System Load Swings

Operating records of the Consolidated Edison Company of New York, Inc., revealed the existence of irregular fluctuations in the loads on generating stations and tie feeders. Tests were conducted to determine the response of parts of the system to changes in load, voltage, and frequency. By analyzing the test results to show the relation between these three quantities under various operating conditions, it was possible to establish the origin of the load swings, as well as to determine their magnitude, duration, and recurrence. Three general types of load swings were observed: small synchronizing power oscillations, short-time swings caused by fluctuating railroad loads, and long-time swings produced by the unco-ordinated adjustments of station loads. These swings are not initiated or sustained by the turbine governors. The synchronizing power oscillations and the short-time swings do not affect system operation, but the long-time swings do affect the loading of the tie feeders and the operation of boiler equipment. It is expected, however, that the greater appreciation of the problem derived from the tests, plus the installation of a common frequency indicator in all stations, will enable the operators to reduce the long-time load swings.