High Voltage Switch Equipment

Circuit breakers
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. In high voltage switchgear, the breaker is a complex device that acts within milliseconds to clear load and fault currents.

Instrument transformers
These high voltage switchgear components act as measuring devices and include current and voltage transformers, commonly abbreviated as CTs and VTs. They reduce current and voltage levels so the amounts flowing through an electric system can be safely monitored. Instrument transformers activate the protective relays, or they may send the fault signal directly to the control center.

Earthing switches
An earthing switch function is to connect an electrical circuit to earth when an isolator is opened or when the breaker opens during a fault. This is usually done to remove residual charges from a line that has been disconnected from the power supply. It ensures the protection of a power system as well as the safety of personnel.

Step up/down transformer
These are the largest (and most expensive) high voltage switchgear parts. The step-up transformer increases the voltage of an electrical signal so it can be transported over long distances with minimal power loss. The step-down transformer does the opposite, decreasing the voltage before it reaches equipment that can’t handle high voltages.

Disconnecting switch
In high voltage switchgear, disconnectors are simple mechanical switches that can open and close an electrical circuit. They are used to connect or disconnect equipment from the power supply usually for maintenance purposes. These HV switchgear parts are also called isolators.

Relays
A relay is an electrically operated switch that can be used to turn on or turn off a circuit. Protective relays automatically detect faults in the electrical network and activate the circuit breaker. The breaker then disconnects the faulty equipment from the power supply while also helping to extinguish the resulting arc.

Busbars
Busbars are located all over a high voltage switchgear installation. They are, by definition, low impedance conductors that connect electrical equipment together. When used in high tension switchgear, busbars connect high voltage circuit breakers and other HV components, helping to deliver power from one point to another.

Surge arresters
A surge arrester is a device used to protect equipment from damage caused by transient overvoltages, such as lightning strikes, and other causes such as switching surges. HV switchgear arresters help to protect equipment by dissipating the surge energy before it reaches the equipment.

Batteries
In many high voltage switchgear installations, batteries are used as a backup power source in case of a power outage. The batteries provide enough power to operate the circuit breaker and other HV components long enough to safely disconnect the equipment from the power supply.

Earthing grid
This is a system of metal rods or plates buried in the ground that helps to dissipate electrical energy into the earth. The earthing grid protects equipment from damage caused by lightning strikes and other transient overvoltages.