1.1Grounding Overview

Grounding is to connect some parts of the equipment or a point of the system to the earth.Its main function is to provide a current release channel and potential reference point.According to the functions,it is classified into lightning protection grounding,protection grounding,and working grounding(system grounding).Its functions are as follows:

★Protect structures from lightning strike

★Prevent static electricity accumulation from causing explosion

★Release the short-circuit current of the power system to ensure the safety of equipment and personnel

★Provides a system zero potential point or circuit logic reference point

1.2 Grounding 

      ★System Grounding(Working Grounding):Functional grounding of one or more points in a power system.

★Protective grounding:To ground a system,device,or equipment at one or more points for electrical safety.

★Lightning pritective grounding:Grounding for lightning protection devices(lightning rod,lightning wire,lightning arrester,etc.)to release lightning current to the earth.

★Static protective grounding:Grounding to prevent dangerous effects of static electricity on fuel oil,natural gas storage tanks,pipelines,etc.

1.3 Technical requirements of the grounding grid

★Reasonable and effective grounding impedance

★The service life that meets the requirements of thermal stability in the life cycle of the equipment

★Electrical connection,complete network,the formation of a good conductive channel

★Scientific and reasonable structure design to meet the safety requirements of equipment and personnel when equipment fault current and lightning current discharge

1.4 Characteristic parameters of the grounding grid

★Grounding impedance

Grounding impedance:Impedance of grounding device to distant potential zero.The value is the ratio of the potential difference between the grounding device and the distant potential zero to the current flowing into the ground through the grounding device.

★Grounding potential rise

Grounding potential rise:The potential difference between the grounding device and the reference ground when electricity flows into the earth through the grounding electrode of the grounding device.

★Surface potential distribution

Surface potential distribution:When the grounding short-circuit fault current flows through the grounding device,the potential distribution distribution formed on the ground surface of the field where the grounding device is located.The potential distribution between two points with a horizontal distance of 1.0m on the ground is called the surface potential distribution in unit field area.

★Touch potential difference

Touch potential difference:When the grounding fault current flows through the grounding device,a distributed potential is formed on the surface of the earth,the potential difference between two points at a horizontal distance of 1.0m from the equipment and a vertical distance of 2.0m from the equipment housing,structure,or wall.

★Step potential difference

Step potential difference:The potential difference between two points on the ground with a horizontal distance of 1.0m when the ground fault current flows through the grounding device.