Megger MT0300 - Transformer Testing; Winding Resistance Testing

AVTMMTO3XX Rev 3 Sept 2013
19
5
Transformer Testing
F
WARNING
When testing a transformer or regulator, make sure that a good
ground is placed on the test specimen as shown on all
connection diagrams.
Winding Resistance Testing
Winding resistance measurements in transformers are of fundamental
importance for the following purposes:
 Calculations of the I2R component of conductor losses (factory test).
 Calculation of winding temperature at the end of a temperature test cycle,
(factory test).
 As a diagnostic tool for field testing a transformer for assessing possible
damage in the field e.g. additional contact resistance in the current paths
from winding to bushing or in the tap changer.
Transformers are subject to vibration. Problems or faults occur due to poor
design, assembly, handing, poor environments, overloading or poor
maintenance. Measuring the resistance of the windings and termination
resistance assures that the connections are correct and the resistance
measurements indicate that there are no severe mismatches or opens. Many
transformers have taps built into them. These taps allow ratio to be increased or
decreased by fractions of a percent. Any of the ratio changes involve a
mechanical movement of a contact from one position to another. These tap
changes should also be checked during a winding resistance test.