JPH0158461B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage measuring device that measures high voltage using an electro-optic crystal.

[Conventional technology]

In the past, various devices have been proposed that measure voltage by utilizing the electro-optic effect of crystals such as LiNbO ₃ , BSO, and BGO (e.g., Japanese Patent Laid-Open No. 1983-1999).
Publication No. 196166, Japanese Patent Publication No. 1961-120864, Japanese Patent Publication No. 1961-120864
56-100364).

[Problem that the invention seeks to solve]

However, conventional measuring devices of this type generally have problems with their high insulation, withstand voltage, and large input impedance, and even if they are for high voltage, they are only 2 to 2.
It was only possible to measure up to about 3KV.

[Means for solving problems]

In order to solve these problems, the present invention has an electro-optic crystal embedded in an insulator, and electrodes are arranged facing each other with the insulator interposed therebetween.

[Function] Conventionally, when voltage was applied by attaching electrodes directly to the electro-optic crystal, creeping discharge occurred along the surface of the electro-optic crystal when the voltage was high, whereas creeping discharge occurred directly between the electrodes. The pressure resistance is improved because there are no gaps.

〔Example〕

FIG. 1a is a plan view showing an embodiment of the present invention, and FIG. 1b is a front view. In the figure, reference numeral 1 denotes a rectangular parallelepiped case made of insulating ceramic (Macol, manufactured by Corning Inc.), in which a recess 101 is provided on the top surface and an electro-optic crystal 2 is embedded therein. The electro-optic crystal 2 is made of a Z-cut crystal, and has a quarter-wave plate 3, a polarizer 4, and an analyzer 5 bonded together in the Z-axis direction with epoxy resin. Further, the side surfaces of the electro-optic crystal 2, polarizer 4, and analyzer 5 in the X-axis direction are adhered to the inner surface of the recess 101 with silicone rubber. Furthermore, recess 1
The inside of 01 is filled with Freon gas (SF ₆ ),
A glass plate 6 is adhered and sealed to the case 1 with silicone rubber.

On the other hand, a recess 102 is provided on the outer surface of the case 1 in the X-axis direction corresponding to the electro-optic crystal 2, and the electrodes 7 (7A, 7B) are embedded therein and fixed by filling with silicone rubber. Therefore, the electrode 7 is disposed to face the electro-optic crystal 2 in the X-axis direction through a part of the side wall of the case 1. A covered lead wire 8 is connected to the electrode 7, and an alligator clip 9 is attached to the tip thereof.

A through hole 103 continuous to the recess 101 is formed in the Y-axis direction on the lower surface side of the case 1, and a rod lens 10 is formed on the lower surface of the polarizer 4 and the analyzer 5.
(10A, 10B) via optical fiber 11 (10A, 10B)
1A and 11B) are connected to each other.

Next, the principle of voltage measurement using such an electro-optic effect element will be explained using FIG. 2. Although omitted in FIG. 1, light outputted from a light emitting element (for example, a light emitting diode) 12 and guided by an optical fiber 11A is converted into parallel light by a lens 10A. Further, the light is linearly polarized at an angle of 45° by the polarizer 4, and is then made circularly polarized by the wave plate 3, before being incident on the crystal 2. Here electrode 7
Under the influence of the voltage Va applied between A and 7B, circularly polarized light becomes elliptically polarized light. The analyzer 5 extracts only the component of the light vector in the 45° direction from this light, and the light is passed through the lens 10B and the optical fiber 11B to the light-receiving element 1 made of, for example, a photodiode.
3 and is converted into an electrical signal. In this way, a change in light intensity corresponding to the voltage can be detected.

Conventionally, electrodes were attached directly to the surface of the electro-optic crystal 2, but as described above, the insulating case 1 is hollowed out and the crystal 2 is embedded therein to form the electrode 7.
By arranging the electrodes externally, the spatial distance between the electrodes was extended and the withstand voltage was improved. Providing the recess 102 and embedding the electrode 7 therein also further enhances the effect of preventing creeping discharge. Furthermore, when the electro-optic crystal 2 is exposed to the atmosphere, the electric field inside the crystal decreases due to the influence of humidity, but this is prevented by placing it in Freon gas.

A quartz crystal was used as the electro-optic crystal 2, but since the electro-optic effect of quartz crystal is smaller than that of conventionally commonly used BSO etc., the part with good linearity of the output characteristics was measured at high voltage (5 to 50 KV). This is advantageous because it can be used for Furthermore, compared to BSO and the like, crystal has a small dielectric constant ε _r of 10 or less, so it has the advantage of being able to increase input impedance. moreover,
In the configuration in which a voltage is applied in the X-axis direction as described above, assembly (alignment) of the wave plate 3, polarizer 4, and analyzer 5 is facilitated due to the optical rotation of the crystal.

As the material for case 1, a material with temperature characteristics (in particular, a linear expansion coefficient similar to that of crystal 2) was selected to reduce the mechanical stress acting on crystal 2.Furthermore, the recess 101 is filled with Freon gas. As mentioned above, the insulating strength is increased by using insulating oil or resin.
In that case, it is desirable to use a substance with low elasticity, such as low-viscosity silicone oil, from the viewpoint of reducing the stress applied to the crystals.

In addition, as a protection mechanism against abnormal voltage, a third
As shown in the figure, the arrester element 14 may be connected in parallel to the electro-optic effect element. In addition, 15, 16
is resistance.

In order to further improve the withstand voltage, a lead-out insulator may be attached to the electrode section.

FIG. 4 shows an example of the configuration of a circuit diagram. This is an example of a ratio detection method, in which an element 20 as shown in FIG.
An AC high voltage is applied as the voltage to be measured between the electrodes 7A and 7B, and the light emitting circuit 22 is driven by the stabilized power supply 21 to cause the light emitting diode 12 to emit light. On the other hand, in the light receiving circuit 23, the electric signal obtained by the photodiode 13 is divided into an AC component and a DC component by an AC transmission filter 24 and a DC transmission filter 25, and the ratio is calculated in a ratio detection circuit 26 to determine the value of AC voltage. It is converted to .
This is converted into a DC voltage by an AC-DC conversion circuit 27, and the value is displayed on a display 28. In addition,
29 is an amplifier.

By adopting the ratio detection method in this manner, it is possible to cope with fluctuations in light loss in the optical fiber 11 and the like.

Similarly, as a means to deal with fluctuations in light, a feedback method as shown in FIG. 5 can also be used. This is to feed back the output obtained from the DC transmission filter 25 to the light emitting circuit 22 and control the amount of light emitted so that the amount of received light is constant. Although the circuit configuration is simpler than the ratio detection method, the signal-to-noise ratio decreases because the maximum amount of light cannot be used. On the other hand, the ratio detection method has the advantage that the light emitting diode can always emit light with the maximum amount of light.

FIG. 6 shows an example of the measurement results. The horizontal axis shows the reading of the electrostatic voltmeter, and the vertical axis shows the measurement results according to the above embodiment expressed in modulation degree M. ○ marks indicate actual measurement points.

Although an example has been described above in which a recess is provided in the ceramic case 1, the electro-optic crystal 2 is embedded therein, and electrodes are arranged on the outside, the present invention is not limited to this. For example, in FIG. 7, a crystal 2 is placed inside an insulating case 1A made of ceramic, and electrodes 7 are placed at a predetermined interval.
Although the entire structure is filled with a silicon-based resin 17 having a low dielectric constant and low viscosity, the insulation strength can be similarly increased.

〔Effect of the invention〕

As explained above, according to the present invention, by embedding an electro-optic crystal in an insulator and arranging electrodes facing each other through the insulator, the insulation strength is improved to about 20 to 50 KV, which was previously difficult to achieve. This makes it easy to measure high voltages.

In addition, unlike conventional methods in which electrodes are attached directly to the crystal, by changing the electrode spacing, it is possible to match the detection element part and the measurement circuit part with the desired input impedance, and the compatibility of the crystal element can be achieved. can be made to last.

Of course, there are no advantages that voltage measuring devices using electro-optic crystals generally have, such as the ability to electrically isolate the detection element section and the circuit section by introducing optical fibers, and eliminate the effects of adverse electromagnetic environments. preserved without damage.

[Brief explanation of drawings]

Fig. 1a is a plan view showing an embodiment of the present invention, Fig. 1b is a front view thereof, Fig. 2 is a diagram for explaining the principle, Fig. 3 is a configuration diagram showing an abnormal voltage protection mechanism, 4 and 5 are block diagrams showing examples of the configuration of the circuit section, FIG. 6 is a diagram showing an example of measurement results, and FIG. 7 is a sectional view showing another embodiment of the present invention. 1,1A...Case, 2...Electro-optic crystal, 7
(7A, 7B)...Electrode, 17...Resin.

Claims (1)

[Claims] 1. In a voltage measuring device equipped with an electro-optic crystal, means for making light incident on the electro-optic crystal, and means for detecting the amount of light passing through the electro-optic crystal, the electro-optic crystal is placed in an insulator. embedded,
A voltage measuring device characterized in that electrodes are arranged facing each other with the insulator interposed therebetween.