The factors that cannot be directly grounded at both ends of a single-core cable mainly include the following points:
1. Induction voltage and circulation problems: When the single-core cable core passes through the current, the metal shielding layer will generate an induced current, and an induced voltage will be generated at both ends of the cable. The induced voltage is proportional to the length of the cable line and the current flowing through the conductor. Especially when the cable line is short-circuited, subjected to lightning or operating overvoltage, a very high induced voltage will be formed on the shielding layer, which may cause the cable outer sheath to be broken down and even cause a fire. In addition, grounding at both ends will also generate a circulation, which can reach 30% to 80% of the normal current of the cable core, which not only reduces the current carrying capacity of the cable, but also wastes electricity and accelerates insulation aging.
2. Personal safety and equipment damage risk: If both ends of the single-core cable are directly grounded, a closed circuit may cause abnormal flow of current, endanger personal safety and may cause damage to the equipment. For example, in some cases, the induced voltage superimposed can reach a level that endangers personal safety.
3. Insulation layer damage: Due to the presence of induced voltage and circulation, the insulating layer of the cable is easily damaged and accelerated aging, which may eventually lead to phase-to-phase short circuit or grounding failure.
4. Design specification requirements: According to the "Power Engineering Cable Design Regulations" (GB50217-1994) and other relevant standards, special grounding methods should be adopted when installing high-voltage single-core cable lines, such as grounding at one end or cross-connecting grounding to avoid the above problems.
Therefore, in order to ensure safety and normal operation of the cable, single-core cables generally do not use direct grounding at both ends, but choose appropriate grounding methods according to the specific circuit situation.