What is the equipment secondary protection grounding?

The secondary grounding of PT (voltage transformer) and CT (current transformer) belongs to protective grounding. Both PT and CT have primary and secondary parts, there is a coupling capacitor between primary and secondary, and there is also a capacitor between secondary and ground. In this way, if there is a problem with the insulation between the primary side and the secondary side or the coupling capacitance suddenly increases, a high voltage will be connected in series with the secondary side. At this time, if secondary grounding occurs, the secondary grounding capacitance disappears (which can also be regarded as the secondary potential being forced to zero), which can prevent the high voltage on the primary side from escaping to the secondary side, causing danger to personnel and equipment. One end of the secondary side of PT and CT must be grounded locally.

The secondary side of CT works in short circuit state. Once the secondary side is open, it can induce high voltage, which will bring great hidden dangers to the safety of instruments, protection, signal circuits or maintenance personnel. Grounding one end of the secondary side of CT can effectively limit the induced high voltage and force it to zero, thus achieving the purpose of protection.

Low voltage neutral point is generally directly grounded.

Advantages are as follows

Effectively reduce the system overvoltage in case of electrical failure.

It is suggested that the enclosure of electrical equipment should be protected by zero connection. PE or PEN conductor can provide an effective channel for the return of fault current. At the same time, the fault current can effectively make low-voltage protection switches (circuit breakers, electric shock protectors) move quickly, disconnect the fault circuit, and protect personal and equipment safety.

In workplaces with special safety requirements, such as coal mines and warehouse workshops with explosion-proof requirements, neutral points can be ungrounded.