Analysis And Calculation Of Short-circuit Current,Losses And Electromagnetic Force In Stator Strands Of Synchronous Compensator

Synchronous compensator is an important reactive power compensation equipment in power grid,with the widespread use of UHVDC transmission lines,the installed capacity has also increased.As a result,the current,circulating current loss and electromagnetic force of the stator bar,which is one of the core components of the synchronous compensator,are significantly increased.So that the force and temperature of the strands are increased,causing insulation damage and local short-circuit may occur in the strands.If it is not treated in time,the reliability of the synchronous compensator will be seriously affected.Therefore,it is of great significance to study the distribution regularities of current,circulating current loss and electromagnetic force between brands under health and short-circuit for finding fault location in time and controlling fault influence to the least extent.In this dissertation,taking 540° stator transposition bar in a 300 Mvar synchronous compensator as an example,to calculate and analyze the current,circulating current loss and electromagnetic force before and after the short-circuit fault in strands.According to the actual transposition structure of stator bar,a three-dimensional physical model of double row 540° transposition stator bar of synchronous compensator is set up,and the stator bar end was simulated by linear approximation method.In view of the complex numerical modeling of 540° transposition stator bar and the problems of splitting and solving,a multi-segment field-path coupling model is proposed based on the principle of multi-segment field-path coupling method and the variation of pitch position of stator bar.Comparing the results of two models in terms of strand current,phase distribution,and the accuracy of the multi-segment field-path coupling model is verified.Aiming at the problem of inaccurate calculation due to the cross transposition of strands when the stator transposition bar has a short-circuit fault,the multi-segment field-circuit coupling method modeling principle is used to establish a short-circuit fault physical model,so as to realize the calculation of the circulating current loss at any spatial position.The circulating current loss is calculated by selecting the short-circuit in the same column and row of strands with different specific positions,and the distribution regularities of short-circuit circulating current loss of strands in the same column and row is given.According to the Lorentz force method,the distribution regularities of electromagnetic force density at different spatial positions of the stator bar in transposition and non-transposition is calculated.The results show that the maximum value of electromagnetic force density decreases obviously after transposition of the strands.According to the degrees of short-circuit,the different schemes are designed to calculate the distribution of local electromagnetic force.According to the severity of the short-circuit in the strands,the distribution regularities of the short-circuit electromagnetic force in different strands is studied.