Differential line protection using dqo components for the communication channel

Differential line protection has been playing a major role in power transmission line protection due to its simplicity, operation speed, and high sensitivity. However, problems with communication channel make current comparisons difficult to achieve. To improve the insensibility to this problem, this paper proposes a new approach. First, the three currents are acquired. Then these currents are transmitted to the other relay. However, instead of sending directly these currents to the other relay, first a Park transformation or ABC-dqo transformation is performed. The received currents are in dqo components. In this way, the transmitted signals are DC components. Before calculating the difference between the currents entering and leaving the protected zone an inverse transformation of the received currents (dqo-ABC) is made. Using this approach, immunity to problems such as sampling misalignment and time delay of the communication channel will be improved. A new methodology associated to this approach was also proposed. The obtained advantage is that it allows the reduction of the number of signals that must be transmitted between relays (using only do components). This methodology also improves the relay sensitivity. Several test results are presented in order to show the effectiveness of the proposed approach.