Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Patent
1992-02-05
1993-08-17
Nguyen, Vinh
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
324117R, 324158R, F01R 3100
Patent
active
052372650
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a fiber optics arrangement for measuring the intensity of an electric current while utilizing the Faraday effect, the magnetic field, which surrounds the conductor through which the current flows, influencing the polarization condition of the light, the path of which leads through the core of an optical fiber which surrounds the conductor in the form of a coil, the light, which is coupled out of the optical fiber, being divided by a beam splitter into two partial light beams, the intensities of which, after passing through one polarizer respectively, being measured by one photodetector respectively.
Arrangements of this type are used particularly in high-voltage systems for measuring currents in lines on a high-voltage potential. Since the beam waveguides consist of glass of which it is known that it is a good electric insulator, no problems exist concerning the insulation of the indicating apparatuses connected with the earth potential with respect to the conductors disposed at the high-voltage potential the current of which is to be measured and indicated.
This type of an arrangement is known from the DE-AS 22 61 151 in which light from a light source is guided through a polarizer to a semitransparent plate. From there, the polarized light arrives in an optical fiber (called "beam waveguide" there) which is partially wound into a coil, a high-voltage conductor extending in its axis and the current to be measured flowing in this conductor. At its end, this fiber coil is provided with a metallized surface, and a mirror is arranged there. The polarized light passes through the whole optical fiber, a rotation of the polarization plane taking place inside the coil-shaped part of the fiber as a result of the Faraday effect as a function of the magnetic field which the current generates which flows in the conductor. At the end of the coil, the light beam is reflected and passes through the coil again in which case another rotation of the polarization plane occurs. The light which is rotated in its polarization plane emerges from the optical fiber, penetrates the semitransparent plate and arrives in an analyzing device which determines and indicates the angle between the polarization plane of the light entering into the optical fiber and the polarization plane of the light emerging from the fiber, in which case the size of this angle is proportional to the path integral above the magnetic field strength.
From the DE-AS 28 35 794, a fiber optics arrangement for the measuring of the intensity of an electric current by utilizing the Faraday effect is also known in which the magnetic field surrounding the conductor through which the current flows influences the polarization condition of the light, the path of which leads through the core of an optical fiber which surrounds the conductor in the form of a coil. In contrast to the DE-AS 22 61 151, in the case of this arrangement, no reflecting surface is provided at the one end of the fiber, but the light is coupled in at the one end and is coupled out again at the other end, in which case the coil wound from the optical fiber must have twice the number of windings in order to obtain the same angle of rotation of the polarization plane because the light passes through the coil only once.
In both above-explained cases, the analyzing device consists of a beam splitter which divides the coupled-out light into two partial light beams, the polarization planes of which, after passing through two polarizers which a oriented perpendicularly with respect to one another, stand perpendicularly on one another, and the intensities of which are measured by means of two photodetectors, the photocurrents of which will then be current-carrying conductor is N. The material-dependent proportionality constant is indicated by ##EQU1## the output signal U.sub.A is then obtained which is a sinusoidal function of the current to be measured.
In order to keep expenditures low for the calculations which have to take place in real-time, the sensor is dimensioned such that
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Hirsch Holger
Peier Dirk
MWB Messwandler-Bau A.G.
Nguyen Vinh
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