In recent years, renewable energy generators have been widely promoted in Ontario to offset their polluting counterparts. Due to connection cost of these generations, most of the renewable generation stations are connected to Hydro One transmission system at nearby HV transmission lines. However, the direct connections of the generation on the transmission line result in increase of apparent impedance of distance protection for these lines. Dependability and security of the transmission protection system can be seriously compromised. The immediate consequence is that reach setting value must be increased to cover entire line fault. In this paper, a solution is developed, which is implemented by using programmable logic within a modern digital relay.
In this solution, the timed zone 2 distance protection can be set with a short and a long delay based on the zone 2 operation sequence and timing conditions. The short time delay is used to coordinate with HV transmission line protection and the long time delay is used to coordinate with LV feeder protection after closing on a permanent fault. With this solution, distance zone 2 elements will provide regular protection to the transmission line faults as usual, and also provide coordinated backup protection to the distribution feeder faults. No additional communication is required within this logic. It is a cost-saving method to solve the challenging protection issue. Results and conclusions have been verified with satisfactory result.