Invention Grant
- Patent Title: Electric motor protection using a virtual speed switch
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Application No.: US14710796Application Date: 2015-05-13
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Publication No.: US09939492B2Publication Date: 2018-04-10
- Inventor: Subhash C. Patel , George E. Alexander
- Applicant: Schweitzer Engineering Laboratories, Inc.
- Applicant Address: US WA Pullman
- Assignee: Schweitzer Engineering Laboratories, Inc.
- Current Assignee: Schweitzer Engineering Laboratories, Inc.
- Current Assignee Address: US WA Pullman
- Agent Richard M. Edge
- Main IPC: G01R31/02
- IPC: G01R31/02 ; G01R27/28 ; G01R31/34

Abstract:
Detection of a locked rotor condition of an electric motor during startup herein uses a virtual speed switch. The methods and systems herein determine whether the motor is in a starting state, and the monitor the motor current to determine if it is greater than a predetermined threshold, and that the motor current decrease exceeds a predetermined threshold after a predetermined amount of time. If the decrease in motor current is not less than a predetermined threshold, then a speed switch bit is set, indicating that the rotor is turning. The methods and systems herein further determine whether a physical speed switch is faulty, and determine a locked rotor condition using the virtual speed switch signal, a physical speed switch signal, and whether the physical speed switch is faulty.
Public/Granted literature
- US20160334468A1 ELECTRIC MOTOR PROTECTION USING A VIRTUAL SPEED SWITCH Public/Granted day:2016-11-17
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