JPH0282167A - Current measuring instrument with optical system - Google Patents

Abstract

PURPOSE:To measure currents in the range from the small to the large currents in the manner of using a single magnetooptical element by branching an optical signal outputted from a light detecting element to plural optical signals having the different light intensities and processing the signals with a photoelectric conversion respectively. CONSTITUTION:By the light detecting element 44, optical signals P0, S0 having the components of a P-polarization and a S-polarization among the optical signals A are transmitted to optical branching devices 56, 58 respectively. In the branching devices 56, 58, the signals P0, S0 are branched to the optical signals P1, P2, S1, S2 respectively and set in the relations of P1>P2, S1>S2, P1/P2=S1/S2. Further, the signals P1, S1 are set to correspond to the currents for the measurement in the small currents range, and the signals P2, S2 are set to correspond to those in the large currents range. The signals P1 - S2 are subjected to photoelectric conversion respectively by light receiving elements 68, 72, 70, 74. Voltage signals VA, VB proportional to the current (i) are calculated in the manner of processing the signals CH-1,CH-2 respectively based on the signals P1, S1 and P2, S2 subjected to the photoelectric conversion. Then, the signal VA is outputted up to the time when the signal VA exceeds a rated value, and when it exceeds the rated value, the signals VB is outputted.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to an optical current measuring device, and in particular, to photoelectrically convert the output of a magneto-optical element that is sensitive to a magnetic field generated from an object to be measured. The present invention relates to an optical current measuring device suitable for measuring current.

[Conventional technology]

Conventionally, in commercial power systems, f[! BACKGROUND ART Current in a power system is measured using a wire-wound current transformer (CT), and the power transmission system of the power system is controlled and protected based on the measured value. However, when CTs are used in power systems of 500,000 volts or 1 million volts, the gear knobs must be made larger to maintain high voltage insulation, and the iron core must be made larger to improve the magnetic saturation characteristics of the iron core. However, there was a problem in that the device had to be larger.

Therefore, in recent years, an optical current measuring device (optical CT) using the magneto-optical effect has been proposed in Japanese Patent Laid-Open No. 153174/1983. In this device, as shown in FIG. 9, the light emitting elements 11 are ff1ilfil1. When emitted by the signal from o, this unpolarized light is transmitted to the collimator 13 via the optical fiber 12, converted into parallel light, and then enters the polarizer 14. The light incident on the polarizer 14 is incident on a Faraday element (magneto-optical element) 15 made of lead glass or the like. The optical signal A of linearly polarized light incident on the Faraday element 15 is reflected by six total reflection surfaces 15A, 15B, and 15G provided on the Faraday element 15.

It is led to the analyzer 17 via 15D, 15E, and 15F. Since the Faraday element 15 forms an optical path around the conductor to be measured 16, the plane of polarization of the optical signal A rotates in accordance with the strength of the magnetic field generated by the conductor to be measured 16. The polarization rotation angle 0 of the optical signal A at this time is expressed by the following equation (1).

0 = f Ve-He-d n...-4
1) Here, ve: Vuelde constant He: Strength of magnetic field in the direction of propagation of light Q = Optical path length in Faraday element (1) From formula (1), the magnitude of the polarization rotation angle θ is generated by the current flowing through the conductor 16 to be measured. It can be seen that it is proportional to the strength of the magnetic field. In other words, the strength of the magnetic field is proportional to the polarization rotation angle O.

When an optical signal with a polarization rotation angle θ is incident on the analyzer 17, the analyzer 17 whose orientation differs by 45 degrees from the polarizer 14 splits it into an optical signal P of P polarization and an optical signal S of S polarization component, and each is sent to a collimator. After the light is focused on 18 and 19, it is transmitted to light receiving elements 22 and 23 via optical fibers 20 and 21. Then, it is photoelectrically converted by the light receiving elements 22 and 23,
The signal processing circuit 24 calculates a voltage signal Vout proportional to the current i flowing through the conductor 16 to be measured. The current i in the conductor 16 to be measured can be calculated from this voltage signal Vout.

By the way, current measurement in power systems is performed for the purpose of controlling and protecting the system, but when measuring current, it ranges from a small current range of several A to several 1 OA below the rated current, to around 150 kA assuming a short circuit accident. It is required to be able to accurately detect large current ranges up to However, the 9th
In the case of the device shown in the figure, it was not possible to accurately detect current from a small current region to a large current region using a single Faraday element 15. That is, Faraday element 1
When a material with a relatively large Werde constant such as lead glass is used as 5, the polarization rotation angle θ increases in proportion to the current i in the small current region, but when this θ becomes larger than π/4, the current The value of θ becomes smaller as the value increases. For this reason, with lead glass where θ=π/4 at 40 to 60 kA, it is no longer possible to measure large currents as in the case of a system failure.

On the other hand, if a material with a small Welde constant is used as the Faraday element 15, even if a short-circuit current of about 150 kA flows, 0 is less than π/4, so this current can be detected. In the current region, the value of θ is small, and even if the current is measured from the value of θ, the S/N will be poor, making it impossible to accurately measure the current.

Therefore, as described in JP-A-59-35-156, a Faraday element made of a material with a large polarization rotation angle is used for small current measurement, and a Faraday element made of a material with a small titer light rotation angle is used. A device has been proposed that is used for measuring large currents and measures current from a small current region to a large current region using a plurality of Faraday elements.

[Problem to be solved by the invention]

However, the conventional technology requires a plurality of Faraday elements and a signal transmission path for transmitting the output signal of each Faraday element, which increases the size of the device and reduces reliability due to an increase in the number of parts. There was fear.

An object of the present invention is to provide an optical current measuring device that can measure current from a small current region to a large current region using a single magneto-optical element.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a light emitting means for generating a non-polarized optical signal, and a polarizer for converting the optical signal from the light emitting means into a linearly polarized optical signal. a magneto-optical element that receives an optical signal output from a polarizer and rotates the plane of polarization of the optical signal according to the strength of a magnetic field generated from an object to be measured; An analyzer that transmits an optical signal of a specific direction component of the signal, an optical branching means that branches the optical signal output from the analyzer into a plurality of optical signals with different light intensities, and each optical signal output from the optical branching means This is an optical current measuring device comprising a photoelectric conversion means for converting into an electric signal according to the light intensity, and a calculation means for calculating the current value of the object to be measured from each electric signal output from the photoelectric conversion means. .

[Effect]

When unpolarized light enters the polarizer from the light emitting means, it is converted into a linearly polarized optical signal and then transmitted to the magneto-optical element. The plane of polarization of this optical signal is rotated according to the strength of the magnetic field generated from the object to be measured, and the optical signal is transmitted to the analyzer. Of this optical signal, an optical signal having a specific direction component is extracted by an analyzer and outputted to the optical branching means. That is, the analyzer outputs an optical signal having a light intensity corresponding to the polarization rotation angle. The optical branching means branches the optical signal output from the analyzer into a plurality of optical signals having different optical intensities, for example, a high-intensity optical signal and a low-intensity optical signal,
The branched signals are each transmitted to photoelectric conversion means. Then, each of these optical signals is converted into an electrical signal corresponding to the light intensity, and a current value of the object to be measured is calculated from this electrical signal. For example, a current value for measurement control is calculated based on a high-intensity optical signal, and a current value for protection is calculated based on a low-intensity optical signal. Thereby, even if a single magneto-optical element is used, current from a small current region to a large current region can be measured.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained based on FIG.

In FIG. 1, a light emitting diode 3 constituting the light emitting means is shown.
2 is connected to a drive circuit, and generates a non-polarized (natural light) optical signal in response to a drive signal from the drive circuit 30. This optical signal is transmitted to the optical fiber 3
The light is transmitted to the collimator 36 via the light beam 4, is converted into parallel light, and then enters the polarizer 38. The polarizer 38 is a Faraday glass 40 as a magneto-optical element.
The optical signal incident on the polarizer 38 is converted into a linearly polarized optical signal and guided into the Faraday glass 40. The Faraday glass 40 is formed to surround a conductor to be measured 42 as an object to be measured, and the conductor to be measured 42 is inserted into a through hole 40A of the Faraday glass 4o. - When the linearly polarized optical signal A goes around the conductor to be measured 42 once through the optical path of the Faraday glass 40, the plane of polarization of the optical signal A changes depending on the strength of the magnetic field generated from the conductor to be measured 42. It rotates accordingly. This polarization rotation angle is expressed by the above equation (1), and the polarization rotation angle has a value proportional to the current i flowing through the conductor 42 to be measured. The optical signal having this polarization rotation angle θ is incident on the analyzer 44.

The analyzer 44 is configured to have an orientation different from the polarizer 38 by 45 degrees, and transmits the optical signal PO of the P-polarized component of the optical signal A to the optical splitter 56 via the prism 46, the collimator 48, and the optical fiber 52. , the S-polarized component optical signal SO is sent to the optical splitter 58 via the collimator 5o and the optical fiber 54.
is configured to transmit to. The optical splitters 56 and 58 as optical branching means are composed of beam splitters or optical fibers, and split the optical signals po and so into a plurality of optical signals PL and P2 having different optical intensities and optical signals SL and S, respectively.
2, and the branched optical signals are each connected to an optical fiber 6.
0.62, 64.66, and light receiving elements 68, 70, 72.74 composed of light emitting diodes such as Si and Ge.
It is designed to be transmitted to.

The optical signals PL, P2 and the optical signals S1, S2 are such that the optical intensity of the optical signals PL, SL is equal to the optical signal P2. It is adjusted by optical splitters 56 and 58 so that it is higher than S2. That is, each signal PL, P2 . The light intensities of S1 and S2 are respectively PL and P2. Sl.

If S2, PL>P2. Sl>S2 and PL/
The distribution ratio of each optical signal is set to the relationship P2=SL/S2. Furthermore, the high-intensity optical signals PL and SL are set to correspond to the currents for measuring currents in the small current region, respectively, and the optical signals P2. S2 is set in association with a current for measuring a current in a large current region.

Optical signals PL, P2. Sl and S2 are light receiving elements 68, respectively.
．． The signals are photoelectrically exchanged by 70, 72.74, amplified by current-voltage conversion amplifiers 76.78, 80.82, and then supplied to dividers 92, 94, 96.98. Note that the amplification degrees of the amplifiers 76.78 and 80.82 are adjusted by the value of the resistor 84°86.88.90. Each divider 92, 94, 96.98 divides the output signal of each amplifier 76.78, 80.82,
The divided values are output to the differential circuit 100° 102, and a voltage signal VA proportional to the current i is obtained from the output signal of each divider 92, 94, 96.98.

It is configured to output VB. Divider 92.9
The outputs of 4 and 96.98 are connected to differential circuits 100.10 and 100.10, respectively.
By calculating the voltage signals VA and VB via 2, even-order distortion of the measurement system is canceled out. Further, by branching the optical signals po and so into the optical signals PL and P2 and the optical signal SL and 82, respectively, to obtain the voltage signals VA and VB, it is possible to suppress errors caused by fluctuations in the light source.

That is, by branching the optical signal transmission system into two systems, the direct current component of the light source can be canceled. Note that the light receiving elements 'f-68, 70, and 72.

74, amplifier 76.78,80,82. Resistance 84°86
．． 88 and 90 constitute a photoelectric conversion element, and dividers 92, 94, 96, 98, and differential circuits 100 and 102 constitute calculation means.

In this way, in this embodiment, the optical signal PI.

P2,31. Since the light intensity of S2 is set to the relationship Pi>P2,5l)S2, as shown in Fig. 2, in the small current region, from the small current Ool, Tn to the rated current In, the divider The voltage signal Va input to 92.94 gradually increases in proportion to the current l, and after the current i exceeds the rated current In, the voltage signal Va becomes constant. On the other hand, the voltage signal vb gradually increases as the current i increases, and reaches its maximum value at the short 18 current Imax. Since the voltage signal Va rises rapidly in the small current region, the current in the small current region can be detected as a signal with a high signal-to-noise ratio.

Here, as Werde's constant (2,0 to 4.0)
0"" (r a d /AT), and even if the current value at the time of a short circuit accident is 150 kA, the polarization rotation angle is π/4
When the ratio error was measured from the voltage signals VA and VB using a magneto-optical element that did not exceed The results show that the -2 ratio error becomes smaller in the large current region. From FIG. 3, it is possible to accurately measure the current of the conductor to be measured 42 even in a small current region to a large current region.

Further, as shown in FIG. 4, the magnitude of the voltage signal VA is determined by the discriminator 104, and the signal of the voltage signal VA is outputted via the switching circuit 106 until the voltage signal VA exceeds the rated value. When the rated value is exceeded, the voltage signal VA
By outputting the voltage signal VB through the switching circuit 106 instead of , and measuring the current of the conductor under test 42 from the output of the switching circuit 106, the dynamic range of the signal processing circuits CH-1 and CH-2 can be increased. Even if it is not wide, it is possible to widen the dynamic range as a whole.

Furthermore, in the above embodiment, the output signal of the analyzer 44 was transmitted to the optical splitter 56.58 via the collimator 48.50 and the optical fiber 52.54. Even if the optical splitter 56 is directly fixed to the prism 46 and the optical splitter 58 is directly fixed to the analyzer 44, the same effect as in the previous embodiment can be obtained. In this case, the collimators 48, 50 . Optical fiber 52.
Since 54 is no longer necessary, the number of parts can be reduced.

Furthermore, in the embodiment described above, the optical signal A is branched into the optical signals PO and So by the analyzer 44, but as shown in FIG.
directly connect the optical signal A to the optical signals PL and P of P polarization components.
2, and the optical signal PL, P2 is sent to the store number 5 voltage signal VA,
It is also possible to calculate VB.

Fig. '7 shows an embodiment in which two-branch optical fibers 108, 110 are used instead of the optical splitter 56, 58, and each branch part M, H of the optical fiber 108, 110 has a different diameter, or Weld optical fibers 108A, 108B, 110A, and 110B with different HA (number of openings) to form each optical fiber 108A, 108B, 110A, 11
Optical signal P1 transmitting 0B. ．． P2. By setting the relationship between the light intensities of SL and S2 as PL>P2 and S l >52, the same effects as in the embodiment described above can be obtained.

Further, as shown in FIG. 8, the optical fiber 108
, 110 respectively branched from each fiber 7 y
-(bar 108A, 108B-108A, ll0A, 1
10B and -11ON are provided, and the optical intensity of the optical signal transmitted through each optical fiber is P 1 > P 2 > P.
By setting n and S 1 > S 2 > S n, it is possible to obtain the same effect as a combination of magneto-optical elements with different Werde constants, such as lead glass, borosilica crown, quartz glass, etc. can.

Further, in the above embodiment, the same effect can be obtained not only by using the Faraday glass 40 as the magneto-optical element but also by using a point sensor or an optical sensor with an iron core.

〔Effect of the invention〕

As explained above, according to the present invention, a single magneto-optical element is used to create a small optical system. Since it is possible to measure currents from a single current region to a large current region, it is possible to contribute to a reduction in the number of parts and an improvement in reliability.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between current and voltage, FIG. 3 is a diagram showing the relationship between current and ratio error, and FIG. 4 is a diagram showing the relationship between current and ratio error. is a block diagram of a discriminator and a switch circuit, FIG. 5 is a block diagram showing another embodiment of the present invention, FIG. 6 is a block diagram of the main part when using an optical signal of one plane of polarization, and FIG. 7 is a block diagram of the optical signal. FIG. 8 is a configuration diagram of main parts showing an example in which an optical fiber is used instead of a splitter; FIG. 8 is a configuration diagram showing an example in which an optical fiber is used instead of an optical splitter; FIG.
The figure is a configuration diagram of a conventional example. 32...Light emitting diode, 36.48.50...Collimator, 38...Polarizer. 40... Faraday glass, 42... Conductor to be measured, 44... Search element, 56.58... Optical splitter. 68.70,72,74...light receiving element, 92.94,
96.98...Divider, 100.102...Differential circuit.

Claims (1)

[Claims] 1. A light emitting means that generates an unpolarized optical signal, a polarizer that converts the optical signal from the light emitting means into a linearly polarized optical signal, and a polarizer that receives the optical signal output from the polarizer and changes the plane of polarization of the optical signal. A magneto-optical element that rotates according to the strength of a magnetic field generated from a measurement target, an analyzer that receives an optical signal output from the magneto-optical element and transmits an optical signal of a specific direction component of the optical signal, and an analyzer. an optical branching means for branching the output optical signal into a plurality of optical signals having different optical intensities; a photoelectric conversion means for converting each optical signal output from the optical branching means into electrical signals corresponding to the respective optical intensities;
1. An optical current measuring device comprising: calculation means for calculating a current value of a target to be measured from each electrical signal output from the photoelectric conversion means.