Protective Relaying for Tapped High Voltage Transmission Lines

It is Ontario Hydro's practice to provide a dual supply to subtransmission or distribution buses supplying loads in excess of approximately 45 MVA. A typical supply station of this type utilizes two transformers which are normally operated in parallel on the low voltage side through circuit breakers, and connected to separate high voltage supply circuits via air break switches. A multi-tapped supply line may cause protection difficulties and the required solutions deviate from the conventional two-ended line protections. In this paper typical protection problems, their solutions and operating experience of the multi-tapped high voltage transmission lines are described.