Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H1/00—Details of emergency protective circuit arrangements
  • H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
  • H02H1/0015—Using arc detectors
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
  • H02H3/50—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to the appearance of abnormal wave forms, e.g. ac in dc installations
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
  • H02H3/44—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to the rate of change of electrical quantities
  • H02H3/445—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to the rate of change of electrical quantities of DC quantities

Definitions

• This invention relates to detection of and/or protection against arcing in dc electrical systems including parallel arcs and series arcs.
• Overload protection is typically provided by either a thermal element which emulates the heating of the distribution wiring and opens a contact when the bimetal reaches a certain temperature, or an electronic circuit which simulates the same thermal process.
• Overcurrent protection is typically provided by an instantaneous trip feature which opens the circuit breaker rapidly if the current exceeds a particular threshold, such as would be reached by a short circuit, and is implemented by a magnetic trip device or an electronic simulation.
• a fuse is a disposable thermal trip unit with no instantaneous capability.
• Arc faults involve a highly concentrated region of heat production, a type of "hot spot", that can result in insulation breakdown, production of combustion products, and the ejection of hot metal particles. It can also result from broken conductors or poor connections.
• Arc faults can be series or parallel. Examples of a series arc are a broken wire where the ends are close enough to cause arcing, or a poor electrical com ection. Parallel arcs occur between conductors of different potential including a conductor and ground. Arc faults occur in series with the source and series arcs are further in series with the load. Arc faults have a relatively high impedance. Thus, a series arc results in a reduction in load current and is not detected by the normal overload and overcurrent protection of conventional protection devices. Even the parallel arc, which can draw current in excess of normal rated current in a circuit, produces currents which can be sporadic enough to yield RMS values less than that required to produce a thermal trip, or at least delay operation. Effects of the arc voltage and line impedance often prevent the parallel arc from reaching current levels sufficient to actuate the instantaneous trip function.
• This invention is directed to apparatus for detecting and protecting against arc faults, both series and parallel, in dc circuits. It includes detection of decreases in the voltage across or current through the load detected by a local sensor and analyzed either locally or remotely. In the case of remote analysis, the sensor and control information can be transmitted by a carrier on the branch circuit or by a separate communication link such as a multiplexed system. It further includes switches which isolate the arc fault locally by disconnecting an affected load downstream of the arc or by turning off the entire branch upstream.
• One aspect of the invention includes the detection of the repetitive step changes produced by the arc.
• series arcs can be detected by momentarily turning off the current upon detection of a step drop in current. If when the current is turned back on the amplitude is about the same as when it was turned off, then some other phenomenon was the cause. If the current after turn on is not about what it was after the step decrease, whether significantly greater, or less, an arc fault which has collapsed to a short or one which has collapsed to an open circuit has occurred, respectively.
• Figure 1 is a current waveform diagram for series arcs in a dc electrical system.
• Figure 2 is a voltage waveform produced by a series arc in a dc electrical system.
• Figure 3 is a schematic circuit diagram illustrating a first embodiment of the invention implementing local series arc detection and load shedding.
• Figure 4 is a schematic circuit diagram of a second embodiment of the invention implementing local detection and local load shedding with communication of source voltage.
• Figure 5 is a schematic circuit diagram of a third embodiment of the invention implementing local sensing for an arc fault with central arc fault detection and response.
• Figure 6 is a schematic circuit diagram of another embodiment employing a multiplexed system for communicating between the load and a central location.
• Figure 7 is a schematic circuit diagram of an embodiment which disconnects the current momentarily to extinguish the arc and then checks the current level.
• Figure 8 is a schematic circuit diagram of another embodiment which detects series arcs and can distinguish between series arcs which collapse to a short circuit and those which collapse to an open circuit.
• Figure 9 is a current waveform diagram for a parallel arc in a dc electrical system.
• Figure 10 is a schematic circuit diagram of an embodiment of the invention similar to that illustrated in Figure 3, but which responds to changes in dc load current.
• Figure 11 is a schematic circuit diagram of an embodiment of the invention similar to that illustrated in Figure 4, but which responds to changes in dc load current.
• Figure 12 is a schematic circuit diagram of an embodiment of the invention similar to that illustrated in Figure 5, but which responds to changes in dc load current.
• Figure 13 is a schematic circuit diagram of an embodiment of the invention similar to that illustrated in Figure 6, but which responds to changes in dc load current.
• Figures 1 and 2 illustrate typical examples of current and voltage waveforms, respectively, produced in a dc electrical system by a series arc.
• Figure 1 at initiation of the arc there are several step changes in current followed by a noisy sustained period. The arc then either collapses to a short, in which case the load current begins to drift upward and then jumps to its former value (trace A), until a second arc occurs, or the arc collapses to an open circuit in which case the current drifts downward and then falls to zero (trace B).
• Figure 2 illustrates that in a 42 volt dc system the source voltage shown in solid line and the voltage across the load shown in the dash line are both at 42 volts until an arc occurs. Voltage across the load then drops substantially as the arc introduces a substantial impedance in series with the load. We have found that a substantial reduction such as to less than about 75% of the normal system voltage is an indication of an arc. Thus, in a 42 volt system, if the voltage across the load falls below about 30 volts, a series arc is indicated. Notice that the source voltage can also be pulled down by the fault but a difference of at least about 12 volts exists between the source voltage and the voltage across the load.
• both the source and load voltage can return to normal until another arc occurs. It is also possible that the load voltage drops to zero if the arc extinguishes to an open circuit. Due to the effects of vibration and/or carbon, a restrike is still possible.
• Figure 3 illustrates schematically a dc electrical system 1 sourced by a battery 3 which can have, for example, a nominal voltage of 36 or 42 volts.
• the battery provides power to a number of branch circuits 5 each protected by a fuse 7 provided in a fuse or control box 9.
• Each branch circuit 5 provides power to one or more loads 11 1 , 11 2 .
• a series arc 13 at the location shown will not appreciably affect the voltage across the load Hi. However, as it is in series with the load 11 2 the voltage across this load will drop, as mentioned, about at least 25% or more initially.
• a detector 15 monitors the voltage across the load 11 2 through voltage sensor 16, and if it falls below a threshold value for more than a predetermined time period for example, for a 42 volt system, below about 30 volts for more than at least about 10 msec and preferably more than about 20 msec, an arc fault is indicated. Detection of the arc can be used to open a local switch 17 in series with the arc.
• FIG. 4 illustrates another embodiment of the invention in which a sensor 21 provides the voltage across the load 11 to a local processor 23.
• This processor also receives a signal representing the source voltage from the power control module 9.
• a source voltage sensor 25 in the power control module generates a signal representing the source voltage which is provided to a transmitter 27 which modulates a carrier signal launched onto the branch circuit 5.
• the modulated carrier signal is picked up by receiver 29 which provides the source voltage indication to the processor 23.
• the processor 23 then subtracts the voltage across the load from the source voltage and if the difference exceeds a selected value for more than a predetermined time period, an arc is indicated and the local switch 17 is opened.
• a series arc is indicated.
• the voltage across the load 11 is sensed locally, converted to a digital signal by the A/D converter 31 and used to modulate a carrier by the transmitter 27 for transmission over the branch circuit 5 to the power control module 9 where it is demodulated by a receiver 29 and provided to microprocessor 33.
• the microprocessor 33 checks for a series arc such as by determining whether the voltage across the load has dropped below the absolute threshold value or the locally measured value below the source voltage for the selected period of time, again, at least about 10 msec, but preferably about 20 msec.
• the microprocessor 33 can actuate a switch 35 in the power control module 9.
• This switch 35 can be, for instance, an arc fault current interrupter which also provides protection for parallel arcs.
• the microprocessor 33 is in the power control module, it is in a position to provide arc fault protection for all of the branch circuits 5.
• the information from the power control module or from the load can be communicated in a packet on a communications bus 34, typically through a sensor/actuator chip 36 as shown in the embodiment of Figure 6, other medium such as wireless communication could be used.
• series arcs could be detected by monitoring the current through the load rather than the voltage across the load. In that case, if the rated current through the load minus the sensed current divided by the rated current were less than a predetermined value such as for instance 0.7, a trip would be indicated. Again, the series arc places an impedance in series with the load which reduces the load current. If current is to be used, the rated current for each load must be known. And, for instance, if the load has multiple operating conditions, such as a number of speed settings, the rated current must be known for the operating condition. In addition to using the drop in current or voltage produced by a series arc, other logic could be used in the embodiments of Figures 3-6.
• This embodiment monitors the branch current for step changes in current.
• a step change in current could be due to the turning off or on of a load or a change in the operating condition of a load
• this technique calls for turning off the current momentarily when a step change of a selected magnitude is detected. This interruption of the current will extinguish an arc.
• an arc can collapse to a short circuit or to an open circuit.
• the current goes to the value before the step decrease, or it goes to zero, the phenomenon was an arc.
• the change in current was not due to an arc, but rather to some other activity in the circuit such as the turning off of a load.
• the period of turn off should be long enough to extinguish an arc, but not long enough to cause serious interruption to the loads.
• An exemplary turn off time is about 5 msec to about 30 msec.
• the protection circuit 37 which is provided in the power control module 9, includes a current sensor 39 and a solid state switch 41 connected in the branch circuit 5.
• the sensed current signal is applied to an event detector 43 which includes a bandpass filter 45 which detects the step change, and a negative step threshold detector 47 which responds to a step drop in current greater than a selected value, such as for instance, about 25% to about 80%, typically about 50%) in a 42V dc system.
• the occurrence of an event along with the sensed current is applied to a processor 49 which applies arc detection logic. Where the processor 49 is a digital processor, the sensed current is converted to a digital signal by an A/D converter provided with the processor.
• the occurrence of an event sets an instantaneous trip logic 51 which turns off the solid state switch 41 to interrupt the current in the branch circuit 5.
• the event signal also starts a timer 53 which measures the preselected disconnect time, such as about 5 to about 30 msec and then resets the instantaneous trip logic 51 to turn the solid state switch back on.
• the arc detection logic subtracts the current before the disconnect, but after the initial step decrease, from the current after the reconnection and divides by the current before the disconnect. If the absolute value of the result is less than a predetermined value, such as about 0.2, then no arc has occurred.
• the processor 49 again sets the instantaneous trip logic 51 to turn off the solid state switch and protect the branch 5 from the detected series arc fault.
• FIG 8 monitors the drift in current following the initial step changes in current produced by a series arc. Referring again to Figure 1, it can be seen that the series arc current either drifts slowly higher and then collapses to a short so that the current returns to its initial value before the arc, or it slowly drifts downward and then collapses to an open circuit. Therefore, in this embodiment of the invention any slow drift in current following a step decrease is identified. If the slow drift is upward, the stored value of current before the step decrease is compared with the value of current after the period of drift, for example, about 0.1 to about 1 second.
• this event detector 43 includes a bandpass filter and a negative threshold detector which detects step decreases in current of greater than a predetermined magnitude.
• Detection of the first step decrease in current starts a timer 57 and also enables a sample and hold circuit 59 which stores the value of the current before the step decrease which has been preserved by a delay circuit 61.
• a slow drift detector 63 which can be a low pass filter, also monitors the current.
• a sign detector 65 detects the polarity of the drift signal. If the polarity is positive, and the timer 57 is timed out, the stored initial current is compared with the existing current in processor 67. If these two currents are about equal, meaning that the arc has collapsed to a short, an arc to short signal is generated which is passed through an OR circuit 69.
• the integrated value of the sensed current is compared with the value for the previous corresponding time interval stored in a sample and hold circuit, with the indications of interval to interval increases and decreases in the integrated sensed values for a selected number, such as 6, of the most recent time intervals stored in a shift register.
• a chaos detector counts the number of changes between increases and decreases for the selected number of most recent corresponding time intervals and accumulates a weighted sum of the counts which is time attenuated. When the sum reaches a predetermined amount, an output such as a trip signal for a circuit breaker is generated.
• 5,933,305 uses time intervals which are multiples of the cycles of the fundamental frequency of the ac current, and are synchronized to the ac cycles by a zero crossing detector.
• the zero crossing detector is not needed and the integration interval is selected as a multiple of cycles of the dominant frequency of the step changes in current produced by an arc, for example about 120-500 Hz.
• this cyclic current integration comparison technique can also be used to detect series arcs as it is independent of the amplitude of the step changes in current produced by arcs and instead depends upon the randomness of the activity.
• the cyclic current integration comparison technique can even be used in a dc electrical system having a PWM drive, such as a light dimmer.
• the integration interval would be coordinated with the repetition rate of the PWM signal.
• the integration could be a multiple of the repetition rate and could even track a slowly changing repetition rate.
• the invention also embraces the detection of a drop in dc current drawn by a dc load to indicate the presence of a dc arc.
• Figures 10-13 illustrate application of this technique of detecting a drop in dc current to the distribution systems illustrated in Figures 3-6 where a drop in load voltage was used to detect arcing.
• a current sensor 75 senses current drawn by the load 11 2 and provides this measurement to the processor 15.
• the load 11 draws a rated current I rat ed-
• a series arc 13 in the branch circuit 5 servicing the load 11 2 introduces a sizeable impedance in series with the load which is sharing the source voltage with the load and results in a reduction in the sensed current drawn by the load 11 .
• an arcing signal is generated which can be used to open the switch 17 to disconnect the load 11 2 from the dc source, and/or provide an indication of the arcing event, such as by lighting an LED 19.
• the processor 23 is provided not only with the current drawn by the load 11 as sensed by the current sensor 77, but also the source voltage V source sensed by the voltage sensor 25 and transmitted over the branch line 5 by a transmitter 27 through modulation of a carrier signal.
• a receiver 29 demodulates the signal to extract the sensed dc source voltage for use by the processor 23.
• the processor 23 In order to accommodate for any variations in the dc source of voltage, the processor 23 generates an arcing signal if the current through the load 11 as sensed by the current sensor 77 is less than .75 of the rated current scaled to the dc source voltage, because if the source voltage drops, the current drawn by the load will drop by a proportional amount.
• the processor 23 is located proximate the load 11. Hence, the sensed dc source voltage had to be transmitted to the processor 23.
• the processor 33 is located remotely from the load 11 and the current drawn by the load 11 and sensed by the current sensor 77 has to be transmitted to the remote processor 33.
• the sensed current is digitized in analog to digital converter 81 and then used by the transmitter 27 to modulate a carrier signal that is sent over the branch circuit 5 and demodulated by the receiver 29 to extract the current signal for processing by the processor 33.
• the processor 33 like the processor 23, generates an arcing signal if the sensed dc current falls at least to .75 times the rated current scaled to the dc source voltage for a period of time, such as at least 10 msec, but preferably 20 msec.
• the arrangement in Figure 13 is similar to that in Figure 12, except that the sensed current detected by the current sensor 79 is provided to the processor 33 over an external communication system such as a multiplex system where information is passed between the power control module 9 and the load 11 in packets over a communication bus 34, typically through an actuator chip 81.
• an external communication system such as a multiplex system where information is passed between the power control module 9 and the load 11 in packets over a communication bus 34, typically through an actuator chip 81.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Emergency Protection Circuit Devices (AREA)
• Power Conversion In General (AREA)
• Control Of Motors That Do Not Use Commutators (AREA)

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• 2001
  • 2001-11-09 MX MXPA03004171A patent/MXPA03004171A/es active IP Right Grant
  • 2001-11-09 CN CNA01818720XA patent/CN1529929A/zh active Pending
  • 2001-11-09 KR KR10-2003-7006498A patent/KR20040028684A/ko not_active Application Discontinuation
  • 2001-11-09 AU AU2002230649A patent/AU2002230649A1/en not_active Abandoned
  • 2001-11-09 EP EP01990886A patent/EP1428303A2/en not_active Withdrawn
  • 2001-11-09 CA CA002426901A patent/CA2426901A1/en not_active Abandoned
  • 2001-11-09 JP JP2002541770A patent/JP3864381B2/ja not_active Expired - Fee Related
  • 2001-11-09 WO PCT/US2001/046929 patent/WO2002039561A2/en active Search and Examination

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