Arc fault detection system and method and circuit interrupter employing same
A DC arc fault detection module includes an LF current section, an LF voltage section, and an HF current section having a plurality of outputs, each output being associated with a respective one of a plurality of frequency sub-bands. The HF current section is structured to, for each of the frequency sub-bands, (i) detect a rise in energy of the frequency sub-band above a first predetermined threshold level for at least a certain amount of time and (ii) cause the associated output to indicate a rise in energy detection in response to detecting the rise in energy above the associated threshold level for at least the associated certain amount of time. The module includes a processing device structured to determine whether a DC arc fault has occurred based on the outputs from the LF and HF current and LF voltage sections.
1. An arc fault detection module for detecting arc faults in a DC electrical system having a DC supply line, comprising:
a low frequency current section having a first output, the low frequency current section being structured to detect a rise in a low frequency current of the DC supply line above a first predetermined threshold level and cause the first output to indicate a rise in current detection in response to detecting the rise in the low-frequency current above the first predetermined threshold level;
a low frequency voltage section having a second output, the low frequency voltage section being structured to detect a dip in a voltage of the DC supply line below a second predetermined threshold level and cause the second output to indicate a dip in voltage detection in response to detecting the dip in the voltage below the second predetermined threshold level; and
a high frequency current section having a plurality of third outputs, each third output being associated with a respective one of a plurality of frequency sub-bands of a predetermined frequency band, the high-frequency current section being structured to, for each of the frequency sub-bands, (i) detect a rise in energy of the frequency sub-band above a third predetermined threshold level associated with the frequency sub-band for at least a certain amount of time associated with the frequency sub-band and (ii) cause the third output associated with the frequency sub-band to indicate a rise in energy detection in response to detecting the rise in energy of the frequency sub-band above the associated third predetermined threshold level for at least the associated certain amount of time; and
a processing device structured to: (i) receive the first output, the second output, and each of the associated third outputs, and (ii) determine whether an arc fault in the DC electrical system has occurred based on the first output, the second output, and each of the associated third outputs.
2. The arc fault detection module according to claim 1 , wherein the processing device is further structured to make a first flag active in response to the first output to indicating a rise in current detection, make a second flag active in response to the second output indicating a rise in voltage detection, and make each of a plurality of third flags active in response to receiving a respective one of the third outputs corresponding to the third flag indicating a rise in energy detection, and wherein the processing device is structured to determine whether an arc fault in the DC electrical system has occurred based on a state of each of the first flag, the second flag, and each of the plurality of third flags.
3. The arc fault detection module according to claim 2 , wherein the processing device is structured to determine that an arc fault in the DC electrical system has occurred by (i) determining that the first flag is active, (ii) starting a timer in response to determining that the first flag is active, and (iii) before the timer expires, determining that the second flag is active and that each of the third flags is active.
4. The arc fault detection module according to claim 3 , wherein the processing device is structured to activate a trip signal for tripping a number of separable contacts in response to determining that an arc fault in the DC electrical system has occurred.
5. The arc fault detection module according to claim 1 , wherein the high frequency current section includes, for each of the frequency sub-bands: circuitry for filtering a signal indicative of current on the DC supply line and providing a filtered signal for only the frequency sub-band, an RF demodulator for generating a lower frequency signal for the frequency sub-band based on the filtered signal for only the frequency sub-band, and a threshold comparator and timer circuit for determining whether the lower frequency signal exceeds the third predetermined threshold level associated with the frequency sub-band for at least the certain amount of time associated with the frequency sub-band.
6. The arc fault detection module according to claim 1 , wherein the low frequency current section includes a threshold detection circuitry for determining whether a signal indicative of the low-frequency current on the DC supply line exceeds the first predetermined threshold level.
7. The arc fault detection module according to claim 6 , wherein the threshold detection circuitry includes a threshold crossing detector coupled to a monostable multivibrator.
8. The arc fault detection module according to claim 1 , wherein the low frequency voltage section includes a threshold detection circuitry for determining whether a signal indicative of the low-frequency voltage on the DC supply line exceeds the second predetermined threshold level.
9. The arc fault detection module according to claim 8 , wherein the threshold detection circuitry includes a threshold crossing detector coupled to a monostable multivibrator.
10. The arc fault detection module according to claim 1 , wherein the processing device is further structured to: (i) determine an estimation of background noise based on at least one signal indicative of a current on the DC supply line, and (ii) for each of the frequency sub-bands, adjust the third predetermined threshold level associated with the frequency sub-band based on the estimation of background noise.
11. The arc fault detection module according to claim 5 , wherein the processing device is further structured to: (i) determine an estimation of background noise based on at least the lower frequency signal for each of the frequency sub-bands, and (ii) for each of the frequency sub-bands, adjust the third predetermined threshold level associated with the frequency sub-band based on the estimation of background noise.
12. The arc fault detection module according to claim 11 , wherein the processing device is further structured to determine the estimation of background noise based on at least the lower frequency signal for each of the frequency sub-bands and a signal indicative of the low-frequency current on the DC supply line.
13. The arc fault detection module according to claim 1 , wherein the plurality of frequency sub-bands include a first sub-band, a second sub-band, and a third sub-band.
14. The arc fault detection module according to claim 13 , wherein the first sub-band is 10-30 kHz, the second sub-band is 140-160 kHz, and the third sub-band is 290-310 kHz.
15. A method of detecting arc faults in a DC electrical system having a DC supply line, comprising:
detecting that all of the following events have occurred in sync with one another: (i) a rise in a low frequency current of the DC supply line above a first predetermined threshold level, (ii) a dip in a voltage of the DC supply line below a second predetermined threshold level, and (iii) for each of a plurality of frequency sub-bands of a predetermined frequency band, a rise in energy of the frequency sub-band above a third predetermined threshold level associated with the frequency sub-band for at least a certain amount of time associated with the frequency sub-band; and
in response to the detecting, determining that an arc fault in the DC electrical system has occurred.
16. The method according to claim 15 , wherein the plurality of frequency sub-bands include a first sub-band, a second sub-band, and a third sub-band.
17. The method according to claim 16 , wherein the first sub-band is 10-30 kHz, the second sub-band is 140-160 kHz, and the third sub-band is 290-310 kHz.
18. The method according to claim 15 , wherein the detecting that (i), (ii) and (iii) have occurred in sync with one another comprises detecting that (i), (ii) and (iii) have all occurred within a certain time period.
19. The method according to claim 18 , wherein the detecting that (i), (ii) and (iii) have occurred in sync with one another comprises detecting (i), and detecting (ii) and (iii) within a predetermined time window following the detecting of (i).
20. The method according to claim 15 , further comprising activating a trip signal for tripping a number of separable contacts in response to determining that an arc fault in the DC electrical system has occurred.
21. The method according to claim 15 , wherein the detecting a rise in energy of the frequency sub-band above a third predetermined threshold level associated with the frequency sub-band for at least a certain amount of time associated with the frequency sub-band includes, for each of the frequency sub-bands, filtering a signal indicative of current on the DC supply line and providing a filtered signal for only the frequency sub-band, and generating a lower frequency signal for the frequency sub-band based on the filtered signal for only the frequency sub-band, and determining whether the lower frequency signal exceeds the third predetermined threshold level associated with the frequency sub-band for at least the certain amount of time associated with the frequency sub-band.
22. The method according to claim 15 , further comprising: (i) determining an estimation of background noise based on at least one signal indicative of a current on the DC supply line, and (ii), for each of the frequency sub-bands, adjusting the third predetermined threshold level associated with the frequency sub-band based on the estimation of background noise.
23. The method according to claim 21 , further comprising: (i) determining an estimation of background noise based on at the least lower frequency signal for each of the frequency sub-bands, and (ii) for each of the frequency sub-bands, adjusting the third predetermined threshold level associated with the frequency sub-band based on the estimation of background noise.
24. The method according to claim 23 , further comprising, for each of the frequency sub-bands, determining the estimation of background noise based on at least the lower frequency signal for each of the frequency sub-bands and a signal indicative of the low-frequency current on the DC supply line.