CN107134777B - Passive filtering device and method with lightning protection isolation and fire prevention early warning functions - Google Patents

Passive filtering device and method with lightning protection isolation and fire prevention early warning functions Download PDF

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CN107134777B
CN107134777B CN201710412135.2A CN201710412135A CN107134777B CN 107134777 B CN107134777 B CN 107134777B CN 201710412135 A CN201710412135 A CN 201710412135A CN 107134777 B CN107134777 B CN 107134777B
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fault arc
sampling
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lightning
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CN107134777A (en
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袁敞
袁洋波
李旷
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Beijing Enrely Technology Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • 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
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/005—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection avoiding undesired transient conditions
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

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Abstract

The invention provides a passive filtering device with lightning protection isolation and fire prevention early warning functions and a method thereof, wherein the device has the functions of ground potential counterattack isolation, fire prevention early warning and passive filtering, shares the current detection part of a fault arc and the current detection part of the passive filtering, adopts the same detection signal, and uses a common main control unit to simultaneously carry out fault arc analysis and harmonic content calculation, so that the device can be sampled before the characteristic current of the fault arc is filtered, and the accurate detection of the fault arc is ensured. The method for detecting the fault arc judges the fault arc by using the judgment result of the current difference parameter as a premise and by using the change rate of the harmonic content rate, can effectively eliminate the interference of nonlinear loads, and can accurately detect the fault arc under the condition of complex equipment by adopting four judgment means for judgment.

Description

Passive filtering device and method with lightning protection isolation and fire prevention early warning functions
Technical Field
The invention relates to the technical field of power quality detection and management, in particular to a passive filtering device with lightning protection isolation and fire prevention early warning functions and a method.
Background
Arcing is a gas discharge phenomenon, which is a momentary spark produced by the passage of current through some insulating medium. With the improvement of the economic level of China, the electricity consumption for life is rapidly increased, and the power distribution system is more and more complex. Because distribution lines space is limited, many wires in the block terminal are bundled together, and can make cable insulation receive the harm when the power consumption is in overload state, and then produce the fault arc and initiate electric fire. In addition, when the power utilization is switched on and off due to poor contact between lines or the influence of environmental factors, fault arcs can be generated at the connecting points, and then fire disasters are caused. Since the voltage effective value of the fault arc is close to the non-fault-time voltage effective value, the protection device is difficult to find when the fault arc occurs.
The passive filter is a filter circuit designed by combining an inductor, a capacitor and a resistor, can remove one or more harmonics, is the most common passive filter structure easy to adopt, and has the advantages of simple structure, low cost, reliable operation, low cost and the like, and is widely applied to harmonic treatment of a system. Passive filters are classified into single-tuned filters, double-tuned filters, and high-pass filters.
However, due to the installation of the passive filter device, high-frequency harmonic components in the current may be filtered, so that the original fault arc detection device cannot normally detect the fault arc, and the normal operation of the fault arc detection device is affected.
Meanwhile, with the continuous progress of industrial production in China, the automation control level is higher and higher, more and more distributed control systems and intelligent instruments are widely applied, in order to prevent the automation products from being damaged by lightning, a power system adopts a large number of lightning protection grounding measures, usually, ground potential counterattack isolation is arranged between a lightning protection ground and a protection ground, and when lightning protection is prevented, ground potential counterattack causes damage to connection equipment of the protection ground. The ground potential counterattack isolation usually presents low impedance when no surge current exists, presents high impedance when the surge current exists, and plays an isolation role on lightning current. However, the ground potential counterattack isolation device may also have an isolation effect on the high-frequency current generated by the fault arc, and affect the normal operation of the fault arc detection device.
Therefore, when the ground potential counterattack isolation device, the fault arc detection device and the reactive power compensation device are operated independently, adverse effects may be caused on each other, resulting in a loss that is difficult to estimate.
Meanwhile, the use of non-linear loads such as capacitors, inductors, thyristors, IGBTs and the like can cause current harmonics in the circuit, and the conventional fault arc detection method can also cause missed judgment and misjudgment. If the change rate of the harmonic content rate is utilized, the interference of the nonlinear load can be eliminated, the change rate is compared with the method, if the nonlinear load is connected into the circuit, the harmonic content rate is increased and exceeds the limit, but the change rate cannot exceed the limit. And when the fault arc occurs, the harmonic content rate can be changed violently, and the change rate of the harmonic content rate between two adjacent periods can be out of limit, so that the fault arc is judged. At present, there is no method for determining a fault arc by using the rate of change of the harmonic content.
Disclosure of Invention
In order to solve the problems in the background art, the invention provides a passive filtering device and a passive filtering method with lightning protection isolation and fire prevention early warning functions. The method for detecting the fault arc judges the fault arc by using the judgment result of the current difference parameter as a premise and by using the change rate of the harmonic content rate, can effectively eliminate the interference of nonlinear loads, and can accurately detect the fault arc under the condition of complex equipment by adopting four judgment means for judgment.
In order to achieve the purpose, the invention adopts the following technical scheme:
a passive filter device with functions of lightning protection isolation and fire prevention early warning is a device with functions of ground potential counterattack isolation, fire prevention early warning and passive filter, and comprises a voltage sensor, a current sensor, a sampling circuit, a signal processing circuit, a master control MCU (microprogrammed control unit), an arc fault alarm circuit, a switching value isolation output circuit, a thyristor drive circuit, a thyristor switch, a capacitor, an inductor and a ground potential counterattack isolation module.
The main control MCU is connected with the voltage sensor and the current sensor through the signal processing circuit and the sampling circuit, and respectively performs fault arc alarm output and TSF switching output after the same voltage and current sampling signal is subjected to fault arc analysis and harmonic current analysis; the device can be sampled before the fault arc characteristic current is filtered, and the accurate detection of the fault arc is ensured.
The ground potential counterattack isolation module is composed of a lightning current frequency impedor, is arranged between a lightning protection ground and a protection ground in series to form lightning isolation protection, presents low impedance under normal conditions and ensures normal and safe grounding of equipment; when lightning current is counterstruck from the lightning protection ground end, the lightning protection isolation element presents high impedance under the frequency of the lightning current, the counterattack of the lightning is isolated, the lightning current is forced to be only released to the grounding grid, the ground end is protected from being damaged by the counterattack of the lightning, and after the lightning current is released, the lightning protection isolation element returns to a low impedance state.
The main control MCU outputs the fault arc alarm and controls the disconnection of the power supply circuit breaker through the switching value isolation output circuit, and the power supply is cut off when the fault occurs.
The capacitor and the inductor are connected in series and in star type to a three-phase alternating current power supply end, and a thyristor switch is connected between the capacitor and the inductor. The main control MCU controls the on or off of the thyristor switch through the thyristor drive circuit, so that the switching of the capacitance and the inductance in the main loop is controlled through the thyristor switch.
A control method of a passive filter device with lightning protection isolation and fire prevention early warning functions comprises the following steps:
firstly, initializing a system, and powering on a device;
collecting three-phase voltage and three-phase current of the system, and sending signals to a signal modulation processing circuit;
step three, the signal modulation processing circuit respectively modulates the voltage signal and the current signal and sends the modulated signals to the main control MCU unit;
fourthly, calculating system harmonic current by the main control MCU unit; meanwhile, processing the current signal and extracting an arc current characteristic value;
judging by the main control MCU unit according to the calculation result, and sending a harmonic suppression instruction to the drive circuit when the harmonic content exceeds a standard; according to the switching state of the filter device fed back by the driving circuit, if the filter device is not put into the driving circuit, sending a switching instruction to the driving circuit, and returning to the step two, if the filter device is put into the driving circuit, sending a locking instruction to the driving circuit, and returning to the step two;
if the harmonic content meets the standard, returning to the step two according to the switching state of the filter device fed back by the driving circuit, if the filter device is not put into the driving circuit, sending a cutting instruction to the driving circuit if the filter device is put into the driving circuit, and returning to the step two;
meanwhile, the main control MCU unit analyzes and judges the extracted arc current characteristic value according to logical calculation, if the extracted arc current characteristic value accords with a fault arc signal, an instruction is sent to a fault arc early warning module, and a power supply circuit breaker is cut off through an output signal, so that a fault arc is cut off; if not, no instruction is sent out, and the step two is returned;
and step six, the driving circuit receives the switching instruction of the control unit from the step five, sends the switching instruction to the thyristor, and simultaneously feeds back the switching state of the filter device to the control unit.
A fault arc detection method in a passive filter device with lightning protection isolation and fire prevention early warning functions adopts four conditions for common judgment, one of the judgment conditions uses a judgment result of a current difference parameter as a premise, adopts a harmonic content rate change rate to judge a fault arc, can effectively detect the fault arc under complex conditions, and comprises the following steps:
step 1: continuously sampling the current (64 or 128 points per cycle according to the actual hardware condition);
step 2: the sampled value of the current is 128 points per cycle or 64 points per cycle. Taking 64 points as an example, the current sampling value is marked as I0、I1、……、I63The normal cycle current is denoted as In0、In1、……、In63(the sampled value and the normal value are both per unit values). Calculating a difference parameter between the current sampling period current and the normal period current:
Figure BDA0001311395420000041
will IperAnd a threshold value S1By comparison, if Iper≤S1Then, the amplitude of the sampled current value is given to the normal period current value, and the normal period current value is updated; if Iper＞S1Then, further analysis and calculation are carried out to judge whether the fault arc occurs;
and step 3: calculating the average value of the current:
Figure BDA0001311395420000042
and judging whether the positive and negative half cycles of the current are symmetrical or not by using the average value of the current. If IaveIf the waveform symmetry is larger than the given threshold S2, the waveform symmetry is considered not to meet the requirement, 1 is assigned to the waveform symmetry indicating parameter m1, and otherwise, 0 is assigned to m 1;
and 4, step 4: calculating the difference value of two adjacent sampling values of the sampling current:
ΔIk＝Ik+1-Ik(k＝0,1,2……62) (3)
using the maximum value K of the differencev＝max[ΔI0，ΔI1，...，ΔI62]To represent the maximum rate of change of the current. If KvIf the current change rate is larger than the threshold S3, the current change rate is considered to be too large, 1 is assigned to the current change rate parameter m2, and if the current change rate parameter m2 is not assigned to zero;
and 5: calculating the wave mode parameters of the current:
Figure BDA0001311395420000043
Figure BDA0001311395420000044
α is set according to actual current, and the peak value of normal current is taken, the wave pattern parameter of current can indicate whether the current contains flat shoulder, if KpIf the current is greater than the threshold S4, the current is considered to contain a flat shoulder, the flat shoulder indicating parameter m3 is assigned with 1, and if not, m3 is assigned with zero;
step 6: the harmonic of the sampling current is detected by FFT, and the content rate of change DeltaP of the higher harmonic of the sampling current (here, the 3 rd, 5 th, 7 th and 9 th harmonics are calculated) is calculatednIf Δ PnIf the harmonic content of the sampled current is larger than the threshold value S4, the harmonic content of the sampled current is considered to be abnormal, the harmonic indication parameter m4 is assigned to be 1, and if not, the harmonic indication parameter m4 is assigned to be 0;
and 7: calculating the sum of four indication parameters in the steps 3 to 6, namely m is m1+ m2+ m3+ m 4; if m > is 2, the indication parameter sum of the fault arc frequency is sum +1, and if sum > is 6, an alarm signal is triggered; if sum is less than 6, returning to the step 2 to continue judging; and if m is less than 2, determining that no fault arc occurs, assigning 0 to sum, and updating the normal current to the current sampling current.
The specific steps of step 6 are as follows:
step 601, calculating the odd harmonic content rate change rate delta P of the sampling periodnAnd setting a threshold value Δ PthComparing; the harmonic content is defined as
Figure BDA0001311395420000051
Wherein I1Is a fundamental current, IhIs the root mean square value of the h-th harmonic current,
Figure BDA0001311395420000052
Xh1the h harmonic current sampling value is obtained, M is the number of sampling points, in this example, 3, 5, 7 and 9 harmonics are taken, and the odd harmonic content is calculated to be
Figure BDA0001311395420000053
Step 602, calculating the change rate delta P of the odd harmonic content of the current in two adjacent power frequency sampling periods by taking the 1 st normal power frequency sampling period current odd harmonic content P judged in the step 2 as a basic valuen，ΔPn＝PnP, the difference of the odd harmonic content rate of the current between two sampling periods is the change rate delta P of the odd harmonic content rate of the sampling periodn。
Compared with the prior art, the invention has the beneficial effects that:
1. according to the passive filter device with the functions of lightning protection isolation and fire prevention early warning, the current detection part of the fault arc and the current detection part of the passive filter are shared, and the same detection signal is adopted, so that the device can be sampled before the characteristic current of the fault arc is filtered, and the accurate detection of the fault arc is ensured.
2. According to the passive filter device with the functions of lightning protection isolation and fire prevention early warning and the control method thereof, the same main control MCU is used for processing the same current data, the fault arc characteristic value and the harmonic content are respectively calculated, and the fault arc alarm circuit and the filtered thyristor drive circuit are respectively controlled, so that the two functions are realized by using a single device, the use is considered, and the problems that the fault arc is missed and misjudged due to the use of the filter device are effectively solved.
3. According to the fault arc detection method of the passive filter device with the lightning protection isolation and fire prevention early warning functions, the judgment result of the current difference parameter is used as a premise, the harmonic content rate change rate is adopted to judge the fault arc, the interference of a nonlinear load can be effectively eliminated, meanwhile, four judgment means are adopted to judge, and the fault arc can be accurately detected under the condition of complex equipment.
4. According to the passive filter device with the lightning protection isolation and fire prevention early warning functions, the ground potential counterattack isolation equipment is integrated into the passive filter device with the isolation fire prevention early warning function, so that the whole equipment has the ground potential counterattack isolation function, does not influence the detection of the fault arc, and has a better fault arc detection effect than the condition that the equipment is independently installed.
Drawings
FIG. 1 is a schematic structural diagram of a passive filter device with lightning protection isolation and fire prevention early warning functions according to the present invention;
FIG. 2 is a schematic diagram of a main control MCU control structure of a passive filter device with lightning protection isolation and fire prevention early warning functions according to the present invention;
FIG. 3 is a schematic diagram of a ground potential counterattack isolation module of a passive filter device with lightning protection isolation and fire prevention early warning functions according to the present invention
FIG. 4 is a structural diagram of a main filtering loop of a passive filtering device with lightning protection isolation and fire prevention early warning functions according to the present invention;
FIG. 5 is a flowchart of a method for controlling a passive filter device with lightning protection isolation and fire prevention pre-warning functions according to the present invention;
fig. 6 is a flowchart of a method for detecting a fault arc in a passive filter device with lightning protection isolation and fire prevention early warning functions according to the present invention.
Detailed Description
The following detailed description of the present invention will be made with reference to the accompanying drawings.
As shown in fig. 1, a passive filter device with lightning protection isolation and fire prevention early warning functions is a device with ground potential counterattack isolation, fire prevention early warning and passive filter functions, and comprises a voltage sensor, a current sensor, a sampling circuit, a signal processing circuit, a master control MCU, an arc fault alarm circuit, a switching value isolation output circuit, a thyristor drive circuit, a thyristor switch, a capacitor, an inductor and a ground potential counterattack isolation module.
As shown in fig. 2, the main control MCU is connected to the voltage sensor and the current sensor through the signal processing circuit and the sampling circuit, and the main control MCU performs fault arc alarm output and TSF switching output after performing fault arc analysis and harmonic current analysis on the same voltage and current sampling signals respectively; the device can be sampled before the fault arc characteristic current is filtered, and the accurate detection of the fault arc is ensured.
As shown in fig. 3, the ground potential counterattack isolation module is composed of a lightning current frequency impedor, and is installed in series between a lightning protection ground and a protection ground to form lightning isolation protection, and presents low impedance under normal conditions, so as to ensure normal and safe grounding of equipment; when lightning current is counterstruck from the lightning protection ground end, the lightning protection isolation element presents high impedance under the frequency of the lightning current, the counterattack of the lightning is isolated, the lightning current is forced to be only released to the grounding grid, the ground end is protected from being damaged by the counterattack of the lightning, and after the lightning current is released, the lightning protection isolation element returns to a low impedance state.
The lightning current frequency impedor is a reactor, the magnetic core material of which can be ferrite magnetic core such as manganese zinc series material, nickel zinc series material, magnesium zinc series material, etc., or alloy magnetic core such as silicon (silicon) steel material, iron powder core, iron silicon aluminum alloy, iron nickel alloy, molybdenum permalloy, amorphous, microcrystal alloy, etc. The wire can be polyurethane enameled wire, polyester enameled wire self-adhesive polyurethane enameled wire, wire-covered wire, stranded wire, electroplated copper wire, three-layer insulated wire, PVC wire and the like. The equivalent model can be expressed as an ideal inductor connected with an equivalent resistor in series and then connected with a parasitic capacitor in parallel, the external characteristic shows that the frequency band with dense lightning current energy presents high impedance, and other frequency bands present low impedance. The device is in a conducting state under normal conditions, the impedance is low, and normal and safe grounding of the device is guaranteed; when the grounding system has lightning current, the element has high impedance under the frequency of the lightning current, and blocks the counterattack of the lightning, so that the lightning current can only be discharged to the ground grid. When the lightning current is discharged, the ground potential counterattack isolation element returns to a low impedance state.
The main control MCU outputs the fault arc alarm and controls the disconnection of the power supply circuit breaker through the switching value isolation output circuit, and the power supply is cut off when the fault occurs.
The capacitor and the inductor are connected in series and in star type to a three-phase alternating current power supply end, and a thyristor switch is connected between the capacitor and the inductor. The main control MCU controls the on or off of the thyristor switch through the thyristor drive circuit, so that the switching of the capacitance and the inductance in the main loop is controlled through the thyristor switch.
As shown in fig. 4, it is a structure diagram of the filtering main loop of the device of the present invention, wherein the thyristor switch is a bidirectional thyristor.
As shown in fig. 5, a control method of a passive filter device with lightning protection isolation and fire prevention early warning functions includes the following steps:
firstly, initializing a system, and powering on a device;
collecting three-phase voltage and three-phase current of the system, and sending signals to a signal modulation processing circuit;
step three, the signal modulation processing circuit respectively modulates the voltage signal and the current signal and sends the modulated signals to the main control MCU unit;
fourthly, calculating system harmonic current by the main control MCU unit; meanwhile, processing the current signal and extracting an arc current characteristic value;
judging by the main control MCU unit according to the calculation result, and sending a harmonic suppression instruction to the drive circuit when the harmonic content exceeds a standard; according to the switching state of the filter device fed back by the driving circuit, if the filter device is not put into the driving circuit, sending a switching instruction to the driving circuit, and returning to the step two, if the filter device is put into the driving circuit, sending a locking instruction to the driving circuit, and returning to the step two;
if the harmonic content meets the standard, returning to the step two according to the switching state of the filter device fed back by the driving circuit, if the filter device is not put into the driving circuit, sending a cutting instruction to the driving circuit if the filter device is put into the driving circuit, and returning to the step two;
meanwhile, the main control MCU unit analyzes and judges the extracted arc current characteristic value according to logical calculation, if the extracted arc current characteristic value accords with a fault arc signal, an instruction is sent to a fault arc early warning module, and a power supply circuit breaker is cut off through an output signal, so that a fault arc is cut off; if not, no instruction is sent out, and the step two is returned;
and step six, the driving circuit receives the switching instruction of the control unit from the step five, sends the switching instruction to the thyristor, and simultaneously feeds back the switching state of the filter device to the control unit.
As shown in fig. 6, a method for detecting a fault arc in a passive filter device with lightning protection isolation and fire prevention early warning functions adopts four conditions for common judgment, one of the judgment conditions uses a judgment result of a current difference parameter as a premise, and adopts a harmonic content rate change rate to judge the fault arc, so that the fault arc can be effectively detected under a complex condition, and the method comprises the following steps:
step 1: continuously sampling the current (64 or 128 points per cycle according to the actual hardware condition);
step 2: the sampled value of the current is 128 points per cycle or 64 points per cycle. Taking 64 points as an example, the current sampling value is marked as I0、I1、……、I63The normal cycle current is denoted as In0、In1、……、In63(the sampled value and the normal value are both the standard valueA value). Calculating a difference parameter between the current sampling period current and the normal period current:
Figure BDA0001311395420000081
will IperAnd a threshold value S1By comparison, if Iper≤S1Then, the amplitude of the sampled current value is given to the normal period current value, and the normal period current value is updated; if Iper＞S1Then, further analysis and calculation are carried out to judge whether the fault arc occurs;
and step 3: calculating the average value of the current:
Figure BDA0001311395420000082
and judging whether the positive and negative half cycles of the current are symmetrical or not by using the average value of the current. If IaveIf the waveform symmetry is larger than the given threshold S2, the waveform symmetry is considered not to meet the requirement, 1 is assigned to the waveform symmetry indicating parameter m1, and otherwise, 0 is assigned to m 1;
and 4, step 4: calculating the difference value of two adjacent sampling values of the sampling current:
ΔIk＝Ik+1-Ik(k＝0,1,2……62) (3)
using the maximum value K of the differencev＝max[ΔI0，ΔI1，...，ΔI62]To represent the maximum rate of change of the current. If KvIf the current change rate is larger than the threshold S3, the current change rate is considered to be too large, 1 is assigned to the current change rate parameter m2, and if the current change rate parameter m2 is not assigned to zero;
and 5: calculating the wave mode parameters of the current:
Figure BDA0001311395420000083
Figure BDA0001311395420000084
wherein α is set according to actual current, generallyTaking the normal current peak value. The wave pattern parameters of the current can be used to indicate whether the current contains a flat shoulder. If KpIf the current is greater than the threshold S4, the current is considered to contain a flat shoulder, the flat shoulder indicating parameter m3 is assigned with 1, and if not, m3 is assigned with zero;
step 6: the harmonic of the sampling current is detected by FFT, and the content rate of change DeltaP of the higher harmonic of the sampling current (here, the 3 rd, 5 th, 7 th and 9 th harmonics are calculated) is calculatednIf Δ PnIf the harmonic content of the sampled current is larger than the threshold value S4, the harmonic content of the sampled current is considered to be abnormal, the harmonic indication parameter m4 is assigned to be 1, and if not, the harmonic indication parameter m4 is assigned to be 0;
and 7: calculating the sum of four indication parameters in the steps 3 to 6, namely m is m1+ m2+ m3+ m 4; if m > is 2, the indication parameter sum of the fault arc frequency is sum +1, and if sum > is 6, an alarm signal is triggered; if sum is less than 6, returning to the step 2 to continue judging; and if m is less than 2, determining that no fault arc occurs, assigning 0 to sum, and updating the normal current to the current sampling current.
The specific steps of step 6 are as follows:
step 601, calculating the odd harmonic content rate change rate delta P of the sampling periodnAnd setting a threshold value Δ PthComparing; the harmonic content is defined as
Figure BDA0001311395420000091
Wherein I1Is a fundamental current, IhIs the root mean square value of the h-th harmonic current,
Figure BDA0001311395420000092
Xh1the h harmonic current sampling value is obtained, M is the number of sampling points, in this example, 3, 5, 7 and 9 harmonics are taken, and the odd harmonic content is calculated to be
Figure BDA0001311395420000093
Step 602, calculating the change rate delta P of the odd harmonic content of the current in two adjacent power frequency sampling periods by taking the 1 st normal power frequency sampling period current odd harmonic content P judged in the step 2 as a basic valuen，ΔPn＝PnP, the difference of the odd harmonic content rate of the current between two sampling periods is the change rate delta P of the odd harmonic content rate of the sampling periodn。
According to the passive filter device with the functions of lightning protection isolation and fire prevention early warning, the current detection part of the fault arc and the current detection part of the passive filter are shared, and the same detection signal is adopted, so that the device can be sampled before the characteristic current of the fault arc is filtered, and the accurate detection of the fault arc is ensured.
According to the passive filter device with the functions of lightning protection isolation and fire prevention early warning and the control method thereof, the same main control MCU is used for processing the same current data, the fault arc characteristic value and the harmonic content are respectively calculated, and the fault arc alarm circuit and the filtered thyristor drive circuit are respectively controlled, so that the two functions are realized by using a single device, the use is considered, and the problems that the fault arc is missed and misjudged due to the use of the filter device are effectively solved.
According to the fault arc detection method of the passive filter device with the lightning protection isolation and fire prevention early warning functions, the judgment result of the current difference parameter is used as a premise, the harmonic content rate change rate is adopted to judge the fault arc, the interference of a nonlinear load can be effectively eliminated, meanwhile, four judgment means are adopted to judge, and the fault arc can be accurately detected under the condition of complex equipment.
According to the passive filter device with the lightning protection isolation and fire prevention early warning functions, the ground potential counterattack isolation equipment is integrated into the passive filter device with the isolation fire prevention early warning function, so that the whole equipment has the ground potential counterattack isolation function, does not influence the detection of the fault arc, and has a better fault arc detection effect than the condition that the equipment is independently installed.
The above embodiments are implemented on the premise of the technical solution of the present invention, and detailed embodiments and specific operation procedures are given, but the scope of the present invention is not limited to the above embodiments. The methods used in the above examples are conventional methods unless otherwise specified.

Claims (1)

1. A control method of a passive filter device with lightning protection isolation and fire prevention early warning functions is characterized in that the passive filter device is a device with ground potential counterattack isolation, fire prevention early warning and passive filter functions, and comprises a voltage sensor, a current sensor, a sampling circuit, a signal processing circuit, a main control MCU unit, a fault arc early warning module, a switching value isolation output circuit, a thyristor drive circuit, a thyristor switch, a capacitor, an inductor and a ground potential counterattack isolation module;
the ground potential counterattack isolation module is composed of a lightning current frequency impedor, is arranged between a lightning protection ground and a protection ground in series to form lightning isolation protection, presents low impedance under normal conditions and ensures normal and safe grounding of equipment; when lightning current counterattacks from the lightning protection ground end, the lightning current frequency impedor presents high impedance under the lightning current frequency, lightning counterattack is isolated, lightning current can only be released to a grounding grid, the ground end is protected from being damaged by lightning counterattack, and after lightning current release is completed, the lightning current frequency impedor returns to a low impedance state;
the control method is characterized by comprising the following steps: the main control MCU unit is connected with the voltage sensor and the current sensor through the signal processing circuit and the sampling circuit, and respectively performs fault arc alarm output and TSF switching output after respectively performing fault arc analysis and harmonic current analysis on the same voltage and current sampling signal; the device can be sampled before the fault arc characteristic current is filtered, so that the accurate detection of the fault arc is ensured;
the method comprises the following steps:
firstly, initializing a system, and powering on a device;
collecting three-phase voltage and three-phase current of the system, and sending signals to a signal modulation processing circuit;
step three, the signal modulation processing circuit respectively modulates the voltage signal and the current signal and sends the modulated signals to the main control MCU unit;
fourthly, calculating system harmonic current by the main control MCU unit; meanwhile, processing the current signal and extracting an arc current characteristic value;
judging by the main control MCU unit according to the calculation result, and sending a harmonic suppression instruction to the drive circuit when the harmonic content exceeds a standard; according to the switching state of the filter device fed back by the driving circuit, if the filter device is not put into the driving circuit, sending a switching instruction to the driving circuit, and returning to the step two, if the filter device is put into the driving circuit, sending a locking instruction to the driving circuit, and returning to the step two;
if the harmonic content meets the standard, returning to the step two according to the switching state of the filter device fed back by the driving circuit, if the filter device is not put into the driving circuit, sending a cutting instruction to the driving circuit if the filter device is put into the driving circuit, and returning to the step two;
meanwhile, the main control MCU unit analyzes and judges the extracted arc current characteristic value through logic calculation, if the extracted arc current characteristic value accords with a fault arc signal, an instruction is sent to a fault arc early warning module, and a power supply circuit breaker is cut off through an output signal to cut off the fault arc; if not, no instruction is sent out, and the step two is returned;
step six, the driving circuit receives the switching instruction of the master control MCU unit from the step five, sends the switching instruction to the thyristor, and simultaneously feeds back the switching state of the filter device to the master control MCU unit;
the control method also comprises a fault arc detection method, wherein the four conditions are adopted for joint judgment, one judgment condition is on the premise that the judgment result of the current difference parameter is used as a premise, the harmonic content rate change rate is adopted for judging the fault arc, and the fault arc can be effectively detected under the complex condition, and the method comprises the following steps:
step 1: continuously sampling the current, and sampling 64 or 128 points in each period according to the actual hardware condition;
step 2: the sampling value of the current is 128 points per cycle or 64 points per cycle; the current sampling value is marked as I0、I1、……、IM-1M is 64 or 128, M is the number of sampling points per period, and the normal period current is marked as In0、In1、……、In(M-1)The sum of the sampled valuesThe normal values are per unit values; calculating a difference parameter between the current sampling period current and the normal period current:
Figure FDA0002532143740000021
will IperAnd a threshold value S1By comparison, if Iper≤S1Then, the sampling current value is given to the normal period current value, and the normal period current value is updated; if Iper＞S1Then, further analysis and calculation are carried out to judge whether the fault arc occurs;
and step 3: calculating the average value of the current:
Figure FDA0002532143740000022
judging whether the positive and negative half cycles of the current are symmetrical by using the average value of the current; if IaveIf the waveform symmetry is larger than the given threshold S2, the waveform symmetry is considered not to meet the requirement, 1 is assigned to the waveform symmetry indicating parameter m1, and otherwise, 0 is assigned to m 1;
and 4, step 4: calculating the difference value of two adjacent sampling values of the sampling current:
ΔIk＝Ik+1-Ik(k＝0,1,2……M-2) (3)
using the maximum value K of the differencev＝max[△I0，△I1，……，△IM-2]To represent the maximum rate of change of current; if KvIf the current change rate is larger than the threshold S3, the current change rate is considered to be too large, 1 is assigned to the current change rate parameter m2, and if the current change rate parameter m2 is not assigned to zero;
and 5: calculating the wave mode parameters of the current:
Figure FDA0002532143740000023
Figure FDA0002532143740000024
α is set according to actual current, and the wave pattern parameter of the current can indicate whether the current contains flat shoulder, if KpIf the current is greater than the threshold S4, the current is considered to contain a flat shoulder, the flat shoulder indicating parameter m3 is assigned with 1, and if not, m3 is assigned with zero;
step 6, detecting the harmonic wave of the sampling current by using FFT, calculating the change rate of the odd harmonic content rate of the sampling current, and calculating the change rates of the 3 rd, 5 th, 7 th and 9 th harmonic content rates △ PnIf △ PnGreater than threshold △ PthIf the harmonic content of the sampled current is abnormal, assigning the harmonic indication parameter m4 as 1, otherwise, assigning the harmonic indication parameter m4 as 0;
step 601, calculating △ P of the rate of change of the odd harmonic content in the sampling periodnAnd set threshold △ PthComparing; the harmonic content is defined as
Figure FDA0002532143740000031
Wherein I1Is a fundamental current, IhIs the root mean square value of the h-th harmonic current,
Figure FDA0002532143740000032
xh1、xh2……xhMfor the h harmonic current sampling value, M is the number of sampling points per period, 3, 5, 7 and 9 harmonics are taken, and the odd harmonic content is calculated as
Figure FDA0002532143740000033
Step 602, calculating △ P of the content rate of the odd harmonic of the current in two adjacent power frequency sampling periods by taking the 1 st normal power frequency sampling period current odd harmonic content P judged in the step 2 as a basic valuen，△P1＝P1-P，△Pn＝Pn-Pn-1，n>1, the difference of the odd harmonic content rate of the current between two sampling periods is the change rate △ P of the odd harmonic content rate of the sampling periodn；
And 7: calculating the sum of four indication parameters in the steps 3 to 6, namely m is m1+ m2+ m3+ m 4; if m > is 2, the indication parameter sum of the fault arc frequency is sum +1, and if sum > is 6, an alarm signal is triggered; if sum is less than 6, returning to the step 2 to continue judging; and if m is less than 2, determining that no fault arc occurs, assigning 0 to sum, and updating the normal period current to be the current sampled at the moment.
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