CN108132376A - Modular transformer iron core grounding current on-Line Monitor Device - Google Patents
Modular transformer iron core grounding current on-Line Monitor Device Download PDFInfo
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- CN108132376A CN108132376A CN201711469068.4A CN201711469068A CN108132376A CN 108132376 A CN108132376 A CN 108132376A CN 201711469068 A CN201711469068 A CN 201711469068A CN 108132376 A CN108132376 A CN 108132376A
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical group [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims abstract description 37
- 238000005259 measurement Methods 0.000 claims abstract description 67
- 238000000034 method Methods 0.000 claims abstract description 33
- 238000001914 filtration Methods 0.000 claims abstract description 28
- 238000004422 calculation algorithm Methods 0.000 claims abstract description 25
- 238000012544 monitoring process Methods 0.000 claims abstract description 17
- 238000004364 calculation method Methods 0.000 claims abstract description 15
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- 238000012795 verification Methods 0.000 claims abstract description 3
- 238000013461 design Methods 0.000 claims description 16
- 238000006243 chemical reaction Methods 0.000 claims description 12
- 238000012545 processing Methods 0.000 claims description 10
- 238000012806 monitoring device Methods 0.000 claims description 5
- 230000003139 buffering effect Effects 0.000 claims description 4
- 230000008859 change Effects 0.000 claims description 4
- FNMKZDDKPDBYJM-UHFFFAOYSA-N 3-(1,3-benzodioxol-5-yl)-7-(3-methylbut-2-enoxy)chromen-4-one Chemical compound C1=C2OCOC2=CC(C2=COC=3C(C2=O)=CC=C(C=3)OCC=C(C)C)=C1 FNMKZDDKPDBYJM-UHFFFAOYSA-N 0.000 claims description 3
- 238000012986 modification Methods 0.000 claims description 3
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- 238000003199 nucleic acid amplification method Methods 0.000 abstract description 7
- 230000006641 stabilisation Effects 0.000 abstract description 4
- 238000011105 stabilization Methods 0.000 abstract description 4
- 230000001429 stepping effect Effects 0.000 description 18
- 230000005611 electricity Effects 0.000 description 13
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- 238000005538 encapsulation Methods 0.000 description 8
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- 238000010586 diagram Methods 0.000 description 5
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/08—Circuits for altering the measuring range
- G01R15/09—Autoranging circuits
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
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- Physics & Mathematics (AREA)
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Abstract
The invention discloses a kind of modular transformer iron core grounding current on-Line Monitor Devices, it is characterized in that the signal wire that goes out of Verification of Measuring Current Transformer has concatenated several different sample resistances, by the different resistance of the analog switch short circuit of microprocessor control, the switching of different measuring ranges is realized.Alternating voltage on sample resistance is switched to DC pulse moving voltage, smoother DC voltage is obtained after capacitance-resistance filter by the single supply absolute value circuit specially designed, without amplification, directly inputs AD converter.The digital output of AD converter is sent into microprocessor, after microprocessor calculation process, you can obtain high-precision current measurement value.The Dynamic Hysteresis filtering algorithm of original creation, makes measuring device have excellent anti-interference, has fully ensured that the accurate stabilization of measurement data.The modular form that circuit is simplified with structure, considerably reduces cost.Both it can be matched with special secondary meter, and also can form remote online monitoring system with host computer.
Description
Technical field
The invention belongs to power electronics fields, are related to a kind of modular transformer iron core grounding current monitoring device.
Background technology
Power transformer is one of equipment crucial in electric system, its normal operation is that electric system can be supplied normally
The important guarantee of electricity.When transformer is installed, iron core has a ground wire.During transformer normal operation, iron core grounding current
Generally there was only several milliamperes~tens milliamperes.If the problems such as local electric leakage, short circuit occurs in inside transformer, can be produced in core interior
Raw circulation, causes hot-spot, the reliability service of iron core localized burn, serious threat transformer and power grid can be caused when serious.
Under this situation, transformer grounding electric current can significantly increase.According to regulatory requirements, when iron core grounding current reaches 100 milliampere hour,
Must just corresponding measure be taken to be handled.
In order to find the failure of transformer in time, traditional approach is that manually periodically earth current is carried out with clamp on amperemeter
Inspection.The defects of this method is most apparent be exactly, and due to being regular visit rather than real time on-line monitoring, fault discovery obtains not enough
In time, there is the risk for generating serious problems.With the rapid development of electronic technology, more and more occasions all employ microelectronics
Technology is monitored on-line, and avoiding problems the defects of manual type.
On-line monitoring, the size in addition to can measure current value, some equipment can also be come by analyzing the harmonic content of electric current
Speculate the operation conditions of transformer.But the theoretical foundation that accident analysis is carried out with harmonic content only exists in the exploratory stage, especially
Such equipment manufacturing cost is high, is not suitable for being widely used to promote.Really convenient for what is popularized, there is the scheme of practical significance, be online
Monitor the virtual value of transformer iron core grounding current.At present, the production of each producer and user in the on-line monitoring dress used
It puts, is such mostly.The present patent application is also the technology close with this type.Therefore, it is related humorous to electric current progress
The scheme of wave analysis is no longer inquired into detail below.
Measuring transformer iron core grounding current is wanted, will consider the acquisition of current signal first.In order to ensure transformer fe
The reliable ground of core, iron core grounding line are not allow any measuring device of connecting.Therefore, the measurement of earth current can only use
The indirect measurement of induction type.At present, most generally, most common method be exactly using current transformer.It will be grounded across electric current
Mutual inductor measures earth current indirectly by the sensing electric current of mutual inductor coil.In addition, also a kind of utilize hall sensing principle
Measuring method.But this method needs the hall sensing original paper specially designed, very minority, seldom uses.Thus, it utilizes
Current transformer measures, almost unique scheme of transformer iron core grounding current monitoring.
Monitored on-line using microelectric technique, from measuring technique in itself for, " transformer iron core grounding current " only
Only it is one kind in ten million kind of tested electric current, the measurement with common alternating current seems to have no difference.But in fact, with common
Current measurement is compared, and the measurement of transformer iron core grounding current has the characteristics of following two apparent：
First, transformer, when there is dependent failure, iron core grounding current has abnormal increase, there are several amperes, even
It is possible that more than 10 amperes.Current value can be accurately measured, there is important references value to analyzing failure cause.Therefore, it is desirable to
Monitoring device can have larger measurement range.The range of general this kind of product is generally 10 amperes, and what is also had can reach 20 amperes.
Second, transformer, in normal operation, iron core grounding current generally only has several milliamperes to more than ten milliamperes, Huo Zhegeng
It is larger.If reaching tens of milliamperes, just there is abnormal trend.According to regulatory requirements, when earth current reaches 100 milliamperes
When, it must just take corresponding measure.Therefore, under normal circumstances, measurement range only has 0~100 milliampere.
Two above feature causes the particularity of transformer iron core grounding current measurement.It seeks to 10 amperes of ranges
Current transformer measure the electric current within 100 milliamperes.In other words, measured value is less than the 1% of current transformer full scale.
Between this situation, height is not only required measurement accuracy, the index of tie-in accuracy of measurement is all difficult regulation.Routinely survey
For amount, if saying that measurement accuracy is 1 grade, the meaning is exactly 1% that measurement error is not more than full scale.But if by this convention
Carry out the measurement accuracy of regulation transformer iron core grounding current, it is just problematic.Because full scale is 10 amperes, 1% error, just
It is 100 milliamperes of error.And when normally measuring, measured value only has several milliamperes to more than ten milliamperes, and ratio error is also small.In other words,
When tested electric current is also smaller than the measurement error of measuring apparatus, measurement result is completely incredible.Therefore, by full scale
1% to carry out specification error index obviously unreasonable.
It is certainly out of question from application angle if the 1% of specifying measurement value is used as error criterion.But technically, small electricity
During flow measure, can not just it realize.Such as measured value is 1 milliampere, 1% error is exactly 0.01 milliampere.With 10 amperes of full scale
Current transformer, it is desirable that measurement error is 0.01 milliampere, is equivalent to the 1/10 of full scale6, it is clear that it is hardly possible to accomplish.
If by measurement range stepping, for example it is divided into 3 grades：0~100mA, 100mA~1A, 1A~10A.Provide each shelves
1% of measurement error no more than every grade of greatest measurement.In this way, 0~100mA grades common, measurement error is not more than
1mA can meet the required precision actually measured, technically can also realize.But it is in this shelves of 100mA~1A, the 1% of 1A
10mA.For the measured value of 100mA, the error of 10mA is obviously excessive, this is also unreasonable.
In conclusion most rational error regulation should be：
When measured value is within 100mA, error is not more than 1mA (the 1% of 100mA)；When measured value is more than 100mA, error
No more than the 1% of measured value.Requirement of engineering can be met in this way, technically can also be realized.
If transformer does not break down, actual measured value is always within 100mA.That is with full scale 10A's
Current transformer obtains the measurement result that error is not more than 1mA.The 0.01% of 10A full scales is equivalent to, difficulty is quite high
's.This is also on-Line Monitor Device problem to be solved.
It is required to meet measurement accuracy, current solution, there are mainly two types of.A kind of is different with two ranges
Current transformer, to measure electric current of different sizes respectively；Another kind is the method using stepping, is selected for different current values
Suitable gear is selected to be respectively processed.
For above-mentioned technical problem, many people propose different solutions.At present, it is related with on-Line Monitor Device
, having obtained the Chinese invention patent of mandate has 3：
Patent 1：Application No. is 200710061733.6 patents, disclose a kind of " power transformer iron core grounding current
On-line monitoring and overcurrent limitting device ".The patent using DSP as microprocessor, with the current transformer of 2 difference ranges come
Measure earth current of different sizes, and excessive earth current is limited with current-limiting resistance.
Patent 2：Application No. is 201010297146.9 patents, and disclosing one kind, " transformer iron core grounding current is online
Monitoring system and its implementation ".The patent has given full play to the advantage of DSP, can not only measure the size of earth current value, also
The harmonic characteristic of fft algorithm analysis grounding electric current can be utilized, calculate the amplitude of power frequency component and each harmonic, by analyze come
The operation conditions of true transformer.
Patent 3：Application No. is 201110210033.5 Chinese patents, disclose a kind of " transformer iron core grounding current
On-Line Monitor Device and its monitoring method ", the patent simplify the structure of patent 1, and 2 current transformers are simplified
It is 1, ensures measurement accuracy in the form of stepping measurement.In addition it also adds current value and the functions such as keeps records of.
This 3 patents respectively have feature：
The utility function of patent 1 is more comprehensive, but because employ 2 current transformers and outside the structural Case that seems it is complicated.
The emphasis of patent 2 is in the frequency analysis of electric current and the discussion of algorithm, to wide range transformer measurement low current, such as
What ensures that the problem of measurement accuracy does not account for.Therefore its Practical significance largely popularized is little, no longer deeply visits below
It begs for.
Patent 3 measures the scheme instead of 2 current transformers using stepping, simplifies structure.At present on the market mostly
Number measuring devices structural principle all with it relatively.It can emphasis discussion below this patent.
By the technical background analysis of front it is found that the master that the measurement of transformer iron core grounding current is measured with common current
It will difference lies in measure the low current within 100mA, it is necessary to solve measurement accuracy with the current transformer of 10A ranges
Problem.The stepping measurement scheme of patent 3 is more practical, is the scheme that current most manufacturers use.Below just to this patent side
Case is once analysed in depth.
According to the claim of patent 3, current monitoring method, step are：
(1), straight-through current transformer is sleeved on transformer core grounding line and obtains an iron core grounding current letter
Number；(2), the primary current signal of acquisition is converted into secondary current signal, and this is secondary using straight-through current transformer
Current signal is converted into voltage signal；(3), by voltage signal by gear switch enhanced processing after, using voltage signal tune
It is sent into after reason circuit in the AD circuits that controller carries and carries out calculation processing；And be compared with pre-set alarm threshold value,
When signal occurs abnormal, controller control display screen shows alarm signal；(4), by the signal one of calculation processing in (3) step
Aspect is shown by display screen, and measurement result and measurement time on the other hand are stored in FLASH memory, is with post analysis iron core
Earth current working condition provides foundation.
Thus statement is as it can be seen that its current monitoring method and structural principle are all the routine sides of ac current measurement technical field
Method and conventional structure.
The description that related stepping measures in patent 3 is just had a look below, and the 3rd article of claims, the full text follows：
" monitoring method of 3. transformer iron core grounding current on-Line Monitor Devices according to claim 1, feature
It is：The method of measuring transformer current effective value is as follows：
I1For transformer grounding primary current value, pass through 1000:The secondary electricity of gained after the straight-through current transformer of 1 no-load voltage ratio
Flow valuve is I2,
That is I2=I1/1000
After current-to-voltage converting circuit, voltage U1=I2R
U1After voltage signal conditioning circuit, voltage is enlarged into U1*K
Wherein K=R2/R1, according to range difference, R2And K values will change therewith
After a DC stacked circuit in voltage modulate circuit, the voltage for being input to AD mouthfuls of controller is U1*K+
Uok
0≤U1*K+Uok≤Uref
UrefFor AD reference voltages
Work as U1*K+Uok≥UrefWhen, i.e., more than current range ability when, processor will adjust K value sizes, with satisfaction 0≤
U1*K+Uok≤UrefCondition；
Voltage fundamental virtual value into AD is acquired by Fourier Transform Algorithm；
Voltage fundamental virtual value is obtained, is derived by multiple averaging processing and reversely, what is obtained is that transformer core connects
Earth-current virtual value.”
By set forth above it is found that its method is to adjust different amplification factors according to different size of tested electric current, with
So that amplified voltage adapts to the conversion range of AD converter as far as possible.
But problem it is crucial that how amplification factor adjusts not provide illustrates.
In addition, the current effective value computational methods of patent 1,2,3, all employ alternating voltage being directly fed to AD conversion
Device after alternating voltage waveform is digitized, carries out alternating voltage waveform complicated calculation process by microprocessor, calculates
Go out the virtual value of earth current.High-fidelity amplification is carried out, then carry out high-speed transitions by speed A/D converter to AC signal, not only
Cost is greatly improved, computational accuracy is also more difficult to guarantee.It is especially harsher to the requirement of processor, DSP or ARM can only be used
Processor could be competent at.
Simple measurement current value, either common multimeter or the pincerlike meter for specially surveying alternating current, without exception
All employ simple and reliable mean value method.Specifically, the alternating voltage that will be obtained by alternating current by sample resistance passes through
Absolute value circuit switchs to the DC voltage of pulsation, then is filtered with simple RC, obtains smoother DC voltage.AD is sent into turn
After parallel operation, average value is can obtain through simple process.Average value divided by 0.9 be can obtain into virtual value.
Current producer each on the market is manufacturing, and user's functionally similar equipment currently in use is all adopted mostly
With stepping measurement scheme, and the calculating of electric current, almost all use above-mentioned mean value method.Its stepping measurement scheme, is skill
Completely enforceable in art, not that is enforceable for patent 3.It is given below what a row industrial customers were actually used
The typical scenario of current monitoring instrument：Stepping measurement+mean value calculation scheme.
Solution principle is referring to Fig. 1.The output current of current transformer is concatenated into sample resistance, representative value is 250 Ω.From
Sample resistance both ends obtain ac voltage signal, this voltage are inputed to 3 circuits respectively, the function of each circuit is similar：
Alternating voltage is first switched into pulsating dc voltage by absolute value circuit, then by DC voltage be amplified at straightened filtering
Reason, obtains DC voltage average value.The difference of 3 circuits is that last amplification factor is different, and typical amplification factor is respectively 2
Again, 20 times, 200 times.3 road average voltages are separately input to multichannel AD converter, and microprocessor is sent into after switching to digital quantity.
Microprocessor is according to the size of 3 road signals, and all the way in reasonable range, progress calculation process obtains current measurement for selection
Value.
Now analyze the canonical parameter of said program.Current transformer typical case no-load voltage ratio is 1000:1.Maximum current 10A
When, sensing electric current is 10mA.On the sample resistance of 250 Ω, the alternating voltage of 2.5V can be generated.At absolute value circuit
Reason, then after amplifying 2 times, the DC voltage of 5V can be obtained, give the AD converter that input range is 0~5V.And 100mA's is tested
Electric current, the sensing electric current of current transformer is 0.1mA.On the sample resistance of 250 Ω, the alternating voltage of 25mV can be generated, is passed through
Absolute value circuit processing is crossed, then after amplifying 200 times, can also obtain the DC voltage of 5V.
More than measurement scheme and its analysis of measurement errors are all built upon in stringent Fundamentals of Electronic Technology, practical
Scheme.Voltage signal on sample resistance is directly divided into 3 tunnels, respectively obtains 3 kinds of different size of AD conversion values.So-called point
Shelves are by microprocessor in 3 AD conversion values, select one most reasonably, principle is very simple.It does not need to as patent
It is mentioned in 3, carrys out stepping by method can not implementing, changing resistance value at all.
Either using stepping measurement scheme or the scheme using 2 different range current transformers, current each factory
This kind equipment of family's production is exactly that complicated, volume is relatively bulky, which results in its cost residences all there are one popular feature
It is high not under, very big obstruction is caused to promotion and popularization.
Invention content
Goal of the invention：The present invention provides a kind of essence for the problem of estimated current on-Line Monitor Device volume is big, price is high
Letter design, cheap, superior performance modular transformer iron core grounding current on-Line Monitor Device, to promote entire industry
The universal and raising of on-line monitoring technique application.
In order to achieve the above object, the present invention provides a kind of modular transformer iron core grounding current on-line monitorings to fill
It puts, the signal wire that goes out of Verification of Measuring Current Transformer has concatenated several different sample resistances, the simulation controlled by microprocessor
The different resistance of short circuit is switched, realizes the switching of different measuring ranges；High integration, modular integrated design, externally only 4
Bar line；2 direct current supply lines；2 RS485 connections；Both it can match with special secondary meter, can also be formed with host computer
Remote online monitoring system.
Preferably, the signal processing circuit design simplified is employed：
(1), the mutual inductor of measuring transformer iron core grounding current, output current line have concatenated several different sampling electricity
Resistance, by using the different number of resistance of analog switch short circuit that microprocessor controls, to realize the switching of different measuring ranges；
(2), the alternating voltage on sample resistance is switched to DC pulse electricity by the single supply absolute value circuit specially designed
Pressure.The conversion of positive and negative half-wave, precision higher are completed by an operational amplifier；
(3), the DC pulse moving voltage of absolute value circuit output, obtains smoother DC voltage, nothing after capacitance-resistance filter
It needs to amplify, directly inputs AD converter；The digital output of AD converter is sent into microprocessor, through microprocessor calculation process
Afterwards, you can obtain high-precision current measurement value；
(4), the power supply of whole device, the DC power supply of 9~24V are applicable；5VDC voltage stabilizings are employed inside device
Device, whole device only need 5VDC single supplies that can run.
Preferably, the Dynamic Hysteresis filtering algorithm of original creation is employed, measuring device is made to have excellent anti-interference, fully
It ensure that the accurate stabilization of measurement data.
Preferably, equipped with the secondary meter specially designed；The RS485 buses of module use standard Modbus communications protocol
Externally carry out data exchange；The secondary meter specially designed, equal to this both without display, also without the mould of operation button
Block formula monitoring device increases display and operation button, can carry out various behaviour to device as fully functional instrument
Make：Including correcting current, Configuration of baud rate, device number modification and various parameters setting.
Preferably, the Dynamic Hysteresis filtering algorithm is to establish an input data buffering area, calculates number of buffer in real time
According to maximin difference Δ X；When interference signal is smaller, the value of Δ X can be smaller；When interference signal increases, the value of Δ X
Also can increase；It, as Dynamic Hysteresis amount, is calculated with the variable Δ Z of the generally proportionate variations of Δ X for forming Dynamic Hysteresis filtering
Method realizes Dynamic Hysteresis filtering；The representative function relationship of variable Δ Z and Δ X is：Δ Z=Δ X-2, functional relation can be with input
The difference of signal and interference signal and have respective change adjustment.
It summarizes, key technology scheme of the invention is as follows：
(1), the mutual inductor of measuring transformer iron core grounding current, output current line have concatenated several different sampling electricity
Resistance, by using the different number of resistance of analog switch short circuit that microprocessor controls, to realize the switching of different measuring ranges.
(2), the alternating voltage on sample resistance is switched to DC pulse electricity by the single supply absolute value circuit specially designed
Pressure.The conversion of positive and negative half-wave, precision higher are completed by an operational amplifier.
(3), the DC pulse moving voltage of absolute value circuit output, obtains smoother DC voltage, nothing after capacitance-resistance filter
It needs to amplify, directly inputs AD converter.The digital output of AD converter is sent into microprocessor, through microprocessor calculation process
Afterwards, you can obtain high-precision current measurement value.
(4), the Dynamic Hysteresis filtering algorithm of original creation is employed, measuring device is made to have excellent anti-interference, is fully protected
The accurate stabilization of measurement data is demonstrate,proved.
(5), the power supply of whole device, the DC power supply of 9~24V are applicable.5VDC voltage stabilizings are employed inside device
Device, whole device only need 5VDC single supplies that can run.
Relative to the prior art, the present invention has the following advantages：
(1), that creates switches sample resistance with analog switch, realizes the scheme that stepping measures, not only simplifies design, also
Improve measurement accuracy.
(2), the single supply absolute value circuit specially designed, positive and negative two half-waves are turned using same operational amplifier
It changes, overcomes caused by positive and negative two half-waves of circuit common are remerged with the processing of two operational amplifiers that two waveforms may not
The defects of consistent.
(3), the DC pulse moving voltage of absolute value circuit output, obtains smoother DC voltage, nothing after capacitance-resistance filter
It needs to amplify, so that it may directly input AD converter.
(4), the Dynamic Hysteresis filtering algorithm of original creation is employed, measuring device is made to have excellent anti-interference, is fully protected
The accurate stabilization of measurement data is demonstrate,proved.
(5), entire measuring device circuit employs single 5V power supplies, just so that whole device can be supplied with 2 line external dcs
Electricity, so as to make it possible the modularized design of whole device.Single 5V power supplies, need the support of series of new techniques, at present city
Other same devices on face, structure are impossible to realize that single 5V powers with scheme.
Description of the drawings
Fig. 1 is typical stepping measurement+mean value calculation scheme schematic diagram of current similar product.
Fig. 2 is the analog switch stepping measurement scheme schematic diagram of the present invention.
Fig. 3 is the single supply absolute value circuit schematic diagram of the present invention and input and output voltage oscillogram.
Fig. 4 is the analog switch stepping measuring circuit principle sketch of the present invention.
Fig. 5 is the modular measuring device internal component layout schematic front view of the present invention.
Fig. 6 is the modular measuring device internal component layout diagrammatic top view of the present invention.
Specific embodiment
The present invention will be further described below in conjunction with the accompanying drawings.
1st, analog switch stepping measurement scheme
As shown in Fig. 2, transformer core grounding line passes through current transformer, sensing current output line has concatenated 3 resistances
It is worth different sample resistances, respectively 51 Ω, 470 Ω, 4.7K.The quantity of resistance is asked with parameter just for the sake of illustrating
Topic, can actually adjust as needed.Whether coordinating the closure of 2 analog switches in Fig. 2,3 kinds of different resistance values can be obtained
Sample resistance R.According to the difference of tested electric current I1, rational gear is selected：
During I1≤100mA, 100mA grades are selected, K1 and K2 are not closed, sample resistance R=51+470+4700=5221.
As 100mA ＜ I1≤1A, 1A grades are selected, only K1 is closed, sample resistance R=51+470=521.
As 1A ＜ I1≤10A, 10A grades are selected, K1 and K2 are closed, sample resistance R=51.
Current transformer ratio is 1000:1, when tested electric current I1 is respectively 100mA, 1A, 10A, I2 points of sensing electric current
It Wei not 0.1mA, 1mA, 10mA.When 3 kinds of electric currents select respective gear respectively, the alternating voltage at sample resistance both ends is respectively
522.1mV、521mV、510mV。
Program analysis：
(1) feasibility
In traditional design, analog switch be generally only applicable to transmission low current voltage signal, typical case be do it is more
The channel switching of road AD conversion, this allows for conclusion obtained from the technical indicator of traditional analog switch.It is typically designed personnel
Can not it consider with analog switch come the current signal of direct switching electric current mutual inductor.
But the development of electronic technology is maked rapid progress, and current analog switch technical indicator there has been rapid promotion.This hair
The bright analog switch employed for high-fidelity music center source of sound switching has the characteristics of conducting resistance is small, and conducting electric current is big.Under
Face just provides traditional analog switch CD4016 compared with the parameter of analog switch ADG884 used in the present invention.
By comparison as it can be seen that the conducting resistance due to CD4016 is too big, and allow by electric current it is too small, conducting is not
The occasion of switching electric current can be used in, and ADG884 is then completely out of question.
(2) technical indicator
It analyzes, is switched using analog switch ADG884 steppings again, the attainable technical indicator of institute.
In Fig. 2,10A grades of sample resistance is minimum, is 51 Ω, although the conducting resistance Ron of analog switch is 0.28 Ω,
Account for about the 0.55% of 51 Ω, but can be converted in sample resistance completely.The principal element for influencing precision is conducting resistance
Variation delta Ron.Since Δ Ron only has 0.01 Ω, the 0.02% of 51 Ω are only accounted for, error can be ignored substantially.
And for 1A grades, 0.01 Ω only accounts for the 0.002% of 521 Ω, and error more can be ignored.
At 100mA grades, analog switch does not work, and error caused by analog switch is 0.
Sensing electric current of the current transformer in 10A only has 10mA, and the maximum conducting electric current of ADG884 is up to 300mA,
It is even more out of question.
(3) with other gearshift schemes comparison
The sample resistance of all measurement schemes is all fixed before, and representative value is 250 Ω, and maximum is no more than 500
Ω.Why the sample resistance of bigger cannot be used, first, since total range is larger, during 10A, sensing electric current is 10mA, 500 Ω's
Sample resistance pressure drop is 5VAC.It, need not be big again up to the upper limit of AD converter after switching to direct current.Second is that since increase samples
Resistance can cause the linearity to be deteriorated.When measured value is smaller, the influence of nonlinearity erron is also smaller, when measured value is larger,
The influence of nonlinearity erron can bigger.
At 100mA grades, the sample resistance of the present invention program is the 20 of other conventional schemes (the typical sampling resistance of 250 Ω)
Times or more, the voltage signal of generation is also 20 times.The primary output signal for being equivalent to sensor is just 20 times big, does not all need to follow-up
Amplifying circuit, measurement accuracy understands higher certainly.
Sample resistance more than 5K, although having some linearity errors, since measurement range only has 100mA, it is easy to logical
Software is crossed linearly to be corrected.
(4) analog switch scheme brief summary
Never someone switches the output current of mutual inductor with analog switch before, is primarily due to traditional analog switch
Technical indicator is inadequate.First Application analog switch of the present invention carrys out switching range, not only simplifies structure, also improves precision.Fig. 2
In used 3 sample resistances, during actual design, can determine the quantity and parameter of sample resistance as needed, it is different to form
Stepping measurement scheme.
2nd, single supply absolute value circuit
Since alternating voltage has positive and negative, absolute value circuit is difficult to be realized with single supply power supply.Common absolute value
Circuit is the even higher dual power supplies of ± 12VDC mostly.Usually by 2 amplifiers handle respectively the positive half-wave of alternating current with
Negative half-wave, remerges.This is just very high to build-out resistor requirement, if resistance value consistency is poor, may result in positive and negative two
The unidirectional pulsating wave that half-wave converts is inconsistent.
The single supply absolute value circuit that the present invention specially designs, as shown in figure 3, absolute value circuit is by the double fortune of 1 high-precision
Put composition.In order to ensure the undistorted of alternating voltage, with 2.5V reference voltages, the reference zero of alternating current is lifted to 2.5V.
In this way, alternating current just fluctuates above and below the reference zero of 2.5V.In positive half-wave, U2B'sThe voltage of input terminal is high, output
It is 0, diode 1N4148 is reversely by having no effect U2A.At this point, U2A is only a forward direction 1:1 amplifier,
It exports consistent with input.In negative half-wave, U2B'sThe voltage ratio of input terminalThe 2.5V reference voltages of input terminal are low, U2B
Just into a voltage follower, accurate 2.5V reference voltages are exported, give U2A'sInput terminal.By U2A'sInput
It holds clamped on 2.5V reference voltages.At this point, U2A is just into one 1:1 sign-changing amplifier, output voltage just with the input phase
Instead.Absolute value circuit input and output voltage waveform is also shown in figure 3 together.
Program analysis：
(1) conversion accuracy is analyzed
Alternating voltage is switched into DC voltage, it is ensured that high-precision, the rectification circuit that must not be just formed with diode.Also
There is the special chip that some AC-DC are converted, but by testing, the effect of several special chips is all undesirable.Main cause
Or the measurement of transformer iron core grounding current is too special：The electricity within 100mA is measured with the current transformer of 10A ranges
Stream, has only used 1% range.
Between this situation, just must circuit be designed using the amplifier of higher precision.The OPA2335 that the present invention uses
Double operational, input imbalance is maximum to only have 5 μ V, and offset drift maximum only has 0.05 μ V/ DEG C.It can fully ensure that the essence of conversion circuit
Degree.
(2) comparison of scheme similar with other
By taking the scheme of Fig. 1 as an example, the single amplifier OP07 of absolute value circuit generally use high-precision.OP07 is that current various height refer to
The amplifier being commonly used in mark requirement.The input imbalance of OP07 is 150 μ V, and offset drift is 0.5 μ V/ DEG C.With OPA2335 phases
Than having a long way to go.
Front is talked about, the measurement accuracy in 100mA, no more than 1mA with regard to enough.But this be combine temperature drift, when float, for a long time
The overall accuracy of the factors such as stability.In view of measuring display resolution, precision during design at least needs to improve 10 times.And it surveys
The reading of magnitude, if if 4 bit digitals are shown, the display resolution within 1A should all reach 0.1mA, maximum
999.9mA.Therefore, to have sufficient precision surplus during design.
Since the sample resistance of the present invention is more much larger than Fig. 1 scheme, even if Fig. 1 schemes are same using the present invention
OPA2335, the solution of the present invention advantage are also fairly obvious.
Fig. 1 schemes：The tested electric current of 0.1mA, transformer induced electric current are 0.1 μ A.Pressure on the sample resistance of 250 Ω
The imbalance for being reduced to 25 μ V, OPA2335 is 5 μ V, to be tested the 20% of voltage, precision surplus very little.If with OP07, lacking of proper care is
150 μ V are be tested voltage 6 times, and precision can not ensure at all.
The solution of the present invention：The tested electric current of 0.1mA, transformer induced electric current are 0.1 μ A.In the sampling electricity of 5.221K
The imbalance that pressure drop in resistance is 522.1 μ V, OPA2335 is 5 μ V, the 1% of only tested voltage.There is sufficient precision surplus.
3rd, measurement data resolution analysis
The circuit design of the present invention, employs the scheme of original creation, has than similar scheme and significantly simplify.One of which is exactly
Amplifying circuit is not needed to, is directly AD converted.The attainable Measurement Resolution of this programme institute is just analyzed below.
Since whole system is only with list 5V power supplies, to ensure the undistorted of alternating voltage, also reference zero is increased to
2.5V, measured signal are just not much variation space.
Non- rail-to-rail amplifier, output voltage, also lower 1.5V than supply voltage, the i.e. 3.5V of maximum.And reference zero is
2.5V, so the variation range of measured signal only has：2.5±1V.
By the analysis of front it is found that when tested electric current is 100mA, the voltage that the sample resistance of 5221 Ω generates is
522.1mV.It should be noted that this is virtual value.And corresponding peak value will be multiplied byTherefore crest voltage is 738mV.Due to
Variation range is allowed to only have 1V, 738mV just not to amplify again necessary.
What the present invention selected is sigma-delta formula AD converter, and in the circuit diagram of Fig. 4, the model of selection is MCP3421,
It is 18 bit A/D converters of only 6 feet.Sigma-delta formula AD converter, has the characteristics that technology for integral A/D converter, can be automatic
Cut down the ripple of 50Hz alternating currents.This kind of AD converter is there are many kind selection, and highest resolution is up to 24.
Since the measuring signal processing circuit of the present invention is extremely outstanding, with the AD converter of 18 with regard to enough.Due to
MCP3421 is Differential Input, and AD conversion value is positive and negative two-way.Negative sense takes less than, therefore actually active position is equivalent to only 17
Position.Resolution analysis is just carried out with this below.
When tested electric current is 100mA, the voltage that the sample resistance of 5221 Ω generates is 522.1mV.By absolute value electricity
Road is handled, and after capacitance-resistance filter, can be become with a little 50Hz alternating currents ripple, smoother DC voltage.This
When DC voltage be average value.Since average value and virtual value have following relationship：
UIt is average=0.9UEffectively
Therefore, the corresponding average value of the virtual value of 522.1mV is：470mV.
The reference voltage of 2.048V built in MCP3421,470mV account for the 22.9% of 2.048V
Because 217× 22.9%=30015, so MCP3421 is to the digital resolution of 470mV：
1/30015
It follows that when measured value is 100mA, true resolution is reachable：100mA/30015=0.0033mA
In 1A gears, it is desirable that resolution ratio is up to 999.9mA, also completely out of question.True resolution is reachable： 1000mA/
30015=0.033mA.
In 10A gears, it is desirable that resolution ratio is up to 9.999A, similary out of question.True resolution is reachable： 10000mA/
30015=0.33mA.
In fact, there is 1~8 times of programmable amplifier inside MCP3421,470mV amplifies 4 times, reachable 1880mV,
In the range of 2.048V.Digital resolution at this time can rise to before 4 times：
1/ (30015 × 4)=1/120060
At this point, in the gear of 1A, true resolution is reachable：1000mA/120060=0.0083mA.
In the gear of 10A, true resolution is reachable：10000mA/120060=0.083mA.
Here 18 bit A/D converters of 6 feet why are used, cost is mainly farthest reduced, reduces volume.Such as
Fruit needs, and using the AD converter of 24, can obtain higher resolution ratio and higher measurement accuracy.
In conclusion the measurement scheme of the present invention, in the case where measuring signal is not required to amplification, digital resolution is not only complete
It all can meet the requirements, also sufficiently large resolution ratio surplus.Synthesis precision for whole system provides sufficient guarantee.
4th, Dynamic Hysteresis filtering algorithm
It, can be by various interference in the operation of transformer iron core grounding current on-Line Monitor Device.Particularly quilt
Survey current value it is smaller when, the phenomenon that being interfered, is more obvious.If do not filtered out, it will generate measurement result larger
Error.
Discounting for the volume of whole device, more hardware filtering processing circuit can be increased, to improve entire dress
The antijamming capability put.But for modular device, limited by volume, replace hardware circuit especially heavy with software as possible
It will.Outstanding software filtering scheme, can not only simplify hardware circuit, moreover it is possible to play the role of hardware circuit and not have.
The common digital filtering method with stably measured numerical value has：Extremum method, median method, mean value method, single order is gone to be used to
Synthesis of property filtering algorithm and several algorithms etc..This kind of algorithm, which is primarily adapted for use in, filters out more regular interference signal, and
To mutation formula surprisingly interfere to filter out ability weaker.The slightly stronger one order inertia of ability that filters out that mutation formula is surprisingly interfered is filtered
Wave algorithm, what is actually worked is equivalent to sluggish fixed sluggish algorithm.One order inertia filtering algorithm formula is：
yn=α yn-1+(1-α)xn
Wherein, yn-1For last computation as a result, xnFor this input value, ynFor this result of calculation.α is to be less than 1
Number.
When α values are larger, filter effect is strengthened, more apparent to larger interference signal filtration result.But its practical
The key of effect is since with larger sluggishness, larger sluggishness can cause the sensitivity of small-signal to decline, and cause larger
Small-signal lag error.For example, as α=7/8, one order inertia filtering algorithm formula is：
yn=7/8 × yn-1+1/8×xn
It is assumed that yn-1=8, to make ynIncrease to 9, then at least want xn≥12；To make yn7 are reduced to, then at least wants xn＜
4.One order inertia filtering algorithm herein is equivalent to the sluggish algorithm that fixed time-lag is 3.
When measured value is bigger, such as 1000, there is 3 sluggishness, only account for 0.3%, influence very little.But when measured value compares
Hour, such as 100, the sluggish proportion for having 3 just has 3%, influences just very considerable.When measured value only has 10, there is 3
Sluggish proportion just has 30%.
α values are big, good to the filtration result of interference signal, but the lag error of small-signal can be larger；α values are small,
Lag error is small, can be again bad to the filtration result of interference signal.So with fixed filtering parameter, or perhaps it is fixed
Sluggishness, gamut scope can not be suitable for.
The Dynamic Hysteresis filtering algorithm that the present invention uses can automatically adjust the sluggishness of algorithm according to the size of interference signal
Amount.It is allowed to increase sluggishness automatically when interference signal is larger, reduces sluggishness automatically when interference signal is smaller.Implementation method is such as
Under：
An input data buffering area is established, for example, establishing the buffering area of 8 data.This 8 data can in real time dynamic more
Newly, all it is forever 8 nearest AD conversion values.The algorithm can calculate the difference Δ X of the maximin of this 8 data in real time.When
When interference signal is smaller, the value of Δ X can be smaller；When interference signal increases, the value of Δ X can also increase.The size of Δ X is interference
The characterization of signal magnitude.By Δ X by handling, you can a Dynamic Hysteresis amount Δ Z with the generally proportionate variations of Δ X is obtained,
As filtering parameter, you can Dynamic Hysteresis effect expected from realization.
Above said " by Δ X by handling ", actually establishes one and respective function relationship：
Δ Z=F (Δ X)
In order to illustrate Dynamic Hysteresis filtering principle, functional relation here is by taking Δ Z=Δs X-2 as an example, to carry out specifically
It is bright.
For example, last measured value yn-1=100, suddenly there are one positive transition be 200 disturbing pulse signal, at this time
xn=300, corresponding Δ X=300-100=200, Dynamic Hysteresis amount Δ Z=Δs X-2=198.It is filtered through Dynamic Hysteresis
Measured value is：
yn=100+ (200-198)=102
Since sluggishness is 198, although 200 interference signal is very big, the influence very little to filtered measured value.
And after using the one order inertia filtering of α=7/8, measured value is：
yn=7/8 × yn-1+1/8×xn=7/8 × 100+1/8 × 300=125
The deviation of the latter is the former 12.5 times.It can be seen that Dynamic Hysteresis filtering algorithm filters out ability to unexpected mutation disturbance
It is great.In this instance, then big interference, the influence to filter result are not more than ± 2.
Thus example, which can be seen that, chooses the basic principle of Dynamic Hysteresis Δ Z and is：Choosing is less than Δ X, and close to Δ X, but
Δ X cannot be equal to.Because if Δ Z=Δ X, then result of calculation will be locked, it is impossible to be varied by.Take Dynamic Hysteresis amount Δ Z
=Δ X-2, only simplest scheme, but be not optimal case.It is also big according to measured signal to be optimal effect
Small and interference signal size, is obtained by experimental study.In other words, this relation function is changed with measuring condition
's.For example, under different condition, can use Δ Z=Δ X-1, Δ Z=Δ X-2, Δ Z=Δs X-3 or other, etc..Detail
It repeats no more.
In addition, when not interfering with signal, only saltus step occurs in itself for measured value, also results in Δ X increases.According to calculation
Method, amount of hysteresis at this time can increase, to hinder calculated value saltus step.But after measured value increase, always gradually it is stabilized to new survey
On magnitude, what Δ X always became smaller, calculated value always tracks in place.Therefore, in this case, it is that will not generate measurement error
, only the response time have certain delay.Since this application scenario is monitoring current, do not need at high speed and real time control
Reason, the response time of measurement data have slightly delay to allow completely.
In short, either measuring signal generates saltus step in itself, mutation formula interference signal is still produced, which can all move
State increase is sluggish, to hinder the mutation of result of calculation.And after measuring signal saltus step terminates or be mutated formula interference disappearance, dynamic
Amount of hysteresis can be reduced to normal range (NR) again, make the upper measured value of result of calculation tracking.
5th, the realization of modular arrangement
Another distinguishing feature of the present invention is that entire monitoring device can be designed very compact, realizes modularization.This
In analyze exploitativeness.
It powers as a result of external dc, therefore just eliminates the larger power circuit of volume.Whole system electricity consumption is not
Therefore sufficient 50mA, only needs the patch type 5V voltage-stablizers of a maximum output current 100mA.
The device that measuring circuit uses all is the patch circuit of volume very little.The circuit diagram of Fig. 4, in addition to lacking
RS485 interface circuits, others have.Device encapsulation and the overall size of whole device is listed below：
5V voltage-stablizers LM2940IMPX-5.0, SOT-223 encapsulation, 6.2 × 7mm2。
Analog switch ADG884, MSOP10 encapsulation, 3 × 5mm2。
Double operational OPA2335, VSSOP encapsulation, 3 × 5mm2。
AD converter MCP3421, SOT-23 encapsulation, 3 × 3mm2。
Single chip computer AT MEGA88, TQFP encapsulation, 9 × 9mm2。
485 chip MAX485, VSSOP encapsulation, 3 × 5mm2。
Resistance, capacitance add up to more than 20, are 0805 encapsulation, 2 × 1.2mm2。
Current transformer, φ 35 × 23.
Wire connection terminal, 4.
It is whole components 1 of entire measuring device above, 60 × 40mm can be mounted on2Circuit board 2 on.Circuit
Plate 2 can be packaged as a whole with current transformer 3.The interior space dimension of entire module can be limited in 60 × 40 × 40mm3.Referring to
Fig. 5 and Fig. 6；Specific length L1=60mm；Height H1=40mm；Interior high H2=23；Width A1=40mm；Current transformer 3
It is outer through φ D1=35mm；Internal diameter φ D2=18mm；Mutual inductor axle center to edge distance A2=17.5mm.
6th, special secondary meter
The present invention is a modular detection device, both without display, also without operation button, to the various behaviour of device
Make, including correcting current, Configuration of baud rate, device number modification and various parameters setting etc., all pass through the RS485 of module
Bus carries out.Implementation there are two types of specific, first, being carried out with host computer, second is that being carried out by special secondary meter.
Conventional host computer or secondary meter only need to exchange detection data with measuring device.It generally will not be to measuring
Device carries out the bottom operations such as correcting current.This kind of bottom operation is carried out it is necessary to the secondary meter of design specialized or dedicated
Upper computer software.It only need to increase corresponding program when instrument and upper computer software are developed, be completely enforceable.
Modular detection device is matched with special secondary meter, and for secondary meter, modular detection device is with regard to phase
When in a digitlization transmitter.As long as increasing corresponding software function, the several of current other similar instrumentations of the industry are can be achieved with
Institute is functional.
In summary as it can be seen that the present patent application is built upon in stringent technical foundation, there is complete detailed scheme, be
It is completely enforceable on engineering significance.The present invention seems very novel, but actually not enforceable conceptual hair with that
It is bright entirely different.
The example of the above, only embodiment of the present invention, but protection scope of the present invention is not limited thereto.This hair
Bright technical solution can also be used in ordinary electric current mutual-inductor earth current on-Line Monitor Device, in other words available for any electricity consumption
In the measuring device for flowing output type sensor.It can be simplified structure with the present invention program, be reduced cost, raising precision.It is any
Those familiar with the art in the technical scope disclosed by the present invention, according to the technique and scheme of the present invention and its invents
Design is subject to equivalent substitution or change, should be covered by the protection scope of the present invention.
Claims (5)
1. modular transformer iron core grounding current on-Line Monitor Device, it is characterised in that：Verification of Measuring Current Transformer goes out letter
Number line has concatenated several different sample resistances, and the different resistance of the analog switch short circuit controlled by microprocessor is realized not
With the switching of measuring range；High integration, modular integrated design externally only have 4 lines；2 direct current supply lines；2
RS485 connections；Both it can be matched with special secondary meter, and also can form remote online monitoring system with host computer.
2. modular transformer iron core grounding current on-Line Monitor Device according to claim 1, it is characterised in that use
The signal processing circuit design simplified：
(1), the mutual inductor of measuring transformer iron core grounding current, output current line have concatenated several different sample resistances,
By using the different number of resistance of analog switch short circuit that microprocessor controls, to realize the switching of different measuring ranges；
(2), the alternating voltage on sample resistance is switched to DC pulse moving voltage by the single supply absolute value circuit specially designed；By
One operational amplifier completes the conversion of positive and negative half-wave, precision higher；
(3), the DC pulse moving voltage of absolute value circuit output, obtains smoother DC voltage, without putting after capacitance-resistance filter
Greatly, AD converter is directly inputted；The digital output of AD converter is sent into microprocessor, after microprocessor calculation process, i.e.,
It can obtain high-precision current measurement value；
(4), the power supply of whole device, the DC power supply of 9~24V are applicable；5VDC voltage-stablizers are employed inside device, entirely
Device only needs 5VDC single supplies that can run.
3. modular transformer iron core grounding current on-Line Monitor Device according to claim 2, it is characterised in that：Using
The Dynamic Hysteresis filtering algorithm of original creation, makes measuring device have excellent anti-interference, has fully ensured that the essence of measurement data
Quasi-steady.
4. modular transformer iron core grounding current on-Line Monitor Device according to claim 2, which is characterized in that be furnished with
The secondary meter specially designed；The RS485 buses of module externally carry out data exchange using standard Modbus communications protocol；Specially
The secondary meter of design, equal to, both without display, also the modular monitoring device of no operation button increases aobvious to this
Show device and operation button, various operations can be carried out to device as fully functional instrument：Including correcting current, baud
Rate setting, device number modification and various parameters setting.
5. modular transformer iron core grounding current on-Line Monitor Device according to claim 3, which is characterized in that described
Dynamic Hysteresis filtering algorithm is to establish an input data buffering area, calculates the difference Δ of the maximin of buffer data in real time
X；When interference signal is smaller, the value of Δ X can be smaller；When interference signal increases, the value of Δ X can also increase；It will be with Δ X substantially
The variable Δ Z of proportional variation, for forming Dynamic Hysteresis filtering algorithm, realizes Dynamic Hysteresis filtering as Dynamic Hysteresis amount；
The representative function relationship of variable Δ Z and Δ X is：Δ Z=Δ X-2, functional relation can be with input signal and interference signals not
There is respective change adjustment together.
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| CN112946381A (en) * | 2021-01-19 | 2021-06-11 | 河南检亿科技有限公司 | Unattended aging box and intelligent monitoring method thereof |
| CN112946381B (en) * | 2021-01-19 | 2024-05-10 | 河南检亿科技有限公司 | Unmanned aging box and intelligent monitoring method thereof |
| CN114236247A (en) * | 2021-12-17 | 2022-03-25 | 常州市浦西尔电子有限公司 | Reading method for AC signal output by sensor detection circuit |
| CN114280360A (en) * | 2021-12-24 | 2022-04-05 | 紫光展讯通信(惠州)有限公司 | Current measurement circuit and current measurement method |
| CN115575688A (en) * | 2022-09-29 | 2023-01-06 | 北京航天计量测试技术研究所 | Weak current detection circuit |
| CN115575688B (en) * | 2022-09-29 | 2023-11-07 | 北京航天计量测试技术研究所 | Weak current detection circuit |
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