Why is it not allowed to hang grounding wires on both sides of the current transformer of bus differential protection?

   Hanging grounding wires (or closing grounding switches) on both sides of the current transformer of bus differential protection will greatly reduce its excitation impedance, which may have an adverse effect on the correct operation of bus differential protection. In the event of a bus fault, it will reduce the sensitivity of bus differential protection; in the event of an external fault, it will increase the secondary unbalanced current of bus differential protection, and may even cause maloperation. Therefore, it is not allowed to hang grounding wires (or close grounding switches) on both sides of the current transformer of bus differential protection. If it is absolutely necessary, the secondary side of the current transformer should be disconnected from the operating bus differential protection circuit.