Analysis and Suppression of High-Frequency Common-Mode Electromagnetic Interference for Tunnel Cable PD Monitoring

Underground cables are predominan-tly used in modern cities for electricity transmission. Online partial discharge (PD) monitoring of underground power cables is crucial for early detection of insulation faults, vital for power system reliability. However, the widespread use of power electronic devices, as LED drivers and communication power supplies, introduces high-frequency (HF) electro-magnetic noise, potentially interfering with online PD monitoring. Addressing HF interference problem of online PD monitoring of 500kV power cable in one of Shanghai tunnel, this paper firstly analyzes the frequency components of HF common-mode current in the cable tunnel grounding system, and pinpoint the LED driver as the primary source of HF interference. To counteract this, common-mode chokes and magnetic beads are employed, and their effectiveness across various frequency bands is evaluated. Experimental results show that the switching process of LED driver will generate HF common-mode current within multiples of switching frequency and several MHz, which could introduce interference to PD monitoring via grounding system. The common-mode choke and magnetic beads can effectively attenuate the HF common-mode current generated by LED driver across various dominant frequency bands, enhancing the reliability of online.