Research On Fault Modeling And Identification Of Current Transformer Based On Frequency Response Analysis

Current transformers are the key equipment of substations and even power systems,and their accuracy and reliability are critical to the safe and stable operation of power systems.The accuracy of the current transformer ensures the safety and reliability of functions such as energy metering and relay protection in the power system.The iron core coil is a key sensing component in the current transformer,and its performance is related to the reliability of the entire measurement transformer.At present,there are few researches on the fault diagnosis of the current transformer iron core coil.The slight deformation of the current transformer coil is not easy to be found,and the deformation has a cumulative effect.As the deformation of the coil increases,once a fault occurs,it is likely to damage the equipment and affect the normal operation of the power system.Based on this,the research on the fault diagnosis of the current transformer iron core coil is carried out.The main contents are as follows:1.The equivalent circuit of the current transformer iron core coil is analyzed.The analytical formula method is derived based on the ideal electromagnetic field distribution.It is only applicable to healthy coils,and faulty coils cannot be applied.Therefore,the finite element software ANSOFT is required to calculate the inductance and capacitance parameter matrix of the faulty coil.In this paper,based on the corresponding physical size of the current transformer,the number of coil turns and the insulating medium,modeling and simulation are carried out in the electromagnetic field simulation software,and the current transformer model of the healthy coil and the faulty coil is established,and the RLC parameters in the equivalent circuit are obtained by simulation.2.Use PSPICE circuit simulation software to establish the corresponding coil equivalent circuit,and obtain the comparison between the healthy and the fault spectrum.The results show that: The short-circuit fault between the coils has an impact on the frequency and amplitude compared to the spectrum analysis of the healthy coil.The frequency response curve shifts to the whole right,the frequency of resonance is higher,and the change rate increases with the fault level;the resonance frequency increases by3.71% under 10% inter-turn short-circuit fault,and the resonance frequency increases by28.93% under 50% inter-turn short-circuit fault.In terms of amplitude,the frequency response curve under the fault state shifts downward as a whole,and the shift rate increases with the fault level.The distortion distortion has an effect on the resonant frequency andamplitude of the spectrogram,but it has no effect at the low frequency stage.The main change is above 300 k Hz,and it mainly affects the frequency and has little effect on the amplitude.Compared with the normal coil spectrogram,the radial displacement fault only changes the amplitude and does not change the resonance frequency.The difference between the two is mainly in the high frequency band.There is no obvious shift and distortion of the curve between 0 k Hz and 350 k Hz.In the area above 350 k Hz,the fault condition has a clear change compared with the normal spectrum chart.The frequency at which resonance occurs is almost unchanged.The only change is the amplitude,and the spectrum chart moves down,and the change rate increases with the fault level.3.Based on the morphological image processing method,the fault spectrum map is used to identify the corresponding fault category and level.Based on the image filling theory,the fault curve is compared with the known curve,and the degree of matching of the fault type is obtained by the size of the filled area.The smaller the filled area,the higher the degree of fault matching.And get the upper and lower limits of the fault level,identify the fault type of the current transformer.Since the spectrum library under normal,10% failure,30% failure and 50% failure is obtained above,the 7% inter-turn short-circuit failure spectrum diagram is graphically identified.The results show that the image filling area of the curve to be identified and the distortion and radial displacement fault curves are1684 and 2681,respectively,while the image filling area of the inter-turn short-circuit fault is only 332,so the fault category is identified as inter-turn short circuit.And it is concluded that the fault curve is between 0% and 10% of the turn-to-turn short circuit fault curve,and the fault level is determined.