Research On Resonance Of Multi-circuit Transmission Line With Shunt Reactor On The Same Tower

In UHV long line,shunt reactor is widely used t o compensate positive sequence capacitance(capacitive reactive power)and suppress power frequency transient over-voltage,and a reactor with small capacity is put between the neutral point of the reactor and the ground.It and the three-phase main reactance form three equivalent inter phase reactance,so as to compensate the inter phase reactance of the line.When a short-circuit fault occurs and the reclosing is open,the above parallel compensation wiring will suppress the fault phase ground current(secondary arc current)transferred from the sound phase voltage,and ensure the rapid extinction of the arc and the successful operation of the auto reclosing.When the multi circuit transmission line on the same tower compensated by the shunt reactor has a short circuit fault,some circuits in the line are disconnected by the circuit breaker.During the non full phase operation before the successful reclosing action,the inductance of the shunt reactor will form a series circuit with the inter phase capacita nce and the ground capacitance of the transmission line.If the parameters match,the series resonance phenomenon will occur.The amplitude of resonance over-voltage will rise sharply,its duration is longer than the operation over-voltage,and it may even exist stably.It is necessary to study and analyze the resonance problem of multi-circuit transmission line with shunt reactor on the same tower.Firstly,a coupling model of multi circuit transmission lines on the same tower is built by using EMTP-ATP.The compensation degree of shunt reactor is 60%-90%.The equivalent impedance model of each fault state is obtained by changing the line fault state transformation,and the calculation expression of resonance frequency is derived.The correctness of theoretical analysis is verified by frequency scanning.In order to more intuitively reflect the resonance relationship between shunt reactor and multi circuit transmission line on the same tower,the resonance relationship curve of shunt reactor compensation degree and small reactance at neutral point is made.Combined with the value requirements of small reactance at neutral point,the circuit number of transmission line is changed,and the harmonic characteristics of different circuit number are compared and analyzed.The research results have reference value for the research of resonance law of shunt reactor of multi circuit transmission line on the same tower.Secondly,the long-distance AC transmission line is constrained by the system stability conditions.With the increase of transmission distance,the transmission capacity of the line will continue to decline.Series compensation technology can improve the transmission capacity and system stability.Considering the transmission system with shunt reactor and series compensation capacitor,the series compensation capacitor is added to the coupling model of multi circuit transmission line on the same tower,and the resonance characteristics of the series compensation capacitor connected at different positions of the line are simulated and analyzed.The simulation results show that when the series compensation capacitor is connected at the end of the line,the resonance range of the line is the largest.The specific calculation and analysis of this situation are carried out,and the configuration scheme of series and parallel compensation for optimizing the resonance characteristics of multiple circuit lines is discussed.Finally,the influence of controllable shunt reactor on transmission line resonance is studied.This paper introduces the classification and working principle of the controllable shunt reactor,and analyzes the influence of the graded controllable shunt reactor on the resonance characteristics of the line in the same tower multi circuit transmission line through simulation.The research results of this paper can provide reference for the resonance characteristics and parameter design of EHV/UHV multi circuit transmission lines.