Syncrocheck Relay Malfunction

You mentioned that both transformers are parallel. In case of parallel transformers, the voltage ratio should be same, then why voltages are different. There are other conditions for parallel transformers as well (such as same vector group, %impedance etc.). If the transformers satisfy the parallel conditions, you don't need the synchrocheck relay. The synchocheck relay is needed when the transformers are fed from two different sources and the secondary of the transformers need to be connected (obviously it is not called parallel operation of transformer).

Anyway, the 6.3 KV and 7.3 KV outputs of two different transformers should never be connected. If you do so, it will be a disaster (short circuit) and the short circuit protection must trip in this case.

- MS