SYSTEM FOR ESTIMATING THE FREQUENCY OF THE POWER SIGNAL ON APOWER TRANSMISSION LINE

摘要

The system (10) obtains the three phase voltages on the power line VA, VB an d VC, either from a local primary (14) or local alternative source (16). The selected local source voltages (14, 16) are then applied through switches (2 0, 28), respectively, which are normally closed but are open in the event that the associated pole of each voltage phase is open. The voltages from the closed switches (20, 28) are applied to a calculating circuit (40) which produces a composite of the three voltages in accordance with a preselected formula. The composite voltage output is then normalized (44) and applied to a conventional frequency determination (estimating) circuit (46). This output (FREQ. OUTPUT) is an accurate system frequency for use by the protective rel ay.