What is the NETA Recommended Minimum Insulation Resistance test value for a liquid filled 35,000-4,160V D-D transformer primary winding?

The NETA Recommended Minimum Insulation Resistance test value for a liquid-filled transformer, such as a 35,000-4,160V delta-delta (D-D) transformer, is determined based on the voltage class of the transformer and the insulation requirements to ensure safe and reliable operation.

In this case, a minimum insulation resistance value of 5000 vdc is specified for such a transformer. This particular value is essential because it reflects a standard threshold that indicates the condition of the insulation. Maintaining an insulation resistance at or above this value ensures that the insulation is sufficiently robust to withstand the high voltages associated with the operation of transformers in this class. Testing at this level also helps in predicting the reliability of the insulation over time and can identify potential issues before they result in catastrophic failure, ensuring safety and operational efficiency.

While the other choices present lower or higher voltage test values, they do not meet the recommended standards for a transformer of this specification, potentially jeopardizing safety and operational reliability.