Study On New Principle Of Relay Protection To Deal With High Resistance Ground Fault On High Voltage Transmission Lines

On transmission lines, single-phase ground fault is most likely to occur. Part ofphase-to-phase faults also evolved from it. Therefore improving swift removal ability ofsingle-phase ground fault can enhance the system reliability effectively. Affected by theenvironment along the transmission lines, high resistance ground fault occurs pronely, andthe existing main protection of lines is difficult to deal with them. In the current solution,most use fault component or transient component, and protection can only actinstantaneously. Others have higher requirements to the communication channel, which iscomplex. On the premise of supplementing the existing protection, it is a very meaningfulsubject to research on the high resistance protection which can response single-phase highresistance ground fault under various operation modes, does not need to quit running atany time and is easy to implement.In this paper, first of all, measured impedance loci of distance units on both sides ofline with single-phase grounding fault are analyzed in the complex impedance plane, andthe link and differences between them is discovered. And then by strict formula deriving,we proves that the summation of the measured impedance on both sides of the line is noteqaul to the impedance of the line only when a non-metallic ground fault occurs. And thenwe puts forward the concept of summation impedance and points out that we can constructa protection which can react high resistance fault by using its value differences betweenfault in region and out of region.Then, we use geometric analysis method to analyze the operation mode changesimpact on the size of the impedance values and the impedance value under the mostunfavorable situation is given. Based on this, the paper proposes a summation impedancerelay with a simple criterion. The simulation on PSCAD/EMTDC proves its effectivenessto high resistance fault. At the same time, the simulation also proves it cannot adapt to thechanges of system operation mode and its ability to resist the influence of distributedcapacitance is weak. So the relay can be applied only on ultra-high voltage short lines.Further, the measure current is added into the operation criterion and the start-up criterion,which make it with the adaptive features. The relevant simulation shows that the high resistance protection in the composition of summation impedance relay with adaptivecriterion can react ground fault with300ohm transition resistance on ultra-high voltagemedium or long lines, and its protection region is the whole line. It is able to adapt to thechange of system operation mode. Under open phase operation it does not need to be outof operation. It is easy to implement.At last, the paper tests distance pilot protection and differential pilot protection whichare the most widely used. Results show that their ability of reaction to transition resistanceis insufficient. The high resistance protection in the composition of summation impedancerelay can supplement effectively.