Reco Transformers Pvt. Ltd. Manufactures Core Balance Current Transformer. Reco Transformers Pvt. Ltd. Is an ISO 9001:2000 certified company. The company manufactures Low Tension Current Transformers and Potential and Control Transformers. The Core Balance Current Transformer also known as a ZERO sequence Current Transformer is used for earth leakage and earth fault protection. In Core Balance Current Transformer the three core cable or three single cores of a three phase system pass through the inner diameter of the CT. When the system is fault free, no current flows in the secondary of the CBCT. When there is an earth fault, the residual current [Zero Phase sequence current] of the system flows through the secondary of the CBCT and this operates the relay setting.