The critical use of power in large commercial facilities makes continuous electric power extremely important. In order to provide a more reliable utility supply, the power system often employs redundant utility sources via a transfer scheme that switches from a preferred to an alternate source in the event of a power upset. This is vital due to increased concentration of sensitive electric-powered equipment on tenant premises as well as the dependency of sophisticated building infrastructures on uninterrupted power. A continuous power supply relates to health and safety issues, computer and process loads, and comfort requirements such as HVAC and lighting. With the greater demand for electricity combined with the aging infrastructure of the electric power grid, disturbances such as voltage spikes and sags and severe weather conditions are continually increasing the probability that large buildings will incur the need to transfer between power supplies at increasing intervals. When the transfer does not occur within a few seconds or automatically, both building and tenant operations could be interrupted, quite possibly exposing building owners to extensive liabilities. The frequency of power transfer scheme failures can be attributed to the age of the equipment in these large commercial buildings and the use of archaic technologies that are inadequate for today's power systems requirements. These designs incorporate devices such as electromechanical relays and pneumatic timers known to have a limited service life cycle, which have been supplanted by more advanced micro-processor-based devices.
Reaching a More Reliable Solution The management of ARX Engineering of Calgary, AB has always prided itself in being on the leading edge with the evolution of new technologies that offer more robust protection as well as other advanced performance characteristics. Since 1982, ARX and its predecessor Magna IV Engineering Ltd. have been providing electrical engineering, equipment maintenance, and commissioning services to the utility, industrial, commercial, and institutional sectors. ARX Engineering works with building management and external resources to achieve high performance building infrastructure management. Maintaining an efficient infrastructure-including electrical power systems-is quite significant, because a typical building life cycle is 30% to build and 70% to manage, operate, and maintain over the life of the property (e.g., $300,000,000 to build and $700,000,000 to operate). Over the years, ARX Engineering Ltd. has identified and repaired failures to these systems. However, within a one-year period, at least three major facilities in Calgary experienced a failure of the utility source where power was not automatically restored via the alternate source. These events all resulted in building evacuations. Rather than continue to repair these problematic systems, ARX was determined to design a new modern protection and control scheme. The goal was a solution that would not only improve reliability but also enhance the performance of the system. With the backing of Brookfield Property Management and Oxford Properties, ARX was commissioned to design a retrofit transfer scheme that would improve reliability, meet the current utility requirements, provide enhanced protection features, and provide feedback to the building operators. After consultation with Schweitzer Engineering Laboratories, Inc. (SEL) based in Pullman, Washington, the design was undertaken, utilizing a powerful and flexible microprocessor-controlled protective relay, the SEL-351 Directional Overcurrent and Reclosing Relay. The SEL-351 Relay is widely used at utilities and substations around the world because of its extensive monitoring, protection, communications, and automation features.
Comprehensive System Features Transfer scheme design parameters include a selectable preferred source, automated and synchronized transfer to a second source in case of a power sag or other disturbance, and remote alarm notification to the building engineering staff should there be a loss of the standby (secondary) source. Overcurrent protection and lockout features are standard functions of the SEL-351 Relay and are incorporated into the overall design. With the successful installation of this system at five facilities within the Calgary marketplace, the building owners have seen the benefits of the installation in that they have not experienced any malfunctions and have renewed confidence in the event of a problem with the alternate supply. An unforeseen benefit is that they now are aware when the utility transfers them onto the alternate source without notification, and they are aware if there is a problem with the utility alternate source.
For more information, visit www.magnaivengineering.com.