JPH0248852B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vacuum degree monitoring device for vacuum electrical equipment having a vacuum section to which a voltage is applied.

In general, the performance of vacuum electrical equipment such as vacuum chambers and disconnectors is greatly affected by the quality of the internal vacuum, so it is necessary to monitor the vacuum. For this reason, various vacuum degree monitoring devices have been proposed in the past, but all of them have problems with insulation, size, cost, etc., and are not practical.

Therefore, the present applicant proposed a practical vacuum monitoring device in Japanese Patent Application No. 55-37098 (Japanese Patent Publication No. 60-22288). The basic idea is shown in Figure 1A.
This will be explained with reference to FIG. 2 and FIGS. 3A and 3B. 1A and 1B respectively show a vacuum shield breaker and its equivalent circuit in the energized state, where 1 is a fixed electrode, 2 is a movable electrode, 3 is a fixed lead, 4 is a movable lead, 5 is an insulating cylinder, 6, Reference numeral 7 denotes an end plate sealed to both ends of the insulating cylinder 5, the fixed lead 3 is attached to the end plate 6, and the movable lead 4 is attached to the end plate 7 via a bellows 8.
is sealed. 9 is a shield attached to the middle of the insulating cylinder 5. In addition, 10 and 11 are the power supply and load of the circuit in which the vacuum circuit breaker is installed, respectively, and 1
2 and 13 are the resistance and capacitance between the fixed electrode 1 and the shield 9, respectively; 14 and 15 are the resistance and capacitance between the movable electrode 2 and the shield 9, respectively; 16a and 1
6b is the resistance of the insulating tube 5, and 17 is the capacitance between the shield 9 and the ground.

In the vacuum chamber disconnector described above, the interior of the vacuum container formed by the insulating tube 5 and the end plates 6 and 7 is maintained at a high vacuum, and when the degree of vacuum deteriorates, the capacitance 13, 15 is constant because ε ₀ ≈ε atmosphere, but resistances 12 and 14 decrease rapidly. For this reason, the voltage between the electrodes 1, 2 and the shield 9 becomes small, and the voltages shared at each part of the vacuum shield and disconnector change. For example, when the degree of vacuum is good, the voltage of the power supply 10 is V, the voltage between the fixed electrode 1 and the shield 9 is _V1 , the voltage between the movable electrode 2 and the shield 9 is _{V2, and the voltage between the shield 9 and the ground is V1.} V ₁ as V ₃
= V ₂ = V/2, V ₃ = V-V ₁ = V/2, but if the degree of vacuum deteriorates, V ₁ = V ₂ = V/4, V ₃ = V-V/4 = 3/4V (These examples are shown as examples and may vary depending on the structure of the disconnector and the degree of vacuum.) Therefore, as shown in FIG.
The voltage V ₃ varies greatly depending on the degree of vacuum, and the electric field E near the shield 9 also varies greatly.

Moreover, FIGS. 3A and 3B show the vacuum shield disconnector and its equivalent circuit in the disconnected state, respectively, and 18 and 1
9 indicates the resistance and capacitance between electrodes 1 and 2, respectively. In this case as well, the capacitances 13, 15, 19 do not change depending on the degree of vacuum, but the resistances 12, 14, 18 change depending on the degree of vacuum. Therefore, when the degree of vacuum deteriorates, the voltage of the shield 9 increases, The electric field near the shield 9 also increases. In this way, in a vacuum shield switch, the voltage of the shield 9 changes greatly depending on the degree of vacuum, whether in the energized state or in the energized state.
The nearby electric field also changes significantly. Therefore, by monitoring the electric field on the outside of the shield 9, it is possible to constantly monitor the degree of vacuum in the vacuum shield and the disconnector. still,
At the outer periphery of the vacuum chamber and disconnector, the electric field changes depending on the degree of vacuum even in parts other than the shield 9. Furthermore, the degree of vacuum can also be monitored in vacuum electrical equipment other than vacuum chambers and disconnectors by monitoring the electric field in a portion where the electric field changes depending on the degree of vacuum.

Therefore, in the above proposal, a Pockels element that rotates the plane of polarization of polarized light in proportion to the magnitude of the applied electric field is provided on the outer periphery of the vacuum electrical equipment, and a polarizer and an analyzer are provided on both sides of the element to polarize the light from the light emitting part. The plane of polarization of the polarized light is rotated by a Pockels element in proportion to the electric field, and then the polarized light is transmitted to an analyzer. A vacuum level monitoring device that detects the level of vacuum is shown. However, in this case, KDP (KH ₂ PO ₄ ) or ADP is used as a Pockels element.
(NH ₄ H ₂ SO ₄ ), which are expensive and deliquescent, making them very difficult to handle.
In addition, because it has a large dielectric constant (approximately 10 times that of quartz), it easily disturbs the electric field and causes errors in electric field detection. On the other hand, when quartz is used as the Pockels element, quartz has a low dielectric constant, so it is difficult to disturb the electric field and the electric field can be detected accurately, and quartz is inexpensive and easily available. In addition, quartz has a constant optical loss and is not deliquescent, making it a very stable crystal and easy to handle. However, crystal has so-called natural optical rotation, in which when polarized light is incident in the direction of its optical axis, the plane of polarization rotates regardless of the electric field. Moreover, since this natural optical rotation changes with temperature, the applied electric field and the rotation angle of the plane of polarization are no longer accurately proportional, resulting in insufficient accuracy and reliability of the vacuum level monitoring device.

Therefore, the present applicant filed Japanese Patent Application No. 56-46668 (Japanese Unexamined Patent Publication No.
57-160070), two crystals 20 and 21 having almost symmetrical natural optical rotations with respect to temperature changes are closely connected in series so that their respective natural optical rotations cancel each other out. Pockels element 2
I proposed to form 2. And He-Ne
The linearly polarized light generated from the laser 23 is transmitted through the Pockels element 22 and then transmitted through the analyzer 24, and the transmitted light from the analyzer 24 is added to the light receiving section 25 which outputs an electric signal proportional to the amount of transmitted light. The electric field is detected by the output.

However, in the electric field detection device shown in Fig. 2, crystals 20 and 21 are generally used.
A 45°-Z cut crystal is used, and the temperature characteristics of its polarization plane variation (one crystal) are as shown in Figure 5.The Pockels element 22 is placed in a thermostatic oven 26 and the temperature of its polarization plane variation is When the characteristics were measured, they were as shown in Figure 6, and the temperature was 3% in the temperature range of 20°C to 90°C.
There are variations in degree. This is because it is difficult to find two crystals that have completely symmetrical polarization plane fluctuation temperature characteristics. Furthermore, even if two crystals having almost symmetrical temperature characteristics were to be found, it would take a long time to measure the temperature characteristics, which would be very time-consuming. In addition, the rotation angle of the polarization plane in the Pockels element 22 is proportional to the electric field and also to the element length in the optical axis direction, but the 45°-Z cut crystal does not have very good electric field detection sensitivity (the polarization plane relative to the electric field (The rotation angle is small.) Therefore, in order to improve the sensitivity, it is necessary to increase the length of the crystal.
0 and 21 are closely connected in series, so it is large in size. Furthermore, in order to bring the two crystals 20 and 21 into close contact with each other without an air layer between them and without causing any optical problems, extremely high-precision polishing is required, which makes the manufacturing process troublesome. There were flaws.

In consideration of the above points, it is an object of the present invention to provide a vacuum level monitoring device for vacuum electrical equipment that is small, inexpensive, easy to manufacture, and highly accurate and reliable.

Embodiments of the present invention will be described below with reference to the drawings.
In FIG. 7, reference numeral 27 denotes a Pockels element disposed on the outer circumferential side of the shield 9 of the vacuum shield breaker. A crystal cut in the axial direction is used. A polarizer 28 and an analyzer 24 are placed closely on both sides of the Pockels element 27.
8 is connected to one end of an optical fiber 29, and the other end of the optical fiber 29 is connected to a light emitting section 30 consisting of a photodiode or the like. Further, one end of an optical fiber 31 is connected to the analyzer 24, and a light receiving section 25 is connected to the other end of the optical fiber 31.
A degree of vacuum determining section 32 is electrically connected to the vacuum level determining section 32 .

The operation of the vacuum level monitoring device having the above configuration will be explained using FIG. 9. The light emitted from the light emitting section 30 and vibrating over the entire surface is transmitted to the polarizer 28 through the optical fiber 29 and is linearly polarized by the polarizer 28 . The polarized light is transmitted in the Z direction of the Pockels element 27 (Z-cut crystal). The Pockels element 27 is the shield 9
An external electric field E is applied in the X direction, and the plane of polarization of the polarized light is rotated by an angle θ in proportion to the magnitude of the electric field E. The light from the Pockels element 27 is transmitted to the analyzer 2
The light is transmitted through the analyzer 24 having a polarization plane having a predetermined relationship with the polarization plane of 8, and is transmitted through the optical fiber 31 to the light receiving unit 2.
Added to 5. As shown in Figure 10, the electric field E is small when the degree of vacuum in the vacuum chamber or disconnector is good;
It increases when the degree of vacuum is poor or deteriorated. Therefore, the rotation angle θ of the plane of polarization in the Pockels element 27 is small when the degree of vacuum is good, and becomes large when the degree of vacuum is poor. Therefore, when the polarization planes of the polarizer 28 and the analyzer 24 are perpendicular to each other, if the degree of vacuum becomes poor, the amount of light transmitted through the analyzer 24 increases, and the light receiving section 25 outputs an output according to the amount of light. The output A suddenly increases as shown by the solid line in FIG. Further, when the polarization planes of the polarizer 28 and the analyzer 24 are in a parallel relationship, if the degree of vacuum becomes poor, the amount of transmitted light of the analyzer 24 becomes small, and the light receiving part 25
The output A suddenly decreases as shown by the dotted line in FIG. Therefore, the degree of vacuum determination section 32 outputs A
It detects a deterioration in the degree of vacuum when the value suddenly increases or decreases, and outputs an alarm or display.

In the above embodiment, when the Pockels element 27 is placed in the thermostatic chamber 26 and the temperature characteristics of the variation in the polarization plane are investigated, the temperature characteristics of the variation in the polarization plane are as shown in FIG. Becomes zero. Therefore, the electric field E and the output of the light receiving section 25 correspond accurately, and a highly accurate and highly reliable vacuum level monitoring device can be obtained. In addition, the Z-cut crystal has four times the electric field detection sensitivity compared to the 45°-Z-cut crystal, so the element length can be reduced to just under 1/4, and the Pockels element 27 can be made from one crystal. Therefore, the Pockels element 27 and the entire device can be formed compactly.

As shown in FIG. 9, if a quarter-wave plate 33 is provided between the polarizer 28 and the Pockels element 27, linearly polarized light is converted to circularly polarized light, and in this case, the direction of the electric field E applied to the Pockels element 27 is may be in any of the X, Y, and Z directions. Further, the light emitting section 30 and the polarizing plate 28 can be replaced with lasers. In addition, this vacuum level monitoring device can be applied not only to vacuum shields and disconnectors, but also to other vacuum electrical equipment that has a vacuum section to which voltage is applied, such as vacuum tubes and X-ray tubes. 27 needs to be provided in a part where the electric field changes depending on the degree of vacuum, but the polarizer 28 and analyzer 24 do not need to be provided in this part.

As described above, in the present invention, in a vacuum electric device having a vacuum section to which a voltage is applied, a means for generating linearly polarized light or circularly polarized light and a section where an electric field changes depending on the degree of vacuum outside the vacuum section are provided. A vacuum degree monitoring device is provided, which includes a Pockels element formed of a Z-cut crystal and transmitting the polarized light in the Z direction, and an analyzer transmitting the light transmitted through the Pockels element, and the analyzer The degree of vacuum is detected by the amount of transmitted light, and the structure of the vacuum degree monitoring device is simple, small, and inexpensive. Furthermore, since the Pockels element, analyzer, etc. provided near the vacuum section are made of insulating material, the insulation will not be disturbed. Furthermore, since Pockels elements and analyzers are passive elements, there is no fear of failure and they are highly reliable.

In addition, Pockels elements are inexpensive and easy to process, have good electric field detection sensitivity, and can be shortened in length.
The vacuum level monitoring device is formed from Z-cut crystals and is inexpensive, compact, and easy to manufacture. In addition, since the Z-cut crystal exhibits almost zero change in the plane of polarization due to temperature, the electric field applied to the Pockels element and the rotation angle of the plane of polarization correspond accurately, and therefore the degree of vacuum and the amount of light transmitted by the analyzer can be adjusted. The vacuum level deterioration can be detected accurately, and the accuracy and reliability of the vacuum level monitoring device are improved. In addition, crystal is stable because the optical loss (reflection loss + absorption loss) during light transmission is constant and there is no deliquescent property, and Pockels elements are easy to handle, do not require sealing, and are simple in structure and durable. performance and reliability are improved. Further, since crystal has a low dielectric constant, it does not disturb the electric field used to detect the electric field, and the electric field can be detected accurately, and the degree of vacuum can also be detected accurately.

[Brief explanation of drawings]

Figures 1A and B and Figure 2 are respectively a longitudinal sectional front view of the vacuum shield breaker in the energized state, an equivalent circuit diagram, and a diagram of the relationship between the degree of vacuum and the voltage and electric field of each part, and Figures 3A and B are respectively A longitudinal sectional front view and an equivalent circuit diagram of the vacuum shield breaker in the shielded state, FIG. 4 is a configuration diagram of the electric field detection device previously proposed by the applicant, and FIG.
Temperature characteristic diagram of polarization plane fluctuation of 45°-Z cut crystal,
FIG. 6 is a temperature characteristic diagram of the polarization plane variation of the Pockels element in the electric field detection device, FIG. 7 is a configuration diagram of the vacuum degree monitoring device according to the present invention, and FIGS. 8A and B are respectively the Pockels element according to the present invention A plan view and a front view showing the cut state of the Z-cut crystal used in
Figures 9 and 10 are an explanatory diagram of the operation of the vacuum monitoring device according to the present invention and a diagram of the relationship between the vacuum level, the electric field, and the output of the light receiving section, respectively, and Figure 11 is the temperature characteristic of the polarization plane fluctuation of the Pockels element according to the present invention. figure. 23...He-Ne laser, 24...analyzer, 25...
Light receiving section, 27... Pockels element, 28... polarizer,
30... Light emitting section, 33... 1/4 wavelength plate.

Claims (1)

[Claims] 1. In vacuum electrical equipment having a vacuum section to which a voltage is applied, a means for generating linearly polarized light or circularly polarized light, and a means provided outside the vacuum section where the electric field changes depending on the degree of vacuum, and a Z-cut crystal. a Pockels element configured to transmit the polarized light in the Z direction and rotate the plane of polarization of the polarized light according to the magnitude of an applied electric field; and an analyzer configured to transmit the light transmitted through the Pockels element. A vacuum degree monitoring device for vacuum electrical equipment, which detects the degree of vacuum in the vacuum section based on the amount of transmitted light.