Study On Setting Calculation And Principle Improvement Of Protection System For Large Hydroelectric Generator

With the rapid development of hydroelectric power, large hydroelectric generator hasbecome the main force in hydroelectric power, whose protection configuration, settingcalculation and protection optimization problems has been hot area of research. Based onthe exsiting research, the operation status, fault characteristic and the protectionconfiguration and protection performance improvement of large hydroelectric generator isworth studying.This paper takes large hydroelectric generator in three gorges hydropowerunderground station as the research object. After finishing fault simulation, protectionconfiguration and setting calculation of the generators, several protection setting proplemsare put forward and detailedly analyzed.For self shunt excitation generators, once the frocing excitation system is out ofcontrol, fault forcing excitation may happen, which may damage excitation or the drop outsystem. No-load fault forcing excitation is the most severe forcing excitation fault. Basedon the analsis of the factors that may impact the false forcing excitation current, severalsolutions to decrease excitation current when fault forcing excitation happens are proposed.With comprehensive consideration of the generator protection selective demand, theimprovement method of generator stator overvoltage protection and excitation transformerover-current protection are put forward.Stator single-phase fault is one of the most common faults in the generator, and it isessential to improce stator single-phase grounding protection. This paper firstlysummarizes the several under-using sator single-phase fault protection methods. For largehydroelectric generators, the generator can neither trip casually, which may influence thegrid stability, nor can continuing running when ground current is two strong. Taking intoconsideration of the short circuit current tolerance ability of the generator, the generator cankeep running when specific stator single-phase faults occurs, which improves power supplyreliability. The proposed protection imporve method is verified using Matlab simulationresults. Impedance protection one of the backup protections, but the protection in use can’tmeet the requirements. This paper analyze influence of transformer connection form onmeasured results, pointing out that the protection may refuse to trip under specificsituations, and relative improvement solution is proposed.