JPH01291170A - Optical fiber current measuring instrument - Google Patents

Abstract

PURPOSE:To execute the measurement with high accuracy by inserting a conductor to be measured into the center part of two pieces of optical fiber coils whose number of turns is different, consisting of an optical fiber of a single mode, and bringing two kinds of signals at the time of passing through the optical fiber coil to operation processing. CONSTITUTION:In the periphery of a conductor to be measured 1, an optical fiber coil 2a to which an optical fiber 2 of a single mode has been wound many times, and an optical fiber coil 3b to which an optical fiber 3 of a single mode has been wound several times are provided. In this state, a light beam from a laser light source 9 is resolved into two pieces of optical components whose planes of polarization make an angle of 90 deg. to each other by an analyzing device 12 through a polarizing device 8, a polarization plane maintaining optical fiber 4 and the coil 2a, and the optical components are changed to a signal of the product of both of them by an arithmetic unit 18' through optical fibers 13a, 13b and photodetectors 16a, 16b, respectively. Also, a light beam from a laser light source 11 is inputted to a photodetector 17 through a polarizing device 10, a polarization plane maintaining optical fiber 6, the coil 3b and an analyzing device 14. Subsequently, a signal from the unit 18' and the element 17 is processed by an electric circuit 18 and outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an optical fiber current measuring device using an optical fiber suitable for current measurement that requires high accuracy and high reliability.

(Prior Art) Conventionally, wire-wound instrument current transformers have been mainly used as large current measuring devices used in power transmission and distribution equipment. However, this wire-wound instrument current transformer has drawbacks such as being large, expensive, and distorting the transient current waveform. Therefore, in recent years, instead of this, a method of optically measuring current using a substance having a Faraday effect has been attracting attention. Such optical current measuring instruments have the advantage of being compact and capable of faithfully reproducing transient current waveforms. In recent years, advances in optical fiber manufacturing technology have been remarkable, and current measuring instruments that utilize optical fibers themselves as Faraday effect materials are on the verge of being realized. For example, the magazine rOPTIcs ANDLASERTE
February 1980 issue of CHNOLOGYJ (p, 25-ρ
, 29), “0ptical fibers for
r current o+eagureneentap
Under the title "pHcations", a current measuring means as shown in FIG. Polarizer 10.
It passes through the lens 31 and becomes a linearly polarized wave.

The light is made to enter the optical fiber 3. This light undergoes Faraday rotation due to the magnetic field formed by the current flowing through the conductor 1 to be measured. The light emitted from the other end of the optical fiber 3 passes through the lens 32 . The analyzer 14 detects two polarization planes whose polarization planes are orthogonal to each other.
The light beam is split into two light beams, which enter light receiving elements 17a and 17b, where they are converted into two electrical signals. Based on these two electrical signals, the arithmetic circuit 33
The calculation (1, -L)/CI, +L) is performed and the result is output. Since this output value is approximately proportional to the Faraday rotation angle in a region where the Faraday rotation angle is small, it is ultimately proportional to the magnetic field strength that causes the Faraday rotation, and is proportional to the current value flowing through the conductor 1 to be measured. ,
Therefore, the current value of the conductor 1 to be measured can be measured.

(Problem to be Solved by the Invention) The biggest problem with the current measuring device having such a structure is birefringence that occurs within the optical fiber 3. - In general, an amorphous solid such as glass that constitutes the optical fiber 3 cable is optically isotropic, and the linearly polarized light wave formed by the polarizer 10 does not propagate while maintaining its polarization state. do. However, when stress is applied to the optical fiber 3, the amorphous solid also becomes optically anisotropic and exhibits birefringence.

That is, since the refractive index differs depending on the direction of the polarization plane, the linearly polarized light wave formed by the polarizer 10 is transmitted through the optical fiber 3.
While propagating inside, the polarized JIM changes and becomes elliptical. This is a cause of measurement error. Stresses applied to the optical fiber 3 include, in addition to residual stress applied during manufacturing, stress associated with changes in ambient temperature and stress due to vibration. Therefore, current measuring devices using conventional optical fibers.

They are sensitive to vibrations and changes in ambient temperature, and highly accurate current measurements cannot be made in environments with large vibrations and temperature changes.

An object of the present invention is to provide an optical fiber current measuring device that eliminates the above-mentioned drawbacks and can measure current with high accuracy even in an environment with large vibrations and temperature changes.

[Structure of the invention]

(Means for Solving the Problems) The present invention involves inserting a conductor to be measured into the center of two optical fiber coils each having a different number of turns each consisting of a single mode optical fiber, and transmitting light to these two optical fibers. It is characterized by using the Faraday effect that occurs when passing through a coil to obtain two types of signals as changes in the amount of light received, and then calculating and processing these two types of signals to output one current value. .

Light passing through an optical fiber coil with a large number of turns undergoes a large Faraday rotation, and the amount of light received changes periodically in response to slight changes in the value of the current flowing through the conductor to be measured. The number of one cycle is counted from this signal. This count number represents the current value. On the other hand, light passing through an optical fiber coil with a small number of turns undergoes a small Faraday rotation, so that it becomes a single-valued function within the measurement current range. That is, the amount of received light is set to be a monotonically increasing or decreasing function with respect to a change in the value of the current flowing through the conductor to be measured.

By referring to this signal, it can be determined whether the new count of the number of cycles obtained from the optical fiber coil with a large number of turns is caused by an increase or a decrease in the current value. Therefore, when it is determined that the current value has increased, a new count (+1) is added to the sum of past counts, and when it is determined that the current value has decreased, a new count (+1) is added to the sum of past counts. -1) is added. The total sum of the counts obtained in this way from the past becomes a value proportional to the current value, and it is possible to measure the current.

The present invention decomposes light that has passed through an optical fiber coil with a large number of turns into a large number of components with spatially different polarization planes, takes the value of the product of each signal, and counts the number of periods of this signal. It is characterized by

(Function) Changes in the value of the current flowing through the conductor to be measured may cause a change in the amount of heat generated by the conductor, causing a change in the ambient temperature, or changes in ambient temperature due to sunlight irradiation, changes in outside temperature, etc. Even if the optical fiber is subjected to mechanical stress and birefringence occurs, or even if the optical fiber is subjected to mechanical stress due to vibration of a circuit breaker and birefringence occurs, the absolute value of the amount of light received is changes, but the number and phase of periods do not change.

Therefore, with this method, it is possible to provide a highly accurate and highly reliable current measuring device that is not affected by such temperature changes and vibrations. At this time, if the light passing through an optical fiber coil with a large number of turns is decomposed into n components with spatially different polarization planes, and the value of the product of each signal is taken, the number of periods of the signal is , compared to the case where such an operation is not performed, the number of turns is n times larger for the same number of turns and the same current change, and the resolution is improved. Furthermore, if the resolution is to be kept the same, the number of turns can be reduced to 1/n, which is advantageous in terms of miniaturization and improvement of the S/N ratio.

(Example) An example of the present invention will be described below with reference to FIGS. 1 and 2. An optical fiber coil 2a in which a single mode optical fiber 2 is wound many times and an optical fiber coil 3b in which a single mode optical fiber 3 is wound several times are installed around the conductor 1 to be measured. One end of the optical fiber 2 forming the optical fiber coil 2a is connected to a polarization maintaining optical fiber 4.
and are connected by an optical connector 5. Similarly, one end of the optical fiber 3 forming the optical fiber coil 3b is coupled to the polarization maintaining optical fiber 6 through the optical connector 7. The other end of the polarization-maintaining optical fiber 4 is coupled to a polarizer 8 with their polarization planes matching each other, and the light emitted from the laser beam g9 passes through the polarization device 8 and then is polarized. The light is input into the optical fiber 4.

On the other hand, the same goes for the other end of the polarization maintaining optical fiber 6.

The light that is combined with the polarization device 10 with their polarization planes matching each other and emitted from the laser light source 11 is coupled to the polarization device 1
After passing through 0, the light is input to the polarization maintaining optical fiber 6. The other end of the optical fiber 2 forming the optical fiber coil 2a is coupled to two multimode optical fibers 13a and 13b via an analyzer 12.

That is, the light emitted from the fiber 2 is separated into two light components whose polarization planes make an angle of 90'' to each other by the analyzer 12 installed at an arbitrary angle, and the light is transmitted through the optical fibers 13a and 13b, respectively. The respective light components transmitted in this way are transmitted to the light receiving elements 16a, i
6b, the signal is converted into an electrical signal, input to the arithmetic unit 18', and converted into a signal representing the product of both. The other end of the single mode optical fiber 3 forming the optical fiber coil 3b is connected to the multimode optical fiber 15 via the analyzer 14.
is combined with Here, the direction of the polarization plane of the analyzer 14 is
The linearly polarized light wave formed by the polarizer 10 has an angle of about 45@ with respect to the direction of the plane of polarization that it has just before it enters the analytical bag [14] when no current is flowing through the conductor 1 to be measured. Place it like this. The other end of the optical fiber 15 is.

It is coupled to the light receiving element 17. Signals from the arithmetic unit 18' and the light receiving element 17 are input to the electronic circuit section 18,
It is processed and output as an electrical signal approximately proportional to the value of the current flowing through the object to be measured 1.

Next, the configuration of the electronic circuit section 18 will be explained with reference to FIG. 2. The electrical signal obtained by the arithmetic unit 18' is amplified by the amplifier 21 and input to the comparator 22. On the other hand, the output of the amplifier 21 is simultaneously smoothed by the smoothing circuit 23 and input to the other input terminal of the comparator 22. The comparator 22 compares the magnitudes of both signals and outputs a pulse when they are equal. This pulse is input to the timing pulse generator 24,
A first output from the timing pulse generator 24 is input to an arithmetic unit 25 . A second output from the timing pulse generator 24 is input to a sample hold 27;
At this time, the sample hold 27 samples the magnitude of the electrical signal that has passed through the light receiving element 17 and the amplifier 26,
Hold. The third pulse from the timing pulse generator 24
The output of
compares the magnitude of the electrical signals held in the
is input. The fourth pulse from the timing pulse generator 24
The output of is input to the sample hold 28, and the sample hold 28 is input to the sample hold 28.

The magnitude of the electrical signal held in the sample hold 27 is taken in and held. The arithmetic unit 25 counts the first output from the timing pulse generator 24 and adds 1 to the total count stored in the memory or adds 1 to the total count stored in the memory depending on whether the input signal from the comparator 29 is positive or negative.
Executes a pull operation and outputs an electrical signal proportional to this total count number.

Next, the operation of the embodiment of the present invention shown in FIGS. 1 and 2 will be explained with reference to FIGS. 4 to 6.

FIG. 4(a), (b) = (c) shows that the light receiving elements 16a, 16 change with respect to the current flowing through the conductor 1 to be measured.
b represents the changes 35a and 35b in the received power and the change 35c in the output waveform of the arithmetic unit 18'. Since the number of turns of the optical fiber coil 2a is very large, the light passing through this coiled structure 2a undergoes a large Faraday rotation due to the small amount of current flowing through the conductor 1 to be measured. Therefore, in the current region to be measured, the plane of polarization spatially rotates many times, and the light receiving element 1
The optical power received by 6a and 16b is as shown in Fig. 4, 35a,
As shown in the curve 35b, it changes periodically with respect to the current value. Change in current value that gives a half cycle of this waveform 2
・DELTA is always constant regardless of the current value. Here, the optical power Iap Ib received by the light receiving elements 16a and 16b can be expressed by the following equation with respect to the current value I flowing through the conductor 1 to be measured.

■ Ia=1. sin" (-7C+ '/')
-(1) 4・Δtech■ l3=1. cos” (□π+(f)) ・・
・■4・ΔI ■, ■From formula 1. When determining X Ib, a linear equation is obtained.

Therefore, the output of the arithmetic unit 18' is given by the equation 0,
The waveform becomes as shown in FIG. 4, 35c. It can be seen that this waveform has a period of 172 compared to the waveforms 35a and 35b obtained by the light receiving elements 16a and 16b.

Also, the amount of change Δ in the current value that gives a half cycle of waveform 35c
I is always constant regardless of the current value. - The number of turns of the optical fiber coil 3b is not so large, and the light passing through the optical fiber coil 3b does not undergo a large Faraday rotation due to the current flowing through the conductor 1 to be measured. Therefore, in the current range to be measured. , the optical power received by the light-receiving element 17 is as shown in FIG.
It becomes a monotonically increasing or monotonically decreasing function as shown in the curve 6. The direction of the polarization plane of the analyzer 14 is set to the direction of the conductor 1 to be measured.
45° to the polarization plane of light when no current flows through
By making the angle , it is possible to maximize the current region in which the curve 36 in FIG. 5 is a monotonous function.

The operation of the electronic circuit section 18 will be explained with reference to FIG. 6, taking into account that the optical signal as described above is obtained. Now, when the current value flowing through the conductor 1 under test is changing, the output waveform of the amplifier 21 becomes the waveform shown by the curve 37 in FIG. 6(a). , it is clear from the fact that it is proportional to the output waveform of the arithmetic unit ff18'. Further, the output of the smoothing circuit 23 is set to the level of the average value of one curve 37, as shown by a curve 38 in the figure. Here, the comparator 22 detects the intersection of the curve 37 and the curve 38. For example, if 1=1n intersects and the 5th order intersects at t=, then the magnitude of the current flowing through the conductor 1 to be measured between time 2 t0 and tl increases or decreases by Δt. It turns out it's one or the other. Whether it has increased or decreased can be determined by measuring the output signal of the amplifier 26 shown by a curve 39 in FIG. 6(b). 1=1.
If the output when t=t is larger than the output of the amplifier 26 when t=t, it is increasing, and if it is smaller, it is decreasing. The comparator 29 makes this determination. If the current value when 1=0 is 0, then the current value can be found by adding or subtracting Δ work in the above operation. This operation is executed by the arithmetic unit 25. Here, the current measurement resolution of the current measuring device according to this embodiment is ΔI, and the Faraday rotation angle given by this Δ■ is 45°. Therefore, the number of turns of the single-mode optical fiber 2 must be determined so that the Faraday rotation angle received by the light that makes one round trip through the optical fiber coil 2a is 45° or more for the current value with the resolution required for measurement. It won't happen.

When the amount of heat generated by the conductor changes due to a change in the current value flowing through the conductor to be measured 1, the ambient temperature changes, or when the ambient temperature changes due to the presence or absence of sunlight, changes in the outside temperature, etc. Even if the fiber is subjected to mechanical stress and birefringence occurs, or the optical fiber is subjected to mechanical stress due to the vibration of a breaker, etc., and birefringence occurs, as shown in Figure 4 (
The value of Δfactor shown in a) is not affected by this birefringence and is always constant. In addition, curves 35a and 35 in FIG. 4(a)
Although the amplitude of b changes due to birefringence, the phase does not change. Therefore, the phase of curve 35c also does not change. In the present invention, since only the phase of the curve 35e is measured, it is possible to provide a highly accurate current measuring device that is not affected by birefringence.

As shown in Fig. 4, the light passing through the optical fiber coil 2a is decomposed into two components Ia + Ib, and the product of this signal is
By determining XIb, a signal having a period of 172 of the original wave can be obtained. This means that the resolution is twice as high as when the operation of Ia× is not performed, and if the resolution is the same, the number of turns of the optical fiber 2 can be 172. This not only reduces the size of the optical fiber coil 2a, but also reduces the birefringence that light receives while passing through the optical fiber coil 2a.
2, and the S/N ratio improves.

Generally, by decomposing the light passing through the optical fiber coil 2a into n components and taking the product of these signals, the period can be reduced to 1/1.
n, the resolution can be increased n times for the same number of turns. Therefore, the Faraday rotation angle experienced by the light passing through the optical fiber coil 2a is.

The number of turns may be selected so that the resolution of the current value required for measurement is 90°/n or more. FIG. 7 shows an outline of the light receiving system and arithmetic unit when n=4.

〔Effect of the invention〕

As described above, according to the present invention, a conductor to be measured is inserted into an optical fiber coil in which a single mode optical fiber is wound into a coil shape many times, and a conductor to be measured is inserted from one end of the optical fiber coil.
Light from a laser light source is input, passed through the optical fiber coil, and the light emitted from the other end is decomposed into a number of components with spatially different polarization planes, and the product of the signals obtained from these components is calculated. Since the value of the current flowing through the conductor to be measured is measured from the signal of this product, it is possible to obtain an optical fiber current measuring device that can measure current with high accuracy even in an environment with large vibrations and temperature changes.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram of an optical fiber current measuring device showing an embodiment of the present invention, Fig. 2 is a block diagram showing the 41 structure of the electronic circuit section, and Fig. 3 is an overall diagram of a conventional optical fiber current measuring device. Block diagram, Figure 4 (a) and (b). (C), Fig. 5 is a characteristic diagram showing changes in received light power with respect to current value, Figs. FIG. 3 is a block diagram showing an overview of a light receiving system and a computing device showing another embodiment of the invention. 1... Conductor to be measured 2.3... Single mode optical fiber 2a, 3b.
... Optical fiber coil 4.6 ... Polarization maintaining optical fiber 5.7 ... Fiber connection section 8, 10 ... Polarizer 9, ]1 ... Laser light source 12, 12a, 12b, 14- Analyzer 13a,
13b, 13c, 13d, Is'' multimode optical fiber 16a, 16b, 16e, 16d, 1
7.17a, 17b...light receiving elements 18', 18'',
18'''... Arithmetic device 18... Electronic circuit section 19
... Drive power supply 21.26 ... Amplifier 22
... Comparator 23 ... Smoothing circuit 24,
29...Timing pulse generator 25, 33...Arithmetic circuit 27.28...Sample hold 31, 3
2... Lens 40... Beam splitter representative Patent attorney Rule Ken Chika Yudo Daishimaru Ken Figure 3 Light reception 0 wah (C) Figure 4 Light reception type 0 wah - 9 Tomoe Kuno (07- ( α) (b>

Claims (1)

[Claims] A conductor to be measured is inserted into an optical fiber coil in which a single mode optical fiber is wound into a coil shape, and light from a laser light source is incident from one end of the optical fiber coil.
The light passed through the optical fiber coil and emitted from the other end is decomposed into a number of components with spatially different planes of polarization, the product of the signals obtained from these components is determined, and the signal of the product is used to determine the conductor to be measured. An optical fiber current measuring device characterized by measuring a current value flowing through an optical fiber.