between CT (inclusive of control wiring) and tank
• Verification of WTI & OTI alarms and trips
• Verification of WTI protection circuit via secondary CT injection (current source)

The outcome of the test and inspection found

• Faulty WTI Current Transformer was found
• Multiple instances of corrosion in the control cubicles
• Condensation inside WTI and OTI enclosures
• Inoperable trip switches
• WTI & OTI trip sequence tripping adjacent transformer(s)