Claims
- 1. An arc fault detector for a circuit comprising:
a current shunt resistor coupled in series with said circuit; and an arc discriminator comprising an amplifier sensing a first voltage on a first side of said current shunt resistor, sensing a second voltage on a second side of said current shunt resistor, and producing a first signal proportional to a current flow through said current shunt resistor, said arc discriminator further comprising a change detector receiving said first signal as input and producing an arc fault detection signal as output when said change detector detects a change in said first signal indicative of a presence of an arc fault in said circuit.
- 2. The arc fault detector as recited in claim 1 wherein said change detector comprises a first splitter receiving said first signal as input and providing a second and a third signal as outputs, a delay circuit receiving said second signal as input and producing a delayed signal having a predetermined delay as output, a reference circuit receiving said third signal as input and producing a reference signal as output, and a comparator receiving said delayed signal and said reference signal as inputs, and producing said arc fault detection signal as an output when a difference between said reference signal and said delay signal satisfies a predetermined criteria.
- 3. The arc fault detector as recited in claim 2 wherein said delay circuit comprises an R−C circuit.
- 4. The arc fault detector as recited in claim 2 wherein said delay circuit comprises a low pass filter.
- 5. The arc fault detector as recited in claim 4 wherein said reference circuit comprises an amplifier.
- 6. The arc fault detector as recited in claim 5 wherein said first splitter comprises a buffer.
- 7. The arc fault detector as recited in claim 1, wherein said change detector comprises a series arc detector and a parallel arc detector.
- 8. The arc fault detector as recited in claim 1 wherein said change detector comprises a first buffer having an input coupled to said amplifier, said first buffer having a first and second output; a delay circuit coupled to said first output of said first buffer, said delay circuit providing a delayed signal as an output; a reference circuit coupled to said second output of said first buffer, said reference circuit providing a reference signal as an output; a first comparator having a first input coupled to said delay circuit and a second input coupled to said reference circuit, wherein said first comparator is configured to provide a series arc detection signal only when there is a decrease in voltage of said first signal which thereby causes the voltage of said reference signal to be less than said voltage of said delayed signal; and a logic gate having a first input coupled to said first comparator, said logic gate being configured to generate said arc fault detection signal as an output when said series arc fault detection signal is detected by said first input.
- 9. The arc fault detector as recited in claim 1 wherein said change detector comprises a first buffer having an input coupled with said amplifier, said first buffer having a first and second output; a delay circuit coupled to said first output of said second buffer, said delay circuit providing a delayed signal as an output; a reference circuit coupled to said second output of said first buffer, said reference circuit providing a reference signal as an output; a second comparator having a first input coupled to said delay circuit and a second input coupled to said reference circuit, wherein said second comparator is configured to provide a parallel arc detection signal only when there is a increase in voltage of said first signal which thereby causes the voltage of said reference signal to be greater than said voltage of said delayed signal; and a logic gate having a second input coupled to said second comparator, said logic gate being configured to generate said arc fault detection signal as an output when said parallel arc fault detection signal is detected by said second input.
- 10. An arc fault detector for a circuit comprising:
a current monitor detecting a rate of change in electrical current in said circuit and producing a first signal indicative of said rate of change; a filter connected in series with said current monitor filtering said first signal to substantially eliminate signals outside a selected frequency range, said filter outputting a filtered signal representing changes in said electrical current within said selected frequency range; and an arc determiner producing an arc detection signal when a voltage level of said filtered signal exceeds at least one threshold.
- 11. The arc fault detector as recited in claim 10 wherein said current monitor comprises a coil and a toroidal core.
- 12. The arc fault detector as recited in claim 10 wherein said arc determiner comprises an amplifier.
- 13. The arc fault detector as recited in claim 11 further comprising:
an attenuator connected in series with said current monitor and said filter, said attenuator attenuating at least one of said first and filtered signal, said attenuator comprising a resistor selected so that said voltage level of said filtered signal when generated by operation of a motor commutator is lower than said at least one threshold.
- 14. The arc fault detector as recited in claim 13 wherein said arc determiner comprises a Schmitt Trigger.
- 15. The arc fault detector as recited in claim 10 further comprising a switch transient detector detecting an arc condition caused by an opening of a switch under load, said switch transient detector detecting a voltage differential across said switch and providing a switch transient signal when said voltage differential exceeds a reference value.
- 16. The arc fault detector as recited in claim 15 further comprising:
a switch controller sensing said arc detection signal and switch transient signal and outputting a trip signal, said switch controller being configured such that it is inhibited from outputting a trip signal when it detects a switch transient signal.
- 17. A method of detecting an arc fault in a circuit comprising:
coupling a current shunt resistor in said circuit; monitoring a voltage differential across said current shunt resistor; detecting a change in said voltage differential; comparing said change to at least one threshold; and generating a signal when said change exceeds said at least one threshold.
- 18. A method of detecting an arc fault in a system comprising:
providing a coil wrapped around a toroidal core; passing at least one conductor of said system through the center of said toroidal core; detecting a voltage induced in said coil by a change in current flowing through said at least one conductor; filtering said voltage so as to eliminate signals outside a selected frequency range and to produce a filtered signal; comparing said filtered signal to at least one threshold; and generating an arc detection signal when said filtered signal exceeds said at least one threshold.
PRIORITY
[0001] This application claims benefit of priority from U.S. provisional patent application Ser. No. 60/465461, filed Apr. 24, 2003, which is hereby incorporated by reference.
Provisional Applications (1)
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Number |
Date |
Country |
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60465061 |
Apr 2003 |
US |