Electrical devices or electrical lines charged part of a point connected to the earth, electrical devices or other devices normally not charged part of a point connected to the earth artificially are called grounding; can also be said to power equipment, towers or overvoltage protection devices with grounding wire through the buried in the ground and direct contact with the earth metal conductor and earth connection. The grounded part of the power system is generally the neutral point, can also be a point on the phase line, the grounding part of the electrical equipment is not charged under normal circumstances metal conductor, generally metal shell.
What are the several ways of grounding electrical equipment?
1 work grounding work grounding is also called system grounding, is based on the normal operation of the power system and the need to ground the network at a certain point. For example, the neutral point of the three-phase system grounding, its role is to stabilize the grid to the ground potential, so that the ground insulation can be reduced, can also make the ground insulation flashover or breakdown easy to find out, as well as conducive to the implementation of relay protection measures.
2 protection grounding protection grounding is also called safety grounding, the metal casing of electrical devices, power distribution devices and line towers, etc., due to insulation damage may be charged, in order to prevent the safety of the person and equipment and set up grounding.
3. lightning grounding This is to make a strong lightning flow safely into the ground, in order to reduce the lightning flow over caused by the potential rise, such as lightning rod, lightning line and lightning arrester grounding.
4. anti-static grounding In order to prevent static electricity on flammable, explosive materials such as easy fuel, natural gas storage tanks and pipelines and the dangerous role of grounding.
Connecting electrical equipment to the device and the large resistance between the resistance is called the connection resistance, contains five parts:
(1) electrical equipment and wiring contact resistance.
(2) wiring itself resistance.
(3) the connection body itself resistance.
(4) contact resistance between the body and the large contact resistance.
(5) large resistance.
Different electrical equipment has different requirements for the connection resistance.
(1) large connection short-circuit current system R ≤ 0.5Ω
(2) capacity of more than 100 kVA transformer or generator R ≤ 4 Ω
(3) valve-type lightning arrester R ≤ 5 Ω
(4) low-voltage lines metal rod, concrete rod and chimney connection R ≤ 30 Ω The exact number of reference to the relevant technical specifications requirements Electrician learning network, civil engineering network comprehensive finishing
Source：Electrician basic knowledge network