The main function of an interposing CT is to balance the currents supplied to the relay where there would otherwise be an imbalance due to the ratios of the main CTs.  Interposing CTs are equipped with a wide range of taps that can be selected by the user to achieve the balance required.

As the name suggests, an interposing CT is installed between the secondary winding of the main CT and the relay.  They can be used on the primary side or secondary side of the power transformer being protected, or both.  Interposing CTs also provide a convenient method of establishing a delta connection for the elimination of zero sequence currents where this is necessary.

Application:

Interposing Current Transformers (Resin Cast) for differential protection schemes.