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Has the Transformer Failed?

It’s all about pole-mounted distribution transformers. Like every other utility, line crews at Hydro-Québec (Montreal, Canada) find reclosing on distribution transformers both potentially dangerous and time consuming. With fuses blown and reclosers open, deciding when to re-fuse a transformer and put it back in service can be difficult. Is it just the fuse, or has the transformer faulted?

The Internal Fault Detector (IFD) from IFD Corp. (Vancouver, Canada) was in development for more than a decade, and represents the result of a collaborative research and development effort involving financial and technical support by the National Research Council, a group of utilities and CEA Technologies Inc. (Montreal). The objectives for the IFD were to improve worker productivity, enhance customer service and increase overall safety associated with transformer failures. More than 45% of all new pole-mounted transformers in Canada are now shipped with an IFD.

Until recently, there had not been a sound, reliable test - without disconnecting the transformer and applying voltage - to detect faulted pole-mounted transformers. Hydro-Québec now uses IFDs that physically flag faulted pole-mounted transformers.

The IFD has two functions. It incorporates the pressure-relief device (PRD) and provides a visual indication on whether the transformer has faulted internally. The PRD conforms to ANSI’s PRD standard, and the sensor inside the IFD detects pressure changes in the airspace above the oil that are caused by internal faults.

The IFD sensor is calibrated to respond only to pressure changes due to faults, not to normal pressure changes due to increased load or rising ambient temperatures. When a fault is detected, an orange indicator, which can be seen from the ground, pops out. The line crew knows immediately that the transformer needs to be replaced. No time is wasted even considering the bad decision to reclose on the transformer. No one is placed in danger, and the utility saves time and money.

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