Switching Over-voltage Level Of Dry Core Reactor And Over-voltage Test Technology Research

Dry-type iron core reactors have the functions of limiting short-circuit current,compensating reactive power,and improving power quality,and are widely used in power systems.In the power system,the frequent switching of dry-type iron core reactors may generate overvoltage,resulting in short-circuit faults between the reactor turns.In order to better analyze the reasons for the fault of dry-type iron core reactors,and to find out the defects in the turn-to-turn insulation of dry-type iron core reactors in operation as early as possible,it is necessary to study the cut-off overvoltage level and turn to turn overvoltage test technology of dry-type iron core reactor,which is of great significance to reduce reactor faults and improve the operation reliability of power system.This article uses the equivalent model of the dry-type iron core reactor to find the variation of its equivalent parameters with frequency,and verifies the correctness of the equivalent model through experiments.Based on ATP-EMTP electromagnetic transient simulation software,establish a three-phase ungrounded system to switching off the dry-type iron core reactor simulation circuit model,carry out the simulation test on the switching off overvoltage of the dry-type iron core reactor,and analyze its overvoltage level and its influencing factors.Based on the structural characteristics of the dry-type iron core reactor,analyze the technical problems existing in the inter-turn overvoltage test of the dry-type iron-core reactor,and determine the appropriate test circuit parameters.Set up a turn-to-turn overvoltage test platform,carry out turn-to-turn overvoltage tests on dry-type iron core reactors,verify the technical problems of turn to turn overvoltage test of dry-type iron core reactor,and discuss the feasibility of detecting turn-to-turn short circuit fault of dry-type iron core reactor.The results show that there are overvoltage of cut-off and re-ignition in the process of circuit breaker switching off dry-type iron core reactor.Among them,the level of cut-off overvoltage has nothing to do with the contact breaking time of circuit breaker,and increases linearly with the cut-off value of circuit breaker.However,the level of re-ignition overvoltage increases with the increase of contact breaking time of circuit breaker,and increases with the increase of current cut-off value of circuit breaker.Compared with the cut-off overvoltage,the peak of re-ignition overvoltage is steeper and the oscillation frequency is higher.There are some technical problems in turn-to-turn overvoltage test of dry-type iron core reactor,such as low test voltage efficiency,voltage waveform attenuation speed changing with oscillation frequency.When selecting a charging capacitor for turn-to-turn overvoltage test of dry-type core reactor,it is necessary to comprehensively consider the three factors of test voltage efficiency,oscillation voltage waveform attenuation speed and equipment power supply capacity.If the charging capacitor is too small,the efficiency of test voltage will be low,the attenuation speed of oscillation voltage waveform will be fast,and the oscillation period will be less.If the charging capacitor is too large,the power supply capacity of test equipment will be too large.When there is no fault in dry-type iron core reactor,the waveform oscillation frequency is the same under different voltages.If the dry-type iron core reactor has the turn to turn short circuit fault,the zero crossing point of the oscillation voltage waveform under the test voltage and the standard waveform of the reactor is obviously not coincident,and the oscillation frequency is also obviously increased.It is feasible to detect the turn-to-turn short circuit fault of the dry-type iron core reactor through the turn-to-turn overvoltage test technology.