Microprocessor based setting group controller for protective relay operations

• US 6,222,714 B1
• Filed: 03/15/2000
• Issued: 04/24/2001
• Est. Priority Date: 05/17/1999
• Status: Active Grant

• Current Assignee: Hoffman, Gary R.
• Original Assignee: Hoffman, Gary R.
• Inventors: Hoffman, Gary R.
• Primary Examiner(s): Sherry, Michael J.
• Assistant Examiner(s): HUYNH, KIM NGOC
• Application Number:
  US09/526,218
• Time in Patent Office: 405 Days
• Field of Search: 361/62-66, 361/78-79, 361/83, 361/93.1, 361/93.2, 361/93.3, 361/94, 361/93.8, 361/93.9, 361/103, 700/286, 700/292, 700/299, 702/57-58, 702/60, 702/64-65, 340/540, 340/657, 340/635
• US Class Current: 361/93.2
• CPC Class Codes: H02H 3/006 Calibration or setting of parameters
• CPC Class Codes: H02H 5/04 responsive to abnormal temperature specially adapted for electric machines H02H7/0852

Abstract

A substation for distributing electric power includes protective relays whose trip points are made to be a function of temperature, the protective relays being used to control the opening and closing of circuit breakers for protecting against fault conditions in at least one of the power input and power output portions of the power distribution system. In one embodiment, a temperature probe which is used to sense the temperature at a selected point of the substation supplies the temperature information to a microcontroller which is programmed to set the trip point of selected protective relays as a function of the sensed temperature.

Claims

1. In a substation for distributing electric power, the combination comprising:

a power transformer having a primary winding and a secondary winding;

a circuit breaker connected in series with one of said primary and secondary windings, said circuit breaker for interrupting the flow of current through the power transformer when the current in at least one of the primary and secondary windings exceeds a permissible threshold level;

a temperature sensor located in said substation for sensing at least one of;

(a) the ambient temperature in said substation, (b) the temperature of said power transformer, and (c) the temperature of said circuit breaker, and for producing a signal indicative of the temperature; and

means coupling the signal indicative of the temperature to a microcontroller;

said microcontroller being programmed to be responsive to said temperature indicative signal from said temperature sensor for generating different values of permissible threshold levels corresponding to different temperature signals, said microcontroller having an output coupled to said circuit breaker for controlling the opening and closing of said circuit breaker as a function of the different values of permissible threshold levels corresponding to the different temperature indicative signals from said temperature sensor.

2. In a substation as claimed in claim 1, wherein said microcontroller is also responsive to a voltage at the secondary winding of said transformer for controlling the opening and closing of said circuit breaker as a function of the combination of said temperature sensor and said voltage.

3. In a substation as claimed in claim 1, wherein said microcontroller is also responsive to the amplitude of the current in the secondary winding of said transformer for controlling the opening and closing of said circuit breaker as a function of the combination of said temperature sensor and said current.

4. In a substation as claimed in claim 1, further including a protective relay and wherein said output of said microcontroller is coupled to said circuit breaker by supplying the output of the microcontroller to said protective relay and said protective relay being coupled to said circuit breaker for controlling its opening and closing.

5. In a substation as claimed in claim 4, wherein the protective relay is responsive to said output from the microcontroller and to at least one of the voltage and current conditions at one of the primary and secondary windings for controlling the opening and closing of the circuit breaker as a function of the temperature in the substation and the at least one of the voltage and current conditions.

6. In a substation as claimed in claim 4, wherein the protective relay has a set point at which it trips the circuit breaker;

and wherein the set point of the protective relay is varied by the microcontroller as a function of the temperature in the substation.

7. In a substation as claimed in claim 4, wherein the microcontroller includes comparator means having first and second inputs and an output;

wherein a signal indicative of an actual load condition is supplied to said first input, wherein a reference signal generated by the microcontroller is applied to the second input, which reference signal varies as a function of temperature in response to a signal from the temperature sensor; and

wherein the output of the comparator is used to set the relay and control the trip point of the circuit breaker.

8. In a substation as claimed in claim 7, wherein the microcontroller is preprogrammed to include information regarding different set points of the protective relay and trip points of the circuit breaker for different temperature conditions.

9. In a substation as claimed in claim 1, wherein said circuit breaker includes a first set of circuit breakers connected to the primary winding of the power transformer and a second set of circuit breakers connected to the secondary winding of the power transformer;

and wherein said microcontroller functions to raise the values of the permissible threshold levels when the temperature decreases and to lower the values of the permissible threshold levels when the temperature increases.

10. In a substation as claimed in claim 9, wherein said microcontroller has several outputs;

and further including first and second protective relays;

said first protective relay being coupled between a first output of the microcontroller and said first set of circuit breakers, and said second protective relay being coupled between a second output of the microcontroller and said second set of circuit breakers for respectively controlling the opening and closing of the first and second circuit breakers.

11. In a substation as claimed in claim 10, wherein said second set of protective relays is responsive to the current flowing in the secondary winding and supplies a signal to the microcontroller indicative of the current level, whereby the microcontroller produces an output signal which is a function of the temperature in the substation and the power drawn in the secondary winding.

12. In a substation as claimed in claim 10, further including a third set of protective relays for sensing a differential between the primary and secondary windings of the transformer and said third set of protective relays being responsive to an output signal from said microcontroller.

13. In a substation as claimed in claim 1 wherein said microcontroller includes time delay means for producing output control signals at its outputs only if an input signal condition persists for longer than a predetermined period.

14. A substation comprising:

a power transformer having a primary winding and a secondary winding;

a circuit breaker connected in series with one of said primary and secondary windings;

said circuit breaker for interrupting the flow of current through the power transformer when the current in at least one of the primary and secondary windings exceeds a settable threshold level;

protective relays coupled to said circuit breaker for controlling its opening and closing;

a temperature sensor located in said substation for sensing at least one of;

a) the ambient temperature in said substation, b) the temperature of said power transformer and c) the temperature of the circuit breaker, and for producing a signal indicative of the second temperature;

means for sensing at least one of the voltage and current present in one of the primary and secondary windings and for producing a first signal indicative of the amplitude of any sensed voltage and current; and

a microcontroller for setting different threshold levels of the current breaker as a function of temperature, said microcontroller being responsive to said signal indicative of the sensed temperature from said temperature sensor and to said first signal, said microcontroller being programmed to be responsive to said signal indicative of the sensed temperature for calculating different threshold levels corresponding to different temperature signals and for producing an output signal corresponding to said calculations coupled to said protective relays for controlling the opening and closing of said circuit breaker as a function of the temperature sensed by said temperature sensor and the power being delivered by said transformer.

15. In a substation as claimed in claim 14 wherein the temperature sensor senses the temperature of at least two of:

(a) said ambient temperature in said substation, (b) the temperature of said power transformer, and (c) the temperature of the circuit breaker.

16. In a substation for transferring electric power from an input power line to an output power line, the combination comprising:

a circuit breaker connected between said output power line and a load means, said circuit breaker for interrupting the flow of current through the load when the load current exceeds a permissible threshold level, where the load may be located within, or outside, the substation;

a temperature sensor located in said substation for sensing at least one of;

(a) the ambient temperature in said substation and (b) the temperature of the circuit breaker; and

a microcontroller having an input and an output;

said microcontroller being programmed to determine different permissible threshold levels corresponding to different temperature conditions, the threshol level being generally higher for lower temperatures and lower for higher temperatures;

means coupling the temperature sensor to said input of said microcontroller for producing a threshold level signal condition at the output of the microcontroller which is a function of the temperature sensed by the temperature sensor; and

means coupling the output of the microcontroller to said circuit breaker for controlling the amplitude of load current at which said circuit breaker is opened and closed as a function of the threshold conditions resulting from the temperature signals from said temperature sensor.

17. In a substation as claimed in claim 16 wherein said means coupling the output of the microcontroller to said circuit beaker includes a protective relay, said protective relay having a trip point which is controlled by the signals produced at the output of the microcontroller.

18. In a substation as claimed in claim 17, wherein the microcontroller is preprogrammed to produce different output signals for different temperature input signals.

19. In a substation as claimed in claim 17, further including load current sensing means for sensing the load current flowing along said output power line and for producing a corresponding signal applied to an input of the microcontroller, whereby the microcontroller produces a signal applied to the protective relay which is a function of the temperature in the substation and the current level along the output power line.

20. In a substation for transferring electric power from an input power line to an output power line, the combination comprising:

a microcontroller programmed to establish different threshold values as a function of different temperatures;

a circuit breaker connected between said output power line and a load means, where the load may be located within, or outside, the substation;

said circuit breaker for interrupting the flow of current through the load when the load current exceeds a threshold value established by said microcontroller;

a protective relay coupled to said circuit breaker for controlling its opening and closing;

a temperature sensor located in said substation for sensing at least one of the ambient temperature in said substation and the temperature of the circuit breaker and for producing temperature signals indicative of the sensed temperature;

a load current sensing means for sensing the amplitude of the load current flowing through said output power line; and

said microcontroller being responsive to signals from said temperature sensor and from said load current sensing means for supplying signals setting the trip point of the protective relay for controlling the opening and closing of said circuit breaker as a function of the amplitude of the load current corresponding to the threshold value established for the corresponding value of temperature.