Research On High Frequency Transient Overvoltage Of Tightly-coupled Split Reactor Using In Parallel High-Voltage Circuit Breaker

As the core equipment of Parallel High-Voltage Circuit Breaker, the tightly-coupled split reactor takes the critical task of equalizing and limiting the current flowing through each branche to less than the breaker's interrupting capacity. In the unbalance interuption process, a steep-front impulse voltage, being with the magnitude of half of the phase voltage magnitude will impact the tightly-coupled split reactor at the arc extinguishing moment of first opening breaker. Such a steep-front impulse voltage will exite high frequency electromagnetic oscillations in the reactor, resulting in the high frequency transient overvoltage on the reactor, and this high frequecy transient overvoltage will effect the isolation of reactor and the isolation of the first openning breaker.To analyze the effect of high frequency transient overvoltage on the isolation of Tightly-coupled Split Reactor and the isolation of the first openning breaker, we need to know the potential distribution on the tightly-coupled split reactor.This requies to establish a high frequency equivalent circuit model for Tightly-coupled Split Reactor, which can supply an accurate description of the high frequency electromagnetic oscillations in the reactor. So the primary mission of this thesis is to build a high frequency equivalent circuit of Tightly-coupled Split Reactor and find solution methed of the model.For this purpose, several modelling approaches of windings are presented. The principals, superiorities, shortcomings and validity of these methods are discussed and analyzed.With the consideration of accuracy of model, computation efficiency and the characteristic of the high frequecy electromagnetic oscillations, we chose the lumped modeling approach to model the Tightly-coupled Split Reactor.By analogizing and magnifying the infinitesimal unit circuit and the infinitesimal circuit equations of parallel straight multicongductor system, we easily obtain the lumped high frequency equivalent cicuit of Tightly-coupled Split Reactor and its circuit equations. By the method of seperating coercive variables and striking out correlative variables, we get the simplest cicuit equations with the least variables which is adequate to discribe the circuit state.Meanwhile we deraive numerical solution method of high dimensional differential equations based on trapezoidal rule. Via these two steps, the solution efficiency of the circuit is increased significantly.In addition, we derive the calculate formula of stray cpacitances by using the computation methods of potential caused by ring charges, overcoming the difficulties in calculating the stray capacitances of air core reactor.Using the mondelling and solution method, the high frequecy trasient overvoltage of a 12kV strong-coupling diruptive reactor prototype is caltulated.By analyzing the potential distribution, we find the most dangerous area of interlayer isolation is at the lower part of the reactor, about 55% -85% of the the reactor height,and the most dangerous area of turn-by-burn isolation is within 5 turns of the front and the end of every layer.In the thesis we analyze the high frequency oscillating voltage on extremity of the reactor seperately. We find that the high frequency oscillating voltage on extremity is mostly composed by 4 high frequecy components, which is at MHz frequecy band, and the largest peak value of high frequency oscillation voltage reaches 2.05 times of phase voltage magnitude, so we conjecture that the high frequency electromagnetic oscillations in the strong-coupling disruoptive reactor would enlarge the TRV and the RRV between the breaks of first openning breaker. It's unfavorable to the isolation between the first openning beaker's breaks.