Research On Dielectric Loss Monitoring Device Of Capacitive Electrical Equipment

Since entering the information age,the demand for electricity in our country has been increasing,and the power grid system is gradually developing in the direction of intelligence.In order to build a perfect smart grid system,the first thing is to monitor the operation status of the equipment in the power system in real time or at a fixed time,which can not only help the staff better understand and master the operation status and equipment quality,but also reduce the occurrence of grid accidents.According to statistics,the insulation performance cracking of equipment accounts for more than half in 93 times of 110 kV and above power equipment failure.Therefore,monitoring the insulation performance of equipment in the power system is very significant for the safe operation of the power system.The aging degree of insulating materials in power equipment is generally judged by dielectric loss.At present,the measurement methods of dielectric loss include zero crossing detection,bridge method,fundamental wave method,filter method and fitting method.All these methods have the same result.The final purpose is to obtain the phase difference between the current signal and the voltage signal,and then to obtain the dielectric loss angle.The zero crossing detection method is to detect the zero crossing of the signal so as to obtain the phase value,but it requires hardware circuit to be more professional,and it will also be affected by zero drift and signal distortion;the measurement principle of the bridge method is simple and easy to understand,but the detection process is relatively complex;the measurement accuracy of the fundamental method will be affected by the sampling accuracy;the filtering method has high requirements for the filter in front and the calculation of computer requires high at the same time;the fitting method is to treat the amplitude,angular frequency and phase angle of voltage and current signals as unknown parameters,iteratively obtain the optimal solution of each unknown parameter,and then obtain the phase difference of voltage and current.This method has high accuracy,fast calculating speed,and it also depend less on hardware.Therefore,it has obvious advantages compared with the previous methods.All in all,the fitting method is selected in this paper,and quasi Newton method is used in this method.The dielectric loss monitoring device designed in this paper includes transformer,signal conditioning module,wireless transmission module,main control module and display module.The overall design idea is as follows: After the voltage signal and current signal pass through the respective transformer and signal conditioning module,the signal is conditioned into a signal suitable for sampling.After a period of sampling,the data will be stored in the wireless communication terminal node,the data will be transmitted to the coordinator node through the wireless communication network,and then sent to the main control module through the serial port,and the fitting operation will be carried out to find out the expression and phase difference between the voltage signal and the current signal,so as to get the the dielectric loss.It has been proved by many experiments that the device is easy to operate,stable and accurate,and can meet the general requirements of measuring dielectric loss in power system.