DC voltage is applied between phases or phase to earth to measure leakage current for minimum 1 min. PI test is the ratio of 1 min to 10 min IR test results. These tests are very common and generally done to determine insulation failure or high level of insulation deterioration.

This test is conducted by passing known DC current through the winding and voltage drop is measured to determine winding resistance. Test results can be compared between phases to assess the winding condition in case of original data is unavailable for comparison. This test is carried out to understand any break in winding conductors or strands. It can also be used to determine any high resistance connection by comparing with previous test results.

Known test voltage is applied to one winding and induced voltage is measured in other winding. Test results can be compared between phases to assess the winding condition in case of original data is unavailable for comparison. This test is conducted to determine short-circuited turns or tap changer failure.

In this test, angle between voltage and current is measured through testing instruments and tangent of this angle is an indication of dielectric loss. Insulation will deteriorate over time due to aging and/or moisture absorption and hence increasing Tan Delta value. Normally test results are compared with previous results to assess the deterioration. Alternatively typical value of Tan Delta, depending on type of insulation, can also be used to assess the insulation condition.

In this test, AC voltage is increased across the insulation and power loss is measured (indirectly). This loss is an indication of discharged within insulation. Power factor or dissipation factor is measured at various voltage levels up to rated phase to phase voltage. Tip-up is plotted as a function voltage to determine the voltage at which discharge activity increases. This test is normally conducted if any anomaly is found in Power Factor test results.

This test is conducted by injecting low voltage at one side of the winding and response is measure at the other end. This test is carried out for various frequency range (typically 20 Hz to 2 MHz) and ratio of output to input is potted against frequency. This test generally determines any mechanical movement within the winding and core structure, hence recommended to perform after transportation or after any fault. Test results are normally compared with previous results or between the phases to identify any anomaly.

Fixed current is injected and voltage drop is measured across the contact. This test is conducted on connections to ensure there is no high resistance that may result in hot joint. The test results are compared with previous results or acceptable range as supplied by the manufacturer.

In this test, voltage pulse is applied to windings and output is monitored. If there is any insulation deterioration then output signature of that winding will be different than healthy winding. This test is carried to identify any insulation degradation in early stage.

This test is an AC withstand test normally conducted on high capacitance load such as cable. Typically, frequency range of 0.1 Hz to 0.01 Hz is applied during testing. The test results can be used to assess cable insulation and normally bad results indicates cable failure.

Resistance of current carrying contacts (in close position) in CB is measured by injecting DC current. Test results are analysed to determine excessive heat loss during operation that may result in CB failure over the time.

In this test, resistance of current carrying contacts in CB is measured while CB is operating to assess the condition of main and arcing contacts. Results are compared with the allowable limit to identify any issue with the contacts that may result in CB failure.

As name suggests, time required to operate circuit breaker is measured to confirm integrity of the mechanical parts.