Why the neutral point should be grounded when the transformer is shut down and the power is supplied, and the neutral point DC isolation device

The main reason for grounding the neutral point of the transformer when it is energized is to prevent overvoltage from damaging the transformer. When the transformer is shut down, if the neutral point is not grounded, an operating overvoltage may be generated (the multiple of the overvoltage when the neutral point is not grounded during the transformer energization can reach 4 to 4.5 times the rated phase voltage, and the multiple of the neutral point grounding overvoltage when the transformer is energized generally does not exceed 3 times the phase voltage. This conclusion is based on the understanding of transformer operating overvoltage and actual operating experience). This causes a breakdown short circuit between the neutral point of the transformer or the ground. Therefore, in order to prevent damage to electrical equipment, the neutral point of the transformer needs to be grounded during the shut-down operation. When the neutral point is directly grounded, the amplitude of the operating overvoltage usually does not exceed 3 times the phase voltage. This is because neutral point grounding helps to shunt the neutral point current in the transformer and reduce the voltage drop of the current flowing through the transformer leads, thereby reducing the insulation stress of the equipment and protecting the transformer from excessive voltage damage. Neutral point DC isolation device Neutral point DC isolation device is a device used to solve the DC bias problem of transformers. The device is used for the neutral point of the transformer. By installing the DC isolation device, the adverse effects caused by the DC bias operation of the transformer can be effectively prevented, ensuring the safe and stable operation of the transformer. ‌Principle and operating status‌: Under normal operation, the device switch is in a closed state, and the neutral point of the transformer is directly grounded. When DC current appears at the neutral point of the transformer, the DC isolation device can automatically or manually enter the capacitor grounding operating state, at which time the neutral point of the transformer is grounded through capacitive reactance.