JPH0216471B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current measuring device that detects a current flowing in a conductor by observing Faraday rotation by a magneto-optical element, and measures the amount of current. By using a highly sensitive rare earth iron garnet mixed crystal with small temperature changes in optical properties for the element, we can obtain a highly reliable and compact current measuring device that operates stably over a wide temperature range. be.

Recently, the Fraday effect has been used to replace the conventionally well-known current transformer CT that measures high voltage and current.
A method for non-contact voltage and current measurement using light as a medium has been proposed. Figure 1 shows the principle of the method for measuring voltage and current using the Faraday effect. 1st
In the figure, a magneto-optical element 1 is placed in a magnetic field H generated in proportion to the amount of current flowing through a conductor. Light that has been linearly polarized (indicated by an arrow) by a polarizer 2 is passed through the magneto-optical element 1 .

Due to the Faraday effect, the plane of polarization is rotated in proportion to the magnetic field strength H. Its rotation angle is indicated by θ. The rotated polarized light passes through a polarizer 2 and an analyzer 3 whose transmission polarization direction is different, and the rotation angle θ
The magnitude of is converted into a change in light amount.

For example, when the transmitted polarization directions of the polarizer 2 and the analyzer 3 are different by 45 degrees, the change in the amount of light after passing through the analyzer 3 is expressed by the following equation.

ΔI=κsin2θ...(1) Here, θ=VH, ΔI is the amount of change in light intensity, κ is the proportionality constant, θ is the Faraday rotation angle [degrees], V is the Werde constant [degrees/cmOe], and H is the magnetic field strength [degrees]. Oe〕,
is the thickness [cm] of the magneto-optical element. Also, V is called the Werdet constant, and its unit is [°/cm
Oe], which represents the sensitivity of the magneto-optical element.

Conventionally, lead glass, paramagnetic glass, or Y ₃ Fe ₅ O ₁₂ crystal is often used as a magneto-optical element. Paramagnetic glass, Y ₃ Fe ₅ O ₁₂ Although the Welde constant of lead glass does not change with temperature, it is small at V = 0.15 × 10 ^-2 ° / cmOe and has the disadvantage of increasing the size of the device.
The Welde constant of a crystal changes greatly with temperature, and the biggest drawback of current measuring devices using these magneto-optical elements is that the measurement sensitivity changes with respect to changes in ambient temperature, resulting in large measurement errors.

For example, Y ₃ Fe ₅ O ₁₂ crystal has a Werde constant of V=0.21°/cmOe (room temperature), which is higher than that of glass.
Although it is two orders of magnitude larger, as shown in Figure 2,
The temperature change is large. It shows a change of ±12% in the temperature range of -25℃ to +125℃. Therefore,
Current measuring devices using Y ₃ Fe ₅ O ₁₂ crystals have large measurement errors, making them difficult to use in situations where ambient temperature changes are large and high reliability is required, such as when measuring current on high-voltage power transmission lines. is not suitable.

The present invention has been made in view of the above _- mentioned conventional drawbacks, and is _a rare earth iron garnet _mixed crystal _{( Tb}
(0.1≦X≦0.3), we have realized a highly reliable current measuring device that is stable against temperature changes. FIG. 3 shows the temperature change of the Werde's constant of (Tb _X Y _1-X ) ₃ Fe ₅ O ₁₂ with respect to the terbium concentration.
Temperature range is -25℃ to +125℃, wavelength 1.153μ
It is m. As shown in Figure 3, (0.1≦X≦0.3)
In this case, the change in Weerde's constant due to temperature is suppressed to less than ±6%, and the temperature change is less than half that of Y ₃ Fe ₅ O ₁₂ , which is practically satisfactory for current measurement. is less than ±1.7%. Also, the Werde constant of rare earth garnet mixed crystal is V=0.29°/cmOe
When used as _{a current} measuring device, it is possible to increase the sensitivity _and make the device more compact.

A current measuring device according to an embodiment of the present invention will be described below.

FIG. 4 shows the configuration of a current measuring device according to an embodiment of the present invention. In the same figure, 1 is (Tb _0.19
Y _00.81 ) ₃ Fe ₅ O ₁₂ is a magneto-optical element made of crystal,
Both sides are polished parallel to each other so that the thickness is 1 mm. 2 is a polarizer provided on one end surface of the magneto-optical element 1, and 3 is a polarizer provided on the other surface of the magneto-optical element 1, and is installed so that the transmitted polarization direction is inclined by 45 degrees with respect to the polarizer 2. It is a photon. polarizer,
A Glan-Thompson prism, which has good polarization characteristics against temperature changes, was used as the analyzer. A magneto-optic converter composed of a magneto-optical element 1, a polarizer 2, and an analyzer 3 is arranged at a distance of 60 cm from the current passing conductor 4. Reference numerals 5 and 6 denote self-occurring lenses for converting the light incident on the magneto-optic conversion section or the light transmitted through the magneto-optic conversion section into parallel light beams. 7 and 8 are optical fibers forming an optical transmission path. 9 is a light source that inputs light into the fiber 7, and the wavelength of the light is (Tb _0.19 Y _0.81 ) ₃ Fe ₅ O ₁₂ Among the wavelength range of 1.0 μm to 1.6 μm that has good transmittance to the crystal, the wavelength is 1.153 μm. μm
I used the one from Reference numeral 10 denotes a light detection means for detecting the light output transmitted through the magneto-optic converter, and converts it into an electric signal according to the light intensity detected here.

In such a configuration, by changing the distance between the current passing conductor 4 and the magneto-optic conversion section or by changing the thickness of the magneto-optic element 1, it was possible to detect a current amount of up to 100 KA order. In this case, the measurement error was only ±2% or less for a temperature change from room temperature to 100°C.

As is clear from the above description, according to the current measuring device of the present invention, a current conductor can be detected by using ordinary current measuring means without using any special current detecting means around the magneto-optical element. It is possible to measure the amount of current in the air with high sensitivity and high precision without being affected by environmental temperature changes, and has great industrial value.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the basic principle of a current measuring device using the Faraday effect, and Figure 2 is a diagram for explaining the basic principle of a current measuring device using the Faraday effect.
A diagram showing the temperature change of the Werde constant of Y ₃ Fe ₅ O ₁₂ ,
FIG. 3 is a diagram plotting the temperature change of the Werde constant of (Tb _X Y _1-X ) ₃ Fe ₅ O ₁₂ against the terbium concentration X, and FIG. FIG. 2 is a diagram showing the configuration of a measuring device. DESCRIPTION OF SYMBOLS 1... Magneto-optical element, 2... Polarizer, 3... Analyzer, 4... Current passing conductor, 7, 8... Optical fiber, 9... Light source, 10... Light detection means.

Claims (1)

[Claims] 1 The general formula (Tb _X Y _1-X ) ₃ Fe ₅ O ₁₂ (0.1≦X
≦0.3);
an optical transmission path provided at both ends of the magneto-optic converter; a light generating means for inputting light into the optical transmission path;
and a detection means for detecting an output after the incident light passes through the magneto-optic conversion section, and by arranging the magneto-optic conversion section near the current conductor, the amount of current flowing through the current conductor can be detected by the detection section. A current measuring device characterized by detecting.