| Capacitive equipment occupies more than 40% of the substation and is an indispensable power equipment in the power system.Its insulation status can be collected and analyzed online through the capacitive equipment online monitoring device.The current detection method is to obtain the dielectric loss value after calculating the phase angle difference between the ground current of the last screen and the bus voltage.In actual operation,the ground current signal collected by the capacitive equipment online monitoring device is weak,and the online monitoring results are easily interfered by the surrounding power frequency electromagnetic field.Inaccurate monitoring results and large fluctuations occur from time to time.If the monitoring is not accurate,it will cause false alarms,and the monitoring results cannot be used for reference by operation and maintenance personnel.Therefore,studying the principle of the capacitive equipment online monitoring device and analyzing the mechanism of the influence of the external electromagnetic field on the measurement performance of the device is of great significance to ensuring the accuracy and stability of the online monitoring device.At present,the detection environment of the online monitoring device for capacitive equipment is an ideal environment in the laboratory,which does not fully reflect the on-site electromagnetic field working conditions,and relevant standards do not specify specific requirements for the measurement performance of online monitoring devices under electromagnetic interference,and the external electromagnetic field affects the measurement results of online monitoring devices.The extent of the impact is still unclear,and quantitative research is lacking.Aiming at the shortcomings of the existing research,this paper carries out theoretical analysis,field measurement of electromagnetic environment,and simulation experiment research on the working principle of capacitive equipment online monitoring device,the influence mechanism of external interference electromagnetic field,and the quantitative influence of external interference electromagnetic field on measurement performance.First,this paper systematically analyzes the principle of capacitive equipment insulation state monitoring and the working principle of the capacitive equipment online monitoring system.Then,the coupling mechanism between the external electromagnetic field and the online monitoring device is studied,and the change of the output signal of the current sensor under the interference of the magnetic field and the electric field is deduced.It can be seen that the greater the intensity of the magnetic field,the greater the flux linkage between the magnetic field and the sensor winding,and the greater the amount of signal change.The electric field mainly affects the measurement result of the device through the induced magnetic field.Further,in order to reduce electromagnetic interference,the principle and measures of electromagnetic shielding of the sensor have been studied.Secondly,this article conducts on-site electromagnetic environment measurements on the installation locations of the capacitive equipment online monitoring devices in 5 substations,and analyzes the size and direction distribution of the electric field/magnetic field.Based on the actual measurement results,a power frequency electromagnetic field simulation platform was built in the laboratory.An electric field simulation device was built by using the principle of pressurized parallel pole plates to generate an electric field,and a magnetic field simulation device was built on the principle of a magnetic field generated by a through-flow coil.After testing,the power frequency electromagnetic field simulation platform can simultaneously generate continuously adjustable 0-50 k V/m electric field and 0-0.3 m T magnetic field,meeting the needs of simulating the electromagnetic environment on site.Finally,this paper uses the above simulation platform to carry out a simulation test of the influence of the magnetic field and electric field on the measurement performance of the capacitive device online monitoring device,and tested the quantitative changes in the measurement results of the capacitive equipment online monitoring device under different interference intensities and working conditions.The test results show that when the interference magnetic field is 0-0.2 m T,the accuracy and stability of the device measurement decrease linearly.,and the electric field has little effect on the measurement performance.It is necessary to add 0-30 k V/m,0-0.1 m T interference electromagnetic field inspection to the online monitoring device before connecting to the network.At the same time,it is necessary to focus on the measurement performance of the device when the dielectric loss measurement point is0.1%-1%.In the substation site,the influence of the external electromagnetic environment on the measurement performance can be reduced by changing the installation position of the device or adding a multi-layer electromagnetic shielding sleeve made of permalloy or microcrystalline alloy to the sensor. |
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