The Complexities of High-Voltage Power

Most building electrical services are provided at secondary voltage to the main switchgear by the local electrical utility. However, large facilities, such as multi-building campuses, hospitals or telecommunications and computer data centers, typically employ customer-owned and -maintained primary power distribution and possibly standby or cogeneration systems. The technical experience and equipment necessary to design, construct, commission and operate such facilities are of a higher order than for secondary power systems. For example, a typical office building might have a low-voltage power system consisting of service entrance switchboards, panel boards, motor control centers, dry transformers, cables/bus ducts, and finally, generators and automatic transfer switches. The testing associated with start-up and commissioning for such facilities is straightforward: Insulation resistance measurements of low-voltage transformers, power cables, bus ducts and switchgear. Torque testing of switchgear-bolted connections. Setting and testing of the ground-fault protection at the service mains. Setting and testing the overload protection for motor starters. Load bank and functional performance testing of generators and transfer switches. Thermographic inspections of operating switchgear and panels. However, with a primary power system, especially one that's facility-owned and -maintained, a much greater effort—and responsibility—is required. In fact, local code enforcement, and the utilities themselves, will often require that an independent electrical testing agency, such as the International Electrical Testing Assn., be employed to test and certify that the installation is safe to energize and operate. Size matters The size range of primary power systems covers a broad spectrum.