Intelligent automatic bypass for a motor control device fault

• US 20040252423A1
• Filed: 04/30/2004
• Published: 12/16/2004
• Est. Priority Date: 05/02/2003
• Status: Active Grant

• Current Assignee: ABB Incorporated (ABB Limited)
• Original Assignee: ABB Incorporated (ABB Limited)
• Inventors: Boren, Steven G.
• Granted Patent: US 7,558,031 B2
• Time in Patent Office: Days
• US Class Current: 361/23
• CPC Class Codes: H02H 11/005 in case of too low isolation resistance, too high load, short-circuit; earth fault
• CPC Class Codes: H02H 3/006 Calibration or setting of parameters
• CPC Class Codes: H02H 3/06 with automatic reconnection
• CPC Class Codes: H02H 7/0833 for electric motors with control arrangements

Abstract

An intelligent automatic bypass for a motor control device determines if a fault that is occurring in the motor control device is a restricted or non-restricted fault. A restricted fault is one that may damage or destroy the motor if an automatic switch to bypass is allowed to occur for all faults that occur in the motor control device. The intelligent automatic bypass allows the automatic switch to bypass only if the fault is a non-restricted fault and blocks the automatic switch to bypass if the fault is a restricted fault.

Claims

1. A system for controlling an AC motor comprising:

a motor controller comprising a motor control device and means for identifying a fault occurring in said motor control device and determining if said occurring fault is a restricted fault;

an output contactor connected between said motor control device and said motor, said output contactor closed in the absence of any fault in said motor control device; and

a bypass contactor connected between a source of AC power, said motor control device and said AC motor, said bypass contactor open in the absence of any fault occurring in said motor control device;

said motor controller opening said output contactor upon said fault identifying means determining the occurrence of a restricted fault in said motor control device.

2. The system of claim 1 wherein said fault identifying means also determines if a fault occurring in said motor control device is a non-restricted fault and said motor controller upon said fault identifying means determining the occurrence of a non-restricted fault first opening said output contactor and then closing said bypass contactor.

3. The system of claim 2 wherein said motor controller further comprises a bypass contactor controlling device and said bypass contactor controlling device in response to said fault identifying means determining the occurrence of a non-restricted fault in said motor control device closing said bypass contactor after said output contactor is opened.

4. The system of claim 3 wherein said bypass contactor controlling device is a relay.

5. The system of claim 1 wherein said motor control device is a variable frequency drive.

6. A system for controlling an AC motor comprising:

a motor controller comprising a motor control device and means for identifying a fault occurring in said motor control device as either a non-restricted fault or a restricted fault;

a normally open output contactor connected between said motor control device and said motor, said output contactor closed in the absence of any fault in said motor control device; and

a bypass contactor connected between a source of AC power, said motor control and said AC motor, said bypass contactor open in the absence of any fault occurring in said motor control device;

said motor controller first opening said output contactor and then closing said bypass contactor upon said fault identifying means identifying a non-restricted fault in said motor control device and said motor controller opening said output contactor upon said fault contactor identifying the occurrence of a restricted fault in said VFD.

7. The system of claim 6 wherein said motor control device further comprises a bypass contactor controlling device and said bypass contactor controlling device in response to said fault identifying means determining the occurrence of a non-restricted fault in said motor control device closing said bypass contactor after said output contactor is opened.

8. The system of claim 7 wherein said bypass contactor controlling device is a relay.

9. The system of claim 6 wherein said motor control device is variable frequency drive.

10. A method for controlling an AC motor by a motor control device upon the occurrence of a fault in said motor control device, said motor control device connected to said AC motor by an output contactor, said output contactor closed when said AC motor is operating in the absence of any fault occurring in said motor control device, and a bypass contactor connected between a source of AC power, said motor control device and said AC motor, said bypass contactor open when said motor is operating in the absence of any fault occurring in said motor control device, said method comprising:

determining the occurrence of a restricted fault in said motor control device; and

opening said output contactor upon the determination of a restricted fault occurrence in said motor control device.

11. The method of claim 10 further comprising:

determining the occurrence of a non-restricted fault in said motor control device; and

opening said output contactor and then closing said bypass contactor upon the determination of a non-restricted fault occurrence in said motor control device.

12. A method for controlling an AC motor by a motor control device upon the occurrence of a fault in said motor control device, said motor control device connected to said AC motor by an output contactor, said output contactor closed when said AC motor is operating in the absence of any fault occurring in said motor control device, and a bypass contactor connected between a source of AC power, said motor control device and said AC motor, said bypass contactor open when said AC motor is operating in the absence of any fault occurring in said motor control device, said method comprising:

determining the occurrence of a fault in said motor control device as either a non-restricted fault or a restricted fault;

opening said output contactor and then closing said bypass contactor upon the determination of a non-restricted fault occurrence in said motor control device; and

opening said output contactor upon the determination of a restricted fault occurrence in said motor control device.

13. A controller for an AC motor, said controller intermediate between a source of AC power and said AC motor, comprising:

means for determining the occurrence of a fault in said motor controller;

means for identifying said determined fault occurrence as a restricted fault; and

means for causing said AC motor to be disconnected from said motor controller when said identified occurring fault is a restricted fault.

14. The motor controller of claim 13 further comprising:

means for identifying said determined fault occurrence as a non-restricted fault; and

means for first causing said motor to be disconnected from said motor controller when said identified occurring fault is a non-restrictive fault and then causing said motor to be connected to said source of AC power through a bypass contactor.