New Protection Principle Of Control Winding For 500kV Magnetically Controlled Shunt Reactor

The resources and demands of energy distribute reversely in China,nearly 76% of coal resources are distributed in north and northwest China,68% of hydropower resources are distributed in southwest China,however,70% of electricity consumption is concentrated in eastern coastal areas.In order to solve this problem,the super/uhv power grid should is applied into long-distance transmission.Since the uhv transmission line has huge capacity and large length,which brings a great challenge to the control of reactive voltage,thus the reactive power compensation equipment is needed.Although the traditional reactive power compensation equipment can compensate the reactive power and limit the overvoltage level,its compensation capacity is not adjustable,the capacitive power should be added when the overcompensation occurs in operation.Magnetic-controlled Shunt Reactor(MCSR)can dynamically output inductive reactive power to compensate capacitive power,reduce ground capacitance current,restrain overvoltage of power frequency and operation overvoltage,what's more,it also has the advantages of excellent steady-state characteristics,low harmonic contents and continuous smooth adjustable capacity,which makes it has a wide application prospect.Since the body structure and working principles of MCSR are special,its relay protection is different from that of others controllable reactor,and the research on the protection of MSCR is pretty rare.The control winding of MCSR is the core part for controlling the output of reactive capacity,which is vulnerable to failure due to environmental factors and improper operation.Moreover,the existing protection of the control winding has disadvantages of low sensitivity and large dead area.Thus,the research on the protection of MCSR control winding is urgent,and it also has an important theoretical significance and practical value.In this paper,Aiming at a magnetically controlled shunt reactor which has been put into operation,the equivalent circuits of the control windings for grounding fault,interphase short circuit and inter-turn short circuit are given,the formulas are derived and analyzed strictly,the corresponding fault characteristics are summarized.Based on all the obtained fault characteristics,a new principle for protecting the windings in response control is proposed,and the setting calculation principle is also given.The dead zone is eliminated effectively by using the combination of low voltage protection with overcurrent protection as the grounding protection;the protection sensitivity is improved by reflecting the phase-to-phase short circuit with the phase-comparison protection of base wave currents in two wings of each phase;a slight inter-turn short circuit can be acted reliably by applying the current-variation based protection into inter-turn short circuit protection.Finally,a model of 500 kV magnetically controlled shunt reactor is built on PSCAD/EMTDC,and the simulation results verify the correctness of the proposed protection principle.