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Quick-Check Provides Quicker and Safer Transformer and Capacitor Testing

Utility Products Showcase, July 1999

by HD Electric Company

A "lights out" is reported from several homes on a warm summer afternoon. The trouble crew finds that all the houses are served by one pole transformer and the transformer cutout fuse is blown. No dead wildlife is found, no nearby tree branches, and the lightning arrester is on the line side of the fuse. In short, no obvious suspects. Does the crew refuse and hope for the best? The last time they did, the cover blew off the transformer leaving the customers without power for 24 hours and the company had to replace a customer's backyard shed.

A blown cutout fuse is hanging from one phase of a three-phase switched overhead capacitor bank. The unbalanced capacitor load is causing voltage problems at a nearby manufacturing facility. The trouble crew finds no bulged or blown capacitors. Refusing and closing the cutout into a shorted capacitor bank would cause a voltage dip or an outage that would cause still more problems for the manufacturer. The load dispatcher says "don't disconnect the VARs".

A new padmount transformer is installed and connected to buried secondaries feeding several homes in a new subdivision. When the transformer is livened from a nearby pole, the overhead cutout fuse blows. Where's the problem? Is it the transformer itself? Is it a shorted secondary cable run? Is it a miswired meter socket on one of the houses?

Sounds like yet another typical day for our trouble crew. In fact, all of these situations now have a solution with a new, portable, hand held, battery-powered tester for quickly identifying shorted or open transformers, capacitors and cables.

Until now, there has been no single piece of test equipment, much less a portable battery-powered unit, capable of testing the equipment in all of these situations. While most linemen and trouble crews now carry portable digital volt-ohmmeters, these instruments are not very useful for testing transformers or capacitors. To a basic ohmmeter, every transformer winding looks like a short and every capacitor looks like an open. The Quick-Check however, can readily tell the difference between a shorted secondary cable run connected to a transformer secondary and the transformer secondary coil itself.

The Quick-Check is a handheld device with two rugged coiled test leads and large copper alligator clips for connecting to transformer or capacitor bushings or lugs. A single push button starts the tester and super bright lights and a beeper indicate whether the connected equipment is a transformer or capacitor and whether it is shorted, open or O.K. That's it, just a single button to test any connected equipment, no range switches, no on/off switch or anything else to set. The Quick-Check also contains built-in self test circuitry so the unit can be tested in the field just before it is used. It is powered by a single nine volt battery and includes a low battery indication. In normal use, the battery lasts several months to a year.

The Quick-Check uses a special high frequency signal to tell the difference between a connected transformer or capacitor. It also tells the unit if it is connected to a short or if the leads are open and not connected to anything. Analyzing the high frequency signal tells the Quick-Check it is connected to an inductive circuit, such as a transformer coil, a capacitive circuit such as a power factor correction capacitor or a resistance such as a cable fault or shorted winding. A simple test takes just a few seconds. In less than a minute, a typical single phase transformer can be checked across the secondary windings, the primary windings, and from primary to secondary. The tests will also reveal an open internal fuse or circuit breaker or a shorted internal lightning arrester. Three-phase transformers can be checked across all three phases and from each phase to ground.

In a transformer shop, the Quick-Check can perform a kind of "triage" as transformers are removed from service and brought into the shop. The Quick-Check is used to quickly screen incoming and outgoing transformers for both primary and secondary shorts or opens, including any internal fuses or breakers. If all combinations of primary and secondary connections pass the test, then the transformer can be more thoroughly inspected, for example, turns ratio analysis and hipot. If the transformer does not pass the test, it is known immediately that the transformer has some more significant defect and will need repair. For those cases such as the transformer shop where only transformers need to be checked and not capacitors, a version of the Quick-Check called the TILT tests transformers only. It has all the features of the Quick-Check except the ability to test capacitors.

Because the Quick-Check is designed for quick and easy field testing, it cannot detect all types of transformer or connection defects. For example, it may not detect a partially shorted transformer coil such as a turn to turn short. The Quick-Check may also not detect such high resistance leakage paths to ground as tracking on a primary side bushing. The Quick-Check works best as a quick check for gross defects most typically caused by wiring or connection errors. It saves time, it saves fuses, it provides a safer test for trouble crews and it helps to provide a better level of service to your customers.

Copyright © 2000 HD Electric Company

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