【Daily Topic】【Electrical Edition 20160730】
Thread Content
Participation reward: 2 Wealth. Reward for the correct answer: 9 Wealth. Question: Why must one end of the metal shielding layer of a single-core high-voltage cable be connected to ground through a grounding device?
⑴ When lightning waves invade or the system experiences severe overvoltage, the very high voltage levels can cause the grounding device to break down, allowing the excess current generated by the overvoltage to flow into the ground. ⑵ Under normal operating conditions, due to the high resistance of the ground device at low voltages, it is as if one end of the cable’s metal shielding is open-circuited; as a result, the operating current in a single-core cable does not induce any circulating current in the metal shielding. This prevents problems such as the burning of the cable’s metal outer layer caused by circulating currents, as well as a reduction in the cable’s current-carrying capacity due to the heat generated by such currents.
⑴ When lightning waves invade or the system experiences severe overvoltage, the very high voltage levels can cause the grounding device to break down, allowing the excess current generated by the overvoltage to flow into the ground. ⑵ Under normal operating conditions, due to the high resistance of the ground device at low voltages, it is as if one end of the cable’s metal shielding is open-circuited; as a result, the operating current in a single-core cable does not induce any circulating current in the metal shielding. This prevents problems such as the burning of the cable’s metal outer layer caused by circulating currents, as well as a reduction in the cable’s current-carrying capacity due to the heat generated by such currents.
⑴ When lightning waves invade or the system experiences severe overvoltage, the very high voltage levels can cause the grounding device to break down, allowing the excess current generated by the overvoltage to flow into the ground. ⑵ Under normal operating conditions, due to the high resistance of the ground device at low voltages, it is as if one end of the cable’s metal shielding is open-circuited; as a result, the operating current in a single-core cable does not induce any circulating current in the metal shielding. This prevents problems such as the burning of the cable’s metal outer layer caused by circulating currents, as well as a reduction in the cable’s current-carrying capacity due to the heat generated by such currents.
It provides protection; I’m not quite sure about the details. Please explain
Under normal conditions, the resistance at the grounding terminal is high, which prevents the generation of loop currents and thus protects the metal shielding layer from being damaged. There is also the function of releasing excess pressure in case of overload.
During high-voltage transmission, due to the long distance and high voltage, as well as the grounding of the metal protective layer, electric shock accidents are less likely to occur, right?
⑴ When lightning waves invade or the system experiences severe overvoltage, the very high voltage levels can cause the grounding device to break down, allowing the excess current generated by the overvoltage to flow into the ground. ⑵ Under normal operating conditions, due to the high resistance of the ground device at low voltages, it is equivalent to an open circuit at one end of the cable’s metal shielding layer; as a result, the operating current in a single-core cable does not induce any circulating current in the metal shielding layer. This prevents problems such as the deterioration of the cable’s metal outer layer caused by circulating currents, as well as a reduction in the cable’s current-carrying capacity due to the heat generated by those currents.
⑴ When lightning waves invade or the system experiences severe overvoltage, the very high voltage levels can cause the grounding device to break down, allowing the excess current generated by the overvoltage to flow into the ground. ⑵ Under normal operating conditions, due to the high resistance of the ground device at low voltages, it is as if one end of the cable’s metal shielding is open-circuited; as a result, the operating current in a single-core cable does not induce any circulating current in the metal shielding. This prevents problems such as the burning of the cable’s metal outer layer caused by circulating currents, as well as a reduction in the cable’s current-carrying capacity due to the heat generated by such currents.