Study On On-line Monitoring Technology For Insulation Fault Of Air-core Power Reactor

In recent years,with the dry-type air-core reactor being widely used in the power grid,masses of damage accidents of dry-type air-core reactor have taken place in several electric power bureaus,which attracted the attention of the society and electricity sector gradually.The main cause of the damage accidents is turn-to-turn insulation short circuit.However,at the beginning of the malfunction happening to the turn-to-turn insulation,change rate of electrical parameters of the dry-type air-core reactor is low,and thus,in actual operation process,one method of far-infrared temperature detection is relied on,but monitoring in time and effectively can't be achieved through this method limited to environmental temperature and location of monitoring equipment,so it is necessary to take an research on on-line monitoring technology for turn-to-turn insulation of dry-type air-core reactor.A new method,called on-line monitoring method of loss factor,of on-line monitoring on turn-to-turn insulation fault was proposed.Equivalent circuit model of air-core reactor under normal circumstances was built.Several methods for calculating the inductance of a solenoid model were summarized,and the inductance calculation of a thin-walled solenoid model in air-core reactor was investigated through Neumann's Formula combined with integral formula method.Equivalent circuit model of air-core reactor in the case of failure was built,and change of coaxial thin wall solenoid model and recalculation method of inductance matrix were analyzed during short circuit happening to turn-to-turn insulation.And then,calculation method of branch current,equivalent impedance,equivalent resistance,and loss factor of air-core reactor were investigated under normal circumstances and in the case of failure respectively.Finally,under normal circumstance and in the case of failure,the software of calculating electrical parameters of air-core reactor was programmed through MATLAB.Taking 10 k V series and parallel air-core reactor as simulation objects,various electrical parameters of two air-core reactors were measured.The method of on-line monitoring loss factor was discussed as well.The framework technical scheme was proposed.The reactor current and the voltage signal were extracted by current transformer and signal conditioning circuit was designed.Taking AT89C55 MCU as the core,signal after amplification filter was uploaded to the computer and the loss factor of the change was calculated by programming.According to fact whether the rate of change is more than threshold or not,occurrence of a fault was determined.The following rules are obtained: when short circuit happens to turn-to-turn insulation of air-core reactor,the change rate of the loss factor is the largest among these four monitoring parameters.When short circuit happens to turn-to-turn insulation of air-core reactor,the change rates of loss factor and equivalent resistance increase first and then decrease from the inner to the outer,that is to say,this two parameters increase fastest in the middle layer and slowest in innermost layer and outermost layer.The absolute values of the change rates of equivalent reactance and resistance increase first and then decrease from the outer layer of the inner layer,and equivalent reactance and resistance decrease fastest in the middle two layer,while they decrease slowest in innermost layer and outermost layer.When short circuit happens to turn-to-turn insulation,change of loss factor,equivalent resistance,equivalent reactance and equivalent impedance of air-core reactor becomes slow with the growth of temperature.