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Power Terminology – Switchgears

Switchgear is the general term covering a wide range of equipment concerned with switching and protection. The apparatus used for controlling, regulating, and switching on or off the electrical circuit in the electrical power system is known as switchgear. Switchgears can be classified in different ways including:

  1. Voltage Level (High Voltage or HV Switchgears, Medium Voltage or MV Switchgears, Low Voltage or LV Switchgears)
  2. According to working environment (Outdoor Switchgears and Indoor Switchgears)

Switchgears are necessary at every switching point in the power system because there are several voltage and fault levels which have to be controlled and protected by accessible switching devices and for isolation if the need arises. Switchgear panels house Circuit Breakers in most cases especially 11KV voltage level. Switchgear panels and breakers are named after the manufacturers hence we have

  • ABB Breaker
  • Reyroll Breaker
  • GEC Breaker

Examples of Switchgears

Circuit Breakers

A Circuit Breaker is a device capable of making and breaking an electric circuit under normal and abnormal conditions such as short circuits. It is therefore a switching and current interrupting device. During abnormal or fault conditions such as short circuits, it switches off to avoid the flow of current through the protected equipment.

Classifications of Circuit Breakers

  1. Rated Voltage – 11KV, 33KV Circuit Breakers
  2. Medium of arc extinction – Air Break, SF6, Vacuum Circuit, Mineral Oil
  3. Types of operating mechanism – charged spring/ pneumatic/ hydraulic operated Circuit Breaker
  4. Operating environment – Indoor and Outdoor Circuit Breakers

Isolators

Isolators are mechanical switches used to make or break the flow of current to a circuit or equipment. Isolators can be manually operated or motorized Isolators are made up of two sets of contacts namely fixed contact and moving contact. The contacts are supported on bushings which carry the contact blades. While a Circuit Breaker has arc quenching medium, the surrounding air becomes the arc quenching medium for isolators. While the Circuit Breaker can be operated on rated and fault current, the isolator must be operated at minimal or no load.

Classifications of Isolators

  1. Manual
  2. Motorised
  3. Dropping type
  4. Single Break Rotating type
  5. Double Break Rotating type