A novel Instantaneous Equivalent Impedance (IEI) based bus-bar protection technique is proposed in this paper. By analyzing the fault component networks of bus-bar for the internal fault and the external fault, respectively, the equivalent models for different fault states are established. Based on the parameter estimation technique, the amplitudes of IEI of bus-bar and each circuit connected to bus-bar can be calculated and the external fault and the internal fault can be distinguished correctly by comparing the amplitude of IEI of bus-bar with that of the parallel connecting result of all the circuits connected to bus-bar. The new technique is immune to the impact of current transformer (CT) saturation, so the CT saturation detection unit is avoided for the new protection. As an time-domain based technique, it can operate more rapidly comparing with the traditional phasor based bus-bar protection. Moreover, the proposed technique has the inherently immunity to the impact of fault current flowing out when a fault occurs in the protection zone of the breaker-and-a-half bus-bar. Simulation results of the Electromagnetic Transients Program (EMTP) show that the presented technique has high sensitivity and reliability.

Bus-bar protection, current transformer (CT) saturation, instantaneous equivalent impedance, parameter estimation