Protection system for an electric motor

• US 4,286,303 A
• Filed: 03/19/1979
• Issued: 08/25/1981
• Est. Priority Date: 03/19/1979
• Status: Expired due to Term

• Current Assignee: Franklin Electric Company Incorporated (EBW, Inc.)
• Original Assignee: Franklin Electric Company Incorporated (EBW, Inc.)
• Inventors: Whitney, John A., Genheimer, Stephen R., Reinhard, Linda M.
• Primary Examiner(s): Salce, Patrick R.
• Application Number:
  US06/021,613
• Time in Patent Office: 890 Days
• Field of Search: 361/24, 361/25, 361/26, 361/28, 361/31, 361/22, 361/23, 361/93, 361/94, 361/95, 361/96, 361/97, 361/35, 361/37, 361/103, 361/105, 318/798, 318/806, 340/310 R, 340/310 A, 364/483
• US Class Current: 361/24
• CPC Class Codes: H02H 3/07 and with permanent disconnection after a predetermined number of reconnection cycles
• CPC Class Codes: H02H 7/08 for dynamo-electric motors
• CPC Class Codes: H02H 7/0852 directly responsive to abnormal temperature by using a temperature sensor in a control circuit H02H7/0833

Abstract

This disclosure relates to apparatus and method for controlling and protecting an electric motor. A transmitter is coupled to the motor and to the power lines for generating pulses on the power lines in certain circumstances such as during an overheated motor condition. A control unit is coupled to the power lines and senses the pulses and monitors the power current magnitude in the lines. The unit compares the current level with previously established upper and lower limits. If the current level is outside the limits for a preset length of time, a fault condition exists and the motor is turned off for a length of time that depends upon the severity of the fault. The unit also turns off the motor upon the receipt of pulses from the transmitter when a certain number of pulses regularly recur. The unit includes indicators for displaying the nature of the fault. The unit may be adjusted for automatic operation wherein it will turn the motor on again after a time interval, or for manual operation wherein the motor can only be restarted manually.

Claims

1. A method of controlling and protecting an electric load that is adapted to be connected to a power supply by two or more power lines, said method comprising the steps of:

(a) coupling to at least one of the lines to sense the level of power current flowing through the line;

(b) comparing the power current level with an upper limit and a lower limit;

(c) comparing the length of time it is outside the limits with a preselected time interval when the current level is outside of said limits and determining that a fault condition exists when the level is outside said limits longer than said time interval;

(d) disconnecting the power from the load when a fault condition exists;

(e) starting a reset time interval;

(f) reconnecting the power to the load at the end of said reset time interval;

(g) counting the number of faults that occur due to the current level being above the upper limit; and

(h) varying the length of said reset time interval dependent on said number of said faults.

2. The method of claim 1, and further including the steps of:

(a) indicating that a fault condition exists after the power is reconnected to the load at the end of the reset time interval.

3. The method of claim 1, wherein a pulse transmitter is coupled to the power lines and generates pulses on the power lines in response to a condition of the load, and further including the steps of:

(a) coupling to at least one of said power lines to sense said pulses;

(b) determining whether a predetermined number of pulses occur in regular succession; and

(c) disconnecting the power from the load when said predetermined number appear in regular succession.

4. The method of claim 1, and further including the step of:

(a) starting said count of faults at zero when a fault has not occurred for a predetermined length of time.

5. A method of controlling and protecting an electric load that is adapted to be connected to a power supply by two or more power lines, said method comprising the steps of:

(a) coupling to at least one of the lines to sense the level of power current flowing through the line;

(b) comparing the power current level with an upper limit and a lower limit;

(c) comparing the length of time it is outside the limits with a preselected time interval when the current level is outside of said limits and determining that a fault condition exists when the level is outside said limits longer than said time interval;

(d) disconnecting the power from the load when a fault condition exists;

(e) starting a reset time interval;

(f) reconnecting the power to the load at the end of said reset time interval;

(g) comparing the power current level with a low current value when the current level is below said lower limit;

(h) repeating the foregoing step (2) to form a series of cycles;

(i) determining whether the power current level was within said limits during a previous cycle; and

(j) disconnecting the power from the load for an off delay interval when the current level was within said limits during a previous cycle but is presently below said lower limit.

6. A method of controlling and protecting an electric load that is adapted to be connected to a power supply by two or more power lines, the load having a pulse transmitter mounted adjacent it and the transmitter being coupled to at least one power line, the method comprising the steps of:

(a) coupling to a power line to sense any pulses appearing on said line;

(b) repeatedly sensing at regular intervals whether pulses appeared on the line during an interval;

(c) counting successive intervals during which pulses appear on the power line;

(d) comparing said count with a selected number;

(e) disconnecting the power from the load when the count equals said number;

(f) starting a reset time interval;

(g) reconnecting the power to the load at the end of said reset time interval;

(h) counting the number of times the load is disconnected; and

(i) vary the length of said reset time interval dependent on the said number of times.

7. The method of claim 6, and further including the steps of:

(a) coupling to a power line to sense the power current to the load;

(b) comparing the power current with overload and underload current limits; and

(c) disconnecting the power from load when the power current is outside said limits.

8. Apparatus for controlling and protecting an electric load that is adapted to be connected to a power supply by two or more power lines, said apparatus comprising:

(a) means for coupling to at least one of the lines to sense the level of power current flowing through the line and comparing the power current level with an upper limit and a lower limit;

(b) means for comparing the length of time it is outside the limits with a preselected time interval when the current level is outside of said limits and for determining that a fault condition exists when the level is outside said limits longer than said time interval;

(c) means for disconnecting the power from the load when a fault condition exists

(d) means for starting a reset time interval;

(e) means for reconnecting the power to the load at the end of said reset time interval;

(f) means for counting the number of faults that occur due to the current level being above the upper limit; and

(g) means for varying the length of said reset time interval dependent on said number of said faults.

10. Apparatus as in claim 8, wherein a pulse transmitter is coupled to the power lines and generates pulses on the power lines in response to a condition of the load, and further including:

(a) means for coupling to at least one of said power lines to sense said pulses;

(b) means for determining whether a predetermined number of pulses occur in regular succession; and

(c) means for disconnecting the power from the load when said predetermined number appear in regular succession.

11. Apparatus as in claim 8, and furtherincluding:

(a) means for starting said count of faults at zero when a fault has not occurred for a predetermined length of time.

9. Apparatus as in claim 9, and further including:

(a) means for indicating that a fault condition exists after the power is reconnected to the load at the end of the reset time interval.

12. Apparatus for controlling and protecting an electric load that is adapted to be connected to a power supply by two or more power lines, said apparatus comprising:

(a) means for coupling to at least one of the lines to sense the level of power current flowing through the line;

(b) means for comparing the length of time it is outside the limits with a preselected time interval when the current level is outside of said limits and for determining that a fault condition exists when the level is outside said limits longer than said time interval;

(c) disconnecting the power from the load when a fault condition exists;

(d) means for starting a reset time interval;

(e) means for reconnecting the power to the load at the end of said reset time interval.

(f) means for comparing the power current level with a low current value when the current level is below said lower limit;

(g) means for determining whether the power current level was earlier within said limits; and

(h) means for disconnecting the power from the load for an off delay interval when the current level was earlier within said limits but it below said lower limit.

13. Apparatus for controlling and protecting an electric motor that is adapted to be connected to a power supply by at least two power lines, comprising:

(a) current sensor means adapted to be connected to at least one line for sensing power current therethrough;

(b) processing means for comparing said power current with underload and overload current limits, determining whether said power current is outside said limits for a time interval and in such event indicating a fault condition and forming a reset time interval;

(c) means connected to said processing means for disconnecting power from said motor during said reset time interval,

(d) header means connected to said processing means for setting said current limits in said processing means;

(e) pulse sensor means coupled to said power lines for sensing pulses thereon, and said processing means including means responsive to a regular succession of pulses for disconnecting power from said motor;

(f) said pulse sensor means and said current sensor means comprising a current transformer including a core and separate sensor windings.

14. Apparatus as in claim 13, and further including indicator means for indicating a fault condition, and said processing means including means for energizing said indicator means after said reset time interval.

15. Apparatus as in claim 13, and further including a tramsmitter adjacent said motor and coupled to the power lines, said transmitter being heat responsive and generating pulses on said lines when the motor is heated to above a predetermined level.