System and method for monitoring current and providing motor protection

• US 20040056615A1
• Filed: 09/23/2002
• Published: 03/25/2004
• Est. Priority Date: 09/23/2002
• Status: Active Grant

• Current Assignee: Siemens Industry Incorporated (Siemens AG)
• Original Assignee: Siemens Energy & Automation Incorporated (Siemens AG)
• Inventors: Wakefield, Scott, Mayhew, Scott, Zuzuly, Daniel, Jonsson, Gregg
• Granted Patent: US 6,924,613 B2
• Time in Patent Office: Days
• US Class Current: 318/434
• CPC Class Codes: H02P 29/02 Providing protection against overload without automatic interruption of supply protection against faults of stepper motors H02P8/36

Abstract

A motor controller system comprises solid state switches for connection between an AC line and motor terminals for controlling application of AC power to the motor. A user input elements selects a current imbalance parameter. Current sensors sense current in each winding of the motor. A control circuit controls operation of the solid state switches. The control circuit compares the sensed currents with the selected imbalance parameter to determine if a fault condition exists.

Claims

1. A motor controller system comprising:

solid state switches for connection between an AC line and motor terminals for controlling application of AC power to the motor;

a user input element for selecting a current imbalance parameter;

current sensors for sensing current in each winding of the motor; and

a control circuit for controlling operation of the solid state switches, the control circuit comparing the sensed currents with the selected imbalance parameter to determine if a fault condition exists.

2. The motor controller system of claim 1 wherein the control circuit compares a ratio of a lowest motor winding current to a highest motor winding current with the selected imbalance parameter to determine if a fault condition exists.

3. The motor controller system of claim 1 wherein the control circuit determines a ratio of each motor winding current to each other motor winding current and compares a lowest determined ratio with the selected imbalance parameter to determine if a fault condition exists.

4. The motor controller system of claim 1 wherein the user input device further selects an imbalance disable level and the control circuit ignores a fault condition if all motor winding currents are lower than the imbalance disable level.

5. The motor controller system of claim 1 wherein the control circuit comprises a programmed processor.

6. The motor controller system of claim 1 wherein the current sensors comprise current transformers.

7. An elevator starter comprising:

solid state switches for connection between an AC line and motor terminals for controlling application of AC power to the elevator;

current sensors for sensing current in each winding of the motor; and

a control circuit connected to the current sensors for controlling operation of the solid state switches, the control circuit including a user input element for selecting a current imbalance parameter and a processing circuit comparing the sensed currents with the selected imbalance parameter to determine if a fault condition exists.

8. The elevator starter of claim 7 wherein the control circuit compares a ratio of a lowest motor winding current to a highest motor winding current with the selected imbalance parameter to determine if a fault condition exists.

9. The elevator starter of claim 7 wherein the control circuit determines a ratio of each motor winding current to each other motor winding current and compares a lowest determined ratio with the selected imbalance parameter to determine if a fault condition exists.

10. The elevator starter of claim 7 wherein the user input device further selects an imbalance disable level and the control circuit ignores a fault condition if all motor winding currents are lower than the imbalance disable level.

11. The elevator starter of claim 7 wherein the control circuit comprises a programmed processor.

12. The elevator starter of claim 7 wherein the current sensors comprise current transformers.

13. A motor controller system comprising:

solid state switch means for connection between an AC line and motor terminals for controlling application of AC power to the motor;

user input means for selecting a current imbalance parameter;

current sensing means for sensing current in each winding of the motor; and

motor control means operatively connected to the current sensing means for controlling operation of the solid state switch means, the motor control means comparing the sensed currents with the selected imbalance parameter to determine if a fault condition exists.

14. The motor controller system of claim 13 wherein the motor control means compares a ratio of a lowest motor winding current to a highest motor winding current with the selected imbalance parameter to determine if a fault condition exists.

15. The motor controller system of claim 13 wherein the motor control means determines a ratio of each motor winding current to each other motor winding current and compares a lowest determined ratio with the selected imbalance parameter to determine if a fault condition exists.

16. The motor controller system of claim 13 wherein the user input means further selects an imbalance disable level and the motor control means ignores a fault condition if all motor winding currents are lower than the imbalance disable level.

17. The motor controller system of claim 13 wherein the motor control means comprises a programmed processor.

18. The motor controller system of claim 13 wherein the current sensing means comprise current transformers.

19. A method of monitoring current and providing motor protection comprising:

providing solid state switches for connection between an AC line and motor terminals for controlling application of AC power to the motor;

selecting a current imbalance parameter;

sensing current in each winding of the motor;

controlling operation of the solid state switches; and

comparing the sensed currents with the selected imbalance parameter to determine if a fault condition exists.

20. The method of monitoring current and providing motor protection of claim 19 wherein comparing the sensed currents with the selected imbalance parameter compares a ratio of a lowest motor winding current to a highest motor winding current with the selected imbalance parameter to determine if a fault condition exists.

21. The method of monitoring current and providing motor protection of claim 19 wherein comparing the sensed currents with the selected imbalance parameter comprises determining a ratio of each motor winding current to each other motor winding current and comparing a lowest determined ratio with the selected imbalance parameter to determine if a fault condition exists.

22. The method of monitoring current and providing motor protection of claim 19 wherein the user input means further selects an imbalance disable level and the motor control means ignores a fault condition if all motor winding currents are lower than the imbalance disable level.