6
RMO60TD Designated Use, Functionality
4.2 Tap Changer Test
The TapC menu offers a user friendly way of measuring winding resistance in tap changers. The
RMO60TD test set measures the winding resistance of individual taps of a power transformer’s tap
changer, and checks whether the On-Load Tap Changer (OLTC) switches without a discontinuity. In the
moment the tap is changed from tap to tap, the device detects the sudden, very short drop of the current
flow. A properly working tap changer differs from a malfunctioning one in a discontinuity during the
change, by the magnitude of the current ripple value.
Comparison with ‘’fingerprint’’ results, which were taken when the unit was in a known (good) condition,
and comparing with other phases, allows for an efficient analysis. Disposition of all current ripple
changes (or of the current flow on the graph) depends on a particular transformer and OLTC design, so it
is always recommended to compare results obtained on the same unit with previous measurements.
Note: In TapC menu only Ch:1 is the active channel. Maximum test current selected in the TapC mode is
20 A.
At the start of the test a check of cable continuity is performed. In case of disconnection, an alarm is
activated, and the error message is shown on the display.
Note: Using DV-Win in TapC menu the results could be stored to a PC. By pushing the Ω button a
resistance result and current ripple value are stored in internal memory location, and the memory
location is automatically increased to the next one.
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