what is pi test in transformer?

A pi test, or insulation resistance test, is performed on transformers to assess the integrity of their insulation system. This test involves applying a high DC voltage to the transformer windings while measuring the insulation resistance between the windings and the ground. The results help identify potential insulation failures or degradation, ensuring the transformer operates safely and efficiently. A high resistance value indicates good insulation, while low values may signal issues that require attention.