CN1271413C - A photoelectric current transformer - Google Patents

Abstract

The present invention discloses a photoelectric current transformer which comprises two sensing elements, a polarizer and an analyzer, wherein the polarizer and the analyzer are respectively arranged on both ends of the sensing elements. The two sensing elements are in vertical arrangement, and have the same material and the length. A permanent magnet is parallel with the second sensing element, and is perpendicular to a stop conductor, and thus, a current sensing head is jointly formed by the components. The current sensing head is connected with an optoelectronic processing unit through optical fibers and optic cables. The optoelectronic processing unit comprises two light sources, four photoelectric detectors, an amplifier and a signal processing unit. The lights sent by the two light sources are transmitted to the current sensing head by the optical cables, are modulated by current signals, are divided into four light paths, and are transmitted to four photoelectric detectors through the optical cables, the optical signals are converted into the electric signals, and are amplified by the amplifier, and the electric signals enter the signal processing unit to complete signal processing. Digital signals are output to a display device. The present invention introduces a standard magnetic filed, achieves the purposes of real-time compensation on the influence of birefringence on the measurement due to temperature and vibration, and obtains long-term stability of OCT.

Description

A kind of photoelectric current inductor

Technical field

The present invention relates to a kind of mutual inductor, specifically, is a kind of photoelectric current inductor.

Background technology

There is following shortcoming in induction current transformer (Current Transducer, be called for short CT): (1) potential the danger of catastrophic failure, for example sudden blast; (2) if output load is in open circuit, high voltage is arranged; Large-scale heavy and essential bracing frame; Be subject to electromagnetic interference (EMI); (3) the primary current changing condition in the time of can not correctly reflecting electric power system fault is difficult to adapt to the requirement of protecting electrical power system.For this reason, developed country is all at the electric power networks of seeking the optical sensing technology is used for high-voltage great-current.What this was wherein relatively more successful is the current transformer (Optical currentTransducer is called for short OCT) that utilizes Faraday magnetooptical effect.From the sixties so far, a series of linked network trial run progress has also been obtained on the existing certain research basis of this technology, also produces on a large scale and uses but never really enter the practical stage.Main reason be because: OCT is subject to the birefringent interference that temperature and vibration cause when measuring, thereby makes accuracy and the stability measured be affected.For this reason, the researchist has adopted thousand and one way to be improved, and wherein, more influential have:

(1) with the relevant method of polarization state modulation, but this method implements the religion complexity, also is subjected to the influence of temperature rise rate, different temperature rise rates, and the curve of compensation will change, and therefore, can not really reach practical purpose.Concrete visible Peter Menbe, Thomas Bosselmann.Temperaturecompensation in magneto optic AC current sensors using an intelligentAC-DC signal evaluation, Journal of lightwave technology, 1995,13 (7): 1362-1370.

(2) by the temperature of survey sensor place environment, the measuring error that the birefringence that temperature is caused causes compensates, but under high voltage environment, with the ordinary hot galvanic couple is not all right, can only use fibre optic temperature sensor, certainly will make total system become more complicated like this, reduce reliability.Simultaneously, for the OCT of protection purposes, temperature compensation must be accurate to 1 ℃; For the OCT of metering purposes, temperature compensation must be accurate to 0.1 ℃, so high temperature survey requirement, and fibre optic temperature sensor may reach hardly, thereby the method can not be used under high voltage environment.Concrete visible W.Lain Madolen etal.Temperature compensation for optical current sensors.OpticalEngineering, 1999,38 (10): 1699-170

Summary of the invention

The present invention is directed to the defective that exists in the prior art, a kind of photoelectric current inductor is provided, its stability is not subjected to the influence of environment temperature and vibration basically, and is simultaneously simple again, is convenient to batch machining production.

Photoelectric current inductor of the present invention, comprise the first responsive unit and lay respectively at first polarizer and first analyzer at these sensitivity unit both ends, it is characterized in that: this mutual inductor also comprises the second responsive unit, the both ends of this sensitivity unit also are provided with second polarizer and second analyzer, and vertically placement and material are identical with length mutually in two responsive units; Permanent magnet is parallel with the second responsive unit, and vertical with current, and above-mentioned each parts constitute current sensing head jointly; This current sensing head links to each other with the photoelectricity processing unit by optical fiber, optical cable, the photoelectricity processing unit comprises two light sources, four photoelectric detectors and amplifier and signal processing unit, the light that two light sources send reaches current sensing head through optical cable, after the current signal modulation, be divided into four road light, transfer to four photoelectric detectors through optical cable, with light signal conversion becoming electric signal, be amplified into signal processing unit to amplifier again, finish signal Processing, the output digital signal is to display device.

The present invention has introduced a standard Magnetic Field, the size in this magnetic field temperature influence not in ambient temperature range (40 ℃ ~+80 ℃), or influence minimum by (＜1 * 10 ^-4, utilize reference path to measure this magnetic field size, make reference path be subjected to Temperature Influence consistent during design with measuring light path, by comparative measurement method, eliminate this influence then.Promptly by the introducing of standard Magnetic Field, reach birefringence that real-Time Compensation temperature, vibration cause to measuring the purpose of influence, to obtain the long-time stability of OCT.Particularly, the present invention has following technique effect:

1, the present invention can eliminate the influence of birefringence to measuring that temperature and vibration cause on the principle fully.

2, opticator processing of the present invention is very simple, is fit to the requirement that batch machining is produced, and production cost is significantly less than bulk and the strip glass sensing unit that generally adopts now simultaneously.

Description of drawings

Fig. 1 is the structural representation of photoelectric current inductor of the present invention;

Fig. 2 is the structural representation of current sensing head among Fig. 1;

Fig. 3 is the structural representation of photoelectricity processing unit;

Fig. 4 is flow chart of data processing figure, and wherein K is a calibration coefficient.

Embodiment

Structure of the present invention comprises current sensing head 2, photoelectricity processing unit 7, display device 8 and the optical fiber, the optical cable that are used for light transmission as shown in Figure 1.

The structure of current sensing head 2 is as shown in Figure 2: it comprise vertical mutually place and material is identical with length two responsive first 9,10, be positioned at first polarizer 11, first analyzer 12 at first responsive first 9 both ends, be positioned at second polarizer 14, the analyzer 15 at second responsive first 10 both ends, and with the second responsive unit, the 10 high stability permanent magnets 13 that are parallel to each other.Permanent magnet 13 is vertical mutually with current 1, so that the magnetic field that current produces does not influence permanent magnet magnetic field.The effect of the polarizer 11,14 is that directional light is become polarized light, and the effect of analyzer 12,15 is to be converted into light intensity with the angle that is directly proportional by signal.

Photoelectricity processing unit 7 as shown in Figure 3, two reference power supplies 15,16 make two light emitting diodes 19,20 luminous by two driving circuits 17,18.Two road light reach the sensing head of higher-pressure region through optical cable, after the current signal modulation, be divided into four road light, transfer to four photoelectric detector 21-24 through optical cable opto-electronic conversion is become electric signal, be amplified into signal processing unit 29 to amplifier 25-28 again, export after finishing the calculation function among Fig. 4.Signal processing unit 29 can be finished computing with the dsp chip programming, also can finish relevant computing with analog device.

Luminotron in the photoelectricity processing unit 7 inputs to optical cable 6 with light beam, through optical fiber connecting box 5 light is reached optical fiber 4, is with composite insulator full skirt 3 outside the optical fiber 4, and light beam inputs to current sensing head 2 by optical fiber, and current sensing head 2 is enclosed within on the current 1.During use measured conductor is connected with current 1, when electric current passes through, light beam obtains the information of tested electric current by current sensing head 2, this light beam is promptly modulated, the photodetector demodulation of modulated light in optical fiber, optical cable reach photoelectricity processing unit 7 again transported to display device 8 with this electric signal and shown tested current value after signal processing unit processes.

During use, measured conductor is connected with the current 1 that is positioned at mutual inductor, two light sources that are positioned at photoelectricity processing unit 7 are I ' with light intensity respectively ₀, I ₀Two light beams feed responsive unit 9,10 respectively by optical fiber, optical cable.According to the Faraday magnetooptical effect principle, when current 1 galvanization, detect tested current information respectively by responsive unit 9,10, both detected current informations are compared (promptly being divided by) in signal processing unit, because both are under the same environmental baseline, the birefringence influence is eliminated in comparison.Can accurately measure tested size of current.Specify as follows:

The first responsive unit 9: adopt magneto-optic memory technique,, be used to measure the magnetic field size that measured conductor produces, this magnetic field size and the direct proportional relation of tested size of current as dense flint glass with Faraday magnetooptical effect.

The second responsive unit 10:, be used to measure the size in the reference magnetic field that the high stability permanent magnet produces with the first responsive unit, 9 identical materials.

Make the length of responsive unit 9 and 10 identical during design, take from same uniformity coefficient massive material preferably, can think that then the intrinsic linear birefrigence in two block of material equates, when having birefringence in the responsive unit, illustrated responsive unit 9 based on Faraday effect is output as

In the formula: I ' ₀Be the light intensity of first light source,

_ACFor the faraday's deflection angle that causes of tested electric current, proportional with i;

δ is the phase delay of introducing owing to the linear birefrigence in the responsive unit;

Birefringence two parts that the birefringence of responsive unit is introduced by intrinsic birefringence in the sensitive material and extraneous factor are formed, when the intrinsic birefringence of selecting material greatly the time, i.e. and δ 〉=, then, Δ ≈ δ, at this moment, and (1), (2) formula becomes:

Analyze (3), (4) formula, we can see, when δ changes, owing to Sin δ ≠ δ, thereby make measurement be subjected to extraneous birefringent influence of introducing, and bring than mistake.

(3) and (4) formula is suitably handled: Can obtain

Or to I ₁And I ₂In any one the tunnel carry out AC and DC and separate, and be divided by and can get:

The second responsive unit 10 is output as:

In the formula, I ₀---be the light intensity of secondary light source,

_N---the faraday's deflection angle that causes for the magnetic field of permanent magnet.

δ---the phase delay of introducing owing to the linear birefrigence in the responsive unit.

(8), (9) formula are carried out

Computing is to eliminate light intensity I ₀The influence that changes can get

With formula (5)/(10),

Ask formula (6)/(10)

Ask formula (7)/(10)

The negative sign of formula (13) only influences the phase place of tested current i, can be by eliminating with the comparison and the demarcation of normalized current, so can not consider in following derivation.And _ACBe the linear function of tested current i, i.e. _AC=f (i); _NIt is the magnetic field H of permanent magnet _NLinear function, (H herein _NBe a constant) be _N=f (H _N).

Then $f\left(i\right)=\frac{I}{{I^{\′}}_N}f\left(H_N\right)\·\·\·\left(14\right)$

$f\left(i\right)=\frac{I_1^{\′}-I_2^{\′}}{I_N^{\′}}\·f\left(H_N\right)\·\·\·\left(15\right)$

$f\left(i\right)=\frac{{I^{\′}}_1}{{I^{\′}}_N}f\left(H_N\right)\·\·\·\left(16\right)$

$f\left(i\right)=\frac{{I^{\′}}_2}{{I^{\′}}_N}f\left(H_N\right)\·\·\·$ $\left(17\right)$

Wherein, (14), (15) are the double light path computing formula, (16) reaching (17) is respectively monochromatic light road computing formula, all can obtain F (i) with any one formula in (14), (15), (16), (17) formula, again the size that just can obtain tested current i by comparison and demarcation with normalized current.

Because H _NBe the magnetic field of the permanent magnet generation of high stability, in the temperature range below 80 °, H _NSize is not subjected to the influence of temperature and vibration, it is a constant, thereby, by the light intensity output of responsive unit 9,10 being carried out after opto-electronic conversion becomes electric signal, carry out above-mentioned corresponding computing, resultingly be one and eliminated a birefringence influence that external environment factor temperature, vibration introduce and a signal that is directly proportional with tested current i, so, with the size that just can obtain tested electric current after normalized current comparison and the demarcation, and this measuring process is not subjected to the influence of external environment factor, has high accuracy and long-time stability.Its flow chart of data processing as shown in Figure 4.

Claims (2)

1, a kind of photoelectric current inductor, comprise the first responsive unit, and lay respectively at first polarizer and first analyzer at this sensitivity unit both ends, it is characterized in that: this mutual inductor also comprises the second responsive unit (10), one end of this sensitivity unit (10) is provided with second polarizer (14), the other end is provided with second analyzer (15), and vertical mutually placement of two responsive units (9,10) and material are identical with length; Permanent magnet (13) is parallel with the second responsive unit (10), and vertical with current (1), and above-mentioned each parts constitute current sensing head (2) jointly; This current sensing head (2) passes through optical fiber, optical cable links to each other with photoelectricity processing unit (7), photoelectricity processing unit (7) comprises two light sources (19,20), four photoelectric detectors (21,22,23,24) and amplifier (25,26,27,28) and signal processing unit (29), two light sources (19,20) light that sends reaches current sensing head (2) through optical cable, after the current signal modulation, be divided into four road light, transfer to four photoelectric detectors (21 through optical cable, 22,23,24), with light signal conversion becoming electric signal, again to amplifier (25,26,27,28) be amplified into signal processing unit (29), carry out mould/number conversion and data operation, export display device (8) again to.

2, photoelectric current inductor according to claim 1, it is characterized in that: described signal processing unit (29) obtains f (i) according to following arbitrary formula, the size that obtains tested current i by comparison and demarcation with normalized current again, wherein f (i) is the linear function of tested current i, H _NBe the magnetic field of permanent magnet,

Wherein, _ACBe faraday's deflection angle that tested electric current causes, the phase delay that δ introduces for the linear birefrigence in the responsive unit; _NThe faraday's deflection angle that causes for the magnetic field of permanent magnet:

$f\left(i\right)=\frac{I}{{I^{\′}}_N}f\left(H_N\right)$

$f\left(i\right)=\frac{I_1^{\′}-I_2^{\′}}{I_N^{\′}}\·f\left(H_N\right)$

$f\left(i\right)=\frac{{I^{\′}}_1}{{I^{\′}}_N}f\left(H_N\right)$

$f\left(i\right)=\frac{{I^{\′}}_2}{{I^{\′}}_N}f\left(H_N\right).$

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