The following test to be conducted for a current transformer.
1. Insulation Resistance Test.
2. Winding Resistance Test.
3. Polarity Test.
4. Knee point Test.
5. Ratio Test.
1) Insulation Resistance Test:
To know the insulation value of CT windings. We will be applying primary to Earth 5kv for 60 seconds, primary to secondary 2.5 kv for 60 seconds & secondary to Earth 1000v for 60 seconds.
2) Winding Resistance Test:
To verify the winding resistance as specified by the manufacturer and to check for any damage in the CT winding resistance arrived by injecting DC current through the winding and measuring the voltage drop compare the reading with factory test report.
3) Polarity Test :
This test is necessary to see the relative polarity of the primary and secondary terminals when terminals are not marked or to establish the correctness of the marking if already marked. This test is carried out with help of 9v (or) 12v DC battery. Apply the DC source between primary Terminals P1 (+) P2 (-) and measure the secondary side using Null deflection analog ammeter and check the correct deflection of meter & compare with polarity mark.
4) knee point voltage:
Saturation point of CT core is measured by applying voltage in secondary by keeping primary open the point where the exciting current increase by 50% for a 10% increase in secondary voltage is referred as saturation region.
5) Ratio Test:
To verify the ratio error of the CT this test is performed with help of primary injection kit. Inject the current through P1- P2 (primary of CT Terminals) and measure the corresponding secondary side output current and calculate the ratio error from actual and measured values.
1. Insulation Resistance Test.
2. Winding Resistance Test.
3. Polarity Test.
4. Knee point Test.
5. Ratio Test.
1) Insulation Resistance Test:
To know the insulation value of CT windings. We will be applying primary to Earth 5kv for 60 seconds, primary to secondary 2.5 kv for 60 seconds & secondary to Earth 1000v for 60 seconds.
2) Winding Resistance Test:
To verify the winding resistance as specified by the manufacturer and to check for any damage in the CT winding resistance arrived by injecting DC current through the winding and measuring the voltage drop compare the reading with factory test report.
3) Polarity Test :
This test is necessary to see the relative polarity of the primary and secondary terminals when terminals are not marked or to establish the correctness of the marking if already marked. This test is carried out with help of 9v (or) 12v DC battery. Apply the DC source between primary Terminals P1 (+) P2 (-) and measure the secondary side using Null deflection analog ammeter and check the correct deflection of meter & compare with polarity mark.
4) knee point voltage:
Saturation point of CT core is measured by applying voltage in secondary by keeping primary open the point where the exciting current increase by 50% for a 10% increase in secondary voltage is referred as saturation region.
5) Ratio Test:
To verify the ratio error of the CT this test is performed with help of primary injection kit. Inject the current through P1- P2 (primary of CT Terminals) and measure the corresponding secondary side output current and calculate the ratio error from actual and measured values.
