What should be done if a PI test on a transformer ends unexpectedly at 8 minutes?

In a power insulation (PI) test on a transformer, if the test ends unexpectedly at 8 minutes, the appropriate response is to discharge the specimen for a duration that is four times the applied time before retesting. This is because a premature termination of the test can indicate that the insulation may not have held up adequately under the applied conditions. By discharging the transformer for a longer duration, you ensure that any residual charge is safely removed, minimizing the risk of dielectric breakdown when reapplying voltage.

This approach allows for a more accurate assessment of the insulation's condition. If a test is stopped early, simply retesting without proper discharge or increasing voltage may not provide reliable results. It is essential to adhere to best practices in insulation testing to ensure the safety and reliability of the transformer’s insulation system. Discharging the specimen adequately also prepares the system for the retest, leading to improved accuracy in determining the health of the transformer insulation.