01 Grounding method for three-core cables
Generally, three-core cables will choose the method of grounding at both ends. This is because when the cable is in operation, the sum of the currents flowing through the three cores is zero, resulting in almost no induced voltage at both ends of the cable metal shielding layer. This grounding method is common in cables with voltage levels of 35kV and below.
02 Grounding method for single-core cables
▣ Reasons for not recommending grounding at both ends
For single-core cables with voltage levels of 35kV and above, it is generally not recommended to use direct grounding at both ends. This is because when current passes through the core of a single-core cable, its metal shielding layer will generate an induced current, which will in turn generate an induced voltage at both ends of the cable. The level of this induced voltage is closely related to the length of the cable line and the current flowing through the conductor. Especially when a short circuit occurs in the cable line, it is struck by lightning or operates overvoltage, the induced voltage on the shielding layer may be very high, endangering personal safety, and may even break through the outer sheath of the cable.
▣ Problems caused by circulating current
In addition, direct grounding at both ends of a single-core cable may also cause circulating current in the metal shielding layer. According to relevant reports, this circulating current may reach 30% to 80% of the normal current transmitted by the cable core. This will not only reduce the current carrying capacity of the cable, causing energy waste and loss, but also accelerate the aging of the cable insulation. Therefore, for single-core cables, it is generally not recommended to use direct grounding at both ends.