Research On Propagation Of Partial Discharges In HV XLPE Cable System

With the continuous development of Chinese power industry,high voltage(HV)XLPE insulated power cable is increasingly widely used.Its safe and reliable operation has aroused great attention.Partial discharge is an effective means to monitor the insulation condition of HV cables.However,in XLPE cables,the amplitude of partial discharge will be attenuated during transmission.In addition,the waveform is distorted with increasing distance.These will result in the detected signal distortion.Besides,HV cable cross-bonded grounding will increase the complexity of the partial discharge signal transmission path,exacerbate the partial discharge signal attenuation and distortion.In this paper,the attenuation and distortion of PD signal transmission in HV XLPE cable and internet the transmission path in the cable cross-bonded grounding system are studied.By means of simulation calculation and experimental verification,HV cables and cross-bonded grounding system,and based on the characteristics of unique polarity and amplitude relation in the HFCT of the cross-bonded box on the basis of the location of PD in different locations,PD signal identification method and section location method,and verify the effectiveness of the cross-bonded capacitance method in the cross-bonded grounding box for PD signal identification and phase detection,providing for the HV cable line live detection and status evaluation work technical basis and reference,can effectively improve the HV XLPE cable system partial discharge detection effectiveness.The results show that sinusoidal signals are attenuated in the high frequency range and different from the frequency range if considering the frequency characteristics of the semi-conductive shielding layer and the semi-conductive water-blocking layer,and whether to consider the semiconducting layer at 10 MHz frequency will make the signal attenuation coefficient differ by an order of magnitude.When the sinusoidal signal is transmitted in the same cable,with the frequency increases,the signal will show a significant negative exponential decay,for the same frequency of different lengths of cable,the signal attenuation with the length of the increase also showed a similar negative exponential changes;After the simulation model of the attenuation coefficient correction,the signal attenuation coefficient is proportional to the square root of the frequency.When a PD signal is generated at a different location in the cable connector,cross-bonded box in the ground and cross-bonded copper row on the detection of different signal amplitude ratio and polarity.When a partial discharge occurs outside the cable connector,the signal amplitude ratio detected at the ground and cross-bonded copper row is approximately-2:3:-1 and 2:3.5:1.5,when a localized partial discharge occurs inside the cable connector,the signal amplitude ratio detected by the ground and cross-bonded copper row is approximately-2: :1 and 2:1:1,so compared to the ground line on the cross-bonded copper row on the detection of the signal is more conducive to PD recognition and phase;the three phases were connected across the capacitive circuit,the capacitive loop detected in the signal amplitude ratio is quite different,when the 500 pC PD signal is injected,the amplitude of the PD phase signal is about twice that of the non-PD phase,and the polarity is opposite,so the cascaded capacitive loop on the cross-bonded system of partial discharge signal stringing and shunt effect is significantly reduced,is conducive to the PD signal discrimination.As HFCT of the cross-bonded box side can detect the polarity and amplitude of the signal when the discharge source occurs at different positions,a PD signal identification and localization rule table is formed,and the partial discharge signals are preliminarily discriminated and segmented.However,this method requires more sensors and the higher detection accuracy.Therefore,it is possible to use single-phase and three-phase bridge capacitor across the two methods to compare cross-bonded before and after the interconnection of copper on the HFCT detected signal contrast relationship to achieve the external electromagnetic interference of the PD signal under the environment for effective identification and phase.