Function of a transformer : The function the same as a general transformer.
Lightning surge withstand voltage has a high level.
Function of lightning surge reduced
The translate of the common mode (between power line and the earth) lightning surge which invade from the primary side to the secondary side can be inhibit.
It can decrease a primary lightning surge less than 1/1000 (-60dB)
Performance of lightning impulse withstand voltage
This is a transformer of low voltage class, and able to endured 30kV lightning impulse voltage between primary winding and earth.