E-m Switchgear designs, manufactures and supplies advanced switchgear systems for the utility, industrial, commercial and residential sectors.
-> Components
A switchgear has two types of components:
Power conducting components, such as switches, circuit breakers, fuses, and lightning arrestors, that conduct or interrupt the flow of electrical power
Control systems such as control panels, current
transformers, potential transformers, protective relays, and associated circuitry, that monitor, control, and protect the power conducting components
-> Functions
One of the basic functions of switchgear is protection, which is interruption of short-circuit and overload fault currents while maintaining service to unaffected circuits. Switchgear also provides isolation of circuits from power supplies. Switchgear is also used to enhance system availability by allowing more than one source to feed a load.
->History
Switchgears are as old as electricity generation. The first models were very primitive: all components were simply fixed to a wall. For reasons of fire protection, the wood was replaced by slate or marble
-> Housing
Switchgear for lower voltages may be entirely enclosed within a building. For higher voltages (over about 66 kV), switchgear is typically mounted outdoors and insulated by air, although this requires a large amount of space. Gas-insulated switchgear saves space compared with air-insulated equipment, although the equipment cost is higher. Oil insulated switchgear presents an oil spill hazard.
->Circuit breaker types
A switchgear may be a simple open-air isolator switch or it may be insulated by some other substance. An effective although more costly form of switchgear is the gas-insulated switchgear (GIS), where the conductors and contacts are insulated by pressurized sulfur hexafluoride gas (SF6). Other common types are oil or vacuum insulated switchgear. The combination of equipment within the switchgear enclosure allows them to interrupt fault currents of thousands of amps. A circuit breaker (within a switchgear enclosure) is the primary component that interrupts fault currents. The quenching of the arc when the circuit breaker pulls apart the contacts (disconnects the circuit) requires careful design. Circuit breakers fall into these five types: GAS Hybird VacuumCarbon Dioxide
-> Circuit breakers and fuses
Circuit breakers and fuses disconnect when current exceeds a predetermined safe level. However they cannot sense other critical faults, such as unbalanced currents—for example, when a transformer winding contacts ground. By themselves, circuit breakers and fuses cannot distinguish between short circuits and high levels of electrical demand.
->Distance relays
A short circuit at the end of a long transmission line appears similar to a normal load, because of the impedance of the transmission line limits the fault current. A distance relay detects a fault by comparing the voltage and current on the transmission line. A large current along with a voltage drop indicates a fault.
