Study Of Secondary Arc Extinction In UHV Transmission Line With Series Capacitors

With the improving of power system, series capacitor compensator is widely used toimprove the system stability and increase transmission capacity of power lines. Single-phasereclosing is an important means in power system to ensure continuity of power supply andimprove the circuit reliability. Rapid extinction of secondary arc is the key in makingsingle-phase reclosing successfully in series compensation system, but because of theexistence of series compensation device, the extinction of secondary arc in seriescompensation system are more complex than conventional series compensation system, thus aseries of problems need to be studied and solved.Various influence factors of secondary arc current and recovery voltage in seriescompensating system are studied in this paper; both steady state and transient state of thesecondary arc current and recovery voltage are analyzed, methods of secondary arc extinctionin series compensation system are proposed. The main research contents are as follows:Adding series compensation will make great effect on the electrical parameters of thetransmission lines, the problems caused by series compensation device are discoursed in thispaper, such as line overvoltage, secondary arc current, transient recovery voltage of circuitbreaker (TRV) and sub synchronous resonance (SSR), etc. thus to avoid errors in settingparameters when building EHV series compensated transmission lines. Meanwhile, thesecondary arc current is an important factor in determining whether secondary arc canself-extinguishing, the determine of grounding resistance plays an important role incalculation of secondary arc current. According to Thevenin theorem, the influence of valueof the grounding resistance on the secondary arc current in transmission lines is analyzed inthis paper.According to analysis of EMTP simulation and power spectrum, the secondary arccurrent will generate low frequency component under certain conditions in seriescompensation system without pararell compensation; the secondary arc current will generate low-frequency components, as well as recovery voltage will generate low frequencycomponent and the phenomenon of "beat frequency" in series compensation system withpararell compensation. By using of Laplace transform, the frequency characteristics ofsecondary arc current and recovery voltage in series-parallel compensation system areanalyzed, so as to explain the above-mentioned phenomenon in theory.In the series-parallel compensation system, a method of adopting bypassing the seriescompensation in fault phase are used to eliminate the influence of low frequency component,but the direct current component will increase in secondary arc current, in some cases, thevalue of direct current component itself is great, thus the certain resistances are used to shortcircuit with fault phase as well as the small reactance are used in neutral point of shuntreactors, so as to extinguish the secondary arc current, theoretical analysis have shown thatthis method can not only eliminate low frequency components in the secondary arc currentand recovery voltage but also accelerate the reduction of direct current component insecondary arc current.