A grounding switch is a mechanical device that grounds the maintenance-side circuit when a switch is de-energized. Its primary function is to ensure the safety of maintenance personnel. Even if a sudden power surge occurs during maintenance, it can direct power to the ground, forcing the switch to trip. It can also be used to artificially create a system ground short circuit for control and protection purposes. It is typically used on the high-voltage side of a step-down transformer.
Working Principle of a Grounding Switch
A grounding switch has the ability to close short-circuit currents. After clearing a ground fault on a line, it creates a shallow current in the faulty line through adjacent operating lines. Closing the fast-acting grounding switch eliminates the shallow current, and the grounding switch is then quickly opened to ensure successful automatic reclosing of the line. Typically, a fast-acting grounding switch is installed on the line side of the outgoing disconnector. It has two main functions: first, it interrupts capacitive currents generated by classical induction and inductive currents generated by electromagnetic induction in parallel overhead lines. Second, if creepage occurs on insulators or arcing occurs within the casing, the fast-acting grounding switch quickly grounds the conductive main circuit, interrupting the fault current via the circuit breaker.
The function of grounding switch
There are two types of grounding switches: maintenance grounding switches and fast-acting grounding switches. Maintenance grounding switches are located next to the isolating switches on either side of the circuit breaker and simply serve to ground both sides during circuit breaker maintenance. Fast-acting grounding switches, on the other hand, are located on the outgoing line near the soundproofing switch.
They serve two purposes: 1. They can open and close the capacitive circuits generated by electrostatic induction and the currents generated by electromagnetic induction in parallel overhead lines. 2. If creepage occurs on the insulators inside the casing or an arc occurs inside the casing, the fast-acting grounding switch quickly grounds the main circuit, clearing the fault current through the circuit breaker.
Grounding switch classification
E0-class earthing switches: Suitable for use in power transmission and distribution systems, meet the general requirements of the GB1985-2014 High-voltage AC disconnectors and earthing switches standard, and lack short-circuit making capability.
E1-class earthing switches: Suitable for use in power transmission and distribution systems, meet the general requirements of the GB1985-2014 High-voltage AC disconnectors and earthing switches standard, and have the ability to withstand two short-circuit making operations. Note: This class of earthing switches can withstand two making operations at the rated making current.
E2-class earthing switches (earthing switches with rated voltages up to 40.5 kV): Suitable for use in systems with nominal voltages up to 35 kV, meet the general requirements of this standard, and have the ability to withstand five short-circuit making operations. Note: The increased number of making operations in the E2 class is limited to voltages up to and including 40.5 kV and is based solely on the typical operating conditions and protection systems of such networks.
M0-class earthing switches: Suitable for use in power transmission and distribution systems, meeting the general requirements of this standard and capable of withstanding 1,000 operating cycles.
M1-class earthing switches: With an extended mechanical life of 3,000 operating cycles, they are primarily designed for use in conjunction with circuit breakers of the same rating.
M2-class earthing switches: With an extended mechanical life of 10,000 operating cycles, they are primarily designed for use in conjunction with circuit breakers of the same rating.
