T&D World Magazine
LTC tester

Accessory Power Supply Allows Transformer Load Tap Changers to be Easily Tested

The new LTC135 uses dynamic resistance measurement (DRM) techniques to perform advanced diagnostic tests on transformer load tap changers.

Designed for use in conjunction with the company’s circuit breaker analyzers, the new LTC135 accessory power supply from Megger allows transformer load tap changers to be tested easily and comprehensively.

Since tap changers are the only moving parts in transformer systems and are, therefore, the parts most prone to failure, the accurate condition assessment made possible by the LTC135 is an invaluable aid to detecting developing faults at an early stage.

The new LTC135 uses dynamic resistance measurement (DRM) techniques to perform advanced diagnostic tests on transformer load tap changers. The tests are made during tap changer operation and include load tap changer timing and continuity checks and crucially, make before break operation of the tap changer contacts.

The unit takes measurements when connected to any of Megger’s circuit breaker analyzers, such as the EGIL, TM1600, TM1700 or TM1800, and the results are displayed, recorded and analyzed either on board the instrument or within Megger’s CABA Win software. The unit can also be used with Megger EGIL instruments to carry out dynamic voltage measurement (DVM) tests that provide similar information.

The tests reliably detect problems that include build up of pyrolytic carbon and thick organic films on the tap changer contacts (coking), long-term degradation of the contacts, deviation in switching times, damaged transition resistors and reactors, and excessive increase in resistance of the main or arcing contacts. Much of the information provided by the tests cannot be conveniently be determined by other methods.

Depending on the model of circuit breaker analyzer with which it is used, the LTC135 also offers additional options. These include static winding resistance measurements, three-phase DRM analysis, and monitoring of the current drawn by the motor that operates the LTC mechanism.

For those that have, or are thinking about purchasing a Megger circuit breaker analyzer, the LTC135 offers additional versatility; the ability to test transformer tap changers with a useful diagnostic tool.

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