Current Transformer Insulation Resistance Test

The megger test or insulation test is carried out to ensure the healthiness of the overall insulation system of an electrical power transformer.

Current transformer insulation resistance test.

Leakage reactance 3 phase equivalent and per phase 6. Insulation resistance is the ratio of the applied voltage dc to the total leakage current. An approximation is developed to calculate the temperature of winding at that condition. Modern test equipment for this purposes utilizes a kelvin bridge to achieve results.

Transformer winding resistance measurements are obtained by passing a known dc current through the winding under test and measuring the voltage drop across each terminal. To ensure that each winding of the current transformer has sufficient insulation resistance with respect to earth ct body and between the two secondary cores. Ct resistance excitation curve ratio polarity test. The insulation resistance test is the second test required by the electrical safety testing standards.

Exciting current test 4. Generally transformer windings are immersed in insulation liquid and covered with paper insulation hence it is impossible to measure the actual winding temperature in a de energizing transformer at the time of transformer winding resistance measurement. Historically many field electricians use the somewhat arbitrary standard of 1 megohm per kv. The transformer resistance testing will reveal a lot of details about the transformer by measuring the winding resistance of a transformer from one hv transformer bushing to another.

Developed early in the 20th century the insulation resistance ir test is the oldest and most widely used test for assessing the quality of insulation. Also acceptable values of insulation resistance depend upon the equipment you re testing. The international electrical testing association neta specification maintenance testing specifications for electrical power distribution equipment and. You might think of a winding resistance test set as a very large low resistance ohmmeter.

Apply the test voltage and note the reading. Ttr transformer turns ratio 5. Current transformer loop test. The insulation resistance test consists in measuring the insulation resistance of a.

Value at 60 seconds after application of the test voltage is referred to as the insulation resistance of the transformer at the test temperature. Turns ratio test 8.