1, a single capacity of more than 100kVA or the use of the same grounding device running in parallel and the total capacity of more than 100kVA power transformers or generators shall not be greater than 400 a single capacity of not more than 100kVA;
Or the use of the same grounding device running in parallel and the total capacity of not more than 100kVA power transformers or generators shall not be greater than 10120 in the soil resistivity greater than 1000f~m area, when the difficulty of achieving the above grounding resistance value can be increased to more than how much? Grounding resistance value shall not be greater than 10120 in the soil resistivity greater than 1000f ~ m in the area, when the above grounding resistance value is difficult to achieve, the work of the grounding resistance value can be increased to 3 Ⅸ 2.
2, IN system of the protection of the zero line must be done in the distribution room or the main distribution box to do in addition to repeat the ground, but also in the middle of the distribution system and the end of the repeated grounding. In the TN system, the grounding resistance value of each repeated grounding device of the protective zero line should not be greater than 10 Q. In the power system where the working grounding resistance value is allowed to reach 10 Q, the equivalent resistance value of all repeated grounding should not be greater than 10 Q.
Expanded Information：
Grounding resistance of the relevant introduction:
1, principle: the basic principle of grounding protection is to limit the leakage of leakage equipment to the ground leakage current, so that it does not exceed a certain safety range, once it exceeds a certain value protector will be able to cut off the power supply; the principle of the zero protection is to use the zero line, so that the equipment in the insulation is damaged after touching the shell to form a single-phase metal. The principle of zero protection is to use the zero line, so that the equipment in the insulation is damaged after touching the shell to form a single-phase metallic short-circuit, the use of short-circuit current to prompt the rapid action of the protective device on the line.
The essence of the normal and accident and cable system internal overvoltage, lightning overvoltage, the use of the earth as a current loop, the cable ground potential is fixed in the allowable ground potential. Grounding potential is not only related to the waveform and amplitude of the incoming current, but also with the geometry of the grounding body, earth resistivity and other parameters.
2, the scope of application:
According to the load distribution, load density and load nature and other relevant factors, "rural low-voltage electric power technical regulations" will be the above two power network operation system is divided into the scope of use. tt system is usually applied to rural public low-voltage power network, the system belongs to the protection of the ground protection mode of protective earthing.
TN system (TN system can be divided into TN-C, TN-C-S, TN-S three kinds) is mainly applicable to the towns and cities of the public low-voltage power network and factories, mines and other power customers of the special low-voltage power network, the system belongs to the protection of the ground in the protection of the zero protection mode.
Currently China's existing low-voltage public power distribution network, usually used in the TT or TN-C system, the implementation of single-phase, three-phase mixed power supply. That is, three-phase four-wire 380/220V power distribution, at the same time to the lighting load and power load power supply.
Baidu Encyclopedia - Grounding
Baidu Encyclopedia - Protective Earthing