Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Patent
1994-07-21
1996-01-23
Wieder, Kenneth A.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
G01R 3100
Patent
active
054867541
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the measurement of electric current using optical techniques.
The measurement of electrical current is conventionally undertaken by current transformers utilising an iron core with a toroidal winding but a number of disadvantages arise from these devices which lead to operational incompatabilities with modern compact medium or high voltage electrical systems.
The present invention provides a current measuring device comprising a sensor which is coupled via optical fibres to source and detection circuitry and which incorporates a material exhibiting the Faraday magneto-optic effect, the source being arranged to deliver an unpolarised light signal which is subsequently polarised by a first polariser to enable a linearly polarised light signal to be incident on the material, the quantum of rotation in the plane of polarisation imposed on the signal emerging from the material being monitored via a second polariser as a measure of the electrical current flowing through an electrical conductor located adjacent the material.
It is preferred that the sensor comprises a module releasably connected to the optical fibres, the module incorporating a length of magneto-optic crystal material with the first and second polarisers respectively separating the ends of the crystal material from first and second graded-index lenses each arranged to function as a collimator.
Preferably also the module is located within a housing of known dimensions whereby the crystal material can be disposed at a known distance from the adjacent electrical conductor by abutment of the housing against the conductor. Such abutment may be achieved by hand-held or cable clipped means.
The module may be one of a plurality of such modules forming the sensor, different modules having different crystal materials and/or different lengths of crystal material or more than one crystal material whereby different ranges of measurement can be provided and, additionally, inherent temperature and vibration compensation can be achieved.
It is preferred that the optical fibres are of the multi-mode type with non-conducting connectors for attachment to the sensor. The source circuitry preferably includes one or more light-emitting diodes and the detector circuitry preferably includes one or more photo diodes. With this arrangement both the source and the detector components can be selected to be wavelength compatible with the crystal material of the sensor to permit optimal operation of the device. By way of example if the crystal material is YIG (Yttrium Iron Garnet) it is preferred that both the source and detector components operate at a wavelength of about 1300 nm whereas if the crystal material is either TGG (Terbium Gallium Garnet) or BSO (Bismuth Silicate) is is preferred that both the source and detector components operate at a wavelength of about 880 nm.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which;
FIG. 1 schematically illustrates a basic form of sensing device in accordance with the present invention;
FIG. 2 illustrates Verdet characteristics as a function of temperature for two different crystal materials which may be used in the FIG. 1 device;
FIG. 3 illustrates the ratio of the FIG. 2 Verdet constants as a function of temperature;
FIG. 4 illustrates a dual channel sensing device in accordance with the present invention for compensating against temperature effects;
FIG. 5 illustrates a dual wavelength sensing device in accordance with the present invention for compensating against vibration effects;
FIG. 6 illustrates a dual channel sensing device in accordance with the present invention for compensating against cross-talk effects from neighbouring conductors; and
FIG. 7 illustrates a dual channel dual wavelength sensing device in accordance with the present invention providing compensation against the combined effects of temperature, vibration and cross-talk..
Turning now to the drawings in more detail, FIG. 1 illustrates a basic form of c
REFERENCES:
patent: 5149962 (1992-09-01), Maurice
Abstract--Appln. No. 56-139026; Issued Mar. 8, 1983; for "Measuring Apparatus Of Electric Current"; Japan.
Abstract--Appln. No. 89--213114; Issued 23 Jan. 1989; for "High Voltage"; Great Britain.
Abstract--Appln. No. 55-112585; Issued Feb. 26, 1982; for "Current Measuring Device"; Japan.
"Proceedings Of The Institution Of Electrical Engineers"; vol. 125; Oct. 1978 pp. 935-941; A. M. Smith.
Allan Kenneth
Andonovic Ivan
Cruden Andrew J.
McDonald James R.
Porrelli Raymond A.
Instrument Transformers Limited
Khosravi Kourosh Cyrus
Wieder Kenneth A.
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