Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Patent
1997-02-18
1999-10-05
Patidar, Jay
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
3242441, 250225, 356364, G01R 3302, G01R 3100, G01R 1524
Patent
active
059630264
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a method and device for the measurement of currents in at least two measuring ranges in a conductor.
Optical measurement devices are known for measuring an electric current in a conductor using the Faraday effect, also referred to as magneto-optical current converters. The Faraday effect is the rotation of the polarization plane of linearly polarized light caused by a magnetic field. The rotation angle is proportional to the line integral over the magnetic field along the path traveled by light with the Verdet constant as the proportionality constant. The Verdet constant in general depends on the material, temperature, and wavelength. A Faraday element made of an optically transparent material, such as glass, for example, is arranged near the conductor to measure the current. The magnetic field generated by the current causes the plane of polarization of the linearly polarized light emitted by the Faraday element to rotate by an angle that can be analyzed as a measuring signal. In general, the Faraday element surrounds the conductor, so that the light used for measurement travels around the conductor in a basically closed path. The absolute value of the rotation angle in this case is directly proportional, with a good approximation, to the amplitude of the current to be measured. The Faraday element can be designed as a solid glass ring around the conductor, through which the light passes once only, or it can also surround the conductor in the form of a measuring coil made of a light-conducting monomode fiber (fiber coil). In a solid Faraday element, the measuring range of the current converter is adjusted by choosing the appropriate material; smaller Verdet constants are used for larger currents than those used for smaller currents. In the case of a measuring coil, the measuring range of the current converter can also be adjusted via the number of spires in the coil, since the Faraday rotation angle is also proportional to the number of spires, i.e., the number of turns of the light around the conductor. A current range over which the Faraday angle is a unique function of the current is selected as the measuring range. Since techically no distinction can be made between two polarization states of the measuring light that are antiparallel to one another, i.e., rotated by an angle .PI. in relation to one another, the measuring range of the magneto-optical current converter corresponds to a rotation angle interval with a maximum length of .PI./2.
In a magneto-optical current converter known from European Patent B-0,088,419, two Faraday glass rings are arranged in parallel around a common conductor. Both glass rings are made of Faraday materials with different measurement sensitivity and therefore different current measuring ranges. Each Faraday glass ring has a transmitter unit for transmitting linearly polarized measuring light into the glass ring, a Rochon prism, a Wollaston prism or another polarizing beam splitter as an analyzer to split the measuring light rotated after passing through the respective glass ring into two sub-beams with different polarization planes, photodiodes for converting the sub-beam signals of each of the two Faraday glass rings into electrical signals, as well as an analyzer unit to calculate the measurement signal for the corresponding Faraday rotation angle. The two measurement signals of the two Faraday glass rings are supplied to an OR gate, which provides a maximum signal of the two measurement signals. A larger measuring range can be covered with this maximum signal. Different measuring ranges of the two glass rings can also be achieved even using the same glass material for both glass rings, by using measuring light of different wavelengths. The wavelength-dependence of the Faraday rotation is made use of in this case.
For today's measuring technology, current converters for measuring and counting applications should be able to measure nominal currents in a predefined measuring range of up to 2000 A, for example, with a hi
REFERENCES:
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patent: 5051577 (1991-09-01), Lutz et al.
Chatrefou et al., "A Great Step In The Industrialization of Optical Measuring Reducers," International Conference of Large High Voltage Electric Systems, CIGRE 1988, pp. 1-10.
Bush, S. et al., "Dual-channel Faraday-effect current sensor capable of simultanoues measurement of two independent currents," Optical Society of America, Jun. 15, 1991, vol. 16, No. 12, 955-957.
Bartelt Hartmut
Bosselmann Thomas
Patidar Jay
Siemens Aktiengesellschaft
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