New Algorithm of Wide-Area Protection Based on Current Polarity and Energy Relative Entropy

In order to improve the fault tolerance and sensitivity of wide-area relay protection, a new algorithm of wide-area relay protection based on current polarity and energy relative entropy was proposed. It combines bus-bar sampling value protection with differential protection principle for fault component of lines. Firstly, the protection correlative domain of line IED was divided, so that the fault component currents of positive sequence frequency were extracted accurately according to different correlative domains. Meanwhile, the concepts of boundary current, synthetic calculated current and synthetic virtual current were presented. Secondly, the energy relative entropy of the synthetic current sample was defined to quantify the difference of the synthetic current. At the same time, the angle between the boundary currents of the correlative domain was calculated to characterize the polarity relation of the boundary current, and the correlation between the current sample energy entropy and the polarity relation was utilized to identify the inner and outer faults of the correlative domain. Finally, utilizing IEEE 3-machine and 9-bus system constructed by the software of PSCAD/EMTDC, different fault types were set at different fault points to test eh algorithm performanc. The results reveal that when fault occurs in the correlative domain, the synthetic current is almost the same, with the relative entropy being very small, close to 0, and the angle between the boundary currents is less than /2 with approximate polarity. When the fault is outside the domain, the synthetic current waveform is significantly different from sampling value, with the relative entropy larger than 1, and the angle between the boundary currents is close to , with nearly opposite polarity. The distinction between the faults inside and outside the domain is obvious. Simulation results show that when single-phase earth fault occurs in the domain, the maximum relative entropy is 0.428 and the maximum angle is 0.388 in the condition of high resistance of 800 , which still meets the reliable criterion and has high sensitivity. The experimental results verify that the algorithm performance is basically not affected by the transition resistance, and can overcome the influence of unfavorable factors such as TA saturation and data distortion.