Overview:
Working grounding refers to connecting a certain point of the power system (such as the neutral point) directly to the ground, or connecting it to the ground metal through arc suppression coils and resistors, such as neutral point grounding of transformers and transformers.
Application:
(1)System operation needs
The neutral point grounding of the high-voltage system can make the grounding relay protection device operate accurately and eliminate the single-phase arc grounding overvoltage. Neutral point grounding can prevent zero-sequence voltage offset and keep the three-phase voltage basically balanced.
For low-voltage systems, single-phase power can be used conveniently. In two-wire one-ground power supply systems, one-phase work can be grounded to reduce costs.
(2) Reduce human body contact voltage
In the neutral point insulation system, when one phase is grounded and the human body touches the other phase, the contact voltage will exceed the phase voltage and become the line voltage, which is the double of the phase voltage. When the neutral point is grounded, the grounding resistance of the neutral point is close to zero, and the potential difference with the ground is close to zero, which reduces the contact voltage of the human body.
(3) Quickly cut off the faulty equipment
In the neutral point insulation system, when one phase is short-circuited, the grounding current is very small, and the protection device cannot cut off the current quickly. When the neutral point is grounded, the one-phase ground current becomes a large single-phase short-circuit current, and the protection device must be able to cut off the fault line accurately and quickly.
(4) Reduce the design insulation level
When one phase is grounded in the neutral point grounding system, the voltage of the other two phases to the ground does not rise to twice the phase voltage, but is close to the phase voltage. In the neutral point grounding system, the insulation level of electrical equipment and lines should be designed Only consider the phase voltage to reduce the cost.
