Introduction
The high-voltage grounding switch is an important component used as a grounding protection device in high-voltage switchgear. Today, we will discuss some relevant knowledge about it, hoping to be of help to those in the electrical industry.

01. Definition
A grounding switch is a mechanical device used to ground the maintenance side of a circuit when the power is off. Its main function is to ensure the safety of maintenance personnel by directing any sudden electrical flow during maintenance into the ground, forcing the switch to trip. It can also be used to deliberately create a system ground short circuit to achieve control and protection purposes, typically used on the high side of step-down transformers.

02. Classification of Grounding Switches

· E0 Grade Grounding Switch: Suitable for use in transmission and distribution systems, meeting the general requirements of the GB1985-2014 standard for high-voltage AC disconnectors and grounding switches, but lacking short-circuit making capability.

· E1 Grade Grounding Switch: Suitable for use in transmission and distribution systems, meeting the general requirements of the GB1985-2014 standard, with the capability to withstand two short-circuit making operations. Note: This grade of grounding switch can withstand two making operations at the rated making current.

· E2 Grade Grounding Switch (for rated voltage 40.5 kV and below): Suitable for systems with a nominal voltage of 35 kV and below, meeting the general requirements of the standard, with the capability to withstand five short-circuit making operations. Note: The additional making operations for E2 grade are limited to voltages up to and including 40.5 kV, based on the typical operating conditions and protection systems of such networks.

· M0 Grade Grounding Switch: Suitable for use in transmission and distribution systems, meeting the general requirements of the standard, with the capability to withstand 1000 operating cycles.

· M1 Grade Grounding Switch: A grounding switch with an extended mechanical lifespan of 3000 operating cycles, mainly used in scenarios where the grounding switch is associated with the operation of circuit breakers of the same level.

· M2 Grade Grounding Switch: A grounding switch with an extended mechanical lifespan of 10000 operating cycles, mainly used in scenarios where the grounding switch is associated with the operation of circuit breakers of the same level.

· Combination Function Grounding Switch: A grounding switch with a shared contact system, used for grounding and at least one of the following functions: isolation, making and/or breaking load current, or making and/or breaking current up to the rated short-circuit current.

· Class A Grounding Switch: A grounding switch designated for use in circuits with shorter or weaker coupling lengths to adjacent live lines.

· Class B Grounding Switch: A grounding switch designated for use in circuits with longer or stronger coupling lengths to adjacent live lines. Note: Grounding switches with making capabilities (E1 and E2 grades) classified as Class A or B will have a combined grade symbol, such as A+E1 or B+E2.

03. Working Principle of Grounding Switches
The grounding switch has the capability to make short-circuit current. After clearing a line ground fault, shallow supply current is formed through adjacent operating lines. The rapid operation of the grounding switch is used to eliminate the shallow supply circuit and then quickly open the grounding switch to ensure the success of automatic reclosing. Generally, the rapid grounding switch is installed on the side of the outgoing isolator switch close to the line, with two major functions: one is to break the capacitive current generated by classic induction in parallel overhead lines and the inductive current generated by electromagnetic induction; the other is that when the internal insulator of the casing experiences creepage or internal arcing, the rapid grounding switch will quickly ground the conductive main circuit, and the circuit breaker will cut off the fault current.

04. Functions of the Grounding Switch
There are two types of grounding switches: maintenance grounding switches and rapid grounding switches. The maintenance grounding switch is installed beside the isolators on both sides of the circuit breaker, serving the function of grounding both sides during circuit breaker maintenance. The rapid grounding switch is installed on the outgoing circuit near the line side of the isolator switch, with two functions:

1. To break the capacitive current induced by static induction in parallel overhead lines and the current induced by electromagnetic induction.

2. When the internal insulator of the casing experiences creepage or internal arcing, the rapid grounding switch will quickly ground the main circuit, and the circuit breaker will cut off the fault current.

05. Short-Circuit Duration of Grounding Switches
According to the DL/T593-2016 "Common Technical Requirements for High-Voltage Switchgear and Controlgear Standards," the time interval for which switchgear can carry the rated short-time withstand current in the closed position is specified as 2 seconds for 550-1100kV and 3 seconds for switchgear and controlgear rated at 363kV and below.
The DL/T486-2010 standard specifies that unless otherwise specified, the rated duration for the short-time withstand current of a grounding switch should be at least 2 seconds. The GB1985-2014 standard also specifies that switchgear and controlgear in the closed position should be capable of carrying the rated short-time withstand current for a standard duration of 2 seconds. If necessary, a duration greater than 2 seconds can be selected, with recommended values being 3 seconds and 4 seconds. Unless otherwise specified, the rated duration for the short-time withstand current of a grounding switch is 2 seconds.
The GB1985 and DL/T486 standards set the short-circuit duration for grounding switches at not less than 2 seconds, aligning with international standards. There have been no operational issues due to the 2-second short-circuit duration of grounding switches in recent years, and operational experience has proven good results. Therefore, a 2-second short-circuit duration for grounding switches is sufficient, and it is not necessary to meet the same requirements as isolators.

06. Long-Term Current Carrying Issues of Grounding Switches
Grounding switches are mechanical devices used to ground circuits, capable of carrying short-circuit current for a specified period under abnormal conditions (such as a short circuit), but not required to carry current under normal circuit conditions. This is the main difference between grounding switches and isolators. In actual operation, the following procedure must be strictly followed: when the isolator is closed, the grounding switch must be open; after the isolator is open, the grounding switch can be closed. This indicates that the grounding switch does not have the possibility of carrying the operating current long-term, so the grounding switch does not have rated current and loop resistance parameters.