Fault Analysis And Diagnosis Technology Of Synchronous Condenser System

With the wide application of UHVDC transmission project,the problem of insufficient dynamic reactive power at the transmission and receiving networks becomes more and more prominent.The synchronous condenser has large dynamic reactive power capacity and strong voltage support ability,which can reduce the transient overvoltage and suppress the commutation failure of the power grid,so it has been applied in the UHVDC transmission system.In the process of operation,the synchronous condenser system is prone to various faults due to the influence of operating conditions and harsh environment.In order to solve this problem,it is very important to implement fault diagnosis of the synchronous condenser system.In this thesis,fault diagnosis of the synchronous condenser system,including resistive asymmetry fault,interturn short-circuit fault and thyristor open-circuit fault,is systematically investigated.Some fault diagnosis methods are proposed.Both the simulation and experimental results are given to verify the theoretical analysis.The thesis mainly includes the following several parts:(1)The research background of the thesis is summarized.The current research status of the resistive asymmetry fault,interturn short-circuit short and thyristor open-fault are clarified.(2)The synchronous condenser is modeled and analyzed.The working principle of the synchronous condenser system is introduced,and the mathematical model of the synchronous condenser is described.Based on this,the simulation platform is established by using the finite element software,which provides support for the subsequent fault diagnosis research.(3)The two common faults of stator windings are studied.The mathematical models of the synchronous condenser are established under these two faults.Especially,the zero-sequence voltage component(ZSVC)under the two faults are analysed.Due to the direct connection between the synchronous condenser and the power grid,the fundamental component of ZSVC under the interturn short-circuit fault is not affected by the stator currents,while the resistive asymmetry fault is just the opposite.Hence,the amplitude of fundamental component in ZSVC is used to detect the fault occurrence.Then,the change of the fundamental component in ZSVC is observed by changing the excitation current to discriminate the fault type.The effectiveness of the proposed method is verified by the simulation and experimental results.(4)The fault diagnosis of open-circuit fault for thyristor-based excitation system is studied.An error-current-based diagnosis method is proposed.In the proposed diagnosis method,the branch error currents are utilized,which has the advantages of fast detection speed and strong robustness.First,the branch error currents are calculated.Then,the fault detection variables are obtained by the error currents to detect the fault.Finally,the fault switches are judged by the fault location flags.This method can diagnose all 78 faults in single or double switches.The effectiveness of the proposed diagnosis method is verified by the experimental results.(5)The experiment platform of synchronous condenser system is built.Referring to the actual synchronous condenser system,the experimental platform of the low-power synchronous condenser system is built with the low-power synchronous motor as the core.Based on the experimental platform,these fault diagnosis methods are verified.