Bus Bar Protection

I think you can Use a CT with taps.that CT should be multi cored.

for your case. we need a CT with 1200/1 with taps so that we get 600/1.

this core should be used for Busbar protection.

Search for CT of 1200/1 with taps to make it 600/1.

Good Luck.

If you have high-impedance bus differential protection, you need to have all the CTs be the same ratio. It is also important that they all be of the same accuracy. It is beneficial if the conductor lengths from the CTs to the relay all be of similar lengths, so that burden from the wiring not unbalance the currents. The CTs in a high-impedance scheme are all connected in parallel, so that the currents through them normally sum to zero vectorially. If there is any fault, at least one of the CTs will differ, and a voltage develops at the paralleled connection due to to "missing" current.

If you change to low-impedance diff protection relay, it will have separate inputs for each of the CTs, and you can set each input for the associated CT ratio. Then the relay will do the compensation to get the zero sum.

So you have a choice: Change the CTs so they all match, or change the relay to low-impedance type and the wiring arrangement so that you can use differing CTs.