Research On Petersen Coil Optimization Based On The Method Of Injecting Current

Optimal control method of Petersen Coil is usually carried out in the normal operation of the power grid currently, but there have been few studies when ground fault occurs. In resonance grounding system, when single-phase to ground fault occurs, the principles of traditional Petersen Coil tuning can achieve good results under the premise of symmetrical grid parameters, but when grid parameters are asymmetrical, the compensation current of Petersen Coil is not same when the fault phase is differernt. In a word, Petersen Coil is required to be adjusted to different inductors when the fault phase is differernt, thereby the role of Petersen Coil can give full play. If the method when the grid parameters are symmetrical is still adopted, it will have a greater residual current componence which has 90 degrees difference with zero-sequence voltage phase. The larger residual current may make arc maintain, which will cause over-voltage and further accidents.Therefore, the optimal control scheme of Petersen coil is proposed based on the method of injecting current. Under the premise that the residual current of ground fault point is zero, the corresponding inductance value can be got when the fault phase is different, then adjust Petersen Coil to the corresponding inductance value in order to ensure the optimization of Petersen coil. To achieve this goal, firstly a series of technical issues need be solved which includes the total capacitive current measurement of circuit, single-phase capacitance measurement, the identification of single-phase to ground fault via a transition resistance and fault phase identification.To solve above problems, this paper proposes the corresponding solutions. For the total capacitive current measurement of circuit, this paper introduces a variable step size tuning method of Petersen coil. For the single-phase capacitance measurement, the method of combining zero-sequence voltage and complex equations is introduced. The identification of ground fault and fault phase are realized based on the method of injecting current. Firstly a special target current is injected into the grid to eliminate the asymmetry of the distribution network. Then, the neutral point voltage is only caused by the grounding phase, at last the grid offset degree(the ratio of the size of neutral voltage and the power supply voltage) and the range of neutral voltage phase changing with fault resistance can be used to realize the identification of ground fault and fault phase respectively.Because the magnitude and phase of target current are difficult to be determined during the fault, the magnitude and phase of target current are determined during the normal operation of the grid firstly, and then inject the same magnitude and phase current when ground fault occurs to achieve this goal. But the traditional active compensation techniques ignore the line insulation resistance resulting in the control effect is not ideal, a new method of neutral voltage is introduced based on the method of injecting current. By injecting an initial current into the neutral point of distribution network firstly, then the magnitude and phase of the current can be controlled simultaneously. Observing the changes of the neutral point voltage, the magnitude and phase of injected current can be obtained ultimately. When introducing ground fault and ground phase identification, the impact of residual current based on the method of ingecting current is also analyzed.Finally, the above objectives are verified by simulations, and the simulation results verify the correctness and validity of the proposed theory.