Switchgear is basically equipment used switch ON or OFF generators, transmission lines, distributors and other equipment under both normal and abnormal conditions. Switchgear consists of switching and protecting devices such as switches, fuses, circuit breakers, relays, and so forth. In other words switchgear can be defined as equipment used for switching, controlling and protecting the electrical circuits and apparatus.
Typically in a normal operation, the switchgear allows to switch ON or OFF transmission lines, generators, distributors and other electrical apparatus. But when a failure such as short circuit occurs on any part of power system, heavy current flows through the equipment that might cause damage to the equipment and as a result cause interruption of service to customers. In this case the switchgear detects the fault and disconnects the unhealthy segment of the system. In this manner, switchgear protects the system from damage and ensures continuity of supply.
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Fundamental Features of Switchgear
Any switchgear equipment should possess the following vital features:
- Absolutely certain discrimination – when a fault takes place on any section of the power system, the switchgear must be able to separate the faulty segment and the healthy segment. It should isolate the faulty section from the system without affecting the healthy section. This ensures continuity of supply.
- Complete reliability – When a fault occurs on any section of the power system, the switchgear must operate to isolate the faulty section from the remainder of the circuit.
- Quick operation – when a fault takes place on section of the power system, switchgear must operate quickly so that there is no damage to generators, transformers and other equipment by the short-circuits currents. If the fault is not cleared by switchgear quickly, it is likely to spread into healthy sections, thus posing a danger of complete shutdown of the system.
- Provision for manual control – switchgear should have provision for manual control. In instance where the electrical or electronics control fails, the required operation can be carried out through manual control.
- Availability of the necessary instruments – the required instruments such as current and voltage transformers for connecting to the main switchgear or a separate instrument panel must be provided.
Failure of Switchgear
Hazards associated with switchgear failure include fire, explosion and electric shock. Oil circuit breakers and fuse switches are some of the main causes of most accidents associated with switchgear. Additionally many accidents are caused by mechanical problems with auxiliary equipment such as isolators and from failure of routine and emergency operating procedures.
Common Causes of High-Voltage Switchgear Failures
The causes of high-voltage switchgear failures include:
- Poor maintenance leading to contamination of insulation and loose connections, etc.
- Incorrect or inappropriate use of test equipment on live equipment.
- Unrestricted repeated operations of oil circuit breakers (OCBs) leading to breakdown of the oil insulation and/or to contact collapse.
- Hesitant operation of manually closed switches onto faulted circuits leading to panic opening on fault and as a result fault arc drawn at the contacts of a non-rated switch.
- Failures of potential transformers (PTs), also referred to as voltage transformers (VTs) and failures of current transformers (CTs).
Related articles:
- Types of Busbar Arrangements in Grid Stations and Substations
- Power System Protection
- Common Causes of Failures of Power Transformers
- Types of Insulators used in Power Systems
- Key Factors to Consider In Substation Design
- Miniature Circuit Breakers (MCBs)
