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

Patent metadata

Field	Value
Publication number	US-2016276115-A1
Application number	US-201514663890-A
Country	US
Kind code	A1
Filing date	Mar 20, 2015
Priority date	Mar 20, 2015
Publication date	Sep 22, 2016
Grant date	—

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; 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.

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 vary the current threshold during an interval following a closure of the set of contacts and to provide a fixed current threshold thereafter.

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 5 , wherein the reference signal generator circuit comprises:
a voltage regulator with an input voltage coupled to an output of the current transformer, and an output voltage coupled to a first node; a first resistor and a first capacitor connected in parallel, and coupled to the first node and to a second node; and a second resistor and a second capacitor connected in parallel, and coupled to the second node and to ground.

7 . The circuit breaker of claim 6 , wherein the trip signal generator circuit comprises:
a first variable resistor coupled to the current detection signal; and an instantaneous trip comparator with a first input coupled to the second node and a second input coupled to the first variable resistor, wherein the trip signal is an output of the instantaneous trip comparator.

8 . 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.

9 . The circuit breaker of claim 8 , 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.

10 . The circuit breaker of claim 8 , 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.

11 . The circuit breaker of claim 10 , 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.

12 . The circuit breaker of claim 1 , wherein the trip circuit further comprises:
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 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.

13 . The circuit breaker of claim 12 , wherein the reference peak value is configured to rise from an initial reference peak value to a steady-state reference peak value when power is applied to the circuit breaker.

14 . The circuit breaker of claim 13 , 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.

15 . The circuit breaker of claim 13 , wherein the steady-state reference peak value is configured to be dynamically adjustable by altering a variable resistor element within the trip circuit.

16 . 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 thermal diode thermally coupled to the conductor; and a trip circuit coupled to the operating mechanism and to the thermal diode and configured to cause the operating mechanism to open the set of contacts responsive to the thermal diode.

17 . The circuit breaker of claim 16 , further comprising an ambient thermal sensor configured to measure an ambient temperature of the circuit breaker and wherein the trip circuit is configured to cause the operating mechanism to open the set of contacts responsive to the thermal diode and the ambient thermal sensor.

18 . The circuit breaker of claim 17 , wherein the trip circuit is configured to open the set of contacts responsive to a comparison of a temperature signal from the thermal diode to a reference temperature signal, and wherein the trip circuit is configured to vary the reference temperature signal responsive to an ambient temperature signal from the ambient thermal sensor.

19 . The circuit breaker of claim 18 wherein the reference temperature signal is configured to be dynamically adjusted by altering a variable resistor element within the trip circuit.

20 . The circuit breaker of claim 16 , wherein the trip circuit is a first trip circuit and further comprising:
a current transformer coupled to the conductor; and a second trip circuit coupled to the current transformer and the operating mechanism and configured to cause the operating mechanism to open the set of contacts responsive to a current level through the set of contacts that is greater than a saturation level of the current transformer.

21 . The circuit breaker of claim 20 , wherein the first trip circuit and the second trip circuit are powered by the output of the current transformer.

22 . 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 first thermal sensor thermally coupled to the conductor and configured to generate a first temperature signal indicating a temperature of the conductor; a second thermal sensor configured generate a second temperature signal indicating an ambient temperature of the circuit breaker; and a trip circuit coupled to the operating mechanism and to the first and second thermal

Assignees

• Eaton Corp

Inventors

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

Classifications

• H02H1/0007

  concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445) · CPC title

• H01H9/54 Primary

  Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere · CPC title

• H01H2011/0068

  measuring the temperature of the switch or parts thereof · CPC title

• H01H83/20

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

• H01H71/123 Primary

  using a solid-state trip unit (circuits H02H) · CPC title