JPS5883273A - Optical current transformer - Google Patents

Abstract

PURPOSE:To enhance the magnetic field sensitivity without enlarging the shape and increasing dimensions, by winding an optical fiber having the Farady effect into a shape like a search coil and arranging this optical fiber on the outside circumference of a conductor. CONSTITUTION:An insulating supporting member 3 for fixing an optical fiber is arranged on the outside circumference of a conductor 1, and a search coil-shaped optical fiber 4 wound with a prescribed diameter is provided on the outside circumferential face of the insulating supporting member 3. Coils are so arranged that planes of coils are parallel with the conductor 1, and plural coils are cascaded so as to obtain a required sensitivity. The search coil-shaped optical fiber 4 is wound in several turns so that the length of one turn (circumferential length) is 2pi/DELTAB. The value DELTAB is the difference of propagation constant between two linearly polarized waves orthogonal to each other passing in the optical fiber 4. By increasing the number of turns of the coil 4, the length of the optical fiber is increased equivalently to enhance the magnetic field sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical current transformer, and more particularly to an optical current transformer that is most suitable for measuring current using an optical fiber as a magnetic field sensor.

It is well known that a dielectric material having the so-called Faraday effect, in which the plane of deflection of light rotates depending on the strength of a magnetic field, can be used in an optical fiber and used as a current measuring device. The advantage of using this kind of magnetic field that changes depending on the current as an optical current measuring device is that it can be used in high voltage circuits because there is no insulation problem compared to conventional induction type current transformers, and it can be made smaller and lighter. That's true.

FIG. 1 shows an example of an optical current transformer.

An optical fiber 2 is wound several turns around a conductor 1 to be measured. The polarization plane of light passing through the optical fiber 2 rotates in accordance with the current flowing through the conductor 1. Therefore, by measuring the Faraday rotation angle of the output light from the optical fiber 2, the magnitude of the current flowing through the conductor 1 can be measured. In this case, the diameter and number of turns of the optical fiber are appropriately selected depending on the current value. In order to increase the sensitivity of current measurement, that is, to increase the Faraday rotation, the winding spacing of the optical fiber 2 7. ．． It is better to make it longer. However, the light passing through the optical fiber 2 is two orthogonal linearly polarized waves E x gE ,
Propagation constant difference Δβ of mode (its propagation constant is β,,βy)
As the product Δβ·L of (−1β, −β, l) and the length Ll of the optical fiber (ie, the amount of birefringence strain) increases, the output decreases rapidly.

In particular, Δβ・L,=2nπ(n=1.2...
), the birefringence distortion and the Faraday effect cancel each other out, and the output becomes zero. This requires a long optical fiber. is subject to the constraint of (Lyc〈π/Δβ), so in order to increase Ly, it is necessary to make Δβ as small as possible, and for this reason, it is impossible to extract an output proportional to the length of the optical fiber. It was difficult.

In addition, Δ, l? Another drawback is that the output light fluctuates due to external disturbances such as vibration and bending applied to the optical fiber due to the small size.

An object of the present invention is to provide an optical current transformer that can increase magnetic field sensitivity without increasing the size and shape.

In the present invention, an optical fiber having a Faraday effect is wound into a search coil, and this coil is disposed at a predetermined distance from a conductor. A plurality of search coils may be arranged around the conductor as necessary to achieve the desired sensitivity.

FIG. 2 is a perspective view showing an embodiment of the invention.

An insulating support member 3 having a required diameter and width and for fixing an optical fiber is disposed around the outer periphery of the conductor 1. A search coil-shaped optical fiber 4 wound to a predetermined diameter is provided on the outer peripheral surface of the insulating support member 3. The coil has a coil surface parallel to the conductor 1, and a plurality of coils are connected in cascade to obtain the required sensitivity. Further, in order to prevent these search coil-shaped optical fibers 4 from shifting from their installation locations, a groove is provided on the outer circumferential surface of the insulating support member 3, and the optical fibers 4 are buried in this groove. Note that the search coil-shaped optical fiber 4 has a -winding length (circumference length) of 2π/Δβ.
Several turns are wound in this way.

With the above configuration, the cancellation phenomenon of birefringence distortion and Faraday effect does not appear, and Faraday rotation proportional to the length of the optical fiber can be obtained. By increasing the number of turns of the search coil 4, the length of the optical fiber can be reduced to 1. can be increased, and magnetic field sensitivity can be easily increased. As a result of increasing Δβ due to the bent structure, fluctuations in output light due to external disturbances can be reduced.

Although the embodiment shown in FIG. 2 shows an example in which the optical fiber 4 is fixed to the insulating support member 3, this is not particularly necessary if it can be constructed from the optical fiber itself, and even if it is used, the insulation properties can be ensured. If so, the shape and material do not matter.

As is clear from the above, according to the present invention, magnetic field sensitivity can be increased without increasing the shape and dimensions.

In explaining the present invention, only a current transformer is illustrated, but it can be used in various applications that exhibit the Faraday effect, such as a magnetometer,
Applicable to current meters, etc.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a conventional optical current transformer, and FIG. 2 is a perspective view showing an embodiment of the present invention. Figure 2 of the 1st drawing of the drawer

Claims (1)

[Claims] (1) Optical current transformation that measures the magnitude of the current using an optical fiber in which the deflection plane of light rotates and the output light changes depending on the strength of the magnetic field generated in accordance with the current flowing through the conductor. In the device, the optical fiber is wound a required number of times to form a coiled body, and the optical fiber is arranged on the axis of the conductor so that the direction of rotation due to the birefringent type coincides with the direction of rotation due to the Faraday effect. optical current transformer. 2. The optical current transformer according to claim 1, wherein a plurality of the coiled bodies are connected in cascade according to the required sensitivity. 3. The optical current transformer according to claim 1, wherein the outer circumferential length of the coiled body is a value obtained by dividing 2π (π is pi) by a propagation constant difference Δβ.