System for estimating the frequency of the power signal on a power transmission line
AssigneeSchweitzer Engineering Laboratories, Inc.
InventorsArmando Guzman-Casillas, Gabriel Benmouyal
Life of this patent
Estimating the term…
Abstract
The system obtains the three phase voltages on the power line VA, VB and VC, either from a local primary or local alternative source. The selected local source voltages are then applied through switches, 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 are applied to a calculating circuit which produces a composite of the three voltages in accordance with a preselected formula. The composite voltage output is then normalized and applied to a conventional frequency determination (estimating) circuit. This output is an accurate system frequency for use by the protective relay.
Claims9
A system for determining power system frequency for use in a protective relay operating to protect or monitor the power system, comprising:
- means for obtaining three phase voltages on the power line by elements which are local to the protective relay;
- a calculating circuit for producing a composite voltage of the three phase voltages using a preselected equation wherein one or more of the three phase voltages are not applied to the calculating circuit in the event of the occurrence of selected power system conditions;
- a scaler circuit for changing the magnitude output of the calculating circuit depending upon which phase voltages are applied to the calculating circuit;
- and
- means for estimating the power system frequency from the composite voltage, wherein said power system frequency is used by the protective relay in its protective functions for the power system.
A system for determining power system frequency for use in a protective relay operating to protect or monitor the power system, comprising:
- means for obtaining three phase voltages on the power line by elements which are local to the protective relay;
- a calculating circuit for producing a composite voltage of the three phase voltages using the following equation:
- V α = [ V A - ( V B + V C 2 ) ] · K
- where Vα is the composite voltage, K is a scaler quantity and VA, VB, and VC are the three phase voltages, respectively.
Dependencies are inferred from the claim text.