What are the typical grounding modes of power supply system and their advantages and disadvantages?

The initial letter t stands for one or more points where the power supply system is directly grounded; The second letter T or N, T means that the exposed metal part of the equipment and other conductive metals are directly grounded, and N means that the exposed metal of the electrical equipment is connected to the grounding wire provided by the power grid; The third letter is S or C, where S stands for the complete separation of neutral wire and protective ground wire, and C stands for the combination of neutral wire and protective ground wire. 1, TNC:TNC is also called four-wire system, that is, the neutral wire and protective grounding of the system are combined into one-point grounding, and the exposed conductive part of electrical equipment is connected to PE-N. The disadvantage is that when the three-phase circuit is unbalanced or has only one phase, current flows through the PE-N line. When the transformer in the substation is struck by lightning or short circuit, large current will be transmitted to the equipment shell through PE-N line, and people will get an electric shock when they touch the equipment. 2.TT: The zero line of the system and the exposed metal part of the equipment are grounded respectively. The disadvantage is that when the high voltage terminal of the transformer is short-circuited to the enemy, or when the lightning rod is working, the large current on the ground network will raise the ground potential, so that the voltage difference between the equipment shell and the equipment interior exceeds the isolation voltage inside the equipment, resulting in the breakdown or short circuit of the equipment. 3.TNC。 S: TNC. S, also known as four-wire semi-system, separates the neutral line from PE (does not merge) in the building. Its advantages are safety and good electromagnetic compatibility. 4.TNS: TNS is also called five-wire system, that is, five wires come out of the power grid, and N and PE are separated. The advantages are that PE has no current and good electromagnetic compatibility; The disadvantage is high cost. 3. At present, grounding systems are divided into independent grounding system, public grounding system 1 and independent grounding system, including safe grounding, electromagnetic compatibility grounding and lightning protection grounding. Safe grounding means grounding the exposed metal part of the equipment; Electromagnetic compatibility includes shielding ground, filter reference ground, circuit reference ground, etc. Generally, they are connected in terms of electromagnetic compatibility and safety, and lightning protection grounding should be more than 20m away from other grounding points. The specific treatment methods of independent grounding system include the type and material selection of grounding electrode, the requirements of grounding resistance and the resistivity of soil. 2. Public grounding system: In the public grounding system, lightning protection grounding, safety grounding and electromagnetic compatibility grounding are connected through a ground net, and the main reinforcement of the building, underground grounding net, voltage equalizing net of each floor and lightning rod are connected into a Faraday shielding cage for grounding. IV. Lightning protection measures: 1. Reduce grounding impedance and grounding resistance; 2. Use isolation transformer; Shanghai grounding system company