Emergency Power System

Emergency power system
Emergency power systems are a type of system, which may include lighting, generators and other apparatus, to provide backup resources in a crisis or when regular systems fail. They find uses in a wide variety of settings from residential homes to hospitals, scientific laboratories and modern naval ships. Emergency power systems can rely on generators or uninterruptible power supplies.
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Operation in buildings
Utility power (known as normal power) can be lost due to downed lines, malfunctions at a sub-station, planned blackouts or in extreme cases a grid-wide failure. In a modern building, most emergency power systems rely on a diesel engine driven generator, although smaller buildings may use a gasoline engine driven generator. An automatic transfer switch is used to tie the emergency power in. One side is connected to both the normal power feed and the emergency power feed; and the other side is connected to the load designated as emergency. If no electricity comes in on the normal side, the transfer switch uses a solenoid to throw a triple pole, single throw switch. This switches the feed from normal to emergency power. The loss of normal power also triggers a battery operated starter system to start the generator, similar to using a car battery to start an engine. Once the transfer switch is switched and the generator starts, the building''s emergency power comes back on (after going off when normal power was lost.) Emergency lighting (also known as egress lighting) is almost always on a building''s emergency power system. Unlike emergency lights, emergency lighting is not a type of light fixture, it is a pattern of the building''s normal lights that provides a path of lights to allow for safe exit in case of an emergency or light up service areas such as mechanical rooms and electric rooms. Emergency lighting also includes exit signs. Fire alarm systems and the electric motor pumps for the fire sprinklers is almost always on emergency power. Other equipment that may be on emergency power can include smoke isolation dampers, smoke evacuation fans, handicap doors and outlets in service areas. Hospitals use emergency power outlets to power life support systems and monitoring equipment. Some buildings may even use emergency power as part of normal operations, such as a theatre using it to power show equipment because "the show must go on."
Electronic device protection
Computers, communication networks and other modern electronic devices depend on a steady stream of power to continue to operate. If the source voltage drops significantly or drops out completely these devices will fail, even if it is for a fraction of a second. Because of this, even a generator back-up does not provide protection because of the start-up time envolved. To achieve this protection an uninterruptible power supply (UPS) is used. UPS systems can be local or building wide. Local UPS''s are a small box that fits under a desk or a telecom rack and powers a small number of devices. A building wide UPS can take on several different forms, depending on the application. It directly feeds a system of outlets designated as UPS feed and can power a large number of devices.
Structure and operation in utility stations
Diagram of a redundant power supply system.
In recent years, large units of a utility power station are usually designed on a unit system basis in which the required devices, including the boiler, the turbine generator unit, and its power (step up) and unit (auxiliary) transformer are solidly connected as one unit. A less common set-up consists of two units grouped together with one common station auxiliary. As each turbine generator unit has its own attached unit auxiliary transformer, it is connected to the circuit automatically. For starting the unit, the auxiliaries are supplied with power by another unit (auxiliary) transformer or station auxiliary transformer. The period of g from the first unit transformer to the next unit is designed for automatic, instantaneous operation in times when the emergency power system needs to kick in. It is imperative that the power to unit auxiliaries not fail during a station shutdown (an occurrence known as black-out when all regular units temporarily fail). Instead, during shutdowns the grid is expected to remain operational. When problems occur, it is usually due to reverse power relays and frequency-operated relays on grid lines due to severe grid disturbances. Under these circumstances, the emergency station supply must kick in to avoid damage to any equipment and to prevent hazardous situations such as the release of hydrogen gas from generators to the local environment.