Small Transformers Earth Fault Protection

Incoming earth fault protection:

The ZCT is more sensitive than the internal CB ground fault protection. It may not be needed, depending on whether the supply system is solidly grounded. Generally, the value of the transformer determines how much protection is provided. More sensitive or more protection could reduce the damage occurring during a fault.

Outgoing earth fault protection:

A CT on the neutral can protect the transformer for through fault damage, down to about 10% of the secondary windings. In most cases, if the neutral is solidly grounded, there is little to be gained by measuring the current.

If the neutral is resistance or reactance grounded, that current is monitored to detect a ground fault only on the secondary side, and serves as a backup to other protection that can clear the fault to provide power system selectivity. Selectivity is engineered in so that if the ground fault is not eventually cleared, the transformer primary breaker operates.

For this winding configuration, primary ground fault protection cannot detect a secondary ground fault, so expect more damage and cost if a ground fault occurs. Again, the cost and value of the equipment determines the level of protection.

The incoming cable needs to be protected for overcurrent and short circuit. The source of power must be removed eventually in the event of a fault. This is typically done at the source, but can be sensed at the load and cleared at the source. This is the only part of your post that makes little sense.

I'm not an electrical engineer but after reading your post, a question struck me as unusual.
Why on earth (no pun intended) would you want to disable a built in safety device in your ACB ?? In this day of cost cutting, no manufacturer is going to install unnecessary components / systems if they are not needed or it maybe a legal requirement !

Also if it is a "solid state" how do you intend to disable it ?
By doing so, you are then depending on a single protection system instead of 2 independant systems.

Also depending on where your ACB and ELR are located (upstream or downstream) you might not have any Earth protection for your ACB at all if you disable it.
Not to mention any possible legal liabilites if you disable a safety device and something happens !!

Because the outgoing feeders are equipped with RCD, so inorder to provide the back up for the RCD, the Incomer is equipped with ELR with some time delay.

The LSIG or G in the ACB will not provide protection for the earth leakage (in mA) but only for high earth fault currents.

The thinking here is ELR works for both the earth leakage and the high earth fault currents.

Your comment does not describe your system adequately, you need to reference your transformers, with respect to your protection.

Since a delta wye connection does not allow ground fault detection beyond the transformer, if you are describing high side ground fault protection, you need to state whether the high side power system is solidly grounded.

Also, a statement on the value of continued service and the cost of interruption would help you assess the value of the protection.

Incoming earth fault protection:

The ZCT is more sensitive than the internal CB ground fault protection. It may not be needed, depending on whether the supply system is solidly grounded. Generally, the value of the transformer determines how much protection is provided. More sensitive or more protection could reduce the damage occurring during a fault.

Outgoing earth fault protection:

A CT on the neutral can protect the transformer for through fault damage, down to about 10% of the secondary windings. In most cases, if the neutral is solidly grounded, there is little to be gained by measuring the current.

If the neutral is resistance or reactance grounded, that current is monitored to detect a ground fault only on the secondary side, and serves as a backup to other protection that can clear the fault to provide power system selectivity. Selectivity is engineered in so that if the ground fault is not eventually cleared, the transformer primary breaker operates.

For this winding configuration, primary ground fault protection cannot detect a secondary ground fault, so expect more damage and cost if a ground fault occurs. Again, the cost and value of the equipment determines the level of protection.