| Large-scale rotating electric machines are the core equipment in industrial production,and unplanned shutdowns will cause huge economic losses.Insulation damage is the most important factor in the failure of rotating electrical machines.Partial discharge(PD)conditions can effectively characterize most of the insulation defects in the stator windings.Therefore,PD monitoring is an important part of the state monitoring of large rotating electrical machines.At this stage,the partial discharge monitoring system for rotating electrical machines is mainly based on the patented technology of foreign companies such as Iris and Ormicron.It only uses the split-phase current sensor to measure the high-frequency current signal,which leads to the aliasing of the interphase partial discharge and the partial discharge signal to the ground,The measurement data needs expert manual analysis to realize the separation of different types of partial discharge signals.Based on the research on the characteristics of the partial discharge signal and the partial discharge monitoring system,this paper proposes a hybrid sensing method using an air-core coil and a coupling capacitor,which can directly separate the interphase partial discharge and the partial discharge to the ground in the signal sensing stage Signals do not require experts to manually analyze the measurement data,and the analysis accuracy and efficiency are significantly improved,laying the foundation for the wide application of online monitoring.The main work is as follows:1.For the two main types of partial discharges with similar frequency and amplitude of high-frequency signals: internal discharge and end discharge,corresponding circuit models were established for analytical calculations.Using computer simulation technology,the partial discharge of the stator winding insulation was simulated and calculated,and the characteristic frequency of the partial discharge signal was determined to be about 100 MHz,and the amplitude of the pulse current was less than 0.6m A,which provided a basis for the selection of sensor parameters.2.A hybrid sensing scheme combining air-core coil and coupling capacitor is proposed.The sensing scheme uses the characteristics of coupling capacitor to pass high frequency and resist low frequency,filter out power frequency current,and improve the accuracy of high frequency current signal acquisition;Utilizing the characteristics that the three-phase high-frequency current signal only contains the partial discharge signal to ground but not the interphase partial discharge signal,the aircore coil is used to collect the three-phase high-frequency pulse current and the splitphase high-frequency pulse current respectively,which is the interphase partial discharge and The identification of partial discharges to ground provides a data basis to solve the problem of aliasing of two partial discharge signals in traditional partial discharge detection.3.A partial discharge signal acquisition system was developed,including: a hybrid sensor combining air-core coils and coupling capacitors,and a hardware platform based on high-speed FPGA and high-speed A/D signal acquisition.In order to further compress the data size to meet the needs of online monitoring,a data acquisition scheme of "low frequency monitoring,high frequency acquisition" is proposed,and a data processing algorithm based on set operation is developed.The characteristic value set of the three-phase acquisition signal and the phase separation acquisition are compared.The elements in the signal characteristic value set can identify the signals of interphase partial discharge and partial discharge to ground.4.On the motor to be maintained provided by Sinopec,the monitoring system developed in this paper has been verified by functional experiments.The results show that the hybrid sensing method and data processing algorithm used can effectively separate the pulses of the discharge to the ground and the discharge between the phases.The system meets the design requirements. |
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