Electronic trip units powered by current transformers and circuit breakers comprising the same

Patent metadata

Field	Value
Publication number	US-9842709-B2
Application number	US-201514663890-A
Country	US
Kind code	B2
Filing date	Mar 20, 2015
Priority date	Mar 20, 2015
Publication date	Dec 12, 2017
Grant date	Dec 12, 2017

Abstract

A circuit breaker includes a set of separable contacts moveable between a closed position and an open position, an operating mechanism configured to open the set of contacts, a conductor coupled to the set of contacts, a current transformer coupled to the conductor, and a trip circuit coupled to the operating mechanism and to the current transformer and configured to cause the operating mechanism to open the set of contacts when a current through the conductor exceeds a current threshold that is greater than a saturation threshold of the current transformer. The trip circuit is further configured to vary the current threshold during an interval following a closure of the set of the contacts and to provide a fixed current threshold thereafter.

First claim

What is claimed is:

1. A circuit breaker comprising:
a set of separable contacts moveable between a closed position and an open position;
an operating mechanism configured to open the set of contacts;
a conductor coupled to the set of contacts;
a current transformer coupled to the conductor;
a trip circuit coupled to the operating mechanism and to the current transformer and configured to cause the operating mechanism to open the set of contacts when a current level through the conductor exceeds a current threshold that is greater than a saturation threshold of the current transformer; and
a peak detection circuit configured to detect a peak value of an output current from the current transformer which exceeds a reference peak value,
wherein the reference peak value is configured to rise from an initial reference peak value during an initial period after power is applied to the circuit breaker to a steady-state reference peak value during a steady-state period after the initial period.

2. The circuit breaker of claim 1 , further comprising a power supply circuit coupled to the current transformer and configured to supply power to the trip circuit from the current transformer.

3. The circuit breaker of claim 1 , wherein the trip circuit is configured to vary a level of the current threshold based on a state of the set of contacts.

4. The circuit breaker of claim 3 , wherein the trip circuit is configured to increase the current threshold from an initial current threshold value during an interval following a closure of the set of contacts to a steady-state current threshold value thereafter,
wherein the steady-state current threshold value is greater than the initial current threshold value.

5. The circuit breaker of claim 4 , wherein the trip circuit comprises:
a current detection circuit coupled to the current transformer and configured to generate a current detection signal responsive thereto;
a reference signal generator circuit configured to generate a reference signal that varies during the interval following the closure of the set of contacts; and
a trip signal generator circuit configured to generate a trip signal responsive to a comparison of the current detection signal to the reference signal.

6. The circuit breaker of claim 1 , further comprising a thermal sensor thermally coupled to the conductor and configured to generate a temperature signal and wherein the trip circuit is further configured to open the set of contacts responsive to the temperature signal.

7. The circuit breaker of claim 6 , wherein the thermal sensor comprises a thermal diode and wherein the trip circuit is further configured to open the set of contacts responsive to a voltage across the thermal diode.

8. The circuit breaker of claim 6 , wherein the thermal sensor comprises a first thermal sensor that generates a first temperature signal, wherein the circuit breaker further comprises a second thermal sensor configured to generate a second temperature signal indicating an ambient temperature of the circuit breaker, and wherein the trip circuit is further configured to open the set of contacts responsive to the first and second temperature signals.

9. The circuit breaker of claim 8 , wherein the trip circuit is configured to open the set of contacts responsive to a comparison of the first temperature signal to a reference temperature signal, and wherein the trip circuit is configured to vary the reference temperature signal responsive to the second temperature signal.

10. The circuit breaker of claim 1 ,
wherein the reference peak value corresponds to the current level through the set of contacts at which the trip circuit is configured to cause the operating mechanism to open the set of contacts.

11. The circuit breaker of claim 1 , wherein the rise of the reference peak value from the initial reference peak value to the steady-state reference peak value is responsive to a charging of a capacitor by an output of the current transformer.

12. The circuit breaker of claim 1 , wherein the steady-state reference peak value is configured to be dynamically adjustable by altering a variable resistor element within the trip circuit.

13. The circuit breaker of claim 1 , wherein the peak detection circuit is configured to detect the peak value of the output current from the current transformer by comparing a first signal corresponding to the output current from the current transformer to a reference voltage corresponding to the reference peak value.

14. The circuit breaker of claim 13 , further comprising a reference voltage generating circuit configured to generate the reference voltage,
wherein the reference voltage generating circuit comprises at least one reference voltage capacitor configured to store the reference voltage based on a secondary output voltage that corresponds to the output current from the current transformer.

15. The circuit breaker of claim 13 , wherein a level of the reference voltage is generated based on the output current from the current transformer.

16. The circuit breaker of claim 13 , further comprising an input delay circuit configured to delay comparing the first signal corresponding to the output current from the current transformer to the reference voltage corresponding to the reference peak value.

17. The circuit breaker of claim 16 , wherein the input delay circuit delays comparing the first signal corresponding to the output current from the current transformer to the reference voltage corresponding to the reference peak value for 1 to 2 milliseconds.

18. The circuit breaker of claim 1 , wherein the trip circuit is configured to cause the operating mechanism to open the set of contacts responsive to the peak detection circuit detecting that the peak value of the output current from the current transformer exceeds the reference peak value.

19. The circuit breaker of claim 18 , wherein the trip circuit is configured to cause the operating mechanism to open the set of contacts responsive to a first peak value of the output current from the current transformer during the initial period after power is applied to the circuit breaker,
wherein the trip circuit is configured to cause the operating mechanism to open the set of contacts responsive to a second peak value of the output current from the current transformer during the steady-state period after the initial period, and
wherein the second peak value is greater than the first peak value.

20. A circuit breaker comprising:
a set of separable contacts moveable between a closed position and an open position;
an operating mechanism configured to open the set of contacts;
a conductor coupled to the set of contacts;
a current transformer coupled to the conductor; and
a trip circuit coupled to the operating mechanism and to the current transformer and configured to cause the operating mechanism to open the set of contacts when a current level through the conductor exceeds a current threshold that is greater than a saturation threshold of the current transformer,
wherein the trip circuit is configured to vary the current threshold during an interval following a closure of the set of contacts and to provide a fixed current threshold thereafter,
wherein the trip circuit comprises:
a current detection circuit coupled to the current transformer and configured to generate a current detection signal responsive thereto;
a reference signal generator circuit configured to generate a reference signal that varies during the interval following the closure of th

Assignees

• Eaton Corp

Inventors

• Zheng Gerald
• Zhou Xin
• Lagree James Leo
• Miller Theodore James
• Wu Bruce
• Ouyang Sui

Classifications

• H01H37/32

  Thermally-sensitive members · CPC title

• H01H71/125

  characterised by sensing elements, e.g. current transformers (for differential protection H01H83/144) · CPC title

• H02H1/046

  upon detecting saturation of current transformers (for differential protection H02H3/283) · CPC title

• H02H3/08

  responsive to excess current (responsive to abnormal temperature caused by excess current H02H5/04) · CPC title

• H01H83/20

  operated by excess current as well as by some other abnormal electrical condition · CPC title