By Edis Osmanbasic

Diagnostic testing of voltage regulators should include condition assessment of on-load tap changers (OLTCs) by applying dynamic DVtest methodology.

When diagnostic testing is applied to voltage regulators, it includes dynamic tests on tap changers. As regulators have a specific construction, where at neutral point turns ratio is 1:1, familiar dynamic test graphs look very different.

This article is an overview of voltage regulator condition assessment using DVtest methodology, also known as dynamic resistance measurement (DRM).

DVtest, or Dynamic Resistance Measurement (DRM) testing, is an offline, non-destructive test in which a DC current is injected through a transformer winding and tap changer as it moves through all of its positions. Results from the current signatures are examined and compared against previous tests, or similar unit test results. This test on a regulator may be used to detect problems such as slow tap changer transition time, contact problems, and open circuits, among others.

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This article was originally published in the December 2019 issue of the Critical Failure: Modes & Prevention magazine.

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