JPH07280850A - Current measuring method - Google Patents

Abstract

PURPOSE:To provide a method for measuring a high current. CONSTITUTION:The current measuring system comprises a pair of optical units 1, and a lead glass optical fiber 3 forming an optical path around a conductor 2 passing a current to be measured. The lead glass optical fiber 3 comprises a pair of first and second optical fibers 3a, 3b split at positions on the opposite sides of the conductor 2 and each optical fiber 3a, 3b is provided with a reflection means 4 on the peripheral end side. The first and second optical fibers 3a, 3b are arranged such that one incident end intersects the other reflective end on a plane and an optical unit 1 is disposed closely to the intersection. The lead glass optical fiber 3 is split such that the linearly polarized lights propagating through the optical fibers 3a, 3b are subjected to Farady's rotational angle within 45 deg. by the current to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current measuring method, and more particularly to a current measuring method utilizing the Faraday effect of a current magnetic field.

[0002]

2. Description of the Related Art A current measuring method utilizing the Faraday effect in which the plane of polarization of light is rotated by the action of a magnetic field is known. In the current measuring method based on such a principle,
The circuit-integrated current measurement method is caused by non-uniformity of the magnetic field around the conductor and other than the conductor in which the current to be measured flows by making an integer number of turns around the conductor in which the current to be measured flows. There is an advantage that the effect of the magnetic field that occurs can be compensated.

Further, as a method for detecting the Faraday rotation angle, an intensity detecting method which can configure one light source is desirable because it is easy to align the optical axes. However, such a circuit-integrated current measuring method of intensity detection has the following technical problems.

[0004]

That is, in the current measuring method utilizing the Faraday effect, if the intensity detection method is adopted, ± 4 is obtained with respect to the plane of polarization when the current is zero.
The intensity Px, Py of the polarized light in the 5 ° azimuth is Px ∝ cos, where θ is the Faraday rotation angle due to the current flow.
(45 ° −θ) and Py∝sin (45 ° −θ). As can be seen from this formula, since the Faraday rotation angle having the same Px and Py exists within ± 45 ° with respect to the Faraday rotation angle exceeding ± 45 °, when the Faraday rotation angle exceeds ± 45 °, The current cannot be measured.

By the way, in the measurement of the current of the circular integration type, the Faraday rotation angle is determined by the product of the magnitude of the magnetic field, the Verdet constant of the optical path and the optical path length. So, for example,
When the optical path of the Faraday sensor element is installed so as to make an integral number of turns around the conductor in order to eliminate the effects of external magnetic fields, etc., if the optical path length and Verdet constant are constant, a very large current will be measured. When it flows, the Faraday rotation angle exceeds 45 °, and there is a problem that the current cannot be measured.

The present invention has been made in view of such conventional problems, and a first object of the present invention is to provide a method of measuring a current capable of measuring a large current. A second object of the present invention is to provide a method of measuring a current that enables stable measurement with respect to the external deformation force of the fiber when a lead glass fiber having a small photoelastic constant is used.

[0007]

In order to achieve the above object, a method for measuring current according to the present invention is such that an optical path is formed so as to circulate around an outer circumference of a conductor through which a current to be measured flows, and the optical path is formed in the optical path. When passing linearly polarized light, in the method of measuring the current for measuring the Faraday rotation angle of the linearly polarized light that rotates due to the magnetic field effect of the current to be measured, so that the current can be measured, each of the circulating optical paths, The Faraday rotation angle of the Faraday element is divided into a plurality of parts so that the Faraday rotation angle is 45 ° or less, and the Faraday rotation angles of the divided optical paths are added together so as not to be affected by the external magnetic field as a whole. It is characterized in that the magnetic flux density component parallel to the optical path is circularly integrated.

The linearly polarized light can be transmitted from one end of the split optical path to the other end. Further, the linearly polarized light can be reflected on the other end side after propagating from one end to the other end of the split optical path. The optical path may be composed of an optical fiber having a core and a clad. The core and the clad are P
It can be made of glass containing bO and SiO ₂ as main components.

The photoelastic constant of the glass can be set within the range of 1.0 × 10 ⁻⁹ to −1.0 × 10 ⁻⁹ cm ² / kg.

[0010]

According to the current measuring method of the above configuration, the optical path along which the linearly polarized light propagates has an integrated value of the Faraday rotation angle of 45.
Since the Faraday rotation angle of the divided optical path is added, the number of divisions is set to correspond to the magnitude of the current to be measured.
It is possible to measure a very large current of 150 kA like the fault current of the power system.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. 1 to 4 show a first embodiment of a current measuring method according to the present invention. The method shown in the figure is a case where the present invention is applied to the measurement of an alternating current, and the current measuring device comprises a pair of optical units 1;
The lead glass optical fiber 3 forms an optical path around the outer circumference of the conductor 2 through which the measured current I _ac flows.

The lead glass optical fiber 3 has a pair of first and second optical fibers 3a and 3b which are divided into two parts at positions facing each other with the conductor 2 as a center, and are arranged on the circling end side of each optical fiber 3a and 3b. Reflecting means 4 is provided. Also, a pair of first and second optical fibers 3a, 3
In the arrangement state of b, one entrance end and the other reflection end are arranged so as to intersect each other when seen in a plan view, and the optical units 1 are provided in proximity to the intersecting portions.

The split state of the lead glass optical fiber 3 is such that the Faraday rotation angle θ that the linearly polarized light propagating through the optical fibers 3a and 3b receives by the measured current I _ac .
The number of divisions is set so that does not substantially exceed 45 °, and does not necessarily mean two divisions. Table 1 below shows that in a lead glass containing PbO and SiO ₂ as main components, the Faraday rotation angle θ was 45 °.
The interlinkage current value is as follows.

[Table 1] The lead glass optical fiber 3 has a core and a clad, and the composition ratio of the core and the clad is SiO _{2 5 to} 28% B ₂ O ₂ 0 to 10% Al ₂ O ₃ 0 to 5%, but SiO 2 _{2 + B 2 O 2 + Al} 2 O 3 16~28% Na 2 O + K 2 O 0.3~2.5% PbO 69.5~83.7% of those included in the range is desired. Table 2 below shows an example of specific physical property values of the lead glass optical fiber 3 contained in such a composition ratio.

[Table 2] In the following examples including this example, a photoelastic constant of 0.45 × 10 ⁻⁹ cm ² / kg was used, but other than this, the photoelastic logarithm is 0.8 × 10 ⁻⁹ cm. ² / k
When the same evaluation was performed for the same as that of g and -0.8 × 10 ^-9 cm ² / kg, the stability of the measured value was 0.45 × 10 ^-9 cm ² / kg. Although it is slightly lower than that of the silica glass fiber, it was confirmed to be much more stable than the silica glass fiber. In addition, when a photoelastic constant of 0.2 × 10 ⁻⁹ cm ² / kg was evaluated, it was found that the photoelastic constant was 0.4.
It was also confirmed that the stability of measured values was further improved as compared with the case of 5 × 10 ⁻⁹ cm ² / kg.

An example of the optical unit 1 is shown in FIG. 2, in which the unit 1 includes a light source 1a, first and second polarizers 1b and 1c, and polarizers 1b and 1c fixed at both ends. It has a wavefront holding optical fiber 1d. The beam splitter 1e is arranged on the same optical axis of the second polarizer 1c.
A pair of first and second condenser lenses 1f and 1g are arranged with the pair of first and second condenser lenses 1f and 1g interposed therebetween.

On the side of the beam splitter 1e, an analyzer 1h is arranged so that its optical axis coincides with the S-polarized direction of the beam splitter 7, and the vicinity of this analyzer 1h. Is provided with a pair of third and fourth condenser lenses 1i and 1j. The polarization-maintaining optical fiber 1d has a main axis whose first and second polarizers 1b,
The first and second polarizers 1b and 1c are set to have an azimuth of about 45 ° with respect to the azimuth of the S-polarized light of the beam splitter 1e while being aligned with the principal axis of 1c. One ends of the multi-mode optical fibers 1k and 1l are arranged near the third and fourth condenser lenses 1i and 1j, respectively, and photoelectric conversion elements 1m and 1n are connected to the other ends of the multi-mode optical fibers 1k and 1l. Has been done.

The main components such as the second polarizer 1c, the beam splitter 1e, and the analyzer 1h are the case 1o.
It is stored inside. The light source 1a may be one that emits light of a predetermined wavelength, such as a semiconductor laser, but
Polarization-maintaining optical fiber 1 has low temporal coherence, is not affected by returning light, and has high spatial coherence.
A superluminescent diode capable of injecting light into d is desirable.

Also, the first and second polarizers 1b and 1c
Can be directly adhered and fixed to the end face of the optical fiber, and a laminated type, for example, Lamipol (trade name, manufactured by Sumitomo Cement Co., Ltd.) can be used to promote miniaturization. The case 1o is preferably one that is not easily deformed by an external force or temperature change, and the beam splitter 1e is preferably one without a vapor deposition film from the viewpoint of preventing the phase jump of polarized waves.

The reflecting means 4 may be a mirror having a reflecting film formed thereon, but it is preferable to directly form a metal vapor deposition film or a dielectric multilayer film on the round end surface of the lead glass optical fiber 3 to form the round end of the optical fiber 3. The side does not become thick, which is desirable for miniaturization. Figure 3 shows lead glass optical fiber 3
An example of the protection structure of a and 3b is shown. The protective structure shown in the figure includes a metal sleeve 21 which is fitted and fixed in a through hole 20 formed in the case 1o and has both ends opened, and a case 1
The funnel-shaped metal sleeve 22 fixed to one end of the metal sleeve 21 protruding to the outside of o, the protective tube 23 through which the optical fibers 3a and 3b are loosely inserted, and the funnel-shaped metal sleeve 22 and the protective tube 23 are welded. And a heat-shrinkable tube 24.

The protective tube 23 is made of, for example, a silicon resin, has an inner diameter larger than the diameter of the lead glass optical fibers 3a and 3b, and has a diameter of 3 mm.
Is loosely inserted into the tube 23, and when, for example, the fibers 3a and 3b are deformed in a circumferential shape,
The tube 23 slides and moves.
The lead glass optical fibers 3a and 3b are provided in such a protective structure.
When setting, the optical fibers 3a and 3b are first inserted into the protective tube 23, and the funnel-shaped metal sleeve 22 and the heat shrinkable tube 24 are inserted into one end side thereof.

In this state, the optical fibers 3a, 3
One end of b is inserted into the metal sleeve 21 fitted and fixed in the through hole 20 of the case 1o, the funnel-shaped metal sleeve 22 is fitted to the end of the metal sleeve 21, and fixed by welding or the like. . Next, after moving the heat-shrinkable tube 24 to a predetermined position, it is heated and welded. Thereafter, the ferrule 25 is fixed to one end of each of the optical fibers 3a and 3b so that the end faces thereof are exposed, and the metal sleeve 21 is filled with an adhesive and fixed.

By fixing the lead glass optical fibers 3a and 3b to the case 1o with such a protection structure, it is possible to effectively protect the relatively fragile fiber. next,
A method of measuring an alternating current by the current measuring device having the above configuration will be described. The conductor 2 has a measured current I of a predetermined frequency.
_Assuming that _ac is flowing, the light emitted from the light source 1a propagates in the polarization-maintaining optical fiber 1d and is converted into linearly polarized light with a high extinction ratio by the second polarizer 1c,
Lead glass optical fiber 3 through the beam splitter 1e
a and 3b, respectively.

The linearly polarized light introduced into the lead glass optical fibers 3a and 3b propagates toward the round end side thereafter,
After being reflected by each of the reflecting means 4 provided on the round end side, this time, the light propagates from the round end side toward the incident end side,
In these processes, the plane of polarization of the current I _ac is rotated in proportion to the magnitude of the current I _ac under the influence of the magnetic field _{generated by} the current I _ac under measurement.

The rotation angle at this time is based on the Faraday effect.
It is represented by I _ac . As described above, the reflected light whose polarization plane is rotated is then extracted by the beam splitter 1e, and the Faraday rotation angle θI _ac is converted into the light intensity by the analyzer 1h, and the multimode optical fibers 1k and 1l are converted.
Through the photoelectric conversion elements 1m and 1n to the electric signal I _1,
Converted to I ₂ .

FIG. 4 is a diagram showing the relationship between the currents I _ac, I _1, I ₂ and the Faraday rotation angle θI _ac, which are measured by such a current measuring method. The measured current I _ac changes. Then, the output currents I _{1 and} I _{2 of the} photoelectric conversion elements 1m and 1n change in proportion to this, so that the value of the measured current I _ac can be known by _obtaining the output currents I _{1 and} I ₂ . By the way, according to the above current measuring method, the optical path through which the linearly polarized light propagates can be divided into a plurality of pieces so that the integrated value of the Faraday rotation angle becomes 45 ° or less. Correspondingly, by setting the number of divisions of the sensor that circulates the conductor and adding the rotation angle of the polarization plane of the output of each Faraday element, it is possible to cancel the influence of the external magnetic field and measure the current of any size. Become.

In particular, when such a configuration is adopted, when linearly polarized light is reciprocated in the optical fibers 3a and 3b as in the present embodiment, the Faraday rotation twice as much as when light is transmitted is generated. It is possible to effectively prevent the current measurement range from becoming small. Further, in the case of the above-mentioned embodiment, the lead glass optical fibers 3a and 3b, which are circulated around the outer circumference of the conductor 2 in which the measured current I _ac flows and serve as the optical path of the linearly polarized light, have very small photoelastic constants. The effect of the photoelastic effect is very small, and the following remarkable effects are obtained.

That is, the linearly polarized light incident on the lead glass optical fibers 3a and 3b having a specific ratio formed so as to circulate around the outer circumference of the conductor 2 through which the measured current I _ac flows is circulated around the optical fibers 3a and 3b. The light is reflected at the end side, propagates in the optical fibers 3a and 3b again, and then exits.
At this time, the azimuth rotation of the polarization due to the twist of the curved lines of the optical fibers 3a and 3b is the same in the case of going to the round end side after incidence and the case of exiting from the round end side, but the directions are different from each other. It becomes the direction. Therefore, the light emitted after propagating through the optical fiber 3 cancels the azimuth rotation of the polarization due to the twist and is not included at all. For this reason,
In the measuring method of the present embodiment, even if an external force or vibration is applied from the outside, the measured value does not fluctuate at all.

According to the current measuring method of this embodiment, an optical bias can be applied without using a special means such as a permanent magnet, the optical system is simplified, and the lead glass optical fiber 3a, The two polarization components of the light emitted from 3b can be respectively taken out as electric signals, and the subsequent arithmetic processing can be easily performed. 5 and 6 show a second embodiment of the present invention. The current measuring method shown in the figure is a case where the present invention is applied to the measurement of a direct current, and the same or corresponding parts as those in the above-mentioned embodiment are designated by the same reference numerals and the description thereof will be omitted.
Only the characteristic points will be described below.

In the current measuring method shown in FIG. 5, the fourth condenser lens 1i, the multimode optical fiber 1l and the photoelectric conversion element 1n of the emission system are removed from the measuring apparatus for alternating current shown in FIG. Using the optical unit 1 ′ described above, the polarization plane modulator 5 is provided on one end side of each of the lead glass optical fibers 3a and 3b. This polarization plane modulator 5 is specifically composed of coils wound around the outer circumferences of the lead glass optical fibers 3a and 3b.
During the linearly polarized light propagating in the b be those applying a predetermined modulation, the high-frequency current i _m is supplied. In this embodiment, the first polarizer 1b and the polarization plane maintaining optical fiber 1d are used.
And the main axes of the second polarizer 1c are made to coincide with each other, and the main axis of the second polarizer 1c is set to the beam splitter 1
With respect to e, the direction of the P polarized component is matched.

When measuring a direct current with the apparatus constructed as described above, the measured current I _dc is supplied to the conductor 2. Then, the light emitted from the light source 1a is transmitted to the first polarizer 1b,
It is converted into linearly polarized light through the polarization maintaining optical fiber 1d and the second polarizer 1c, and this linearly polarized light is collected by the condenser lens 1
It is introduced into the lead glass optical fibers 3a and 3b via f and 1g and the beam splitter 1e.

The linearly polarized light is a lead glass optical fiber 3
a, a in 3b in the course of round trip undergoes Faraday rotation by both of the modulation frequency current i _m to be measured current I _dc. When the Faraday rotation at this time is .theta.I _dc and .theta.i _m, case also the optical fiber 3a so that the sum of the Faraday rotation angle is 45 ° or less in this embodiment, the number of divided 3b is set. Then, the light reflected from the reflection means 4 and returned is received by the beam splitter 1e, is incident on the analyzer 1h, and a component equal to the azimuth of the S polarization of the beam splitter 1e is extracted as a signal.

The frequency component equal from the signal to the frequency of the modulation frequency current i _m obtained, it retrieves the double frequency component, determine the magnitude of the measured current I _dc from both the ratio of. FIG. 6 is a characteristic diagram showing the relationship between the electric current and the Faraday rotation angle in such a process. By the way, according to the current measuring method as described above, the direct current can be measured while exhibiting the same effects as the alternating current shown in the above-mentioned embodiment, and the crossed Nicols polarization can be obtained without using a permanent magnet or the like. Analysis conditions can be easily obtained, which is advantageous in achieving the S / N ratio of the signal.

In this embodiment, as the beam splitter 1e, it is possible to raise the signal level by using a polarization beam splitter rather than simply using a dielectric material (such as a glass plate). 7 and 8 show a third embodiment of the present invention. The current measurement method shown in the figure is
The present invention is applied to the measurement of an alternating current, and the apparatus comprises two sets of an entrance system and an exit system optical units 6 and 7,
The lead glass optical fiber 3 forms an optical path around the outer circumference of the conductor 2 through which the measured current I _ac flows.

The lead glass optical fiber 3 has a pair of first and second optical fibers 3a and 3b which are divided into two parts at positions facing each other around the conductor 2. The pair of first and second optical fibers 3a and 3b are arranged such that one entrance end and the other reflection end intersect each other when seen in a plan view, and light is incident near the intersecting portion. System and emission system optical units 6 and 7 are provided respectively.

In the split state of the lead glass optical fiber 3, the split number is set so that the Faraday rotation angle θ does not substantially exceed 45 °, as in the above embodiment. FIG. 8 shows an example of the entrance system and the exit system optical units 6 and 7. The incident system optical unit 6 shown in the figure includes a light source 6a, a polarizer 6b arranged on the same optical axis as the light source 6a, and first and second condenser lenses 6c arranged in front of and behind the polarizer 6b. , 6d, and the incident ends of the optical fibers 3a, 3b are installed opposite to each other so as to coincide with the optical axis of the second condenser lens 6d.

On the other hand, the emission system optical unit 7 includes an analyzer 7
a, the third to fifth condenser lenses 7b to 7d, and a pair of photoelectric conversion elements 7e and 7f, and the emission ends of the optical fibers 3a and 3b are installed opposite to each other in the vicinity of the analyzer 7a. In the method of measuring the current in the device configured as described above, the linearly polarized light is introduced from the incident end sides of the optical fibers 3a and 3b, respectively, and is measured when the linearly polarized light is transmitted toward the circulating end sides of the optical fibers 3a and 3b. The Faraday effect in which the plane of polarization rotates due to the magnetic field of the current is received. If the number of divisions of the optical fiber 3 is set so that the Faraday rotation angle θ at this time is 45 ° or less, a large current can be measured as in the above embodiment. It will be possible.

In the above-mentioned embodiment, the case where a lead optical fiber having a specific composition ratio is used as an optical path forming material of the circular integration type has been exemplified, but the present invention is not limited to this and has a different structure. It may be an optical fiber.

[0037]

As described above in detail in the embodiments,
According to the current measuring method of the present invention, it is possible to measure very large direct current and alternating current without being restricted by the magnitude of the current.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a first embodiment of a method for measuring current according to the present invention.

FIG. 2 is a detailed configuration diagram of the optical unit of FIG.

FIG. 3 is an enlarged cross-sectional view of a main part of FIG.

FIG. 4 is a characteristic diagram showing a relationship between a current and a Faraday rotation angle in the first embodiment.

FIG. 5 is an explanatory diagram showing a second embodiment of the current measuring method according to the present invention.

FIG. 6 is a characteristic diagram showing a relationship between a current and a Faraday rotation angle in the second embodiment.

FIG. 7 is an explanatory diagram showing a third embodiment of the current measuring method according to the present invention.

FIG. 8 is a detailed configuration diagram of an optical system of an entrance system and an exit system of a third embodiment.

[Explanation of symbols]

 1, 1'optical unit 2 conductors 3, 3a, 3b lead glass optical fiber 4 reflecting means 5 modulator 6 incident system optical unit 7 reflection system optical unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Sakamoto 3-3-1, Musashino, Akishima-shi, Tokyo Hoya Co., Ltd.

Claims (6)

[Claims] 1. An optical path is formed so as to circulate around an outer periphery of a conductor through which a current to be measured flows, and when linearly polarized light is passed through the optical path, the optical path is rotated by a magnetic field action of the current to be measured. In a method of measuring a current for measuring a Faraday rotation angle of linearly polarized light, the optical path is divided into a plurality of parts such that an integrated value of the Faraday rotation angle is 45 ° or less, and an added amount of the Faraday rotation angle of the divided optical paths is calculated. A method for measuring a current, comprising measuring the current based on the current. 2. The linearly polarized light is transmitted from one end to the other end of the split optical path.
How to measure the described current. 3. The current measuring method according to claim 1, wherein the linearly polarized light propagates from one end of the split optical path to the other end and then is reflected at the other end. 4. The optical path comprises an optical fiber having a core and a clad.
4. The method for measuring current according to any one of 1 to 3. 5. The core and the clad are made of PbO and S.
The current measuring method according to claim 4, which is made of glass containing iO ₂ as a main component. 6. The glass has a photoelastic constant of 1.0.
^{× 10 -9 ~-1.0 × 10} -9 cm 2 / kg measuring method according to claim 4, wherein the current, characterized in that set in the range of.