Consulting-Specifying Engineer - January 2009 - (Page 38) Control your emergency power system System designers and operators must have a good understanding of the emergency power capability and how it is designed and configured to work. BY KOMSON (MAK) WAGNER, PE, Stanley Consultants, Muscatine, Iowa E 38 mergency power systems are vital, particularly in facilities where an interruption in power is unacceptable. From health care facilities to data centers to power plants, many facilities cannot tolerate a power loss for either economic or life safety reasons. Factors such as severe weather, grid disturbances and line switching, or even the influence of animals can disturb or disrupt the normal supply source. Regardless of the cause of the disturbance, the emergency power system must supply continuous electrical service to facility critical loads during a power outage. When the emergency power system fails to perform, it affects the facility’s ability to perform its functions or missions, which may result in financial loss, compromised security, and/or life safety issues, even if the outage is for a short period of time. Too often, facility owners are caught in a situation where the emergency generator fails to start. The emergency loads fail to transfer to an alternate power supply source, causing unnecessary shutdown and restart of equipment, or a failed attempt to preserve critical loads. These events can be minimized if the system designer and facility operator have a good understanding of facility emergency load requirements, emergency power system configuration and design intent, level of redundancy, and the control strategy for emergency response and load restoration. Integrated and coordinated control is essential to a reliable emergency power system. System configuration In the simplest terms, a typical emergency power system consists of a normal power supply source, an alternate power source, and the means to transfer the emergency loads from a normal power source to an alternate power source in the event the normal power supply source fails. Various levels of redundancy can be accomplished by adding multiple power sources, spare power supply and distribution capacity, and multiple paths for emergency load to connect to the alternate power supply sources. The determination of an emergency power system configuration and built-in level of redundancy depends on: • The reliability of the normal power supply source. • The sensitivity of emergency loads to normal power supply disturbance or disrup- Consulting-Specifying Engineer • JANUARY 2009
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