Requirement
There are three purposes for grounding diesel generator sets
In order to ensure the safety of people and the operation needs of the electrical system, there are strict requirements for generator grounding. sets. There are three types of grounding methods: working grounding, protective grounding and protective grounding. The purpose of grounding is:
1. Working grounding is: The purpose of neutral point grounding is:
1) Reduce electric shock voltage. For a system with an ungrounded neutral point, when one phase is grounded and the human body touches one of the other two phases, the electric shock voltage is more than 1.7 times the voltage phase while for a system with a grounded neutral point, the electric shock; voltage It drops to a level close to or equal to the voltagen phase
voltage.
2) Promptly switch off defective equipment. For a system with an ungrounded neutral point, when one phase is grounded, due to the capacitance and insulation resistance between the wires and ground, a current path can form and The grounding current is very small, which is not enough to cause the protection device to work. Cutting off the power supply
cannot guarantee personal safety. For systems with a grounded neutral point, when a phase is grounded and the earth current is large, the protective device will act quickly to disconnect the fault point.
3) Reduce the level of insulation of electrical equipment to earth. In a system with an ungrounded neutral point, when one phase is grounded, the ground voltage of the other two phases rises to the line voltage. PFor systems with a grounded neutral point, when one phase is grounded, the voltage to ground of the other two phases is only close to the phase voltage, so the insulation level electrical equipment and transmission lines can be reduced.
2. Protective Earthing
Protective earthing is often used in low voltage systems where the neutral point is not earthed. Its function is: when the insulation junction of a certain winding of the. motor
If protective earthing is used, when the human body touches the hull, the resistance of the human body is connected in parallel with the resistance of the earth. Since the resistanceance of the human body is much greater than the resistance of the earth, the current passes through the human body. will be very weak and there will be no risk of electric shock.
3. Protective zero connection
The protective zero connection is often used in low voltage systems where the neutral point is grounded. Its function is: to protect the insulation structure from a certain winding. of the motor
When damaged and connected to the hull, due to the use of a zero protection connection, a single-phase short circuit is formed and the fuse of this phase quickly blows , and the hull is no longer charged. Even when the human body touches the box before the fuse blows, because the resistance of the human body is much higher than the resistance of the circuit, the current passing through the human body is very small and there is no risk of electric shock.