Make Proof Earthing Switches

..."Are used for the safe earthing of circuits, even if voltage is present, that is, also in the event that the circuit to be earthed was accidentally not isolated."....

https://electrical-engineering-portal.com/medium-voltage-switchgear-basics-of-switching-devices

https://www.quora.com/What-is-a-high-speed-earth-switch-and-how-does-it-work

Dear sirs,

It appears to me that there are two types of earthing switches: one which is deigned to operate on no load after circuit breaker and disconnector is opened (on no load), and another fast acting earthing switches ( or high speed earthing switches) which can also operate on short circuit (that is why make proof earthing switch). I hope I am correct.

Best regards,

Dear sirs,

In continuation to above, I am not able to understand why high speed earthing switches are needed at the following locations:

1. In voltage transformers to protect the circuit from core saturation caused during isolation/switching off the line.

Why there is problem of core saturation here and how it is avoided by the use of high speed earthing switch?

2. Grounding switches connected at the beginning of feeder bay module shall be of high speed, make proof type. Why?

Best regards,

These are to protect the equipment...like from lightning strikes...

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-9/practical-considerations-transformers/

The earth switch you mentioned is at the entrance of the feeder to the substation, I suppose. The earth switch when closed, earths the feeder including the VT primary and the Surge Arrester connected to the feeder.

If true, the make-proof characteristic ensures that the earth switch will be able to make earth connection safely even if the feeder has not been de-energised (switched-off) from the other end.

Even when the feeder circuit is opened on a high voltage transformer,there remains a DC high voltage on the transformer due to the capacitance of the wiring.

It must be discharged to prevent DC saturation of the transformer.

It must be discharged also before anyone services the equipment to prevent electrocution.