Title: Unit 6 Introduction
Course: WGF 107 DEVELOPMENT > Section: Content

Title | Emergency Electrical Systems (including Stand-by Generators)
Image | A backup generator for a large apartment building
Content
An emergency power system is a standby generator which may include lighting, electric generators, fuel cells, uninterruptible power supplys and other apparatus, to provide backup power 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, data centers,^[1] telecommunication^[2] equipment and modern naval ships. Emergency power systems can rely on generators, deep cycle batteries, flywheel energy storage or hydrogen fuel cells.^[3]^[4] Finally, some homebrew emergency power systems use regular lead-acid car batteries.^[5]

Operation in buildings[edit]

Mains power can be lost due to downed lines, malfunctions at a sub-station, inclement weather, planned blackouts or in extreme cases a grid-wide failure. In modern buildings, most emergency power systems have been and are still based on generators. Usually, these generators are Diesel engine driven, although smaller buildings may use a gasoline engine driven generator and larger ones a gas turbine. However, lately, more use is being made of deep cycle batteries and other technologies such as flywheel energy storage or fuel cells. These latter systems do not produce polluting gases, thereby allowing the placement to be done within the building. Also, as a second advantage, they do not require a separate shed to be built for fuel storage.^[6]

With regular generators, an automatic transfer switch is used to connect emergency power. 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.)

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, or lights up service areas such as mechanical rooms and electric rooms. Exit signs, Fire alarm systems (that are not on back up batteries) and the electric motor pumps for the fire sprinklers are almost always on emergency power. Other equipment on emergency power may include smoke isolation dampers, smoke evacuation fans, elevators, 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 theater using it to power show equipment because "the show must go on."

Electronic Device Protection

Computers, communication networks, and other modern electronic devices need not only power, but also a steady flow of it to continue to operate. If the source voltage drops significantly or drops out completely, these devices will fail, even if the power loss is only for a fraction of a second. Because of this, even a generator back-up does not provide protection because of the start-up time involved.

To achieve more comprehensive loss protection, extra equipment such as surge protectors, inverters, or sometimes a complete uninterruptible power supply (UPS) is used. UPS systems can be local (to one device or one power outlet) or may extend building-wide. A local UPS is a small box that fits under a desk or a telecom rack and powers a small number of devices. A building-wide UPS may take any of 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.

Since telephone exchanges use DC, the building's battery room is generally wired directly to the consuming equipment and floats continuously on the output of the rectifiers that normally supply DC rectified from utility power. When utility power fails, the battery carries the load without needing to switch. With this simple though somewhat expensive system, some exchanges have never lost power for a moment since the 1920s.
Links/Upload | Emergency Power System – Wikipedia http://en.wikipedia.org/wiki/Emergency_power_system Developing and Maintaining Emergency Operations Plans http://www.fema.gov/media-library-data/20130726-1828-25045-0014/cpg_101_comprehensive_preparedness_guide_developing_and_maintaining_emergency_operations_plans_2010.pdf
Attributions | Image and Content courtesy of Wikipedia – The Free Internet Encyclopedia