A new frequency relay for power-system applications

THE interconnection of large power systems with industrial and defense plants having a comparatively small generating capacity is not unusual in these days. These plants require a considerable block of power for 24-hour full-capacity operation, and this power is available by means of the interconnection with the power system. More than one interconnection would assure higher continuity of service, but the general practice of locating defense plants in rural or suburban areas, remote from urban power-system networks, often results in one transmission-line interconnection operating in parallel with plant generators. Like all lines, the interconnection is subject occasionally to faults with resulting temporary loss of power for the plant. During these emergencies, the local generator or generators at the plant which normally contribute to the total load are suddenly called upon to carry all of the plant load. The local generators are not able to supply this load and consequently are heavily overloaded. As a result, the frequency decreases rapidly. However, complete shutdown of the plant can be avoided by dropping some of the load and retaining within the capacity of the local generators the load of the most essential machines and processes.