Pilot Isolation Transformer Working Principle?

[Ollie94]

How do pilot isolation transformers provide insulation for high voltages when there is a difference in ground potential between substations? What happens when there is a difference in ground potential between substations due to a ground fault?

 

[Shanaya]

Insulation transformers often minimise the high-frequency noise being transmitted either from the line to the connected device or from the device back to the line. This is due to the inductance of the transformer series and the grounded Faraday shield, which decreases the capacitive coupling of the transformer.

The insulation transformers provide a separation from the ground power line to prevent ground loops and unintended grounding of the test equipment. They also block high-frequency noise driving at the power source.