JP2580443B2 - Optical voltage sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical voltage sensor constituting a voltage measuring device.

[0002]

2. Description of the Related Art A voltage measuring device is used to detect a fault section, a fault point, and the like by measuring a voltage in a transmission line, a distribution line, or the like of a transmission station or a substation. It consists of. In addition, as shown in JP-A-61-223821 as one type of optical voltage sensor and schematically shown in FIG.
One having a four-wavelength plate 2, an electro-optical element 3, and an analyzer 4 is known. In the optical voltage sensor, the microlens 6a emitted from the light source 5 via an optical fiber
Is transmitted to the polarizer 1, the incident light is converted into linearly polarized light by the polarizer 1 and is incident on the 波長 wavelength plate 2, and π is interposed between polarization components orthogonal to each other by the wavelength plate 2. / 2 is applied to the electro-optical element 3 after being given a phase difference, and the incident light is applied to the analyzer 4 after being subjected to phase modulation according to the voltage to be measured applied to the electro-optical element 3, and is incident on the analyzer 4. The respective polarization components are detected, converted into light intensity changes corresponding to the voltage to be measured, and output.

The light emitted from the analyzer 4 passes through a microlens 6b, is introduced into a light receiver 7a via an optical fiber, is subjected to photoelectric conversion and is divided by a DC / AC distributor 7b into a DC component. While being amplified by the DC amplifier 8a, the AC component is amplified by the AC amplifier 8b. The DC component and the AC component are input to a divider 9 and the divider 9
The calculation of the AC component / DC component is performed, and the value is output as a signal to obtain the voltage intensity.

Incidentally, in the optical voltage sensor,
In order to provide linearity between the voltage applied to the electro-optical element 3 and the light intensity, a quarter-wave plate 2 imparts a phase difference of π / 2 between two orthogonally polarized light components of linearly polarized light. However, since the wavelength plate 2 has a temperature dependence of birefringence, the optical bias point shifts in the incident light, and the measured value is affected by the birefringence temperature characteristic of the wavelength plate 2 and the voltage measurement accuracy is affected. There is a problem that. In order to solve such a problem, the above-mentioned publication discloses an optical voltage sensor in which the temperature characteristics are improved by canceling out the birefringence temperature characteristics of the wave plate (hereinafter, this may be simply referred to as the temperature characteristics of the wave plate). Have been.

As shown in FIG. 3, the optical voltage sensor 10 divides incident light into two linearly polarized light components, a first polarization component and a second polarization component, whose polarization planes are orthogonal to each other, and separates the light into different directions. With the polarizer 11 that emits light ,
A quarter-wave plate 12 is provided on one of the divided linearly polarized light paths.
a, an electro-optical element 13a, a first analyzer 14a, and a multiplexer 15 are arranged in series, and a total reflection mirror 16a for changing an optical path is provided on the other divided linearly polarized optical path,
The optical path whose optical path is changed by the total reflection mirror 16a is 1/4.
Wave plate 12b, electro-optical element 13b, second analyzer 14
b and a total reflection mirror 16b that changes the direction of the outgoing light and makes it incident on the multiplexer 15 arranged on one optical path is arranged in series.

In the optical voltage sensor 10 having such a configuration, the two linearly polarized light beams separated from each other have respective wavelength plates 1.
The light intensity changes based on the birefringence phase difference of 2a and 12b are opposite to each other, and the light intensity changes based on the phase difference change by the electro-optical elements 13a and 13b are configured to be the same. Accordingly, the combined light is constant regardless of the birefringence phase difference of the wave plate, and is not affected by the birefringence temperature characteristic of the wave plate.
Can be called an optical voltage sensor having excellent temperature characteristics.
In FIG. 3, reference numerals 5 to 9 correspond to the reference numerals shown in FIG. 2, and the light source 5, the micro lenses 6a and 6b,
The figure shows a light receiver 7a, a distributor 7b, amplifiers 8a and 8b, and a divider 9.

[0007]

As described above, the optical voltage sensor has excellent temperature characteristics, but as described above, the number of main components is much larger than that of a conventional optical voltage sensor of this type. That is, the main components of the conventional optical voltage sensor shown in FIG. 2 are a polarizer, a wave plate, an electro-optical element,
The main components of the optical voltage sensor 10 shown in FIG. 3 are one polarizer, two wave plates, two electro-optical elements, and two analyzers, whereas the analyzer has four components. 10 parts such as two total reflection mirrors and one multiplexer 15. For this reason, the configuration of the optical voltage sensor 10 becomes complicated due to an increase in the number of components, the size of the sensor becomes large, and the cost increases. Therefore, an object of the present invention is to configure an optical voltage sensor excellent in temperature characteristics with a small number of components to simplify the configuration and downsize the optical voltage sensor.
Another object is to reduce costs.

[0008]

According to the present invention, there is provided a polarizer for converting incident light into linearly polarized light, a wave plate for providing a predetermined optical phase difference between two polarized components of the incident light, and an applied voltage. An electro-optical element for providing an optical phase difference between the respective polarized light components of the incident light, and an analyzer for detecting each of the polarized light components of the incident light, wherein the polarizer and the electro-optic each while adopting the two polarizers and the electro-optical element as the element, and employs two wave plates to have the same value against the value of optical phase difference in positive and negative to each other to impart to the incident light as the wave plate, the A first wave plate and a first electro-optical element are arranged in series between one polarizer and a second polarizer, and a second wave plate is arranged between the second polarizer and the analyzer. A second electro-optical element is arranged in series. Is shall.

[0009] In the optical voltage sensor, it is preferable that the polarity of the voltage applied to the previous SL both electro-optical element in the opposite characteristics.

[0010]

In the optical voltage sensor thus configured, the light intensity emitted from the analyzer is equal to the light intensity modulated between the first polarizer and the second polarizer and the second polarized light. It is proportional to the product of the light intensity modulated between the detector and the analyzer. Further, since the first wave plate and the second wave plate have the same value of the phase difference to be given, which is opposite to each other, the influence of the birefringence temperature characteristics of each wave plate is extremely small and is ignored. Therefore, the optical voltage sensor has excellent temperature characteristics and can improve voltage measurement accuracy. Further, in the optical voltage sensor, the components are two polarizers ,
Two wave plates, two electro-optical elements, and one analyzer. Since these components are arranged in series, the number of components can be reduced, the configuration can be simplified, and the shape can be reduced. And cost can be reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a voltage measuring apparatus employing an optical voltage sensor according to the present invention. The voltage measuring device includes a light source 5, a pair of microlenses 6a and 6b, a light receiver 7a, and a distributor 7 in the same manner as in the related art, except for the optical voltage sensor 20 according to the present invention.
b, a DC amplifier 8a, an AC amplifier 8b, and a divider 9. The optical voltage sensor 20 includes two first and second polarizers 21a and 21b and two first and second wave plates 22.
a, 22b, two first and second electro-optical elements 23a, 2
3b and one analyzer 24. In each of these components, a first polarizer 21a, a first wave plate 22a, a first electro-optical element 23a, a second polarizer 21a
b, the second wave plate 22b, the second electro-optical element 23b, and the analyzer 24 in this order.

The first polarizer 21a and the second polarizer 21b
Is made of optical glass that converts incident light into linearly polarized light. The first wave plate 22a and the second wave plate 22b provide a predetermined optical phase difference between two orthogonally polarized light components of linearly polarized light.
/ 4 wavelength plate, the major axis directions of the respective refractive index ellipsoids form an angle of 90 degrees with each other, and the first polarizer 21a
Are arranged at an angle of 45 degrees with the plane of polarization of the linearly polarized light. Therefore, the first wave plate 22a gives the incident light a phase difference of π / 2, and the second wave plate 22b gives the incident light a phase difference of-(π / 2).

The first electro-optical element 23a and the second electro-optical element 23b are made of LiNbO _{3. In} each of the electro-optical elements 23a and 23b, the z axis is the optical axis with respect to the crystal axis (x, y, z). Equation 1 below in parallel with

[0014]

The optical principal axis x ′ defined by x′≡ {1 / (2) ^1/2 } × (xy) y′≡ {1 / (2) ^1/2 } × (x + y) y ′ is the wavelength plate 22a,
The refractive index ellipsoid 22b is arranged so as to coincide with the major axis direction of the ellipsoid. Further, both electro-optical elements 23a,
23b are connected such that the polarities of the applied voltages are opposite to each other (phase differences Δz, −Δz proportional to the applied voltage). The analyzer 24 has a function of detecting each polarization component of the incident light from the second electro-optical element 23b and emitting the same to the light receiver 7a.

The operation of the voltage measuring device employing the optical voltage sensor 20 configured as described above will be described.
Is transmitted to the microlens 6a via the optical fiber 5a, and is incident on the first polarizer 21a as parallel light by the lens 6a. The incident light is converted into linearly polarized light by the first polarizer 21a, emitted in a right angle direction and incident on the first wavelength plate 22a, and given a phase difference π / 2 by the first wavelength plate 22a. 1 The light enters the electro-optical element 23a. The incident light is the first electro-optical element 23a.
Is applied to the second polarizer 21b. The light emitted from the second polarizer 21b subsequently enters the second wave plate 22b, the second electro-optical element 23b, and the analyzer 24, is detected by the analyzer 24, is collected by the microlens 6b, and is received. Output to the container 7a. During this time, the phase difference − (π / 2) is given to the light incident on the second wavelength plate 22b, and the phase difference −Δz is given to the light incident on the second electro-optical element 23b.

In the optical voltage sensor 20, the light intensity of the light incident on the first polarizer 21a is set to I0, and the first polarizer 2
The light intensity modulated between the first polarizer 1a and the second polarizer 21b is represented by I1,
The light intensity modulated between the second polarizer 21b and the analyzer 24 is I2, the temperature dependence coefficient of the phase difference between the first wave plate 22a and the second wave plate 22b is k, and the temperature difference from room temperature is Δ.
When T is I and the light intensity of the light emitted from the analyzer 24 is I, the following equation 2 is established.

[0017]

I = I1 × I2 = (1/2) × I0 × {1 + sin (k · ΔT + Гz)} × {1−sin (k · ΔT−Гz)} = (1/2) × I0 {1 + sin ( k ・ ΔT) ・ cosГz) + sinГz ・ cos (k ・ ΔT)} × {1−sin (k ・ ΔT) ・ cos (−Гz) −sin (−Гz) ・ cos (k ・ ΔT)} where Гz = (2π / λ) · n ₀ ³ · γ ₂₂ · (L / d) · V, where n ₀
Is the ordinary light refractive index for light of wavelength λ, γ ₂₂ is the optical coefficient of the electro-optical element for light of wavelength λ, L is the electrode length of the electro-optical element, d is the interelectrode element thickness, and V is the applied AC voltage.

In the above equation (2), when ΔT and V are small (k · ΔT), Гz is sufficiently small and (k · ΔT · Гz) is sufficiently small, so that cosГz, cos (−Гz), cos (k
T), cos (k · ΔT · Гz) can be approximated to 1 and sinГz can be approximated to Гz.

[0019]

I = (1/2) × I0 × {1 + sin (k · ΔT) + sin (Гz)} × {1−sin (k · ΔT) + sin (Гz)} = (1/2) × I0 × [1 + 2 sin (Гz) + {(1−cos ² (Гz)} − {1-cos ² (k · ΔT)}] = (1/2) × I0 × (1 + 2sinГz) = (1/2) × I0 × (1 + 2Гz).

The light having the light intensity I is converted into an electric signal by the light receiver 7a and distributed by the distributor 7b. The divided AC and DC components are amplified by the DC amplifier 8a and the AC amplifier 8b, respectively, and output. AC component ｛(1/2) × I
0 × 2 {z} and the DC component {(１ ／) × I0} are calculated by the divider 9 to obtain the output Iout shown in the following equation (4) .
It is.

[0021]

Equation 4] Iout = {(1/2) × I0 × 2Γz} / {(1/2) × I0} This output is free of temperature dependent term (k · ΔT), proportional to the applied voltage.

Therefore, the photovoltaic sensor 20 is a photovoltaic sensor having excellent temperature characteristics and high voltage measurement accuracy. However, the value of the optical phase difference imparted to the incident light as a wavelength plate is set to the same value that is opposite to the positive and negative values. First and second wave plates 22a, 22
b, and the first and second electro-optical elements 23 which have opposite polarities of applied voltages as electro-optical elements.
a, 23b, a first polarizer 21a, a first wave plate 22a, a first electro-optical element 23a, a second polarizer 21b,
Since the second wave plate 22b, the second electro-optical element 23b, and the analyzer 24 are arranged in this order in series, the use of a total reflection mirror can be omitted. Therefore, in the optical voltage sensor 20, the number of components is smaller than that of the conventional optical voltage sensor shown in FIG. 3, the configuration can be simplified, and the shape can be reduced. In addition, cost can be reduced.

In the above embodiment, an example is shown in which all the components of the optical voltage sensor are arranged in series, but in the present invention, the light emitted from the second polarizer 21b is directed in a direction perpendicular to the incident direction. And the second wavelength plate 22b, the second electro-optical element 23b, and the analyzer 24 may be arranged in series in the emission direction.

(Experiment) In the optical voltage sensor 20 shown in FIG. 1, a PBS made of optical glass was used as each of the polarizers 21a and 21b and the analyzer 24, and a 1/4 wavelength plate was used as each of the wavelength plates 22a and 22b. As the optical elements 23a and 23b, an effective electrode length L = 4 mm, an element thickness d = 2 mm, an optical wavelength λ = 850 nm, an applied voltage = 10 V AC voltage, and a temperature = −2.
The results of measuring the output Iout under the conditions of 0 to + 80 ° C. and calculating the rate of change with respect to the same output at an output temperature of 25 ° C. are shown in FIG. 4 (a) and FIG. 4 (b). 2 shows a similar result in the conventional basic optical voltage sensor shown in FIG. 2, and in the optical voltage sensor in which the second polarizer 21 b to the second electro-optical element 23 b in this embodiment are omitted,
FIG. 3C shows the first polarizer 21 in this embodiment.
a to a similar result in the optical voltage sensor in which the first electro-optical element 23a is omitted. Comparing these results, it is clear that the optical voltage sensor 20 of this embodiment has no temperature dependency and has excellent temperature characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a voltage measuring device employing an optical voltage sensor according to one embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a conventional voltage measuring device employing an optical voltage sensor generally employed.

FIG. 3 is a schematic configuration diagram of a conventional voltage measuring device employing an optical voltage sensor having good temperature characteristics.

FIG. 4 is a graph showing a relationship between an output change rate and a temperature in each optical voltage sensor.

[Explanation of symbols]

1,11,21a, 21b ... polarizer, 2,12a, 12
b, 22a, 22b ... wave plate, 3, 13a, 13b, 2
3a, 23b: electro-optical element, 4, 14a, 14b, 2
4 analyzer, 15 combiner, 16a, 16b total reflection mirror, 5 light source, 6a, 6b micro lens, 7, 7
a ... receiver, 8a, 8b ... amplifier, 9 ... divider.

Claims (2)

(57) [Claims] A polarizer for converting incident light into linearly polarized light, a wave plate for providing a predetermined optical phase difference between two polarization components of the incident light, and an optical phase difference corresponding to an applied voltage. An electro-optical element provided between each polarized light component of the incident light, and a light voltage sensor including an analyzer for detecting each polarized light component of the incident light, wherein the polarizer and the electro-optical element each have two polarizers. With the adoption of electro-optical elements,
As the wave plate, two wave plates having the same value of the optical phase difference given to the incident light and having the same value opposite to each other are adopted, and the first wave plate is provided between the first polarizer and the second polarizer. And a first electro-optical element are arranged in series, and
An optical voltage sensor, wherein a second wave plate and a second electro-optical element are arranged in series between the polarizer and the analyzer. 2. The pole of a voltage applied to both electro-optical elements.
The characteristics are set to be opposite to each other.
On-board optical voltage sensor.