Research On Integration Control System In Arc-Suppressing And Fault-Line Selection Of Single-Phase-to-Ground Fault In Resonant Grounded Systems

In China, most 6~66kV power systems are non-effectively grounded systems;and withthe increasing of system capacitive current to ground, more and more power systems becomeresonant grounded systems. It enhances the security and reliability of the power networks,with the system capacitive current compensated by arc-suppression coil. For a long time,researchers pay great attention to the optimization of the compensating ability of thearc-suppression coil. Because of the compensation of the arc-suppression coil, thezero-sequence current signal become weaker and is prone to be disturbed. Then thesingle-phase-to-ground fault line selection problem is never well settled in the resonantsystem. This paper studies the optimization of the compensating ability of the arc-suppressioncoil and the validity of single-phase-to-ground line selection methods.Analyzing the merits and demerits of the arc-suppression coils in existence, this paperproposes and designs a principal-auxiliary arc-suppression coil, which will be in more favorof the extinguishing of all kinds of grounded arcs. This principal-auxiliary arc-suppressioncoil is made up of principal coil and auxiliary coil. The principal coil adopts some automatictap-adjusting arc-suppression coil, and realizes the presetting function. The auxiliaryarc-suppression coil is designed on the TCR technique, composing of N fine-tuning coils,switched by N thyristors, the inductance of witch adopts binary-weave system, which form 2Ncompensation values, and realizes the following-setting function. It makes quick and effectivecompensation through the cooperation of the principal coil and auxiliary coil.Because of the compensation of the arc-suppression coil, the zero-sequence currentsignal become weaker and is prone to be disturbed. The unbalance current existing when thepower system is healthy is one disturbance source, which affects the characteristic of theamplitude and phase-angle. It is proved in the field operating that it is some important factorthat affecting the success-ratio of the single-phase-to-ground-fault line selection in resonantgrounded systems. In this paper, it is proposed that the unbalance current can be brought bythe unbalance of system capacitance to ground of the three phases, but also can be brought bythe parameter unbalance of the three CTs. By the phasor analysis, this paper gives anqualitative relational expression between the lien selection method reliability and unbalanceof system capacitance to ground, fault zero-sequence voltage, damping ratio of the powersystem. This paper considers it a valid method to adopt the method of abrupt change ofzero-sequence current, which could well settle that problem. When the unbalance current isinduced by the parameter unbalance of the three CTs, this paper also proposed some way todiminish its unfavorable affection, in which, the line-to-line voltage is induced as somereference to accordingly subtract the unbalance current signal from the fault zero-sequencecurrent.It is the developing direction in the resonant grounded system to make an integrated andcoordinated control system between the arc-suppression of the arc-suppression coil and thesingle-phase-to-ground fault line selection. This paper puts forward and expatiates theapplication principle of the method of abrupt change of zero-sequence current. But, whensome intermittent grounding arc occurs, it could make mistake with that method used withoutany consideration. This paper induced the wavelet analysis into this method, in which thecontrol system could self-adapt to different line selection method with the different faultstyles.To improve the success ratio of line selection in resonant grounded systems, it issome importance measure to confirm the applicability of all kinds of methods, whichcalls validity of methods. The paper determines the validity of methods through datamining on large numbers of local data based on rough set theory. Using decision tablesas a main tool, this approach can extract the decision rules between the line selection andfault signal features, by discretizing the feature of the fault samples, and then makingreduction of the redundant information.Through the analysis of the field faults, It is found that there are many short-timegrounding fault. This paper proposes the auto-reclosing technique for thesingle-phase-to-ground fault in non-valid grounded systems (for short, named as reclosing onphase-to-ground fault). Also, this paper proposed the integration of the measure, control,record and protection on the single-phase-to-ground fault.This paper introduced the field operation instance of the principal-auxiliaryarc-suppression coil. A 10kV high voltage physical simulation system is also introduced inthis paper.