PLC control system and grounding method of power grid

There are three main ways of grounding the PLC control system and the power grid, namely, the common ground mode, the floating mode, the chassis common ground and the circuit floating.

1. Common mode

In the common ground mode, the entire control system of the PLC is based on the ground, and the chassis is connected with the grounding point and the grounding wire. Some PLC systems in large plants use a common grounding method. In places where the status of the earth is not easy to change, the common ground is adopted. When the earth potential is stable, the potential of the entire wiring system will not easily change, and the way the chassis is grounded will be safer and easier to use.

2. Floating way

In places where the earth potential is unstable, changes in the position of the earth will cause the system potential to be unstable, and the lines in the PLC wiring will be greatly disturbed. In this case, the floating method is more appropriate. In the PLC control system, the chassis is connected to the circuit grounding point and suspended in the air without touching the ground. The insulating rubber pad is mainly used to separate the casing from the ground. At the same time, insulation measures should be taken for the incoming line. Grounding measures in floating mode can also effectively avoid interference, and the earth potential change and electromagnetic induction interference are greatly reduced. However, the disadvantage of this method is that since the entire system line adopts the floating mode, static electricity is generated on the casing, and there is a certain danger in operation.

3. The chassis is common, the circuit is floating

This approach is a combination of a common ground approach and a floating approach. This method has obvious advantages. Because the casing is grounded, it is safer to operate, and at the same time, because the grounding points are independent, the disturbance effect caused by the earth potential change can be attenuated. This kind of grounding method has its rationality and obvious advantages from the perspective of safety production and protection equipment, so it is widely used in ironworks.