Research On Partial Discharge Measurement And Identification Technology Under Pulse And Multi-Source Interference

Partial discharge measurement is an effective means to evaluate and diagnose the insulation state of electrical equipment.In the actual operation of power system,the ground insulation of variable frequency motor withstands square wave pulse voltage for a long time.Electrical equipment due to circuit breakers,power electronic devices and other switching equipment frequent action,will also be subject to high frequency pulse overvoltage impact.Due to the rapid change of rising edge and falling edge of square wave pulse voltage,the generated charging and discharging pulse current will overlap with the partial discharge signal,affecting the partial discharge measurement.During the on-line partial discharge measurement of an electrical equipment,the partial discharge signals of other electrical equipment on the same phase bus and external electromagnetic interference will affect the partial discharge measurement of the equipment.In order to solve the problems above-mentioned of partial discharge measurement technology under square-wave pulse voltage and multi-power equipment paralleled,it is necessary to carry out research on partial discharge measurement technology under square-wave pulse voltage and multi-power equipment paralleled that partial discharge measurement and identification technology under pulse and multi-source interference.In this paper,the suppression methods of periodic narrow band interference and white noise interference in partial discharge measurement are studied firstly.The singular value decomposition method is introduced to suppress the periodic narrowband interference and white noise interference respectively.The singular value distribution corresponding to the periodic narrowband interference is obvious,and the ’singular value pair’ corresponds to the frequency of the periodic narrowband interference.The interference suppression effect is good and is not affected by white noise interference,while the singular value distribution of white noise interference has no obvious law,and the interference suppression effect is not good.Aiming at the shortcomings of singular value decomposition method for white noise interference suppression,this paper proposes an improved 3σ criterion method to suppress white noise interference during partial discharge measurement,which can effectively suppress white noise interference and meet the technical requirements of subsequent research.The interference suppression of the simulated signal and the measured signal is carried out,and compared with the traditional singular value decomposition method and the singular value decomposition method + the empirical mode decomposition method.The results show that the method based on ’singular value decomposition and improved 3σ criterion’proposed in this paper can well suppress the periodic narrowband interference and white noise interference in the partial discharge measurement process.Secondly,the partial discharge measurement technology under square-wave pulse voltage is studied.By analyzing the circuit principle of partial discharge under square-wave pulse voltage,a secondary measurement method is proposed to measure the partial discharge under square-wave pulse voltage.In the practical application of the secondary measurement method,the successive interception comparison method is proposed to solve the problem of time difference in the secondary measurement process.A stepwise approximation method is proposed to determine the optimal value of the measure voltage peak required for the first measurement.Through simulation and measurement,it is verified that the secondary measurement method can effectively extract the partial discharge signal and suppress the charge and discharge pulse current interference generated by the square-wave pulse voltage.Moreover,in the case that the laboratory square-wave pulse voltage source cannot meet the technical requirements,a parallel non-local discharge capacitor method is proposed.The theoretical derivation shows that the derivative of the apparent discharge amount to time is only related to the branch current of the sample and the branch current of the non-partial discharge capacitor.The simulation and experimental results show that the partial discharge signal can be effectively extracted,and the charging and discharging pulse current interference suppression effect under the square-wave pulse voltage is good,which verifies the reliability of the parallel non-partial discharge capacitor method.The partial discharge measurement technology under multi-power equipment paralleled is studied in the end.By studying the coupling path of partial discharge signal and the coupling path of external interference signal under multi-power equipment paralleled,it is concluded that when a partial discharge occurs in an electrical equipment alone,the flow direction of the pulse current generated by the partial discharge of the branch where the discharge equipment is located is opposite to the flow direction of the pulse current of other branches.The external interference pulse current flows in the same direction in all branches.Based on this,this paper proposes a path correlation array analysis method for partial discharge measurement under multi-electrical equipment parallel connection.In the case of allowing parallel non-local discharge capacitors,the parallel non-local discharge capacitor method is also suitable for partial discharge measuring under multiple electrical equipment,and the parallel non-local discharge capacitor method does not need to consider whether there is simultaneous partial discharge in each branch.The parallel non-partial discharge capacitor method and the path correlation array analysis method are compared and analyzed to verify the effectiveness of the two methods.