Standard grounding resistance specification requirements:
1, independent lightning protection grounding resistance should be less than or equal to 10 ohms;
2, independent safety protection grounding resistance should be less than or equal to 4 ohms;
3, independent AC working grounding resistance should be less than or equal to 4 ohms;
4, independent DC working grounding resistance should be less than or equal to 4 ohms;
5, anti-static grounding resistance is generally required to be less than or equal to 100 ohms
6, *** with the grounding body (joint grounding) should be no greater than the grounding resistance of 1 ohms.
1) Power capacity of 100kVA or more transformer or generator motor
work
earthing, R = 4Ω.
(2) Power capacity of less than or equal to 100kVA transformer or generator motor work grounding, R = 10Ω.
(3) 100kVA as well as the following low-voltage power distribution system zero line Repeated grounding, R = 10Ω; when there are more than three repeated grounding, grounding, R = 10Ω.
(4) The protective grounding of the non-electrified metal parts of the electrical equipment, R = 4Ω; the introduction of the line fitted with fuses less than 25A protective grounding of the equipment, R = 10Ω.
(5) Low-voltage line towers of the ground or low-voltage into the house line insulator feet of the grounding, R = 30Q.
(6) The grounding of FZ-type valve-type lightning arrester on the busbar of the transformer and distribution house, RΩ.
(7) The grounding of FS-type valve-type lightning arrester at the outlet end of the line, the grounding of the tube-type lightning arrester, the grounding of the independent lightning rod (individually desirable R=30Ω), and the protective earthing of the industrial electronic equipment (including X-ray machines), are R=10Ω.
(8) Lightning protection of chimneys Protective grounding, R = 30Ω
:Many household appliances, especially large appliances such as refrigerators, washing machines, air conditioners, etc., the use of power cords are three-core. In fact, the use of general utility appliances as long as there are two zero and fire wire can work properly. This extra wire is the ground wire, which means that these appliances must be grounded.
The introduction of grounding technology is initially to prevent electrical or electronic equipment such as lightning and take protective measures, the purpose is to lightning generated by the lightning current through the lightning rod into the earth, so as to play a role in protecting the building. At the same time, grounding is also an effective means of protecting personal safety, when some cause of the phase line (such as poor insulation of wires, line aging, etc.) and equipment shell touch, the shell of the equipment will have a dangerous voltage, which generates a current will be generated by the protection of the earth to the earth, thus playing a role in the protection of personal safety.
Grounding resistance is used to measure the grounding status is good, an important parameter, is the current flow from the grounding device into the earth and then through the earth to another grounding body or to the distant diffusion of the resistance encountered, which includes the grounding wire and the grounding itself, the grounding body and the earth's resistance to the resistance of the contact between the resistance, as well as the earth's resistance between the two grounding body or the earth's resistance to the earth to the infinity of the earth's resistance.
The size of the grounding resistance directly reflects the good degree of contact between the electrical device and the "ground", but also reflects the size of the grounding network. The concept of grounding resistance only applies to small grounding network; with the increase in the footprint of the grounding network and soil resistivity reduction, grounding impedance in the inductive component of the role of more and more large-scale ground network should be used in the design of grounding impedance.
For high-voltage and ultra-high-voltage substations, the concept of "grounding impedance" should be used to replace the "grounding resistance", while recommending that the regulation of the use of contact voltage and step voltage as a safety judgement; should also be used to choose a lightweight, accurate heterodyne measurement system Obtain the correct results of grounding impedance to protect the safety of people and equipment, and contribute to the safe operation of the power system.
Reference:
Baidu Encyclopedia Ground Resistance