SHUTOFF DEVICE

• US 20180131173A1
• Filed: 03/25/2016
• Published: 05/10/2018
• Est. Priority Date: 04/22/2015
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Management Co., Ltd. (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Intellectual Property Management Co., Ltd. (Panasonic Holdings Corporation)
• Inventors: IWAMI, Eiji, IKUSHIMA, Tsuyoshi, FUKUO, Naoki, NISHIGAKI, Tomokazu
• Granted Patent: US 10,396,544 B2
• Time in Patent Office: Days
• CPC Class Codes: G01R 15/04 Voltage dividers
• CPC Class Codes: G01R 15/183 using transformers with a magnetic core
• CPC Class Codes: G01R 19/0015 separating AC and DC
• CPC Class Codes: G01R 19/16571 comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current G01R19/16514, G01R19/16519, G01R19/16528, G01R19/16533, G01R19/1659 take precedence; measuring currents by using elements sensitive to the magnetic field generated G01R15/14; measuring earth resistance G01R27/18; testing for leakage or short circuits in electrical apparatus G01R31/52
• CPC Class Codes: G01R 19/16576 comparing DC or AC voltage with one threshold G01R19/16514, G01R19/16519, G01R19/16528, G01R19/16533 and G01R19/1659 take precedence
• CPC Class Codes: G01R 19/20 using transductors , i.e. a magnetic core transducer the saturation of which is cyclically reversed by an AC source on the secondary side
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• CPC Class Codes: H02H 3/006 Calibration or setting of parameters
• CPC Class Codes: H02H 3/16 responsive to fault current to earth, frame or mass with balanced or differential arrangement H02H3/26 ; monitoring earth connection H02H5/105
• CPC Class Codes: H02H 3/332 with means responsive to dc component in the fault current

Abstract

A magnetic core is electromagnetically coupled to two conductors that allow an AC current to flow through. An exciter is configured to supply a winding with an excitation current that is an alternating current. A current detector is configured to detect a current flowing through the winding. A DC component detector is configured to detect a DC component level from the current detected with the current detector. Two contact elements are respectively disposed along the two conductors. A discrimination controller is configured to: turn the two contact elements on when the DC component level detected with the DC component detector is less than or equal to a threshold; turn the two contact elements off when the DC component level detected with the DC component detector is greater than the threshold; and turn the two contact elements off in de-energized condition.

Claims

1. A shutoff device, comprising

a magnetic core that is electromagnetically coupled to two conductors that allow an AC current to flow through,

a winding that is wrapped around the magnetic core,

an exciter that is configured to supply the winding with an excitation current that is an alternating current,

a current detector that is configured to detect a current flowing through the winding,

a DC component detector that is configured to detect a DC component level from the current detected with the current detector,

two contact elements that are respectively disposed along the two conductors, and

a discrimination controller that is configured to:

turn the two contact elements on when the DC component level detected with the DC component detector is less than or equal to a threshold;

turn the two contact elements off when the DC component level detected with the DC component detector is greater than the threshold; and

turn the two contact elements off in de-energized condition.

2. The shutoff device of claim 1, further comprising a storage device that is configured to store, as an offset value, the DC component level detected with the DC component detector when the two contact elements are off, wherein

the discrimination controller is configured to judge that the DC component level detected with the DC component detector is greater than the threshold, when a value obtained by subtracting the offset value from the DC component level detected with the DC component detector is greater than the threshold.

3. The shutoff device of claim 1, further comprising a storage device that is configured to store, as an offset value, the DC component level detected with the DC component detector when the two contact elements are off, wherein

the discrimination controller is configured to increase the threshold with an increase in the offset value.

4. The shutoff device of claim 3, wherein

the discrimination controller has a voltage divider circuit composed of resistors, and is configured to adjust the threshold based on voltage obtained by dividing constant voltage by the voltage divider circuit,

the resistors including at least one adjustment resistor,

the voltage divider circuit further includes at least one semiconductor switch individually connected to said at least one adjustment resistor, and

the discrimination controller is configured to individually turn said at least one semiconductor switch on or off according to the offset value, thereby varying a division ratio of the voltage divider.

5. The shutoff device of claim 1, wherein

the current detector comprises an impedance circuit that is configured to produce a voltage signal whose level is proportionate to a level of a current flowing through the winding, and

the exciter is configured to supply the winding with the excitation current whose amplitude varies according to the level of the voltage signal produced through the impedance circuit, the exciter having an adjuster circuit that is configured to adjust an impedance value of the impedance circuit.

6. The shutoff device of claim 5, wherein

the impedance circuit includes resistors connected in parallel, the resistors including at least one adjustment resistor, the impedance circuit further including at least one semiconductor switch individually connected in series to said at least one adjustment resistor, and

the adjuster circuit is configured to individually turn said at least one semiconductor switch of the impedance circuit on or off, thereby adjusting the impedance value of the impedance circuit.

7. The shutoff device of claim 5, wherein the adjuster circuit is configured to, when the two contact elements are off, adjust the amplitude of the excitation current to first amplitude for demagnetizing the magnetic core, and subsequently vary the impedance value of the impedance circuit so as to adjust the amplitude of the excitation current to second amplitude smaller than the first amplitude.

8. The shutoff device of claim 2, wherein

the current detector comprises an impedance circuit that is configured to produce a voltage signal whose level is proportionate to a level of a current flowing through the winding, and

the exciter is configured to supply the winding with the excitation current whose amplitude varies according to the level of the voltage signal produced through the impedance circuit, the exciter having an adjuster circuit that is configured to adjust an impedance value of the impedance circuit.

9. The shutoff device of claim 3, wherein

the current detector comprises an impedance circuit that is configured to produce a voltage signal whose level is proportionate to a level of a current flowing through the winding, and

the exciter is configured to supply the winding with the excitation current whose amplitude varies according to the level of the voltage signal produced through the impedance circuit, the exciter having an adjuster circuit that is configured to adjust an impedance value of the impedance circuit.

10. The shutoff device of claim 4, wherein

the current detector comprises an impedance circuit that is configured to produce a voltage signal whose level is proportionate to a level of a current flowing through the winding, and

the exciter is configured to supply the winding with the excitation current whose amplitude varies according to the level of the voltage signal produced through the impedance circuit, the exciter having an adjuster circuit that is configured to adjust an impedance value of the impedance circuit.

11. The shutoff device of claim 8, wherein

the impedance circuit includes resistors connected in parallel, the resistors including at least one adjustment resistor, the impedance circuit further including at least one semiconductor switch individually connected in series to said at least one adjustment resistor, and

the adjuster circuit is configured to individually turn said at least one semiconductor switch of the impedance circuit on or off, thereby adjusting the impedance value of the impedance circuit.

12. The shutoff device of claim 9, wherein

the impedance circuit includes resistors connected in parallel, the resistors including at least one adjustment resistor, the impedance circuit further including at least one semiconductor switch individually connected in series to said at least one adjustment resistor, and

the adjuster circuit is configured to individually turn said at least one semiconductor switch of the impedance circuit on or off, thereby adjusting the impedance value of the impedance circuit.

13. The shutoff device of claim 10, wherein

the impedance circuit includes resistors connected in parallel, the resistors including at least one adjustment resistor, the impedance circuit further including at least one semiconductor switch individually connected in series to said at least one adjustment resistor, and

the adjuster circuit is configured to individually turn said at least one semiconductor switch of the impedance circuit on or off, thereby adjusting the impedance value of the impedance circuit.

14. The shutoff device of claim 6, wherein the adjuster circuit is configured to, when the two contact elements are off, adjust the amplitude of the excitation current to first amplitude for demagnetizing the magnetic core, and subsequently vary the impedance value of the impedance circuit so as to adjust the amplitude of the excitation current to second amplitude smaller than the first amplitude.

15. The shutoff device of claim 8, wherein the adjuster circuit is configured to, when the two contact elements are off, adjust the amplitude of the excitation current to first amplitude for demagnetizing the magnetic core, and subsequently vary the impedance value of the impedance circuit so as to adjust the amplitude of the excitation current to second amplitude smaller than the first amplitude.

16. The shutoff device of claim 9, wherein the adjuster circuit is configured to, when the two contact elements are off, adjust the amplitude of the excitation current to first amplitude for demagnetizing the magnetic core, and subsequently vary the impedance value of the impedance circuit so as to adjust the amplitude of the excitation current to second amplitude smaller than the first amplitude.

17. The shutoff device of claim 10, wherein the adjuster circuit is configured to, when the two contact elements are off, adjust the amplitude of the excitation current to first amplitude for demagnetizing the magnetic core, and subsequently vary the impedance value of the impedance circuit so as to adjust the amplitude of the excitation current to second amplitude smaller than the first amplitude.

18. The shutoff device of claim 11, wherein the adjuster circuit is configured to, when the two contact elements are off, adjust the amplitude of the excitation current to first amplitude for demagnetizing the magnetic core, and subsequently vary the impedance value of the impedance circuit so as to adjust the amplitude of the excitation current to second amplitude smaller than the first amplitude.

19. The shutoff device of claim 12, wherein the adjuster circuit is configured to, when the two contact elements are off, adjust the amplitude of the excitation current to first amplitude for demagnetizing the magnetic core, and subsequently vary the impedance value of the impedance circuit so as to adjust the amplitude of the excitation current to second amplitude smaller than the first amplitude.

20. The shutoff device of claim 13, wherein the adjuster circuit is configured to, when the two contact elements are off, adjust the amplitude of the excitation current to first amplitude for demagnetizing the magnetic core, and subsequently vary the impedance value of the impedance circuit so as to adjust the amplitude of the excitation current to second amplitude smaller than the first amplitude.