CN104655908B - A kind of method for transmitting signals for current transformer - Google Patents

A kind of method for transmitting signals for current transformer Download PDF

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Publication number
CN104655908B
CN104655908B CN201510102017.2A CN201510102017A CN104655908B CN 104655908 B CN104655908 B CN 104655908B CN 201510102017 A CN201510102017 A CN 201510102017A CN 104655908 B CN104655908 B CN 104655908B
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signal
current
luminous tube
luminous
voltage
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CN104655908A (en
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王玮
徐丙垠
张新慧
陈羽
梁栋
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Shandong University of Technology
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Shandong University of Technology
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Abstract

A kind of method for transmitting signals for current transformer, belongs to electric measurement field.The primary side (1) and secondary side (6) connected including optical fiber (4), it is characterised in that:Described primary side (1) includes the coil being sequentially connected, signal condition unit, constant current driving unit end, and secondary side (6) includes photoelectric detection unit, signal extraction unit.Comprise the following steps:Step 1, multigroup (U, P) numerical value is obtained.Step 2, luminous tube power drive voltage curve is obtained.Step 3, primary side (1) parameter is stored in secondary side (6).Step 4, secondary side direct voltage reference value and power frequency component virtual value are obtained.Step 5, obtain primary side (1) power-frequency voltage signal virtual value.Step 6, the bus current virtual value of primary side (1) is obtained.The present invention can accurately calculate the virtual value of primary side power-frequency voltage signal and bus current, in the design that may be used on high-precision current transformer.

Description

A kind of method for transmitting signals for current transformer
Technical field
A kind of method for transmitting signals for current transformer, belongs to electric measurement field.
Background technology
In power generation, electrical power transmission system and power equipment, current transformer is to realize that electric energy measurement and system are protected The visual plant of shield.Traditional electromagnetic current transducer due to insulation it is difficult, easily by electromagnetic interference, volume be big, cost The high shortcoming for itself being difficult to overcome and gradually replaced by new current transformer.In various novel current transformers, Electronic mutual inductor is by its good insulation preformance, strong antijamming capability, small size, low cost, measurement dynamic range be wide, sensitivity Ideal substitute that is high, running the advantages such as safety and be increasingly becoming conventional electromagnetic current transformer.
Electronic mutual inductor is based on electronic technology and fibre-optic transmission system (FOTS), and its general principle is to use primary current sensor Bus current is transformed to the analog current signal of fractional value by (such as air core coil or iron-core coil) according to the turn ratio of coil, then The current signal is converted into analog voltage signal, analog voltage signal is converted into data signal thereafter through AD samplings, by CPU sends into luminous tube drive circuit and is converted to digital optical signal by electrical/optical after being encoded to data signal, utilize optical fiber By optical signal transmission to secondary side circuit, the digital output that bus current size is obtained after optical electrical conversion, decoding is sequentially completed Or the signal of output reflection bus current waveform is changed after decoding by D/A.
The electronic current mutual inductor designed using principles above is had as a drawback that:
(1) because its primary side has AD conversion link, cause primary side circuit power consumption higher, and current transformer is once The powerup issue of side is also one of problem of estimated current transformer design.
(2) transmission of the whole system to signal uses data signal, therefore sample frequency during AD samplings is just limited The bandwidth for the signal to be transmitted, according to higher sample frequency, then system power dissipation is bigger, therefore the sampling of real system Frequency generally can not be too big so that the travelling wave signal of higher frequency is limited by sample frequency when high-frequency harmonic in electric current or failure And can not transmit to secondary side.And these high-frequency signals are exactly the important letters of power quality analysis or line fault analysis Breath, so make the limited efficacy of current transformer.
(3) in real system, because three-phase bus there will be current transformer, therefore bus current size will represented Coding must be synchronized to the signal on each road, before digital quantity feeding electrical/optical change-over circuit so that three tunnels that secondary side is received Signal can be synchronous, therefore adds the complexity of system design to a certain extent.
The luminous tube used in electric mutual inductor is general by current drive-type device such as LED or the pole of laser two Pipe LD realizes that the size of its luminous power depends on flowing through the electric current of luminous tube, when the electric current for flowing through luminous tube is increased to necessarily During degree, the luminous power P of luminous tube and the electric current I for flowing through it are linear.The electric current I that photoelectric tube is exported when there is illumination It is also linear relationship with the intensity of illumination P that is subject to.
Using the above characteristic of luminous tube and photoelectric tube, it is existing in the prior art have by primary side into luminous tube drive Analog voltage signal (i.e. power frequency component) directly modulator glow tube before dynamic circuit is luminous, will the analog voltage signal directly become The optical electrical change-over circuit that optical fiber passes to secondary side is sent into for analog optical signal, then can avoid the AD sampling rings of a lateral circuit Section, so that the problem of also just solving too high primary side circuit power consumption and limited transmission signal band;Simultaneously as directly by mould Intend signal modulation transmission, synchronized without the three-phase data to real system, then can make the complexity of system design significantly Reduction.So also just solve the above mentioned problem present in current electronic current mutual inductor.
In actual applications, when primary side is modulated using analog signal to optical signal, one is generally provided admittedly Determine the DC offset voltage signal of size, the signal also serves as reference signal, modulated-analog signal is raised to by the signal The linear zone of luminous tube, so as to realize the transmission of analog optical signal, this is to realize the basic of analog signal transmission using luminous tube Principle.However, optical signal can be damaged in transmitting procedure because of the coupling loss between luminous tube and the joints of optical fibre, optical fiber transmission The reason such as luminous power decline is so as to lead caused by coupling loss, luminous tube aging between consumption, the joints of optical fibre and photoelectric tube Signal magnitude is caused to decay, to calculate the big of primary side power frequency current signal by measuring secondary side power frequency component size It is small, it must be understood that the decay of power frequency component, can simply by decay of the decay of DC reference signal as power frequency component, but Due to the decay of two signals and unequal, therefore the error for the current transformer designed in this way is larger, this method Current transformer for design protection is feasible, but by this method for designing high-precision Verification of Measuring Current Transformer It is then unworkable.
The content of the invention
The technical problem to be solved in the present invention is:Overcoming the deficiencies in the prior art, there is provided a kind of simple and convenient, cost is low It is honest and clean, can accurately calculate primary side power frequency current signal size, may be used on being used in the design of high-precision current transformer The method for transmitting signals of current transformer.
The technical solution adopted for the present invention to solve the technical problems is:This is used for the signal transmission dress of current transformer Put, including the primary side and secondary side connected by optical fiber, it is characterised in that:In described primary side, the coil of bus is connected Output end connect the input of signal condition unit, the output end of signal condition unit connects the input of constant current driving unit End, the output end of constant current driving unit connects one end of the optical fiber;
The input of photoelectric detection unit in the other end connecting secondary side of optical fiber, the output end connection of photoelectric detection unit The input of signal extraction unit, the output of signal is carried out by the output end of signal extraction unit.
It is preferred that, described signal extraction unit at least includes capacitance and CPU, and described photoelectricity is visited The signal for surveying unit is divided into two-way:It is connected all the way by capacitance with CPU, another road is directly handled with center Unit is connected.
It is preferred that, described photoelectric detection unit at least includes:Convert optical signals to current signal photoelectric tube and The current signal that photoelectric tube is converted to is converted to the current-voltage conversion circuit of voltage signal.
It is preferred that, described signal condition unit at least includes:The voltage reference chip of DC reference voltage can be generated, with And the signal mixed circuit that the power frequency component and reference voltage for exporting the coil are mixed.
It is preferred that, the voltage signal that described constant current driving unit at least includes exporting signal condition unit is converted to electricity Flow the transfer resistance of signal and luminous luminous tube is driven by the current signal that transfer resistance is converted to.
It is preferred that, described luminous tube is communication luminous tube.
It is preferred that, described transfer resistance is the thermistor of negative temperature coefficient.
Method for transmitting signals for current transformer, it is characterised in that:Comprise the following steps:
Step 1, the different DC voltage of multigroup numerical value is exported to constant current driving unit, driving luminous tube is with different power It is luminous, obtain multigroup U-P numerical value of luminous tube;
Step 2, the multigroup U-P numerical fittings obtained by step 1 obtain luminous power-driving voltage of luminous tube (2) P-U relation curves:P=aU+b, then calculates according to heat-sensitive coefficients method of testing and obtains temperature-sensitive electricity in constant current driving unit The temperature coefficient of resistance, completes the selection to thermistor, parameter a, b in P-U relation curves is kept constant;
Step 3, by coefficient a, b in P-U relation curves in step 2 and by the voltage reference core in signal conditioning circuit The DC reference voltage signal V that piece is producedDC is referred toValue be stored in secondary side in the CPU of signal extraction unit;
Step 4, CPU circuit is sampled respectively to the signal that photoelectric detection unit is exported, and is calculated through light The DC reference signal value V ' decayed after fibre transmissionDC is referred toValue and power frequency component virtual value VPower frequency
Step 5, calculated according to power frequency component calculation formula and obtain first siding ring output or changed by signal condition unit Obtained power frequency component VPower frequency
Step 6, obtained power frequency component V is calculated according to step 5Power frequencyCalculate the virtual value for obtaining bus.
It is preferred that, the power frequency component calculation formula described in step 5 is:
Wherein, a, b are respectively the P-U relation curves P=aU+b of luminous tube coefficient, VDC is referred toFor in signal condition unit The DC reference voltage produced using voltage reference chip, V 'DC is referred to、V’Power frequencyThe decay that respectively CPU sampling is obtained Reference voltage and power frequency component afterwards.
It is preferred that, the heat-sensitive coefficients method of testing described in step 2 comprises the following steps:
Step a, under normal temperature T1, a constant driving DC voltage is exported to constant-current drive circuit;
Step b, replaces thermistor using potentiometer and measures the initial resistivity value R1 of potentiometer;
Step c, luminous power P1 of the record luminous tube under temperature T1;
Step d, is increased to T2, and record the luminous tube under temperature T2 using heating device by the operating temperature of luminous tube Luminous power P2;
Step e, the operating temperature for keeping luminous tube is T2, and constantly reduces the hair of the resistance, now luminous tube 2 of potentiometer Luminous power starts rise, when the luminous power of luminous tube rises to P1, the potentiometer resistance R2 of record now;
Step f, the difference DELTA T=T2-T1 of the operating temperature by calculating luminous tube, and potentiometer resistance drop-out value Δ R=R1-R2, calculating obtains the temperature coefficient that thermistor should have, and is realized according to step a~step f to thermistor Selection.
Compared with prior art, the present invention is had an advantageous effect in that:
1st, the present invention is not exclusively calculated when calculating power frequency component virtual value by reference to the attenuation degree of signal, Therefore primary side power frequency component virtual value can be accurately calculated, in the design that may be used on high-precision current transformer, simultaneously With simple and convenient, with low cost advantage.
2nd, in signal extraction unit, by setting capacitance and CPU, can be achieved deamplification every Calculated from accurate.
3rd, in signal condition unit, the voltage reference chip of exportable reference voltage is set, on the one hand can make luminous tube It is in linear output range, the reference that on the other hand can be calculated as power frequency component.
4th, the transfer resistance in constant current driving unit is the thermistor of negative temperature coefficient, be compensate for caused by temperature rise Luminous tube luminous power declines, and coefficient a, b in its P-U relation can keep constant.
5th, in this signal transmitting apparatus for being used for current transformer, the power frequency analog signal of primary side can directly be passed Secondary side is transported to, sampling element need not be set in once surveying, primary side circuit power consumption is lower, and circuit design is simple.
Brief description of the drawings
Fig. 1 is the signal transmitting apparatus functional-block diagram for current transformer.
Fig. 2 is the signal transmitting apparatus signal extraction unit functional-block diagram for current transformer.
Fig. 3 is the method for transmitting signals flow chart for current transformer.
Fig. 4 is luminous tube driving current I- luminous efficiency P curve maps.
Fig. 5 is luminous tube input voltage U- luminous power P curve maps.
Fig. 6 is input voltage U- luminous power P curve maps under different temperatures.
Fig. 7 is the heat-sensitive coefficients test flow chart of thermistor.
Wherein:1st, primary side 2, luminous tube 3, the joints of optical fibre 4, optical fiber 5, photoelectric tube 6, secondary side.
Embodiment
Fig. 1~7 are highly preferred embodiment of the present invention, and 1~7 the present invention will be further described below in conjunction with the accompanying drawings.
As shown in figure 1, the signal transmitting apparatus for current transformer, including the primary side 1 that is connected by optical fiber 4 and secondary Side 6.Primary side 1 includes coil, signal condition unit, constant current driving unit.The input of coil is connected with bus, its output end The input of signal condition unit is connected, the output end of signal condition unit connects the input of constant current driving unit, and constant current is driven The output end of moving cell connects one end of optical fiber 4 by the joints of optical fibre 3 in primary side 1, and secondary side 6 passes through the optical fiber in it Connector 3 connects the other end of optical fiber 4.Secondary side 6 includes photoelectric detection unit and signal extraction unit.Photoelectric detection unit The joints of optical fibre 3 of input connecting secondary side 6, its output end connect signal extraction unit input.
Coil is generally air core coil or iron-core coil.In actual product, air core coil generally passes through built-in integration Bus current is changed into analog voltage signal and directly exported by circuit;The generally built-in shunt resistance of iron-core coil is by bus current Analog voltage signal is converted to directly to export;Also it can be realized using the iron-core coil of traditional direct output analog current signal, Now to set corresponding transfer resistance that current signal is changed into analog voltage signal in signal condition unit.When coil is used When any one of above-mentioned three types is realized, its analog voltage signal directly or indirectly exported is designated as VPower frequency.In signal Output DC reference voltage signal V is provided with conditioning unitDC is referred toVoltage reference chip, and passed through by signal condition unit Signal mixed circuit in it is by d. c. voltage signal VDC is referred toWith analog voltage signal VPower frequencyExported after being mixed, be used as constant current The input voltage signal U of driver elementi, i.e. Ui=VDC is referred to+VPower frequency, signal mixed circuit can utilize prior art, pass through integrated fortune Calculate the mixing that amplifier realizes two signals.Blended voltage signals UiIt is admitted to after constant current driving unit, is driven by constant current single Member is converted to current signal and drives the luminous tube 2 in it to light.The light that luminous tube 2 is sent enters optical fiber 4 through the joints of optical fibre 3 And deliver in the joints of optical fibre 3 of secondary side 6.
The optical signal that primary side 1 is sent is admitted to after secondary side 6, is initially entered in photoelectric detection unit, through photodetection Photoelectric tube 5 in unit converts optical signals to current signal, then will through the current-voltage conversion circuit in photoelectric detection unit Electric current is converted into voltage signal UoOutput.Current-voltage conversion circuit at least includes one and current signal is converted into voltage letter Number feedback resistance and integrated operational amplifier.The voltage signal U obtained by current-voltage conversion circuitoCompared to more electric Press signal UiCan be because of the coupling loss between luminous tube 2 and the joints of optical fibre 3, fiber transmission attenuation, the joints of optical fibre 3 and photoelectricity Luminous power declines and causes decay caused by coupling loss, the aging of luminous tube 2 between pipe 5, therefore Uo=V 'DC is referred to+V’Power frequency, V’DC is referred toAnd V 'Power frequencyReference voltage signal V after respectively decayingDC is referred toWith analog voltage signal VPower frequency.Voltage signal UoIt is admitted to letter In number extraction unit, signal extraction unit as shown in Figure 2 includes CPU and capacitance, and photoelectric detection unit is defeated The voltage signal U gone outoIt is divided into two-way, sends into CPU through capacitance all the way, another road is sent directly into central processing Unit.Remove d. c. voltage signal V ' through capacitanceDC is referred toRetain analog voltage signal V ' afterwardsPower frequency, CPU is according to two The signal of road feeding is respectively to V 'DC is referred toAnd V 'Power frequencySampled and calculated, reduction obtains original analog voltage signal VPower frequency
As shown in figure 3, the method for transmitting signals for current transformer, comprises the following steps:
Step 1, (U, P) numerical value under multigroup normal temperature is obtained.
Before equipment is dispatched from the factory, at room temperature, different straight of multigroup numerical value is exported to constant current driving unit by signal generator Voltage signal Uc is flowed, drives luminous tube 2 to light by different DC voltage Uc constant current driving units, and obtained by light power meter To corresponding multigroup performance number, multigroup (U, P) numerical value of luminous tube 2 is obtained.
Luminous tube 2 (such as LED) is current mode device, and its drive circuit is driven using constant current, i.e. its luminous power P is by flowing through Its electric current I is determined.The complete P-I relation curves of luminous tube 2 as shown in figure 4, due to luminous tube 2 when luminous dead zone voltage In the presence of so that the curved line relation is not fairly linear relation close to the relation of second order polynomial.It is electric however as LED is flowed through Good linear relationship is then gradually presented in the continuous increase of stream, its P-I relation.As shown in figure 4, electric current I is from I1Its P-I is closed afterwards System is linear relationship.
, can be by hardware circuit (such as control DC offset voltage when implementing the method for transmitting signals of this current transformer Size or constant-current drive circuit in thermistor size) control operating current scope in I1And I2Between, then the P- of this section I relations are naturally also linear.In real system, because the LED drive circuit that the present invention is applied drives for constant current, therefore flow through The LED electric current I and input voltage U of the constant current driving unit is resistance R multiple proportion, therefore in use, only The P-U relations for measuring the constant current driving unit used in the LED are needed without measuring P-I relations.Its reason is that constant current driving is single The reality output of signal condition unit before member is exactly an analog voltage signal rather than current signal.
Step 2, luminous tube power-driving voltage curve is obtained.
Multigroup (the U, P) numerical fitting obtained by step 1 obtains the P-U relation curves of luminous tube power-driving voltage, P-U relation curves meet formula:P=aU+b.In actually implementing, the magnitude of voltage exported due to signal condition unit output end For d. c. voltage signal VDC is referred toWith analog voltage signal VPower frequencyMagnitude of voltage U after being mixedi, therefore magnitude of voltage U after mixingiEqually Meet above-mentioned formula, obtain formula (1):
P=aUi+ b formula (1)
As shown in figure 5, for a specific model communication with LED (such as wavelength be 650nm red visible LED), In good (U1, the U2) section of the P-U relations linearity, its P-U relations coincidence formula (1):P=aUi+ b, wherein b < 0.It is right A, b value answered using signal generator can apply several (U by the constant current driving unit to the LED1, U2) interval straight Voltage signal is flowed, the corresponding luminous power value of each voltage signal is measured accordingly, using software (such as Matlab) to these points Carry out curve fitting and can obtain a, b value.Measurement to the luminous power of luminous tube 2 is realized using light power meter.
When the present invention is applied to current transformer, it can cause in power system when bus current is larger in current transformer The temperature rise in portion, and then cause the rise of the temperature of luminous tube 2.The luminous power of luminous tube 2 can decline with the rise of temperature, This changes the value for causing coefficient a and b in P-U relations.
As shown in fig. 6, being understood through actual test:In 25 DEG C and 70 DEG C, in (U1, U2) section, its P-U relation is all line Property, but coefficient a ', the b ' when coefficient a, b at 25 DEG C and 70 DEG C are unequal, i.e. and the corresponding coefficient a and b of P-U relations is meeting Vary with temperature and change, this is unfavorable for the implementation of the method for transmitting signals of this current transformer.In order to ensure in temperature liter Gao Shi, the coefficient a and b of constant current driving unit P-U relations used is constant, can accordingly increase when temperature is raised and flow through luminous tube 2 electric current.Specific implementation method is in constant current driving unit, by voltage UiIt is converted into the electricity used in the driving current of luminous tube 2 The thermistor (NTC) that R uses negative temperature coefficient is hindered, its resistance value can be lower when temperature is higher for such thermistor, so that The electric current for passing through luminous tube 2 is automatically increased, to voltage UiFor, it also just compensate for the caused luminous tube 2 of temperature rise and send out Coefficient a, b in optical power down, its P-U relation can be kept approximately constant.Thereby guarantee that in temperature change, use this method High-acruracy survey can still be realized.
Thermistor will be according to sensitivity of the luminous tube 2 to temperature, if the luminous power of luminous tube 2 is to temperature when selecting Sensitivity is big, then selects the larger thermistor of temperature-coefficient of electrical resistance, otherwise selects the less temperature-sensitive electricity of temperature-coefficient of electrical resistance Resistance.As shown in fig. 7, when carrying out the heat-sensitive coefficients test of thermistor, comprising the following steps:
Step a, under normal temperature (such as 25 DEG C) T1, a constant driving DC voltage is exported to constant-current drive circuit.
Step b, replaces thermistor using potentiometer and measures the initial resistivity value R1 of potentiometer.
Step c, luminous power P1 of the record luminous tube 2 under temperature T1.
Step d, (is made the operating temperature of luminous tube 2 using heating device (such as heater box) with the temperature of luminous tube pad For luminous tube temperature) T2 is increased to, and record the luminous power P2 of the luminous tube 2 under temperature T2.
Step e, the operating temperature for keeping luminous tube 2 is T2, and constantly reduces the resistance of potentiometer, now luminous tube 2 Luminous power starts rise, when the luminous power of luminous tube 2 rises to P1, the potentiometer resistance R2 of record now.
Step f, the difference DELTA T=T2-T1 of the operating temperature by calculating luminous tube 2, and potentiometer resistance decline It is worth Δ R=R1-R2, calculating obtains the temperature coefficient that thermistor should have, and the selection to thermistor is completed according to the principle.
Step 3, the parameter of primary side 1 is stored in secondary side 6.
By coefficient a, b in P-U relations and DC reference voltage signal VDC is referred toIt is stored in signal extraction list in secondary side 6 In the CPU of member.
Step 4, calculate and obtain secondary side direct voltage reference value and power frequency component virtual value.
When equipment works at the scene, the CPU circuit in secondary side 6 in signal extraction unit is to photodetection After the DC reference signal value of unit output and power frequency component sampling, the DC reference signal value V ' after decay is calculatedDC is referred to's The virtual value V ' of value and power frequency componentPower frequency
Step 5, calculating obtain the power frequency component virtual value of primary side 1.
As shown in Figure 1, it is assumed that the luminous power that luminous tube 2 is sent is P, the light that luminous tube 2 is sent sequentially passes through optical fiber connection Device 3 (such as FC interfaces) is coupled into optical fiber 4 (such as plastic optical fiber), enters photo-detector circuit after completing transmission through optical fiber 4 Photoelectric tube 5.In the transmission of above-mentioned optical signal, each link will cause the decay of luminous power.Assuming that being finally coupled into The luminous power of photoelectric tube 5 is P ', then P ' and P relation meets formula (2):P '=α P, wherein α < 1.
Photo-detector circuit is substantially " electric current-voltage " change-over circuit, photodetector (photoelectric tube therein 5) optical signal received is converted into current signal, recycles feedback resistance to convert the current into voltage signal UoOutput.It is logical Cross operational amplifier, the photodetector of " optical-electronic " characteristic of the linearity well and " the zero offset electricity from Low-bias Current The circuit design method of die pressing type " may be such that the input optical signal P ' of the photo-detector circuit and the voltage signal U of outputoIt Between coincidence formula (3):Uo=β P '.
According to formula (1)~formula (3):P=aUi+ b, P '=α P and Uo=β P can release formula (4):Uo= α·β·(a·Ui+b).Wherein a and b is determined by the P-U characteristics of luminous tube 2, and causes a by using the design of thermistor Keep constant with b value;α then represents luminous aging shadow of the optical fiber 4 to the decay of optical signal, coupling attenuation and luminous tube 2 Ring;β is a constant, it comprises the conversion efficiency of photodetector, the feedback resistance of current-voltage conversion circuit it is big It is small.
In this practical application, if only inputting a DC reference signal V to LED constant current driver elementDC is referred to, then by formula (4) formula (5) is obtained:V’DC is referred to=α β (aVDC is referred to+b).Wherein a, b, VDC is referred toFor datum, V 'DC is referred toCan be in secondary side Measurement is obtained in 6 signal extraction unit, it is possible thereby to obtain formula (6)
As shown in figure 5, for constant current driving unit, the voltage signal of its actual input input is Ui=VDC is referred to+ VPower frequency。VDC is referred toIt can be realized by hardware mode and produce (the DC reference as exported a 2.5V using voltage reference chip REF5025 Signal), the luminous power of corresponding luminous tube 2 is also with PDC is referred toOn the basis of, with VPower frequencyThe change of signal and change, excursion (U1, U2) determined according to the maximum current of the current transformer bus to be measured;If the current work model of measured bus Enclose larger, V can be improvedDC is referred toValue, that is, improve circuit quiescent point, while in constant-current drive circuit thermistor choosing When selecting, the less thermistor of resistance is selected.Photo-detector circuit output voltage values U in the secondary side 6 of current transformeroFor Uo=V 'DC is referred to+V’Power frequency, V 'DC is referred to、V’Power frequencyIt can first be sampled in the signal extraction unit of secondary side 6, recycle center processing single Member is calculated and obtained.According to formula (5), formula (7) is obtained:V’DC is referred to+V’Power frequency=α β [a (VDC is referred to+VPower frequency)+b], formula (7) subtract each other with formula (5) and obtain formula (8):V’Power frequency=α β aVPower frequency, wherein a be, it is known that α β are obtained by formula (6), V’Power frequencyObtained in secondary side 6 by the CPU measurement in signal extraction unit, then obtain formula (9):
The analog voltage signal V that coil is exported can be obtained by above-mentioned formula (9)Power frequency
Step 6, the bus current virtual value for obtaining primary side 1 is calculated.
The formula (9) drawn is analyzed in step 5 and calculates obtained analog voltage signal VPower frequencyWith flowing through coil (iron core line Circle or air core coil) the size of bus current be only a multiple proportion, it is first that the size of the multiple depends on coil used The turn ratio of level winding and any one when being realized using above-mentioned three kinds different coils in corresponding situations below:It is hollow The design of coil integrating circuit or the size of iron-core coil shunt resistance or traditional iron-core coil turning in signal conditioning circuit Change the size of resistance.Obtained analog voltage signal V is calculated according to formula (9)Power frequency, in signal extraction unit in secondary side 6 CPU by VPower frequencyThe size of bus current can be calculated by being multiplied by the multiple.The need for secondary side apparatus, center Processing unit connects secondary set again so as to the combining unit for exporting the size of bus current to secondary side in the form of digital quantity It is standby;The V ' for the simulation that CPU can also export signal extraction unitPower frequencySignal directly feeds survey after carrying out programming amplifying Measuring appratus or protective relaying device.
The above described is only a preferred embodiment of the present invention, being not the limitation for making other forms to the present invention, appoint What those skilled in the art changed or be modified as possibly also with the technology contents of the disclosure above equivalent variations etc. Imitate embodiment.But it is every without departing from technical solution of the present invention content, the technical spirit according to the present invention is to above example institute Any simple modification, equivalent variations and the remodeling made, still fall within the protection domain of technical solution of the present invention.

Claims (9)

1. a kind of method for transmitting signals for current transformer, real by a kind of signal transmitting apparatus for current transformer Existing, described signal transmitting apparatus includes the primary side (1) and secondary side (6) connected by optical fiber (4), it is characterised in that:Institute In the primary side (1) stated, the output end for connecting the coil of bus connects the input of signal condition unit, signal condition unit Output end connects the input of constant current driving unit, and the output end of constant current driving unit connects one end of the optical fiber (4);
The input of other end connecting secondary side (6) interior photoelectric detection unit of optical fiber (4), the output end of photoelectric detection unit connects The input of signal extraction unit is connect, the output of signal is carried out by the output end of signal extraction unit;
Comprise the following steps:
Step 1, the different DC voltage of multigroup numerical value is exported to constant current driving unit, driving luminous tube (2) is with different power It is luminous, obtain multigroup U-P numerical value of luminous tube (2);
Step 2, the multigroup U-P numerical fittings obtained by step 1 obtain the P-U of luminous power-driving voltage of luminous tube (2) Relation curve:P=aU+b, then calculates the temperature for obtaining thermistor in constant current driving unit according to heat-sensitive coefficients method of testing Coefficient is spent, the selection to thermistor is completed, parameter a, b in P-U relation curves is kept constant;
Step 3, produced by coefficient a, b in P-U relation curves in step 2 and by the voltage reference chip in signal conditioning circuit Raw DC reference voltage signal VDC is referred toValue be stored in secondary side (6) in the CPU of signal extraction unit;
Step 4, CPU circuit is sampled respectively to the signal that photoelectric detection unit is exported, and is calculated through optical fiber (4) the DC reference signal value V ' decayed after transmittingDC is referred toValue and power frequency component virtual value V 'Power frequency
Step 5, calculated according to power frequency component calculation formula and obtain first siding ring output or be converted to by signal condition unit Power frequency component VPower frequency
Step 6, obtained power frequency component V is calculated according to step 5Power frequencyCalculate the virtual value for obtaining bus.
2. the method for transmitting signals according to claim 1 for current transformer, it is characterised in that:Described signal is carried Unit is taken at least to include capacitance and CPU, the signal of described photoelectric detection unit is divided into two-way:A-road-through Cross capacitance with CPU to be connected, another road is directly connected with CPU.
3. the method for transmitting signals according to claim 1 or 2 for current transformer, it is characterised in that:Described light Electric probe unit at least includes:Convert optical signals to the photoelectric tube (5) of current signal and be converted to photoelectric tube (5) Current signal is converted to the current-voltage conversion circuit of voltage signal.
4. the method for transmitting signals according to claim 1 for current transformer, it is characterised in that:Described signal is adjusted Reason unit at least includes:The voltage reference chip of DC reference voltage, and the power frequency component that the coil is exported can be generated And the signal mixed circuit that reference voltage is mixed.
5. the method for transmitting signals according to claim 1 for current transformer, it is characterised in that:Described constant current is driven The voltage signal that moving cell at least includes exporting signal condition unit is converted to the transfer resistance of current signal and by changing The current signal that resistance is converted to is driven luminous luminous tube (2).
6. the method for transmitting signals according to claim 5 for current transformer, it is characterised in that:Described luminous tube (2) it is communication luminous tube.
7. the method for transmitting signals according to claim 5 for current transformer, it is characterised in that:Described conversion electricity Hinder the thermistor for negative temperature coefficient.
8. the method for transmitting signals according to claim 1 for current transformer, it is characterised in that:Described in step 5 Power frequency component calculation formula be:
Wherein, a, b are respectively the P-U relation curves P=aU+b of luminous tube (2) coefficient, VDC is referred toFor in signal condition unit The DC reference voltage produced using voltage reference chip, V 'DC is referred to、V’Power frequencyThe decay that respectively CPU sampling is obtained Reference voltage and power frequency component afterwards.
9. the method for transmitting signals according to claim 1 for current transformer, it is characterised in that:Described in step 2 Heat-sensitive coefficients method of testing, comprise the following steps:
Step a, under normal temperature T1, a constant driving DC voltage is exported to constant-current drive circuit;
Step b, replaces thermistor using potentiometer and measures the initial resistivity value R1 of potentiometer;
Step c, luminous power P1 of the record luminous tube (2) under temperature T1;
Step d, is increased to T2, and record the luminous tube under temperature T2 using heating device by the operating temperature of luminous tube (2) (2) luminous power P2;
Step e, the operating temperature for keeping luminous tube (2) is T2, and constantly reduces the hair of the resistance, now luminous tube 2 of potentiometer Luminous power starts rise, when the luminous power of luminous tube (2) rises to P1, the potentiometer resistance R2 of record now;
Step f, the difference DELTA T=T2-T1 of the operating temperature by calculating luminous tube (2), and potentiometer resistance drop-out value Δ R=R1-R2, calculating obtains the temperature coefficient that thermistor should have, and is realized according to step a~step f to thermistor Selection.
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