Measure insulation resistance between low voltage windings and the main body of the transformer.
Insulation resistance test standard for transformer.
With a little record keeping and common sense however you can get a good picture of the insulation condition from values that are only relative.
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The test is performed with a power factor test kit and the connections are the same as for the megger test the insulation resistance test.
Value at 60 seconds after application of the test voltage is referred to as the insulation resistance of the transformer at the test temperature.
Leakage current should be as small as possible therby ir value should be as high as possible r v i.
B kv is the rated machine terminal to terminal voltage.
Insulation resistance is the ratio of the applied voltage dc to the total leakage current.
Steps of this test.
This test can be repeated during the service life of the transformer and verified against the result obtained during manufacturing as a check to determine if the insulation is malfunctioning or decaying.
Values based on ieee std 43 2013.
Insulation resistance test of transformer is divided into three parts.
Value at 60 seconds after application of the test voltage is referred to as the insulation resistance of the transformer at the test temperature.
Clean the terminals of the transformer.
The transformer neutral bushing is to be disconnected from earth during the test.
Apply the test voltage and note the reading.
Ansi neta mts 2015 table 100 11 insulation resistance test values rotating machinery for one minute at 40 c.
The megger insulation tester is a small portable instrument that gives you a direct reading of insulation resistance in ohms or megohms.
Use the megger test at a low voltage side.
Apply the test voltage and note the reading.
A rated line to line voltage for three phase ac machines line to ground voltage for single phase machines and rated direct voltage for dc machines or field windings.
Insulation resistance decreases in temperature or moisture.
