Transformer Testing and Monitoring

Using Gas-in-Oil Standards to Improve the Accuracy of DGA Results and Diagnosis

By M. Duval

Dissolved gas analysis (DGA) is widely used to monitor the condition of transformers and other pieces of oil-filled equipment in service. Wrong diagnoses may be drawn, however, if the DGA results coming from the lab are not accurate. For instance, an electrical fault may be mistaken as a thermal fault, which may have serious consequences for the equipment. Several CIGRE and IEC round robin tests (RRTs) have shown that the repeatability (precision) of DGA labs is generally good, but that their accuracy (deviation from true value) is often poor.

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Load Tap Changer (LTC) Position Indicators

LTC position monitors are IEDs that are used for monitoring a transformer’s tap position and changing it remotely based on fluctuations in the power load. The device converts the output of an electromagnetic position or displacement sensor (synchro transmitter) to a user-definable panel display and electrical output. The INCON Model 1250 for example employs a proprietary synchro conversion technique that is performed entirely in preprogrammed software. This approach uses few electrical components, thus ensuring a more stable and reliable output at a very reasonable cost.
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