CN103116093A - Series connection fault arc pre-warning system and detection method thereof - Google Patents
Series connection fault arc pre-warning system and detection method thereof Download PDFInfo
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Abstract
The invention provides a series connection fault arc pre-warning system. The series connection fault arc pre-warning system comprises a power circuit, a current transformer, a current sensing circuit, a signal processing circuit, a voltage zero balancing comparison circuit, a microprocessor and a fault output circuit. The current transformer, the current sensing circuit, the signal processing circuit and the microprocessor are successively connected. The voltage zero balancing comparison circuit and the fault output circuit are respectively connected with the microprocessor. The current transformer collects a current signal in a power network to transform the current signal into a voltage signal through the current sensing circuit to input to the microprocessor through the signal processing circuit, and the voltage zero balancing comparison circuit outputs a voltage zero balancing pulse signal to the microprocessor. The invention further provides a series connection arc fault detection method. The series connection fault arc pre-warning system and the series connection arc fault detection method have the advantages that due to the fact that a signal is directly processed in time domain after sampling, the complicated Fourier transform is saved, the fault arc and normal wave form can be distinguished accurately, and the computation time is saved. The series connection fault arc detection can be achieved by the more economical microprocessor. The detection is reliable and effective, and effective and timely pre-warning information can be supplied to workers.
Description
Technical field
The present invention relates to detection technique, particularly a kind of series fault arc early warning system and detection method thereof.
Background technology
According to the statistics of " the Chinese fire protection yearbooks " of 2005, had 142568 of breaking out of fires altogether in 2004, wherein electrical fire has 2948, accounts for 20.7% of total fire number.Electrical fire has caused 398 people dead, and 427 people are injured, and direct economic loss has reached 4,800,000,000 yuan, accounts for by 42% of investigation fire total losses.In wildfire, electrical fire has 10, accounts for 37% of 27 of sums, and direct economic loss reaches 2,100,000,000 yuan, has accounted for 74%.Electrical fire has brought serious threat for people's life security and national wealth.And in causing numerous reasons of electrical fire, fault electric arc is one of topmost reason.
The occurring mode of fault electric arc generally can be divided into serial electric arc, when three kinds of parallel electric arc and ground arcs, serial arc occur due to its fault electric arc, electric current is less, and the characteristic of fault electric arc is with the impact of loadtype and size, thereby more difficult accurate detection is so danger is also relatively large.
At present, the method for arc-detection roughly can be summarized as three classes both at home and abroad:
(1) set up Arc Modelling, and detect electric arc by detecting corresponding parameter, but due to the restriction of this method service condition, and need the parameter of detection too much, at present, utilize the method to carry out the Detection progress of fault electric arc very slow, generally only rest on simulation stage;
The physical phenomenon that produces when (2) occuring according to electric arc detects electric arc, can find according to the forming process of electric arc, when electric arc forms, can be accompanied by some obvious physical phenomenons, as arc light, and noise, radiation, temperature variation etc.Produce electric arc in power distribution cabinet, because electric current is larger, these physical phenomenons are very obvious, show as high temperature, high pressure, noise etc., utilize this method can detect preferably the generation of fault electric arc.
And in family or public place power supply-distribution system, the scope that need to detect is very large, and the physical phenomenon of electric arc when occuring relatively a little less than, be not easy in this way to detect the generation of electric arc.So the physical phenomenon when occuring by detection failure electric arc reaches the method that judges whether that fault electric arc occurs, and is not suitable for detection and the prevention of large-scale fault electric arc.
Electric current when (3) occuring according to electric arc, voltage waveform change detection electric arc.When electric arc occured, the voltage and current in circuit can be undergone mutation because produced electric arc in circuit, with wavelet transformation, three periodic methods etc., voltage current waveform was at this moment analyzed, and whether Characteristic Extraction can judge the generation of electric arc.Utilize wavelet transformation that the current signal of electric arc is analyzed, can reflect the moment of current signal sudden change, the size of sudden change can also be detected.And then these information are carried out comprehensive analysis, effective detection failure electric arc.But due to the current waveform that exists some with the waveform similarity of fault electric arc, so can accurately distinguish fault electric arc or normally waveform is the major issue that wavelet transformation faces in electrical network.
In patent " detecting equipment and the method for arc fault ", the implication of three periodical algorithms (they being TCA) is provided, is expressed as follows:
TCA＝|(|V
[n-1]-V
[n]|+|V
[n+1]-V
[n]|-|V
[n+1]-V
[n-1]|)|
Wherein, V
[n-1]Expression and corresponding the first voltage measurements of First Line voltage cycle, V
[n]Representative and the second corresponding second voltage measurement result of line voltage cycle, and, V
[n+1]Representative and the 3rd corresponding tertiary voltage measurement result of line voltage cycle.TCA can be used for determining the fluctuation of voltage, thereby can distinguish fault electric arc and upset load.But, after this patent is sampled, need to carry out Fourier transform to sampled signal, this just needs long calculating of time, needs more high performance microprocessor, causes calculation of complex and hardware system cost very high.
Summary of the invention
The objective of the invention is to overcome defects, the system and method that provides a kind of series fault arc to detect, can accurately distinguish fault electric arc and normal waveform, save computing time, and the more economic microprocessor of employing, realize reliable, effectively series fault arc detection, for the staff provides early warning information timely and effectively.
for achieving the above object, series fault arc early warning system provided by the invention, comprise power circuit, current transformer, current sensing circuit and signal conditioning circuit, also comprise microprocessor, fault output circuit and the voltage zero-cross comparator circuit that is connected with electrical network, described current transformer, current sensing circuit, signal conditioning circuit is connected successively with described microprocessor, described voltage zero-cross comparator circuit is connected with described microprocessor respectively with the fault output circuit, described current transformer gathers the current signal in electrical network, through described current sensing circuit, current signal is converted into voltage signal, again through the described microprocessor of described signal conditioning circuit input, described voltage zero-cross comparator circuit output voltage zero-crossing pulse signal is to described microprocessor, described microprocessor-based control sequence is carried out following steps:
Step 101, the microcontroller initialization;
Step 102, register configuration comprises AD register and timer register;
Step 104 is carried out difference to the current value in adjacent two cycles and is calculated, and gets Y
k=X2 (k)-X1 (k), wherein, k=1,2 ..., N;
Step 105, the value of use mean square root method design factor Z:
In formula, Y
1,, Y
2..., Y
nBe the difference of N sampled point corresponding to adjacent two cycles, and the threshold values that coefficient Z is set is the first threshold values;
Step 106, calculate the rate of change between adjacent two Z values:
Wherein, Z
nBe the value of n coefficient Z, Z
n+1Be the value of n+1 coefficient Z, and the threshold values that rate of change δ is set is the second threshold values;
Whether step 107, the value that judges Z more than or equal to the value of the first threshold values Zb, if more than or equal to Zb, and execution in step 108; Otherwise, return to step 103;
Whether step 108, the value that judges δ more than or equal to the value of the second threshold values δ b, if more than or equal to δ b, and execution in step 109; Otherwise, return to step 103;
Step 109, the threshold values that the arc event number of times is set is the 3rd threshold values, whether judges timer just in timing, if timer just in timing, execution in step 110; Otherwise, execution in step 111;
Step 110, counter adds one, and the electric arc cycle has appearred one time in expression;
Step 111, timer begins timing, and counter adds one;
Step 112 judges whether timer reaches 0.5s, if reach 0.5s, and execution in step 113; Otherwise return to step 103;
Whether step 113 judges counter more than or equal to the 3rd threshold values and generation electric arc number of times threshold values, if more than or equal to the 3rd threshold values, and execution in step 114; Otherwise, execution in step 115;
Step 114, the early warning information that the output fault electric arc occurs is controlled hummer through described fault output circuit and is rung;
Step 115, clear timer, counter.
Series fault arc early warning system of the present invention, wherein said current sensing circuit comprises the RC wave filter, and described current transformer is arranged on the zero line or live wire of electrical network, and its output signal is connected to the RC wave filter, and the output terminal of RC wave filter is connected with signal conditioning circuit.
Series fault arc early warning system of the present invention, wherein said signal conditioning circuit comprise low-pass filter and the totalizer that is attached thereto, and described low-pass filter is connected with current sensing circuit, and the output terminal of totalizer is connected with microprocessor.
Series fault arc early warning system of the present invention, wherein said voltage zero-cross comparator circuit comprise bleeder circuit, comparer and the shaping circuit that is connected successively, electrical network access bleeder circuit, and the shaping circuit output terminal is connected with the input end of microprocessor.
Series fault arc early warning system of the present invention, wherein said fault output circuit comprises hummer.
For achieving the above object, series arc faults detection method provided by the invention arranges power circuit, current transformer, current sensing circuit, signal conditioning circuit, voltage zero-cross comparator circuit, microprocessor and fault output circuit, and the method comprises:
1) begin to gather original load current Xi(n by the line voltage amplitude from negative extremely positive zero crossing), wherein: n=0,1,2,3 ..., N-1, N counts for gathering, and N=T/Ts, T are the line voltage cycle, and Ts is the sampling period;
2) calculate the difference of each sampled point current value that adjacent two cycles collect;
3) utilize root mean square formula design factor Z value by the difference of N sampled point current value;
4) the Z value in adjacent two cycles is carried out the rate of change analysis, design factor Z rate of change δ;
5) threshold values that coefficient Z is set is the first threshold values, and the threshold values of coefficient Z rate of change δ is the second threshold values, and the threshold values of arc event number of times M is the 3rd threshold values;
6) whether the Z value that gone out by i cycle and i+1 computation of Period of judgement is more than or equal to described the first threshold values;
7) whether judge by Z value rate of change δ more than or equal to described the second threshold values;
8) if the current i cycle meet the following conditions: a) coefficient Z 〉=the first threshold values, b) rate of change δ=the second threshold values, judge that the i cycle is the fault electric arc cycle;
9) if at the appointed time in t, arc event number of times M 〉=the 3rd threshold values, fault electric arc, output fault electric arc generation signal have occured this moment in judgement.
Series arc faults detection method of the present invention, wherein said step 1) comprising:
A) judge whether the line voltage amplitude is 1 from negative extremely positive zero crossing zone bit ZeroFlag, if ZeroFlag is 1, execution in step b);
B) start the A/D sampling, gather load current signal, each cycle all gathers N point, and i periodic current sampled value is Xi(n), wherein, n=0,1,2 ..., N-1, N=T/Ts, T are the electrical network cycle, Ts is collection period;
C) when the number of signals collecting reaches N, execution in step d), otherwise, interrupt returning;
D) to n and ZeroFlag zero clearing, prepare next periodic sampling.
Series arc faults detection method of the present invention, wherein said step 2) comprise that the value with first sampled point of second period deducts the value of first first sampled point of cycle, is made as Y
k=X2 (k)-X1 (k), wherein, X2 (1) is the numerical value of first point of second period, X1 (1) is the numerical value of first point of first cycle, by that analogy, obtains Y
1,, Y
2..., Y
nBe total to N value.
Series arc faults detection method of the present invention, wherein said step 3) design factor Z adopts following formula:
In formula, Y
1,, Y
2.., Y
nDifference for N sampled point corresponding to adjacent two cycles.
Series arc faults detection method of the present invention, wherein said step 4) calculate the following formula of rate of change employing between adjacent two Z values:
Wherein, Z
nBe the value of n coefficient Z, Z
n+1It is the value of n+1 coefficient Z.
Advantage and the good effect of series fault arc early warning system of the present invention and detection method thereof are: owing to directly signal being processed on time domain after sampling, saved complicated Fourier transform, can accurately distinguish fault electric arc and normal waveform, saved computing time, can adopt more economic microprocessor to realize that series fault arc detects, detect reliably, effectively, for the staff provides early warning information timely and effectively.
Be elaborated with reference to accompanying drawing below in conjunction with embodiment.
Description of drawings
Fig. 1 is the block scheme of series arc faults early warning system of the present invention;
Fig. 2 is the circuit theory diagrams of series arc faults early warning system of the present invention;
Fig. 3 is the process flow diagram of series arc faults detection method of the present invention;
Fig. 4 is for gathering the process flow diagram of load current signal;
Fig. 5 is the normal running current oscillogram of electric iron;
Current waveform figure when Fig. 6 is electric iron generation electric arc;
Fig. 7 is the normal running current oscillogram of electric fan;
Current waveform figure when Fig. 8 is electric fan generation electric arc.
Embodiment
The method that series fault arc of the present invention detects, when electric arc occuring and electric arc not occuring according to, the difference of current value in circuit, utilization difference-mean square root method carries out computational analysis to current value, realizes the judgement of series arc faults.
The below describes the method that series fault arc of the present invention detects.
With reference to Fig. 3, the method that series fault arc detects comprises:
1) begin to gather original load current by the line voltage amplitude from negative extremely positive zero crossing.
In conjunction with reference to Fig. 4, step 1) gather the load current value method and specifically comprise:
A) judge whether the line voltage amplitude is 1 from negative extremely positive zero crossing zone bit ZeroFlag, if ZeroFlag is 1, execution in step b);
B) start the A/D sampling, gather load current signal, each cycle all gathers N point, and i periodic current sampled value is Xi(n), wherein, n=0,1,2 ..., N-1N=T/Ts, T are the electrical network cycle, Ts is collection period;
C) when the number of signals collecting reaches N, execution in step d), otherwise, interrupt returning;
D) to n and ZeroFlag zero clearing, prepare next periodic sampling.
2) calculate the difference of each sampled point current value that adjacent two cycles collect.
Step 2) comprise that specifically the value with first sampled point of second period deducts the value of first first sampled point of cycle, is made as Y
k=X2 (k)-X1 (k), wherein, X2 (1) is the numerical value of first point of second period, X1 (1) is the numerical value of first point of first cycle, by that analogy, obtains Y
1,, Y
2..., Y
nBe total to N value.
3) utilize root mean square formula design factor Z value by the difference of N sampled point current value.
Step 3) specifically comprise employing root mean square formula design factor Z:
In formula, Y
1,, Y
2..., Y
nDifference for N sampled point corresponding to adjacent two cycles.
4) the Z value in adjacent two cycles is carried out the rate of change analysis, design factor Z rate of change δ:
In formula, Z
nBe the value of n coefficient Z, Z
n+1It is the value of n+1 coefficient Z.
5) threshold values that coefficient Z is set is the first threshold values, and the threshold values of coefficient Z rate of change δ is the second threshold values, and the threshold values of arc event number of times M is the 3rd threshold values.
6) whether the Z value that gone out by i cycle and i+1 computation of Period of judgement is more than or equal to described the first threshold values.
7) whether judge by Z value rate of change δ more than or equal to described the second threshold values.
8) if the current i cycle meet the following conditions: a) coefficient Z 〉=the first threshold values, b) rate of change δ=the second threshold values, judge that the i cycle is the fault electric arc cycle.
9) if at the appointed time in t, arc event number of times M 〉=the 3rd threshold values, fault electric arc, output fault electric arc generation signal have occured this moment in judgement.
The below adopts the series fault arc early warning system of series fault arc guard method with example explanation the present invention.
With reference to Fig. 1, series fault arc early warning system circuit of the present invention comprises power circuit 1, Current Transmit, current sensing circuit 2, signal conditioning circuit 3, voltage zero-cross comparator circuit 4, microprocessor 5 and fault output circuit 6.
Current Transmit, current sensing circuit 2, signal conditioning circuit 3 are connected successively with microprocessor 5.Current Transmit is connected with electrical network with voltage zero-cross comparator circuit 4.Voltage zero-cross comparator circuit 4 is connected with microprocessor 5 respectively with fault output circuit 6.Current Transmit gathers the current signal in electrical network, through current sensing circuit 2, current signal is converted into voltage signal, then passes through signal conditioning circuit 3 input microprocessors 5, and voltage zero-cross comparator circuit 4 output voltage zero-crossing pulse signals are to microprocessor 5.The signal fault output circuit 6 that microprocessor 5 failure judgement electric arcs occur is to User Alarms.
With reference to Fig. 3, the control sequence of microprocessor 5 is carried out following steps:
Step 101, the microcontroller initialization comprises variable, interrupts AD etc.;
Step 102, register configuration comprises AD register and timer register;
Step 103 judges whether the line voltage amplitude is 0 from negative extremely positive zero crossing zone bit ZeroFlag, when it is 0, and execution in step 104; Otherwise, wait for, until ZeroFlag is 0;
Step 104 is carried out difference to the current value in adjacent two cycles and is calculated, and gets Y
k=X2 (k)-X1 (k), wherein, k=1,2 ..., N;
Step 105, the value of use mean square root method design factor Z:
In formula, Y
1,, Y
2..., Y
nBe the difference of N sampled point corresponding to adjacent two cycles, and the threshold values that coefficient Z is set is the first threshold values;
Step 106, calculate the rate of change between adjacent two Z values:
Wherein, Z
nBe the value of n coefficient Z, Z
n+1Be the value of n+1 coefficient Z, and the threshold values that rate of change δ is set is the second threshold values;
Whether step 107, the value that judges Z more than or equal to the value of the first threshold values Zb, if more than or equal to Zb, and execution in step 108; Otherwise, return to step 103;
Whether step 108, the value that judges δ more than or equal to the value of the second threshold values δ b, if more than or equal to δ b, and execution in step 109; Otherwise, return to step 103;
Step 109, the threshold values that the arc event number of times is set is the 3rd threshold values, whether judges timer just in timing, if timer just in timing, execution in step 110; Otherwise, execution in step 111;
Step 110, counter adds one, and the electric arc cycle has appearred one time in expression;
Step 111, timer begins timing, and counter adds one;
Step 112 judges whether timer reaches 0.5s, if reach 0.5s, and execution in step 113; Otherwise return to step 103;
Whether step 113 judges counter more than or equal to the 3rd threshold values and generation electric arc number of times threshold values, if more than or equal to the 3rd threshold values, and execution in step 114; Otherwise, execution in step 115;
Step 114, the early warning information that the output fault electric arc occurs is controlled hummer through described fault output circuit (6) and is rung;
Step 115, clear timer, counter.
See figures.1.and.2, in the embodiment of series fault arc early warning system of the present invention, Current Transmit is arranged on the zero line or live wire of electrical network, the current signal in Current Transmit sensing load circuit.Current sensing circuit 2 comprises the RC wave filter, and the Current Transmit current signal is connected to the RC wave filter, and the output terminal of RC wave filter is connected with signal conditioning circuit 3.Signal conditioning circuit 3 comprises low-pass filter U31 and totalizer U32, and its output terminal is connected with microprocessor 5.Voltage signal after current sensing circuit 2 transforms is through the AD input port of signal conditioning circuit 3 input microcontrollers 5.Voltage zero-cross comparator circuit 4 comprises bleeder circuit, comparer U41 and shaping circuit, and electrical network input connects bleeder circuit two ends, the input end of shaping circuit output termination microprocessor 5.Input to the external interrupt port of microcontroller 5 through the zero-crossing pulse signal of voltage zero-cross comparator circuit 4.After microcontroller 5 each periodic signal process computational analysis of difference-mean square root method with the AD sampling, carry out the judgement of fault electric arc, determine whether to have in circuit fault electric arc to occur.Fault output circuit 6 is comprised of hummer.When having fault electric arc to occur in circuit, microcontroller 5 sends the hummer in high level triggering fault output circuit 6, and the staff is known has fault electric arc to occur.
The below describes formation and the course of work of series fault arc early warning system of the present invention in detail.
With reference to Fig. 2, power circuit 1 comprises transformer T1, rectifier bridge VT, capacitor C 11-C18 and voltage transitions chip U11-U12.Capacitor C 11 and C15 series connection are to two output terminals of rectifier bridge, and capacitor C 12 is in parallel with capacitor C 11, and capacitor C 16 is in parallel with capacitor C 15.Capacitor C 13 series connections are to the output terminal of voltage transitions chip U11, and capacitor C 14 is in parallel with capacitor C 13, and capacitor C 17 series connections are to the output terminal of voltage transitions chip U12, and capacitor C 18 is in parallel with capacitor C 17.The input end of voltage transitions chip U11 is connected with the positive output end of rectifier bridge, and its output terminal is the power supply VCC of whole device.The input end of voltage transitions chip U12 is connected with the negative output terminal of rectifier bridge, and its output terminal is the power supply VCC of whole device.
Signal conditioning circuit 3 comprises operational amplifier U31, resistance R 31-R33, capacitor C 31 and operational amplifier U32.Resistance R 34-R37, operational amplifier U31, resistance R 31-R33 and capacitor C 31 form the anti-phase input low-pass filter.The output terminal of resistance R 31 1 termination current sensing circuits 2, the negative terminal of a termination operational amplifier U31.The negative terminal of resistance R 33 1 termination operational amplifier U31, the output terminal of another termination operational amplifier U31.Capacitor C 31 is in parallel with resistance R 33.The anode of resistance R 32 1 termination operational amplifier U31, other end ground connection.The output terminal of operational amplifier U31 is connected to the input end of totalizer.Do not process owing to having the offset of sinusoidal signal to carry out rectification, must by a totalizer, with sinusoidal signal and reference voltage Vf addition, more than moving 0V on the sinusoidal signal that collects, satisfy the requirement of Chip Microcomputer A/D input port 0-3V with this.Operational amplifier U32, resistance R 34-R37 forms anti-phase adder operation circuit.The output terminal of resistance R 34 1 termination low-pass filters, the negative terminal of another termination operational amplifier U32.Resistance R 36 1 termination reference voltage Vf, the negative terminal of another termination operational amplifier U32.The negative terminal of resistance R 37 1 termination operational amplifier U32, the output terminal of another termination operational amplifier U32.The anode of resistance R 35 1 termination operational amplifier U32, other end ground connection.The output terminal of operational amplifier U32 is connected to the AD input port of microcontroller 5.
Voltage zero-cross comparator circuit 4 comprises resistance R 41-R45, diode D41 and operational amplifier U41.Resistance R 41 and the input of R43 series connection power, and minute voltage power input.Resistance R 42 and R44 and operational amplifier U41 form voltage zero-crossing comparator.The node place of resistance R 42 1 termination R41 and R43, the positive input terminal of a termination operational amplifier U41.The negative input end of compensating resistance R44 one termination operational amplifier U41, an end ground connection.Greater than zero the time, the output terminal of operational amplifier U41 is output as high level when the voltage at the node place of resistance R 41 and R43, and less than zero the time, the output terminal of operational amplifier U41 is output as low level when the voltage at the node place of resistance R 41 and R43.The output terminal of resistance R 45 1 termination operational amplifier U41, the negative terminal of a terminating diode D41.Diode D41 one terminating resistor R45, other end ground connection.When the output terminal of operational amplifier U41 was output as low level, diode D41 conducting was pulled to zero to the voltage at the node place of resistance R 45 and diode D41.
Microcontroller 5 adopts the TMS320F28035 chip U5 of TI company, also can select the single-chip microcomputer of other models of other companies, detects needs as long as can satisfy.The AD input port pin 1 of microcontroller 5 connects the output terminal of signal conditioning circuit 3, i.e. the output port of operational amplifier U32, input load current signal.The external interrupt port pinout 2 of microcontroller 5 connects diode D41 and resistance R 45, reads the voltage over zero pulse signal of voltage zero-cross comparator circuit 4.The output port pin 3 of microcontroller 5 meets the hummer U6 in the fault output circuit.
Fault output circuit 6 comprises hummer U6.Output port pin 3, the one end ground connection of hummer U6 one termination microcontroller 5.Judge current breaking down during electric arc when microcontroller 5, it exports high level, triggers hummer, makes the staff know existing fault electric arc and occurs.
Fig. 5 to Fig. 8 has listed respectively typical home load electric iron and electric fan, normally moves and the current waveform figure when breaking down electric arc, can find out that by figure significant change can occur the electric current in circuit when in circuit, electric arc occuring.Hence one can see that uses difference-mean square root method to carry out computational analysis to current value in circuit, and failure judgement electric arc is practicable.
Embodiment recited above is described the preferred embodiment of the present invention; be not that the spirit and scope of the present invention are limited; do not breaking away under design proposal prerequisite of the present invention; various modification and improvement that in this area, common engineering technical personnel make technical scheme of the present invention; all should fall into protection scope of the present invention; the technology contents that the present invention asks for protection all is documented in claims.
Claims (10)
1. series fault arc early warning system, comprise power circuit (1), current transformer (CT), current sensing circuit (2) and signal conditioning circuit (3), it is characterized in that: also comprise microprocessor (5), fault output circuit (6) and the voltage zero-cross comparator circuit (4) that is connected with electrical network, described current transformer (CT), current sensing circuit (2), signal conditioning circuit (3) is connected successively with described microprocessor (5), described voltage zero-cross comparator circuit (4) is connected with described microprocessor (5) respectively with fault output circuit (6), described current transformer (CT) gathers the current signal in electrical network, through described current sensing circuit (2), current signal is converted into voltage signal, pass through again described signal conditioning circuit (3) and input described microprocessor (5), described voltage zero-cross comparator circuit (4) output voltage zero-crossing pulse signal is to described microprocessor (5), the control sequence of described microprocessor (5) is carried out following steps:
Step 101, the microcontroller initialization; Step 102, register configuration comprises AD register and timer register;
Step 103 judges whether the line voltage amplitude is 0 from negative extremely positive zero crossing zone bit ZeroFlag, when it is 0, and execution in step 104; Otherwise, wait for, until ZeroFlag is 0;
Step 104 is carried out difference to the current value in adjacent two cycles and is calculated, and gets Y
k=X2 (k)-X1 (k), wherein, k=1,2 ..., N;
Step 105, the value of use mean square root method design factor Z:
In formula, Y
1,, Y
2..., Y
nBe the difference of N sampled point corresponding to adjacent two cycles, and the threshold values that coefficient Z is set is the first threshold values;
Step 106, calculate the rate of change between adjacent two Z values:
Wherein, Z
nBe the value of n coefficient Z, Z
n+2Be the value of n+1 coefficient Z, and the threshold values that rate of change δ is set is the second threshold values;
Whether step 107, the value that judges Z more than or equal to the value of the first threshold values Zb, if more than or equal to Zb, and execution in step 108; Otherwise, return to step 103;
Whether step 108, the value that judges δ more than or equal to the value of the second threshold values δ b, if more than or equal to δ b, and execution in step 109; Otherwise, return to step 103;
Step 109, the threshold values that the arc event number of times is set is the 3rd threshold values, whether judges timer just in timing, if timer just in timing, execution in step 110; Otherwise, execution in step 111;
Step 110, counter adds one, and the electric arc cycle has appearred one time in expression;
Step 111, timer begins timing, and counter adds one;
Step 112 judges whether timer reaches 0.5s, if reach 0.5s, and execution in step 113; Otherwise return to step 103;
Whether step 113 judges counter more than or equal to the 3rd threshold values and generation electric arc number of times threshold values, if more than or equal to the 3rd threshold values, and execution in step 114; Otherwise, execution in step 115;
Step 114, the early warning information that the output fault electric arc occurs is controlled hummer through described fault output circuit (6) and is rung;
Step 115, clear timer, counter.
2. series fault arc early warning system according to claim 1, it is characterized in that: wherein said current sensing circuit (2) comprises the RC wave filter, described current transformer (CT) is arranged on the zero line or live wire of electrical network, its output signal is connected to the RC wave filter, and the output terminal of RC wave filter is connected with signal conditioning circuit (3).
3. series fault arc early warning system according to claim 1 and 2, it is characterized in that: the totalizer (U32) that wherein said signal conditioning circuit (3) comprises low-pass filter (U31) and is attached thereto, described low-pass filter (U31) is connected with current sensing circuit (2), and the output terminal of totalizer (U32) is connected with microprocessor (5).
4. series fault arc early warning system according to claim 3, it is characterized in that: wherein said voltage zero-cross comparator circuit (4) comprises bleeder circuit, comparer (U41) and the shaping circuit that is connected successively, electrical network access bleeder circuit, the shaping circuit output terminal is connected with the input end of microprocessor (5).
5. series fault arc early warning system according to claim 4, it is characterized in that: wherein said fault output circuit (6) comprises hummer.
6. series arc faults detection method, it is characterized in that: the method arranges power circuit (1), current transformer (CT), current sensing circuit (2), signal conditioning circuit (3), voltage zero-cross comparator circuit (4), microprocessor (5) and fault output circuit (6), and the method comprises:
1) begin to gather original load current Xi(n by the line voltage amplitude from negative extremely positive zero crossing), wherein: n=0,1,2,3 ..., N-1, N counts for gathering, and N=T/Ts, T are the line voltage cycle, and Ts is the sampling period;
2) calculate the difference of each sampled point current value that adjacent two cycles collect;
3) utilize root mean square formula design factor Z value by the difference of N sampled point current value;
4) the Z value in adjacent two cycles is carried out the rate of change analysis, design factor Z rate of change δ;
5) threshold values that coefficient Z is set is the first threshold values, and the threshold values of coefficient Z rate of change δ is the second threshold values, and the threshold values of arc event number of times M is the 3rd threshold values;
6) whether the Z value that gone out by i cycle and i+1 computation of Period of judgement is more than or equal to described the first threshold values;
7) whether judge by Z value rate of change δ more than or equal to described the second threshold values;
8) if the current i cycle meet the following conditions: a) coefficient Z 〉=the first threshold values, b) rate of change δ=the second threshold values, judge that the i cycle is the fault electric arc cycle;
9) if at the appointed time in t, arc event number of times M 〉=the 3rd threshold values, fault electric arc, output fault electric arc generation signal have occured this moment in judgement.
7. method according to claim 6 is characterized in that: wherein said step 1) comprising:
A) judge whether the line voltage amplitude is 1 from negative extremely positive zero crossing zone bit ZeroFlag, if ZeroFlag is 1, execution in step b);
B) start the A/D sampling, gather load current signal, each cycle all gathers N point, and i periodic current sampled value is Xi(n), wherein, n=0,1,2 ..., N-1, N=T/Ts, T are the electrical network cycle, Ts is collection period;
C) when the number of signals collecting reaches N, execution in step d), otherwise, interrupt returning;
D) to n and ZeroFlag zero clearing, prepare next periodic sampling.
8. according to claim 6 or 7 described methods is characterized in that: comprise that wherein said step 2) value with first sampled point of second period deducts the value of first first sampled point of cycle, is made as Y
k=X2 (k)-X1 (k), wherein, X2 (1) is the numerical value of first point of second period, X1 (1) is the numerical value of first point of first cycle, by that analogy, obtains Y
1,, Y
2..., Y
nBe total to N value.
9. method according to claim 8 is characterized in that: wherein said step 3) design factor Z adopts following formula:
In formula, Y
1,, Y
2..., Y
nDifference for N sampled point corresponding to adjacent two cycles.
10. method according to claim 9 is characterized in that: wherein said step 4) calculate the following formula of rate of change employing between adjacent two Z values:
Wherein, Z
nBe the value of n coefficient Z, Z
n+2It is the value of n+1 coefficient Z.
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