CA2307537A1 - Arc fault circuit interrupter without dc supply - Google Patents
Arc fault circuit interrupter without dc supply Download PDFInfo
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- CA2307537A1 CA2307537A1 CA 2307537 CA2307537A CA2307537A1 CA 2307537 A1 CA2307537 A1 CA 2307537A1 CA 2307537 CA2307537 CA 2307537 CA 2307537 A CA2307537 A CA 2307537A CA 2307537 A1 CA2307537 A1 CA 2307537A1
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- 230000008030 elimination Effects 0.000 abstract 1
- 238000003379 elimination reaction Methods 0.000 abstract 1
- 230000009471 action Effects 0.000 description 10
- 230000007246 mechanism Effects 0.000 description 8
- 238000001514 detection method Methods 0.000 description 7
- 239000004020 conductor Substances 0.000 description 6
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- 238000010586 diagram Methods 0.000 description 3
- 238000007600 charging Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000010278 pulse charging Methods 0.000 description 2
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- 101000713935 Mus musculus Tudor domain-containing protein 7 Proteins 0.000 description 1
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Abstract
Arcing faults are detected by sensing a voltage signal proportional to the rate of change, or di/dt, of the line current when the current steps into an arc fault. A current transformer is used to create the di/dt signal.
The transformer has a selected core type, number of windings, and size which saturates at a pre determined level of primary current. The saturation acts to clamp the maximum di/dt voltage signal at the transformer output, and produce a constant output voltage. The constant output voltage eliminates a signal with a high di/dt, which may occur during a lamp burnout, from producing a much larger di/dt signal than that caused by an arc fault at a lower level of step current. The di/dt signal is passed through a high pass filter, which attenuates 60hz sinusoidal signals, after which the signal is integrated. The integrator acts to delay circuit interruption means until a predetermined number of arcs has occurred. When the integrator voltage reaches a predetermined voltage level, a trigger device activates an electronic switch, which in turn activates circuit interrupting means. One of the novel aspects of this invention is the elimination of the need for a DC power supply.
The transformer has a selected core type, number of windings, and size which saturates at a pre determined level of primary current. The saturation acts to clamp the maximum di/dt voltage signal at the transformer output, and produce a constant output voltage. The constant output voltage eliminates a signal with a high di/dt, which may occur during a lamp burnout, from producing a much larger di/dt signal than that caused by an arc fault at a lower level of step current. The di/dt signal is passed through a high pass filter, which attenuates 60hz sinusoidal signals, after which the signal is integrated. The integrator acts to delay circuit interruption means until a predetermined number of arcs has occurred. When the integrator voltage reaches a predetermined voltage level, a trigger device activates an electronic switch, which in turn activates circuit interrupting means. One of the novel aspects of this invention is the elimination of the need for a DC power supply.
Description
ARC FAULT CIRCUIT INTERRUPTER WITHOUT DC SUPPLY
Cross reference to related applications:
This application is a continuation-in-part of Serial No.
09/211,747 filed December 15, 1998.
S Background of the Invention:
Field of the Invention:
This invention relates to an apparatus for detecting arc faults in electrical power lines, and more particularly to apparatus that does not include a DC power supply.
Description of the Prior Art:
A number of devices and methods have been used in the past to detect arc faults. Some of the prior art devices and techniques have involved the use of E and B field arc sensors, the detection of the amplitude of arc fault rate of change of current signals, the use of non-15 overlapping band-pass filters to detect white noise of arcs, and devices which detect the disappearance of arc faults near current zero crosses.
Most of the prior art of arc detection occurs in circuit breakers where it acts as an enhancement to thermal-magnetic detection elements, which alone may fail to detect arc faults.
20 There is a need for an economical arc fault detector which may be mounted into a wiring device which offers the same down stream protection as an arc fault detecting circuit breaker but at the similar cost advantage that currently exist between ground fault interrupting receptacles and ground fault interrupting circuit breakers. This invention 25 provides that cost advantage.
Summary of the invention:
It is an object of this invention to provide an arc fault circuit interrupter that is simpler and less expensive to manufacture than those previously known. Briefly stated, and in accordance with a presently 30 preferred embodiment of the invention, an arc fault detecting circuit includes a saturating current transformer coupled to the electric power circuit to be protected that senses di/dt arc fault steps in current. A
rectifier is preferably connected to the sensor, and an integrator is connected to the rectifier. The integrator voltage is used to activate a trigger device. The trigger device activates circuit interrupting means.
The device does not require a DC power supply as found in the prior art .
The saturating current transformer produces a constant output voltage at a pre determined level of arc fault current. This eliminates the effect of brief high current pulses of short duration from having the same effect on the detector as a series of smaller amplitude arc faults steps.
In accordance with a further embodiment of the invention, a second integrator and trigger device is used instead of a saturating transformer to mitigate the effect of normal switching arcs and also the brief high current arc pulses.
In accordance with another embodiment of the invention, an inhibit switch is placed between the integrator and trigger device, where it acts to inhibit the di/dt charging integrator from activating the trigger device unless the associated peak 60 Hz component of arc current exceeds a predetermined value.
Brief description of the drawings:
FIG. 1(a-b) illustrate the circuit in which arc fault detection is performed;
FIG. 2 illustrates another embodiment of the circuit of FIG. 1 showing an additional integrator element with a discharge diac;
FIG. 3 is a schematic diagram of an art fault circuit interrupter in accordance with another embodiment of the invention; and FIG. 4(a-e) illustrates waveforms in the circuit of FIG. 3.
Description of the~referred embod'ment~
An arc fault detector in accordance with this invention is intended for incorporation into a.receptacle, plug, or cord type device which is mechanically similar to ground fault interrupter devices such as those shown in U.S. Pats. No. 5,594,358, and 5,510,760.
Referring now to FIG. 1 a, one embodiment of the invention is shown in schematic diagram form, showing an electrical power line, comprising line side neutral and hot conductors 6 and 7 respectively, load neutral and hot conductors 50 and 51 respectively and a load 52. The load neutral SO and hot 51 conductors are both protected by contactor mechanism 45. Contactor mechanism 45 is a spring loaded mouse trap type device, which is controlled by trip mechanism 44. Conduction of SCR 41 activates solenoid 43 which activates trip mechanism 44. When the trip mechanism is activated, the spring loaded contacts 26 and 28 latch open, and stay open until they are manually reset.
An arc fault sensing current transformer 1 is wrapped with a secondary winding 4, which surrounds the line conductor 7. The transformer has a core type, number of windings , secondary loading, and size which are selected to produce an output voltage proportional to step changes (di/dt) in current. The core is also selected to saturate at a predetermined level of primary current. The saturation acts to clamp the 10 maximum di/dt voltage signal at the transformer output. This eliminates the effect of brief high current pulses of short duration from having the same effect on the detector as a series of smaller amplitude arc faults steps.
Clamping the amplitude by saturation prevents false triggering on load events such as lamp filament burnouts which cause brief high current pulses.
The hot conductor 7 is used as the arc fault sensed conductor as any current arcing to neutral or ground will be supplied from this wire. The current transformer 1 is connected to bridge rectifier 10 by way of series capacitor 8. Capacitor 8, which in conjunction with resistor 8a, acts as a 20 high pass filter for rejecting 60hz sinusoidal signals. Capacitor 8 and resistor 8a may be eliminated without loss of arc fault detection but with an increased susceptability to false detection from large magnitude 60 HZ
load currents such as may occur during motor start ups.
When an arc fault occurs, step changes in current produce rectified 25 pulses at the output of bridge rectifier 10. The rectified pulses are .
integrated by an integrator 24, for a predetermined time interval. The repeated charge pulses act to charge capacitor 16, and raise the voltage across capacitor 16 to the trigger threshold of disc 18. Diac 18 is a trigger device which triggers into conduction at one voltage, and which then shuts 30 off at a lower voltage. The diac conduction discharges a portion of the charged stored in capacitor 16 into the gate 22 of SCR 41 triggering the SCR into conduction. SCR 41 conduction energizes solenoid 43, which activates trip mechanism 44, opening contacts 45.
Capacitor 6 is used for transient suppression of noise at frequencies 35 above that required for arc detection. Capacitor 20 acts to suppress noise voltage that may cause false triggering of SCR 41. Zener diode l0a is an optional voltage clamp, or limiter connected between the output of bridge rectifier 10 and circuit common 46, and performs the same function as the saturating current transformer in limiting the di/dt voltage pulses to a 5 constant level. Resistor 14 discharges the integrator capacitor 16 after a pulse charging sequence has terminated. Resistor 8a is a bleeder resistor for capacitor 8 and performs the same function as resistor 14. An optional inductor 11, which negates the need for a saturating current transformer, as shown may be placed between the current transformer 1 and the integrator 24 which acts as an attenuating impedance for large di/dt pulses such as may occur during lamp burnout.
Unlike most or all of the prior art, this design is very simple, and has the advantage of not requiring a DC power supply.
Figure lb shows another circuit embodiment of the sensor 15 transformer , high pass filter, and rectifier. This circuit performs the same functions of high pass filter and rectifier as shown in FIG. la with an additional voltage doubter feature. Capacitors 90 and 92 form a high pass filter with resistors 94 and 96 and also act as voltage doubter elements. An arc step in one direction causes a positive voltage at secondary output 91, 20 developed across winding 4b, with respect to the transformer center tap 83 held at circuit common. The same arc step also produces a negative voltage at secondary output 97, developed across winding 4a, with respect to the center tap 83. The positive voltage at output 91, drives part of the current through capacitor 92, which current is rectified by diode 99, and 25 then passes out to the sensor pulse line 9. At the same time, the negative voltage at 97 causes a current to pass from the center tap 83 through diode 98 and capacitor 90 and back to the transformer secondary at 97. This current charges capacitor 90 with a positive polarity at junction 82, with respect to transformer secondary output 97, and causes the capacitor to 30 store charge. When an arc step in the other direction occurs , output 97 of secondary 4a becomes positive with respect to the center tap. This voltage drives a current through capacitor 90, then part of the current into diode 95, and out to signal line 9. The part current moves most of the stored charge in capacitor 90 plus the new charge arriving with the current from 35 the transformer into the integrator capacitor 16, where it acts to pump the voltage above the level that would have occurred without the stored charge in capacitor 90. The next arc step in of the opposite polarity causes the same charge pump action out of capacitor 92. This action causes capacitors 90 and 92 to act as charge pump capacitors repeatedly charge pumping the integrator capacitor 16. Resistors 80 and 81 are optional bleeder resistors for capacitors 90 and 92. In operation the circuit losses, along with the bleeder resistor discharge action on the capacitors, prevents actual voltage doubling. The voltage doubter action allows a sensor with fewer windings, when responding to lower arc sense pulse amplitudes, to produce the same disc trigger voltage as would occur without the doubter action. Those skilled in the art will understand that the components connected across one half of the secondary shown in figure 1 a could be used with an untapped secondary winding, which produces a voltage doubter circuit that responds only to arc steps in one direction.
Figure 2 shows a further embodiment to the circuit of figure 1. All other like parts are like numbered. In this embodiment integrator 68 is of a lower timer constant than integrator 24. Diac 66 has a higher trigger voltage than diac 18. When integrator capacitor 64 quick charges on a large arc signal pulse, which causes the voltage of the capacitor 64 to reach the trigger threshold of disc 66, a pulse of charge is removed from capacitor 64 by disc 66. In this manner large arc signal pulses caused by lamp burn out type events are mitigated by the charge dump action of disc 66. The diac 66 acts as a superior clamp to that of a zener diode as short duration arc pulses occurring from lamp burnout cause a discharge action on integrator capacitor 64 instead of only a clamping action. In this way the charge effect on the detector of a short duration high current pulse is quickly mitigated. During actual high current arc faults which may also trigger the charge dump disc 66, the repetitive signal pulses pass enough charge into integrator 24 before the charge dump diac 66 is triggered to cause charging action of integrator 24. This activates diac 18 and SCR 41.
Referring now to Figure 3, an arc fault circuit interrupter in accordance with another aspect of this invention is illustrated in schematic diagram form. The interrupter is similar to the embodiment of the invention shown in Figure 1 in many respects, and to that end, like components designated by like reference numbers. Arc fault sensing current transformer 1 is responsive both to the rate of change of current with respect to time (di/dt) and to the 60 Hz arc current produced by an arc fault.
During an arc fault, a large di/dt pulse is typically produced along 5 with a sustained 60 Hz arc current signal. The di/dt current pulse is rectified by bridge rectifier 10 and is conducted by blocking diode 101 to integrator 24 where it acts to charge integrator cap 16. Diac 18 is selected so that if the voltage across intrgrator capacitor 16 exceeds a predetermined magnitude, disc 18 conducts and a signal is applied to the drain of fet 106.
The output of bridge rectifier 10 is also connected through decoupling resistor 118 to zener diode 116. Zener diode 116 clamps and strips the di/dt pulse off of the rectified 60 Hz arc current. The di/dt stripped rectified 60Hz arc current is applied to integrator 114 where it acts 15 to charge capacitor 115. When the voltage across the integrator capacitor 115 rises above the clamp voltage of zener 118, the gate of fet 106 is enabled. In this way, both the the minimum di/dt value and the minimum 60 Hz arc current value must exceed the predetermined thresholds before fet 106 will conduct and provide a turn on signal to gate 22 of SCR 41, 20 which activates solenoid 43 and trip mechanism 44, disconnecting the load from the source. Zener 118 may be replaced by trigger device, such as a second diac, for snap action triggering of the fet 106 gate.
Preferably a zener diode 102 is connected across the output of integrator 24 to limit the voltage applied to diac 18. The zener 102 is 25 required to protect the drain source junction of fet 106 from any excessive voltage that may appear across capacitor 16 and disc 18 when fet 106 is held in the off state. Alternately, zener diode 104 is connected betwen the fet 106 drain and circuit common, to limit the voltage that can be applied at the drain. The diodes 102 or 104 are required when di/dt pulses occur 30 without an accompanying predetermined 60 hz current peak indicative of an arc fault. In this situation diac 18 could not prevent capacitorl6 from continuing to charge past the diac trigger voltage allowing an excessive voltage to build up.at the fet 106 drain. These types of pulses can be generated by light dimmers or phase controlled motor controllers.
The circuit shown in Figure 3 is particularly well suited to discriminate between the high di/dt signals produced by lamp dimmers and the like, which are not accompanied by sustained 60 Hz arc current, from actual arcs which include both a high di/dt current and sustain 60 Hz arc current exceeding a preselected value.
Figure 4(a-e) illustrate waveforms generated in the circuit of figure 1. A typical arcing current waveform is shown at 102 in figure 4a.
Step 104 in figure 4a shows one of the step increases in current that generates waveform 106 shown in figure 4b at the secondary 4 of 10 transformer 1. The arc current 102 in figure 4a will have broad band noise shown at 105. Typically the arc extinguishes at the next current zero cross but in some cases may have a sharp extinguishing edge as shown at 102a in figure 4a which may generate a weak pulse shown at 102b, 102c and 102d in figure 4b, 4c, and 4d respectively. Figure 4c pulse 108 shows the 1 S bridge rectified pulses. Figure 4d charge waveform 112 shows the integrator capacitor 16 pulse charging. At 114 in figure 4d, the iliac triggers into conduction sending a pulse of current 118 into SCR gate 22 causing the SCR to conduct. When the SCR conducts solenoid 43 is energized and activates trip mechanism 44. This opens contact 45 20 disconnecting the load. Waveform 116 in figure 4d shows capacitor 16 discharging to the iliac turn off voltage.
While the invention has been described in connection with a number of presently preferred embodiments thereof, those skilled in the art will recognize that many modifications and changes may be made therein 25 without departing from the true spirit and scope of the invention, which accordingly is accordingly is intended to be defined solely by the appended claims.
Cross reference to related applications:
This application is a continuation-in-part of Serial No.
09/211,747 filed December 15, 1998.
S Background of the Invention:
Field of the Invention:
This invention relates to an apparatus for detecting arc faults in electrical power lines, and more particularly to apparatus that does not include a DC power supply.
Description of the Prior Art:
A number of devices and methods have been used in the past to detect arc faults. Some of the prior art devices and techniques have involved the use of E and B field arc sensors, the detection of the amplitude of arc fault rate of change of current signals, the use of non-15 overlapping band-pass filters to detect white noise of arcs, and devices which detect the disappearance of arc faults near current zero crosses.
Most of the prior art of arc detection occurs in circuit breakers where it acts as an enhancement to thermal-magnetic detection elements, which alone may fail to detect arc faults.
20 There is a need for an economical arc fault detector which may be mounted into a wiring device which offers the same down stream protection as an arc fault detecting circuit breaker but at the similar cost advantage that currently exist between ground fault interrupting receptacles and ground fault interrupting circuit breakers. This invention 25 provides that cost advantage.
Summary of the invention:
It is an object of this invention to provide an arc fault circuit interrupter that is simpler and less expensive to manufacture than those previously known. Briefly stated, and in accordance with a presently 30 preferred embodiment of the invention, an arc fault detecting circuit includes a saturating current transformer coupled to the electric power circuit to be protected that senses di/dt arc fault steps in current. A
rectifier is preferably connected to the sensor, and an integrator is connected to the rectifier. The integrator voltage is used to activate a trigger device. The trigger device activates circuit interrupting means.
The device does not require a DC power supply as found in the prior art .
The saturating current transformer produces a constant output voltage at a pre determined level of arc fault current. This eliminates the effect of brief high current pulses of short duration from having the same effect on the detector as a series of smaller amplitude arc faults steps.
In accordance with a further embodiment of the invention, a second integrator and trigger device is used instead of a saturating transformer to mitigate the effect of normal switching arcs and also the brief high current arc pulses.
In accordance with another embodiment of the invention, an inhibit switch is placed between the integrator and trigger device, where it acts to inhibit the di/dt charging integrator from activating the trigger device unless the associated peak 60 Hz component of arc current exceeds a predetermined value.
Brief description of the drawings:
FIG. 1(a-b) illustrate the circuit in which arc fault detection is performed;
FIG. 2 illustrates another embodiment of the circuit of FIG. 1 showing an additional integrator element with a discharge diac;
FIG. 3 is a schematic diagram of an art fault circuit interrupter in accordance with another embodiment of the invention; and FIG. 4(a-e) illustrates waveforms in the circuit of FIG. 3.
Description of the~referred embod'ment~
An arc fault detector in accordance with this invention is intended for incorporation into a.receptacle, plug, or cord type device which is mechanically similar to ground fault interrupter devices such as those shown in U.S. Pats. No. 5,594,358, and 5,510,760.
Referring now to FIG. 1 a, one embodiment of the invention is shown in schematic diagram form, showing an electrical power line, comprising line side neutral and hot conductors 6 and 7 respectively, load neutral and hot conductors 50 and 51 respectively and a load 52. The load neutral SO and hot 51 conductors are both protected by contactor mechanism 45. Contactor mechanism 45 is a spring loaded mouse trap type device, which is controlled by trip mechanism 44. Conduction of SCR 41 activates solenoid 43 which activates trip mechanism 44. When the trip mechanism is activated, the spring loaded contacts 26 and 28 latch open, and stay open until they are manually reset.
An arc fault sensing current transformer 1 is wrapped with a secondary winding 4, which surrounds the line conductor 7. The transformer has a core type, number of windings , secondary loading, and size which are selected to produce an output voltage proportional to step changes (di/dt) in current. The core is also selected to saturate at a predetermined level of primary current. The saturation acts to clamp the 10 maximum di/dt voltage signal at the transformer output. This eliminates the effect of brief high current pulses of short duration from having the same effect on the detector as a series of smaller amplitude arc faults steps.
Clamping the amplitude by saturation prevents false triggering on load events such as lamp filament burnouts which cause brief high current pulses.
The hot conductor 7 is used as the arc fault sensed conductor as any current arcing to neutral or ground will be supplied from this wire. The current transformer 1 is connected to bridge rectifier 10 by way of series capacitor 8. Capacitor 8, which in conjunction with resistor 8a, acts as a 20 high pass filter for rejecting 60hz sinusoidal signals. Capacitor 8 and resistor 8a may be eliminated without loss of arc fault detection but with an increased susceptability to false detection from large magnitude 60 HZ
load currents such as may occur during motor start ups.
When an arc fault occurs, step changes in current produce rectified 25 pulses at the output of bridge rectifier 10. The rectified pulses are .
integrated by an integrator 24, for a predetermined time interval. The repeated charge pulses act to charge capacitor 16, and raise the voltage across capacitor 16 to the trigger threshold of disc 18. Diac 18 is a trigger device which triggers into conduction at one voltage, and which then shuts 30 off at a lower voltage. The diac conduction discharges a portion of the charged stored in capacitor 16 into the gate 22 of SCR 41 triggering the SCR into conduction. SCR 41 conduction energizes solenoid 43, which activates trip mechanism 44, opening contacts 45.
Capacitor 6 is used for transient suppression of noise at frequencies 35 above that required for arc detection. Capacitor 20 acts to suppress noise voltage that may cause false triggering of SCR 41. Zener diode l0a is an optional voltage clamp, or limiter connected between the output of bridge rectifier 10 and circuit common 46, and performs the same function as the saturating current transformer in limiting the di/dt voltage pulses to a 5 constant level. Resistor 14 discharges the integrator capacitor 16 after a pulse charging sequence has terminated. Resistor 8a is a bleeder resistor for capacitor 8 and performs the same function as resistor 14. An optional inductor 11, which negates the need for a saturating current transformer, as shown may be placed between the current transformer 1 and the integrator 24 which acts as an attenuating impedance for large di/dt pulses such as may occur during lamp burnout.
Unlike most or all of the prior art, this design is very simple, and has the advantage of not requiring a DC power supply.
Figure lb shows another circuit embodiment of the sensor 15 transformer , high pass filter, and rectifier. This circuit performs the same functions of high pass filter and rectifier as shown in FIG. la with an additional voltage doubter feature. Capacitors 90 and 92 form a high pass filter with resistors 94 and 96 and also act as voltage doubter elements. An arc step in one direction causes a positive voltage at secondary output 91, 20 developed across winding 4b, with respect to the transformer center tap 83 held at circuit common. The same arc step also produces a negative voltage at secondary output 97, developed across winding 4a, with respect to the center tap 83. The positive voltage at output 91, drives part of the current through capacitor 92, which current is rectified by diode 99, and 25 then passes out to the sensor pulse line 9. At the same time, the negative voltage at 97 causes a current to pass from the center tap 83 through diode 98 and capacitor 90 and back to the transformer secondary at 97. This current charges capacitor 90 with a positive polarity at junction 82, with respect to transformer secondary output 97, and causes the capacitor to 30 store charge. When an arc step in the other direction occurs , output 97 of secondary 4a becomes positive with respect to the center tap. This voltage drives a current through capacitor 90, then part of the current into diode 95, and out to signal line 9. The part current moves most of the stored charge in capacitor 90 plus the new charge arriving with the current from 35 the transformer into the integrator capacitor 16, where it acts to pump the voltage above the level that would have occurred without the stored charge in capacitor 90. The next arc step in of the opposite polarity causes the same charge pump action out of capacitor 92. This action causes capacitors 90 and 92 to act as charge pump capacitors repeatedly charge pumping the integrator capacitor 16. Resistors 80 and 81 are optional bleeder resistors for capacitors 90 and 92. In operation the circuit losses, along with the bleeder resistor discharge action on the capacitors, prevents actual voltage doubling. The voltage doubter action allows a sensor with fewer windings, when responding to lower arc sense pulse amplitudes, to produce the same disc trigger voltage as would occur without the doubter action. Those skilled in the art will understand that the components connected across one half of the secondary shown in figure 1 a could be used with an untapped secondary winding, which produces a voltage doubter circuit that responds only to arc steps in one direction.
Figure 2 shows a further embodiment to the circuit of figure 1. All other like parts are like numbered. In this embodiment integrator 68 is of a lower timer constant than integrator 24. Diac 66 has a higher trigger voltage than diac 18. When integrator capacitor 64 quick charges on a large arc signal pulse, which causes the voltage of the capacitor 64 to reach the trigger threshold of disc 66, a pulse of charge is removed from capacitor 64 by disc 66. In this manner large arc signal pulses caused by lamp burn out type events are mitigated by the charge dump action of disc 66. The diac 66 acts as a superior clamp to that of a zener diode as short duration arc pulses occurring from lamp burnout cause a discharge action on integrator capacitor 64 instead of only a clamping action. In this way the charge effect on the detector of a short duration high current pulse is quickly mitigated. During actual high current arc faults which may also trigger the charge dump disc 66, the repetitive signal pulses pass enough charge into integrator 24 before the charge dump diac 66 is triggered to cause charging action of integrator 24. This activates diac 18 and SCR 41.
Referring now to Figure 3, an arc fault circuit interrupter in accordance with another aspect of this invention is illustrated in schematic diagram form. The interrupter is similar to the embodiment of the invention shown in Figure 1 in many respects, and to that end, like components designated by like reference numbers. Arc fault sensing current transformer 1 is responsive both to the rate of change of current with respect to time (di/dt) and to the 60 Hz arc current produced by an arc fault.
During an arc fault, a large di/dt pulse is typically produced along 5 with a sustained 60 Hz arc current signal. The di/dt current pulse is rectified by bridge rectifier 10 and is conducted by blocking diode 101 to integrator 24 where it acts to charge integrator cap 16. Diac 18 is selected so that if the voltage across intrgrator capacitor 16 exceeds a predetermined magnitude, disc 18 conducts and a signal is applied to the drain of fet 106.
The output of bridge rectifier 10 is also connected through decoupling resistor 118 to zener diode 116. Zener diode 116 clamps and strips the di/dt pulse off of the rectified 60 Hz arc current. The di/dt stripped rectified 60Hz arc current is applied to integrator 114 where it acts 15 to charge capacitor 115. When the voltage across the integrator capacitor 115 rises above the clamp voltage of zener 118, the gate of fet 106 is enabled. In this way, both the the minimum di/dt value and the minimum 60 Hz arc current value must exceed the predetermined thresholds before fet 106 will conduct and provide a turn on signal to gate 22 of SCR 41, 20 which activates solenoid 43 and trip mechanism 44, disconnecting the load from the source. Zener 118 may be replaced by trigger device, such as a second diac, for snap action triggering of the fet 106 gate.
Preferably a zener diode 102 is connected across the output of integrator 24 to limit the voltage applied to diac 18. The zener 102 is 25 required to protect the drain source junction of fet 106 from any excessive voltage that may appear across capacitor 16 and disc 18 when fet 106 is held in the off state. Alternately, zener diode 104 is connected betwen the fet 106 drain and circuit common, to limit the voltage that can be applied at the drain. The diodes 102 or 104 are required when di/dt pulses occur 30 without an accompanying predetermined 60 hz current peak indicative of an arc fault. In this situation diac 18 could not prevent capacitorl6 from continuing to charge past the diac trigger voltage allowing an excessive voltage to build up.at the fet 106 drain. These types of pulses can be generated by light dimmers or phase controlled motor controllers.
The circuit shown in Figure 3 is particularly well suited to discriminate between the high di/dt signals produced by lamp dimmers and the like, which are not accompanied by sustained 60 Hz arc current, from actual arcs which include both a high di/dt current and sustain 60 Hz arc current exceeding a preselected value.
Figure 4(a-e) illustrate waveforms generated in the circuit of figure 1. A typical arcing current waveform is shown at 102 in figure 4a.
Step 104 in figure 4a shows one of the step increases in current that generates waveform 106 shown in figure 4b at the secondary 4 of 10 transformer 1. The arc current 102 in figure 4a will have broad band noise shown at 105. Typically the arc extinguishes at the next current zero cross but in some cases may have a sharp extinguishing edge as shown at 102a in figure 4a which may generate a weak pulse shown at 102b, 102c and 102d in figure 4b, 4c, and 4d respectively. Figure 4c pulse 108 shows the 1 S bridge rectified pulses. Figure 4d charge waveform 112 shows the integrator capacitor 16 pulse charging. At 114 in figure 4d, the iliac triggers into conduction sending a pulse of current 118 into SCR gate 22 causing the SCR to conduct. When the SCR conducts solenoid 43 is energized and activates trip mechanism 44. This opens contact 45 20 disconnecting the load. Waveform 116 in figure 4d shows capacitor 16 discharging to the iliac turn off voltage.
While the invention has been described in connection with a number of presently preferred embodiments thereof, those skilled in the art will recognize that many modifications and changes may be made therein 25 without departing from the true spirit and scope of the invention, which accordingly is accordingly is intended to be defined solely by the appended claims.
Claims (20)
1. A device for detecting arc faults in an electric power circuit, said device comprising:
a sensor coupled to the electric power circuit which sensor generates a pulse each time an arc is struck;
an integrator connected to the sensor for accumulating pulses and generating an output voltage;
a threshold detector connected to the integrator for generating an arc detecting signal when the voltage reaches a predetermined level;
in which the integrator and threshold detector are powered solely by the pulses.
a sensor coupled to the electric power circuit which sensor generates a pulse each time an arc is struck;
an integrator connected to the sensor for accumulating pulses and generating an output voltage;
a threshold detector connected to the integrator for generating an arc detecting signal when the voltage reaches a predetermined level;
in which the integrator and threshold detector are powered solely by the pulses.
2. A device for detecting arc faults in an electric power circuit, said device comprising:
a sensor coupled to the electric power circuit which sensor generates a pulse each time an arc is struck;
a limiter connected to the sensor for limiting amplitude of said pulses to a predetermined limit value;
an integrator connected to the sensor for accumulating pulses and generating an output voltage; a threshold detector connected to the integrator for generating an arc detecting signal when the voltage reaches a predetermined level;
in which the limiter, integrator, and threshold detector are powered solely by the pulses.
a sensor coupled to the electric power circuit which sensor generates a pulse each time an arc is struck;
a limiter connected to the sensor for limiting amplitude of said pulses to a predetermined limit value;
an integrator connected to the sensor for accumulating pulses and generating an output voltage; a threshold detector connected to the integrator for generating an arc detecting signal when the voltage reaches a predetermined level;
in which the limiter, integrator, and threshold detector are powered solely by the pulses.
3. The apparatus of claim 2 in which the limiter comprises a saturating current transformer.
4. The apparatus of claim 1 in which the sensor is a transformer in which the primary winding is the sensed electric circuit power line and in which the secondary winding produces pulses proportional to the di/dt of the primary current.
5. The device of claim 1 in which the threshold detector is a disc.
6. The device of claim 1 in which the threshold detector is a zener diode.
7. The device of claim 1 comprising a limiter connected between the sensor and the integrator.
8. The device of claim 7 in which the limiter comprises an inductor.
9. The device of claim 1 comprising a bridge rectifier connected to the sensor.
10. The device of claim 1 in which the sensing means is a transformer with a center tapped secondary.
11. The device of claim 1 comprising a high pass filter connected between the sensor and the bridge rectifier.
12. The device of claim 1 comprising;
a charge pump capacitor connected between the sensor and integrator, an integrator capacitor;
in which the charge pump capacitor acts to increase the voltage level across the integrator capacitor above that level occurring without the charge pump capacitor.
a charge pump capacitor connected between the sensor and integrator, an integrator capacitor;
in which the charge pump capacitor acts to increase the voltage level across the integrator capacitor above that level occurring without the charge pump capacitor.
13. An arc fault circuit interrupter comprising:
a sensor responsive to an arc fault for generating a first signal proportional to the rate of change of current with respect to time, and a second signal proportional to the AC power line frequency current produced by the arc;
a first detector responsive to the first signal for generating a first fault signal when the rate of change of current with respect to time exceeds a predetermined value;
a second detector responsive to the second signal for generating a second fault signal if the peak ac power line frequency current exceeds a predetermined value; and a switch for triggering a circuit disconnector only when both the first and second fault signals are generated.
a sensor responsive to an arc fault for generating a first signal proportional to the rate of change of current with respect to time, and a second signal proportional to the AC power line frequency current produced by the arc;
a first detector responsive to the first signal for generating a first fault signal when the rate of change of current with respect to time exceeds a predetermined value;
a second detector responsive to the second signal for generating a second fault signal if the peak ac power line frequency current exceeds a predetermined value; and a switch for triggering a circuit disconnector only when both the first and second fault signals are generated.
14. The arc fault circuit interrupter of claim 13 in which all of the power for the circuit is generated by the sensor, so that no power supply is required.
15. The arc fault circuit interrupter of claim 13 comprising a bridge rectifier connected to the sensor.
16. The arc fault circuit interrupter of claim 13 in which the first detector comprises an integrator connected to the bridge rectifier by a blocking diode.
17. The arc fault circuit interrupter of claim 13 in which the second detector comprises a decoupling resistor, a clamping diode, and an integrator connected to the bridge rectifier.
18. The arc fault circuit interrupter of claim 13 in which the switch comprises a field effect transistor, and wherein the first and second detectors are connected to the field effect transistor.
19. The arc fault circuit interrupter of claim 13 comprising a disc connected between the first detector and the switch.
20. The arc fault circuit interrupter of claim 13 comprising a zener diode connected between the second detector and the switch.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/314,296 US6198611B1 (en) | 1998-12-15 | 1999-05-19 | Arc fault circuit interrupter without DC supply |
| US09/314,296 | 1999-05-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2307537A1 true CA2307537A1 (en) | 2000-11-19 |
Family
ID=23219390
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2307537 Abandoned CA2307537A1 (en) | 1999-05-19 | 2000-05-04 | Arc fault circuit interrupter without dc supply |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2307537A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2480648B (en) * | 2010-05-26 | 2013-02-20 | Ge Aviat Systems Ltd | Measuring transient electrical activity in aircraft power distribution systems |
| US11686758B2 (en) | 2020-09-24 | 2023-06-27 | Abb Schweiz Ag | Arc fault detection device with wideband sensor |
-
2000
- 2000-05-04 CA CA 2307537 patent/CA2307537A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2480648B (en) * | 2010-05-26 | 2013-02-20 | Ge Aviat Systems Ltd | Measuring transient electrical activity in aircraft power distribution systems |
| US8755160B2 (en) | 2010-05-26 | 2014-06-17 | Ge Aviation Systems Limited | Measuring transient electrical activity in aircraft power distribution systems |
| US11686758B2 (en) | 2020-09-24 | 2023-06-27 | Abb Schweiz Ag | Arc fault detection device with wideband sensor |
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