Research On Fast Busbar Protection For Smart Substation

Substation busbar is one of the most important components in power system, the maloperation or malfunction of busbar protection device may have adverse consequences, and even cause the collapse of the regional electrical grid. The current differential principle based on power-frequency components is currently widely used in busbar protection. But it requires strict sampling synchronization and its performance is easily affected by current transformer (CT) saturation, CT ratio-mismatch, load current, and fault ground resistance, etc. Meanwhile, the smart substation’s construction has put forward higher requirements on the performance of relay protection. Therefore, it has significant theoretical meaning and engineering application value to further study the reliable and fast busbar protection suitable for smart substation.The paper proposes two novel fast busbar protection methods based on the transient characteristic of electrical quantities for busbar internal faults and external faults. Firstly, using the propagation theory of traveling waves, a fast busbar protection method based on waveform integral of traveling waves is presented to improve the operation speed of busbar protection. For a busbar fault, the detected traveling waves on all lines connected to the busbar will come from their back, whose directions are defined as positive. For a fault on any one of these lines, the detected traveling waves on all healthy lines have the same positive direction, while the traveling wave direction on the faulted line is negative. Within a specific duration after the fault, the waveforms of directional traveling waves on all lines are integrated, and a criterion discriminating fault direction can be established according to the ratio of directional traveling waves. Through analyzing the fault directions for all lines, whether the fault is internal or external can be identified. In addition, the single aerial mode of the conventional phase-mode transformations, such as Clarke and Karenbauer, cannot reflect all the fault types, so this paper constructs a new phase-mode transformation matrix based on the mathematical principle of phase-mode transformation.Secondly, a novel busbar protection method based on the polarity comparison of superimposed current integral is proposed. Theoretical Analysis shows that all lines connected to the faulted busbar have the same polarities for the superimposed currents in case of an internal fault to busbar; but for a fault occurring on any one of these lines, the polarity on the faulted line is opposite to those on healthy lines connected to the same busbar. According to this important characteristic, the busbar protection criterion can be established. To improve the reliability and anti-interference ability of the busbar protection method, waveforms of superimposed currents are integrated within a short time after the fault. Moreover, a distributed busbar protection scheme is designed according to the proposed principles and smart substation’s system and network structure.Thirdly, referring to the one and a half breakers busbar configuration and system parameters of a real 500 kV extra high voltage substation, a simulation model is built based on software PSCAD/EMTDC, and extensive simulations were carried out to verify the proposed two busbar protection methods. The simulation results demonstrate both the proposed methods are robust, rapid and reliable, and their performances are immune to fault initial conditions, series compensation, switching operation, lightning and CT saturation. Finally, a simple 500kV busbar model was constructed in the power system dynamic model and simulation laboratory to test the proposed methods, and all identification results are correct. What’s more, simulation and test results demonstrate that the new phase-mode transformation can achieve single aerial mode reflect all the fault types. Therefore, the two busbar protection methods are simple and expected to be applied into the actual power engineering.