Measures must be taken to ensure the safe grounding of generator sets

1. Work grounding

(1) Reduce the 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 phase voltage; while for a system with a neutral point grounded, the electric shock voltage drops to close to or equal to the phase voltage. Voltage.

(2) Quickly cut off the faulty equipment. For systems where the neutral point is not grounded, when one phase is grounded, the capacitance and insulation resistance between the conductors and the ground can form a current path. The grounding current is very small, which is not enough to cause the protective device to operate and cut off the power supply, which cannot ensure personal safety. . For systems with a grounded neutral point, when one phase is grounded and the ground current is large, the protection device will act quickly to disconnect the fault point.

(3) Reduce the insulation level of electrical equipment to ground. In a system with an ungrounded neutral point, when one phase is grounded, the ground voltage of the other two phases will rise to the line voltage. For 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 of electrical equipment and transmission lines can be reduced.

2. Protective grounding

Protective grounding is often used in low-voltage systems where the neutral point is not grounded. Its function is: when the insulation structure of a certain winding of the motor has been damaged and the shell is charged, if it is not grounded and the human body touches the shell, it is equivalent to a single-phase electric shock. Risk of electric shock occurs. If protective grounding is used, when the human body touches the shell, the resistance of the human body is connected in parallel with the ground resistance. Since the resistance of the human body is much greater than the ground resistance, the current passing through the human body will be very small, and there will be no risk of electric shock.

3. Protective connection to zero

Protective zero connection is often used in low-voltage systems with a grounded neutral point. Its function is: when the insulation structure of a certain winding of the motor is damaged and connected to the shell, a single-phase short circuit will be formed due to the protective zero connection, which will quickly cause the motor to be connected to zero. The fuse in this phase blows and the shell is no longer charged. Even when the human body touches the casing before the fuse blows, because the resistance of the human body is much greater than the resistance of the circuit, the current passing through the human body is very small, and there is no risk of electric shock.

In addition, it should be noted that the grounding of the neutral line of the generator must consider the specific situation and confirm whether the transformer has leakage protection. Generally, the imported generator set has a zero-ground combination and must be removed when using it. Otherwise, the transformer has leakage protection. Likely to jump. The ground wire of domestic generator sets is usually on the ground and is grounded separately, and the neutral wire and the neutral wire of the mains are connected together. The phase line (three-phase line) needs to use a switch to interlock the mains power and the generator to prevent the mains power from being applied to the generator set.