What is grounding and how to understand grounding circuit

What is grounding?

There is a grounding grid in the ground of the building, like a metal grid, which provides the ground potential for the grounding point of the building. It can be considered that the potential of the earth (ground potential) is zero, and grounding is to fix the potential of the grounding point and the connected conductor to zero. The role of grounding can be divided into protective grounding and working grounding.

Protective grounding: in order to prevent the human body from touching the live parts and causing electric shock when the equipment leaks. Once the insulation of the equipment is damaged, the conductor part of the equipment (such as the metal shell, etc.) may be charged with voltage. At this time, the human body touches the conductive part of the equipment, and the current will flow through the human body and lightning protection grounding cause injury. If the conductor part of the equipment is grounded, the potential of the conductor part can be fixed to zero, and there will be no harm to people after leakage. It is stipulated that household appliances with metal shells with risk of leakage must use a three-hole plug (the upper hole in the three-hole plug/socket is the grounding wire).

Working grounding: Some equipment must obtain a stable zero potential point when working, such as the neutral point of a three-phase motor, or the power electronics inside some electronic equipment. If it is not grounded, the potential of these points will drift, which is unfavorable for work.

Lightning protection grounding: 

The grounding of lightning rods and some metal equipment that are prone to lightning strikes is to quickly introduce the lightning current into the ground and release it when it is struck by lightning, so as to avoid damage to buildings, equipment and personnel who are in contact with the equipment. To say more, lightning rods should actually be called "lightning rods." Because of their height and tip shape, lightning will choose to form a discharge channel on the top of the lightning protection grounding rod to protect surrounding buildings from being directly hit. When thundering, keep a distance from the grounding point of the lightning rod. Because the lightning current is too large (30kA~300kA), it will form a ground position distribution around the grounding point. When people stand with their legs apart, they will be affected by the step voltage. It flows between the legs.

Anti-static grounding: 

Some equipment is susceptible to electrostatic discharge during work, and it must be grounded to neutralize the electrostatic charge in time. For example, in a tanker truck on the road, a chain will rub against the ground at the rear of the car to prevent the fuel tank from accumulating electric charges and sparks from the discharge causing flammable and explosive liquids to burn. Some electronic devices are susceptible to electrostatic discharge from human hands. Therefore, you must wear an anti-static wristband before working and connect your hands to the grounding point.

How To Understand the Circuit

The earth is a good conductor. When a person touches a leakage device, the current is in the direction of the leakage device. It passes through the human hand, then leads to the earth through the human foot, then leads to the ground point of the power system, and finally reaches the neutral point of the power system. Many operations in the power system require standing on insulating mats or wearing insulating shoes to prevent current from flowing through the human body to the ground in the event of an accident. In the high-voltage direct current transmission system, there is a ground loop operation mode, and a current of thousands of amperes flows through the ground electrode of the converter station. Electric current can flow thousands of kilometers and travel deep in the earth.