page_title: Switchgear
section_title: Safety
hierarchical_section_title: Switchgear / Safety
caption_attribution_description: 日本語: GIS方式の遮断器. Srpskohrvatski / српскохрватски: Prekidač sa gasom SF6 za napone do 420 kV. Српски / srpski: Прекидач са гасом SF6 за напоне до 420 kV. English: Sulfur hexafluoride gas circuit breakers in a 420 kV switchyard
context_page_description: In an electric power system, switchgear is composed of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is directly linked to the reliability of the electricity supply.
  The earliest central power stations used simple open knife switches, mounted on insulating panels of marble or asbestos. Power levels and voltages rapidly escalated, making opening manually operated switches too dangerous for anything other than isolation of a de-energized circuit. Oil-filled switchgear equipment allow arc energy to be contained and safely controlled. By the early 20th century, a switchgear line-up would be a metal-enclosed structure with electrically operated switching elements, using oil circuit breakers. Today, oil-filled equipment has largely been replaced by air-blast, vacuum, or SF₆ equipment, allowing large currents and power levels to be safely controlled by automatic equipment.
  High-voltage switchgear was invented at the end of the 19th century for operating motors and other electric machines.
context_section_description: To help ensure safe operation sequences of switchgear, trapped-key interlocking provides predefined scenarios of operation. For example, if only one of two sources of supply are permitted to be connected at a given time, the interlock scheme may require that the first switch must be opened to release a key that will allow closing the second switch. Complex schemes are possible.
  Indoor switchgear can also be type tested for internal arc containment (e.g., IEC 62271-200). This test is important for user safety as modern switchgear is capable of switching large currents.
  Switchgear is often inspected using thermal imaging to assess the state of the system and predict failures before they occur. Other methods include partial discharge (PD) testing, using either fixed or portable testers, and acoustic emission testing using surface-mounted transducers (for oil equipment) or ultrasonic detectors used in outdoor switchyards. Temperature sensors fitted to cables to the switchgear can permanently monitor temperature build-up. SF₆ equipment is invariably fitted with alarms and interlocks to warn of loss of pressure, and to prevent operation if the pressure falls too low.
  The increasing awareness of dangers associated with high fault levels has resulted in network operators specifying closed-door operations for earth switches and racking breakers. Many European power companies have banned operators from switch rooms while operating. Remote racking systems are available which allow an operator to rack switchgear from a remote location without the need to wear a protective arc flash hazard suit. Switchgear systems require continuous maintenance and servicing to remain safe to use and fully optimized to provide such high voltages.
caption: 420 kV gas insulated switchgear
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