JPH08220150A - Optical voltage sensor voltage detection method - Google Patents

Abstract

(57) [Summary] [Objective] To provide a voltage detection method for an optical voltage sensor capable of obtaining stable temperature characteristics of sensor sensitivity. [Structure] Polarizers 3 and 1/4 sequentially arranged along the optical path
A voltage of an optical voltage sensor that includes a wave plate 4, an electro-optic crystal 5, and an analyzer 6, and detects the voltage applied to the electro-optic crystal 5 by performing optical phase modulation using the birefringence of the electro-optic crystal 5. In the detection method, two output lights in which the polarization angles of the polarizer 3 and the analyzer 6 are orthogonal and parallel are converted into electric signals, and then the gain is adjusted by the automatic gain adjusters 82a and 82b. The voltage is obtained from a value obtained by making the direct current component of the output equal to the reference voltage and subtracting the electric signals of the two output lights from each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage detecting method for an optical voltage sensor for highly accurately measuring a voltage in the field of electric power, which is harsh in an electromagnetic field environment.

[0002]

2. Description of the Related Art Conventionally, this type of optical voltage sensor is constructed as shown in FIG. Light emitted from a light source (not shown) formed of a light emitting element such as a light emitting diode is guided by the optical fiber 1, becomes parallel light by the collimator lens 2a, and is reflected or transmitted by the polarizer 3 and then linearly polarized light 3a.
Becomes When the linearly polarized light 3a passes through the quarter-wave plate 4, the linearly polarized light 4a and 4b orthogonal to each other shown in the drawing become a circularly polarized light with a phase difference of 90 degrees. When this circularly polarized light passes through the electro-optical element 5, the optical phase modulation is performed by utilizing the birefringence generated by applying an electric field through the transparent electrodes provided on the front and back surfaces of the crystal. After that, this light is passed through the analyzer 6 to be subjected to analog modulation, condensed by the collimator lens 2b, input to a detector (not shown) via the optical fiber 1b, and the analog modulation is performed according to the degree of analog modulation. The voltage is detected (for example,
10383).

However, in the prior art, the change in the output characteristics of the optical voltage sensor with respect to the temperature change is large, which has been a major obstacle to highly accurate voltage measurement. For example, the conventional wound type PT (Pote)
accuracy class 1P
In order to use it in the same way as the class (error of ± 1% or less in rating), it is necessary to make the relative error 1.0% or less in the voltage range of 70% to 110% of the rated voltage. However,
Keeping this temperature range within the current optical voltage sensor
There was a difficult problem in consideration of the temperature characteristics of the 1/4 wavelength plate, the electro-optic crystal, etc., which are the components. It is an object of the present invention to provide a voltage detection method for an optical voltage sensor that can obtain temperature characteristics with stable sensor sensitivity.

[0004]

In order to solve the above problems, the present invention provides a polarizer, which is arranged in order along an optical path, 1 /
A voltage detection method for an optical voltage sensor, comprising a four-wave plate, an electro-optic crystal, and an analyzer, wherein the voltage applied to the electro-optic crystal is detected by performing optical phase modulation using birefringence of the electro-optic crystal. , After converting the two output light in which the polarization angles of the polarizer and the analyzer are orthogonal and parallel to each other, the gain is adjusted by an automatic gain adjuster,
The direct current component of the output of the automatic gain adjuster is made equal to the reference voltage, and the voltage is detected from the value obtained by subtracting the electric signals of the two output lights from each other. Further, Bi ₁₂ GeO ₂₀ (hereinafter referred to as B
GO) or Bi ₁₂ SiO ₂₀ (hereinafter referred to as BSO), and the temperature dependence of the phase difference between the two output lights in which the polarization angles of the polarizer and the analyzer are orthogonal and parallel. The optical rotation angle determined by the thickness of the electro-optic crystal and the cutting direction of the electro-optic crystal are adjusted so as to be zero.

[0005]

The optical voltage sensor will be divided into a system in which the polarizer and the analyzer are orthogonal to each other and a system in which the polarizer and the analyzer are parallel to each other. Amount of transmitted light P _S (V, T) when the polarizer and analyzer are orthogonal
Is expressed by the following equation (1) as a function of the voltage V and the temperature T. P _S (V, T) = The _{(P 0/2) [1} -cos {δ (V, T) + δ 1/4 (T)}] ... (1), the polarizer and analyzer are parallel When the amount of transmitted light P
Similarly, _P (V, T) is expressed by the following equation (1) as a function of the voltage V and the temperature T. _{P P (V, T) =} (P 0/2) [1 + cos {δ (V, T) + δ 1/4 (T)}] ... (2) where, δ (V, T) is the temperature Retardation that occurs in the electro-optic crystal under the conditions of T (° C) and applied voltage V
Is. δ _1/4 (T) is the phase difference of the quarter-wave plate at the temperature T (° C.). Also, P ₀ is δ (V, T) + δ _1/4 (T) = 0 or π
Is the amount of transmitted light. In FIG. 3, the vertical axis indicates the amount of transmitted light P.
_S (V, T) and the amount of transmitted light P _P (V, T) are given by equations (1) and (2) with the horizontal axis representing the phase difference δ (V, T) + δ _1/4 (T). ) Is a summary of the relationship. As shown in FIG. 3, δ (V,
T) + δ _1/4 (T) increases, the amount of transmitted light P _S (V, T) when the polarizer and analyzer are orthogonal to each other increases, and the amount of transmitted light P _P (V, when parallel) T) decreases.

Next, the phase difference δ used in equations (1) and (2)
The temperature characteristics of (V, T) and δ _1/4 (T) and their sizes will be described. Assuming that the temperature characteristic of the phase difference δ (V, T) of the electro-optic crystal is expressed by the relationship of the temperature T and a linear expression, and its temperature coefficient is κ _c (1 / ° C), δ (V, T T) is represented by equation (3). δ (V, T) = δ ₀ (V) (1+ κ _c T) (3) where δ ₀ (V) is the phase difference of the electro-optic crystal at a temperature of zero (° C) and the applied voltage V Is a function of. Also, 1/4
The temperature characteristic of the phase difference δ _1/4 (T) of the wave plate is assumed to be represented by a linear expression of the temperature T, and its temperature coefficient is κ _1/4 (1 / ° C)
Then, δ _1/4 (T) is expressed by equation (4). δ _1/4 (T) = (π / 2) (1+ κ _1/4 T) (4) In this case, the _1/4 wave plate has a phase difference of π / 2 (at temperature zero (° C)). (Corresponding to 1/4 wavelength).

Next, the temperature characteristics of the transmitted light quantity P _S (V, T) when the polarizer and the analyzer are orthogonal to each other and the temperature characteristics of the transmitted light quantity P _P (V, T) when they are parallel to each other will be described. Amount of transmitted light P _S
(V, T) is expressed by the following equation (5) by substituting equation (3) and equation (4) into equation (1). _{P S (V, T) =} (P 0/2) [1 + sin {δ 0 (V) (1+ κ c T) + (π / 2) κ 1/4 T}] ... (5) Likewise By substituting the equations (3) and (4) into the equation (2), the transmitted light amount P _P (V, T) is represented by the following equation (6). _{P P (V, T) =} (P 0/2) [1-sin {δ 0 (V) (1+ κ c T) + (π / 2) κ 1/4 T}] ... (6) where The value of the phase difference δ ₀ (V) generated in the electro-optic crystal is usually used in the order of 10 ^-2 (rad), and κ _1/4 is 10 ^-4 in the quarter-wave plate using quartz. It is on the order of (1 / ℃). Therefore, the following expression (7) is established within the actual use temperature range. ｜ δ ₀ (V) (1+ κ _c T) + (π / 2) κ _1/4 T ｜ ≪1… (7)

In the configuration in which the polarizer and the analyzer are orthogonal to each other under the condition that the equation (7) holds, the transmitted light amount P _S (V, T) in the equation (5) is
It can be expressed as an approximate expression of the following Expression (8) as a function of the temperature T. _{P S (V, T) ≒} (P 0/2) [{1+ (π / 2) κ 1/4 T} + δ 0 (V) (1+ κ c T)] ... (8) Equation (8 The right side of) indicates that the temperature characteristic of the transmitted light amount P _S (V, T) can be divided into a first term that is irrelevant to the applied voltage V and a second term that is a function of the applied voltage V. . Similarly, the transmitted light amount P _P (V,
T) is calculated from the equation (6) as a function of the temperature T by the following equation (9).
Can be expressed by an approximate expression. _{P P (V, T) ≒} (P 0/2) [{1- (π / 2) κ 1/4 T} -δ 0 (V) (1+ κ c T)] ... (9) Equation (8 ) And (9), the first term is independent of the applied voltage V and represents the influence of the temperature of the quarter-wave plate. When the polarizer and the analyzer are orthogonal and parallel, the sign of (π / 2) κ _1/4 T in this term is opposite, so there are two effects of the temperature change of the quarter-wave plate. The configuration is reversed. On the other hand, the second term on the right side of the formulas (8) and (9) is a term representing the influence of the applied voltage V. When BGO or BSO having the Pockels effect is used as the electro-optic crystal, δ ₀ (V) is applied. The voltage V increases or decreases in proportion to the first order. Comparing these two equations, it can be seen that the signs of the coefficients are opposite, and thus the phase of the amount of transmitted light differs by 180 degrees with respect to the applied voltage. It can be seen that the effects of temperature in the electro-optic crystal are equal for these two configurations, because the sign of κ _c T is equal, despite the phase inversion.

Next, a method for stabilizing the temperature characteristics by using both optical signals when the polarizer and the analyzer are orthogonal and parallel will be described. Therefore, the following signal processing is performed using the sensor sensitivities P _S (V, T) and P _P (V, T) of the formulas (8) and (9). Assuming that the voltage applied to the optical voltage sensor is 60 Hz, the first term on the right side of equations (8) and (9) is the direct current component that includes the temperature change of the quarter wave plate, and the second term is the signal component. Is. Then, first, as shown in FIG. 1, in the case of P _S (V, T), the difference between the direct current component {1+ (π / 2) κ _1/4 } and the reference voltage E _S. Adjust the AGC (Automatic Gain Adjuster) so that becomes zero. On the other hand, in the case of P _P (V, T), the AGC is adjusted so that the difference between the direct current component {1- (π / 2) κ _1/4 } and the reference voltage E _S becomes zero. To do. That is, P _S
For (V, T), the gain is 1 / {1+ (π / 2) κ
_1/4 }, while for P _P (V, T), 1 / {1- (π /
2) The gain is proportional to κ _1/4 }. When the gains are adjusted in this way, if the reference voltages E _S are equal, the DC components become equal between the two signals. Next, when the two signals are subtracted after passing through the AGC, the following equation (10) is obtained. P (V, T) = [1 / {1+ (π / 2) κ _1/4 T}] P _S (V, T)-[1 / {1- (π / 2) κ _1/4 T} _{] P P (V, T)} = (P 0/2) {δ 0 (V) (1+ κ c T)} / {1+ (π / 2) κ 1/4 T} + (P 0/2 ) {δ ₀ (V) (1+ κ _c T)} / {1- (π / 2) κ _1/4 T}… (10) where (π / 2) κ _1/4 T + << 1 In the condition that holds,
Expression (10) can be expressed by an approximate expression of the following Expression (11). P (V, T) ≈ P ₀ δ ₀ (V) (1+ κ _c T) (11) Therefore, two signals P _S (V, T) and P measured simultaneously are
_{If P} (V, T) is processed by the circuit shown in FIG. 1, the temperature coefficient of the sensitivity of the photovoltage sensor is not affected by the temperature characteristics of the quarter-wave plate, and the temperature coefficient κ of the electro-optic crystal is Only affected by _c .

From equation (11), the temperature coefficient of the electro-optic crystal must be κ _c = 0 in order to stabilize the temperature characteristics of the optical voltage sensor of this construction. Here, a method of adjusting the temperature coefficient κ _c of δ ₀ (V) when BGO or BSO is used as the electro-optic crystal will be described. For this reason,
First, the phase difference δ ₀ (V) corresponding to the equation (3) will be described. The voltage applied to the electro-optic crystal is V and the half-wave voltage is V
Assuming that the optical rotation angle determined by _1/2 and the crystal thickness is Φ ₀ (these are values at 0 ° C), and the cutting direction related to the crystal orientation is θ, the phase difference δ that occurs in the crystal
₀ (V) is expressed by the following equation (12). δ ₀ (V) = (πV / V _1/2 ) (sin Φ ₀ / Φ ₀ ) cos (Φ ₀ + 2θ) (12) Next, the formula (3) will be described. Therefore, first, it is assumed that there is a linear relationship with the temperature T, and under the condition that the respective temperature coefficients κ _a and κ _b are established (12), the sensor sensitivity in the configuration in which the polarizer and the analyzer are orthogonal to each other. _{| m V (V, T)} |
Is approximated by the following equation (13). Then half-wave voltage
V _1/2 and the optical rotation angle Φ ₀ are represented by the following equation (13). V _1/2 (T) = V _1/2 (1+ κ _a T), Φ ₀ (T) = Φ ₀ (1+ κ _b T) (13) Under the condition that equation (13) holds, Temperature coefficient κ of (3)
_c is represented by the following equation (14). κ _c =-(κ _a + κ _b ) + κ _b F (Φ ₀ , θ) (14) where F (Φ ₀ , θ) is a function determined by the optical rotation angle Φ ₀ and the crystal orientation θ. It is represented by the equation (15). F (Φ ₀ , θ) = (Φ ₀ / sin Φ ₀ ) {cos (2Φ ₀ +2 θ) / {cos (2Φ ₀ +2 θ)}… (15) κ _a and κ _b are determined by physical properties Therefore, in order to control κ _c , the value of F (Φ ₀ , θ) may be changed and designed. FIG. 4 shows the relationship between the cutting direction θ, which is the crystal orientation, and | δ (V) |
The results calculated using 2) are shown. However, the vertical axis is |
Instead of δ (V) |, the standardized sensor sensitivity | m | _n standardized by πV / V _1/2 is used. The optical rotation angle Φ ₀ is proportional to the crystal thickness d. Further, FIG. 5 shows a result of calculating the relationship between the cutting direction θ and the temperature coefficient κ _c of the sensor sensitivity by using the equations (14) and (15). Thus, by the crystal thickness d proportional to the cutting direction θ and the optical rotation angle Φ ₀ , | δ
It can be seen that (V) | and κ _c can be adjusted. The definition of the cutting direction is shown in FIG.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a signal processing circuit of an embodiment of the present invention, and FIG. 2 is a configuration diagram showing a configuration of an optical voltage sensor. In the figure, 1a is an optical fiber for guiding light emitted from a light source (not shown) including a light emitting element such as a light emitting diode, 2a is a collimator lens for collimating the light from the optical fiber 1, and 3 is a polarization beam splitter. Is used as a linearly polarized light 3a by reflecting light. 4 is 1 /
In the four-wave plate, when the linearly polarized light 3a passes through the quarter-wave plate 4, it becomes linearly polarized lights 4a and 4b orthogonal to each other.
Circularly polarized light with a phase difference of degrees. Reference numeral 5 denotes an electro-optical element. When the circularly polarized light passes through the electro-optical element 5, an electric field is applied through transparent electrodes provided on the front and back surfaces of the crystal to utilize the birefringence to perform optical phase modulation. I do. Reference numeral 6 is a polarizer composed of a polarization beam splitter. The condition that the polarizer 3 and the analyzer 6 are orthogonal to each other is that the polarizer 3 uses reflected light (S-polarized light) and the analyzer 6 uses transmitted light (P-polarized light). It is configured to be used. In this case, in order to facilitate the handling of the optical voltage sensor, the transmitted light amount P _P (V, T) parallel to the polarizer 3 reflected by the analyzer 6 is condensed by the collimator lens 2b, and the optical fiber 1b is collected. It is input to the signal processing circuit 8 via the. Amount of transmitted light that passes through the analyzer 6 and is orthogonal to the polarizer 3 P _S (V, T)
The optical path is bent 90 degrees by the mirror 7, is condensed by the collimator lens 2c, and is input to the signal processing circuit 8 via the optical fiber 1c. In the signal processing circuit 8, the amount of transmitted light P
_S (V, T) is transmitted to the photovoltage converter (O / E) 81a and transmitted light amount P
_P (V, T) is input to the photovoltage converter 81b and converted into a voltage signal. The amount of transmitted light P _S (V, T) converted to a voltage signal,
P _P (V, T) are the automatic gain adjusters 82a and 82b, respectively.
The gain is adjusted with. Automatic gain adjusters 82a, 82b
The DC component of the output of is equal to the reference voltage E _S, and by the electric signal of the two transmitted light amounts P _S (V, T) and P _P (V, T), the calculator 83 calculates the formula (10). Is subtracted to obtain the result of equation (11). Reference numerals 84a and 84b are low-pass filters, and reference numerals 85a and 85b are adders.

In order to stabilize the temperature of the optical voltage sensor in the equation (11), the temperature coefficient κ _c of the electro-optic crystal may be set to κ _c = 0. Here, the cutting direction (5 degrees) and thickness (4 mm) at which the temperature coefficient κ _c = 0 of the BGO crystal of the optical voltage sensor is obtained.
Was selected and its characteristics were obtained by experiments. FIG. 7 shows the result. Note that FIG. 7 also shows the output values of the AC signals of P _S (V, T) and P _P (V, T). In this way, the temperature of the quarter-wave plate changes, and the AC components of P _S (V, T) and P _P (V, T) change with temperature, but the difference between the two signals is The characteristics can be stabilized. This method is 1/4
Since the influence of the temperature of the temperature coefficient κ _1/4 of the wave plate is theoretically removed, there is an advantage that the temperature characteristic of the sensor sensitivity is not affected by the variation of the temperature coefficient κ _1/4 of the quarter wave plate.

[0018]

As described above, according to the present invention, the temperature characteristic of the optical voltage sensor can be set to 1 by optimally selecting the cutting direction with respect to the thickness and crystal orientation of the electro-optical crystal of the optical voltage sensor.
Since the temperature change of the optical voltage sensor is suppressed to be small by making it coincide with the temperature characteristic of the / 4 wavelength plate, it is possible to provide the voltage detecting method of the optical voltage sensor with stable temperature characteristic. Also,
Since the temperature characteristics of the optical voltage sensor can be stabilized by changing only the design condition of the electro-optic crystal, there is an effect that it can be performed without adding new parts.

[Brief description of drawings]

FIG. 1 is a block diagram showing a signal processing circuit according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing the relationship between the amount of transmitted light and the phase difference according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a relationship between a cutting direction and sensor sensitivity according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram showing the relationship between the cutting direction and the temperature coefficient of the electro-optic crystal in the example of the present invention.

FIG. 6 is an explanatory diagram showing a cutting direction of the electro-optic crystal according to the example of the present invention.

FIG. 7 is an explanatory diagram showing temperature characteristics of the optical voltage sensor according to the embodiment of the present invention.

FIG. 8 is an explanatory diagram showing an operation of a conventional example.

[Explanation of symbols]

1 optical fiber, 2a, 2b, 2c collimator lens, 3 polarizer, 4 1/4 wavelength plate, 5 electro-optic crystal,
6 analyzer, 7 mirror, 8 signal processing circuit, 81a,
81b optical voltage converter, 82a, 82b automatic gain adjuster, 83 arithmetic unit

Claims (2)

[Claims] 1. A polarizer arranged in order along an optical path, 1 /
A voltage detection method of a photovoltage sensor, which comprises a four-wave plate, an electro-optic crystal, and an analyzer, and detects the voltage applied to the electro-optic crystal by performing optical phase modulation by utilizing the birefringence of the electro-optic crystal. In, after converting the two output light in which the polarization angles of the polarizer and the analyzer are orthogonal and parallel to each other, the gain is adjusted by the automatic gain adjuster, and the direct current component of the output of the automatic gain adjuster is adjusted. A voltage detecting method for an optical voltage sensor, wherein a voltage is obtained from a value obtained by subtracting the electric signals of the two output lights from each other by making the voltage equal to a reference voltage. 2. The electro-optic crystal is made of either Bi ₁₂ GeO ₂₀ or Bi ₁₂ SiO ₂₀ , and the polarization angles of the polarizer and the analyzer are orthogonal and parallel, depending on the temperature of two output lights. 2. The voltage detection method for a photovoltage sensor according to claim 1, wherein the optical rotation angle determined by the thickness of the electro-optic crystal and the cutting direction that determines the orientation of the electro-optic crystal are adjusted so that the difference between the electric signals becomes zero.