HV and LV Winding resistance Test
The Winding resistance is measured at ambient temperature and then converted to resistance at 75˚C for all practical purposes of comparison with specified design values, previous results and diagnostics.
For star connected winding , the resistance shall be measured between the line and neutral terminal.
For delta connected windings, measurement of winding resistance shall be done between pairs of line terminals.
As in delta connection the resistance of individual winding can not be measured separately, the resistance per winding shall be calculated as per the following formula:
Resistance per winding = 1.5 x Measured value
Insulation resistance Test or Megger Test.
This test is carried out to ensure the healthiness of over all insulation system of an electrical power transformer.
Power Factor and Capacitance Test
Power factor testing is an effective way to detect defective electrical equipment insulation.
Power factor is the ratio of the capacitive or ‘charging’ current (measured in volt-amperes) to resistive or ‘leakage’ current (measured in watts).
The capacitance and dissipation factor test (Tan Delta test) is an AC low voltage maintenance test that is very similar to the power factor test.
In the power factor test procedure, there is no requirements to make connection changes once the initial test set connections are made.
In capacitance and dissipation factor test values are obtained by balancing a null meter for each variable at every the measured variable selector switch positions
Continue to Buchholz Relay Alarm Part 7.
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