Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Reexamination Certificate
1998-12-04
2001-06-26
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
C324S072000
Reexamination Certificate
active
06252388
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a voltage sensor for measuring voltage and is particularly suitable for measuring high voltages such as on high-voltage power transmission lines.
BACKGROUND TO THE INVENTION
The list of known high-voltage voltage transducers includes inductive transformers, capacitive dividers or capacitive voltage transformers, and transducers using bulk-optic electric field sensors. The first two transducers suffer from bandwidth restrictions, expensive failure, extensive maintenance, heavy weight, and output variations. They also suffer from the need for substantial insulation that is both expensive and potentially hazardous to the environment (e.g. oil and/or SF
6
gas).
U.S. Pat. No. 4,939,447 issued Jul. 3, 1990 to Bohnert et al (see also the paper “Fiber-optic sensing of voltage by line integration of the electric field” Optics Letters, vol.4, no.5, Mar. 1, 1989, pp. 290-292) describe a voltage sensor that uses multiple fiber-optic piezoelectric electric field sensors to measure voltage. Accuracy is obtained by the use of a plurality of sensors i.e. the Optics Letters publication indicates that to obtain reasonable accuracy 22 sensors connected in series was required.
Pockels cells are known devices that have been used for measuring voltage particularly high voltage, for example see U.S. Pat. No. 5477134 issued to H. Hamada and U.S. Pat. No. 5731579 issued to G. K. Woods. A preferred form of Pockels cell for use in the present invention is an integrated optics Pockels cell such as that described in U.S. Pat. No. 5,029,273 issued Jul. 2, 1991 to Jaeger the disclosure of which is incorporated herein by reference.
BRIEF DESCRIPTION OF THE PRESENT INVENTION
The present invention reduces significantly the deficiencies inherent to the existing high-voltage transducer technology. The simple structure of the invention removes the need for expensive and/or environmentally unfriendly insulation; may be made lighter, allowing for less expensive transportation, installation, and maintenance; and is compatible with existing standoff structures, allowing for easy construction.
When used with compact electric field sensor technology, such as the integrated optics Pockels cell, the invention offers wide bandwidth and easy interfacing with emerging digital technology.
Broadly the invention relates to a method of measuring the value of voltage difference between two points to provide a measured value V of said voltage difference comprising measuring electric field at at least one location in space to provide a measured value of electric field E for each of said at least one location and using a mathematical combination of the value of electric field E for each of said at least one location, said combination being arranged and said at least one location being chosen so that for any given value of said voltage difference between said two points any practical disturbance in electric field influencing the measured value E does not significantly change the measured value V of said voltage difference.
Broadly the present invention also relates to a method of measuring value of voltage difference between two points to provide a value V of said voltage difference comprising choosing at least two locations spaced distances x
i
from one of said two points, measuring and providing values of electric fields E
i
at said at least two locations, applying weighting factors &agr;
i
to said measured electric fields E
i
at said corresponding positions spaced their respective distance x
i
from said one point to obtain a value V based on
V
=
∑
i
=
1
n
α
i
E
i
wherein
n=the number of electric field sensors and is at least 2
x
i
and &agr;
i
are selected so that dE
i
representing any changes in E
i
measured at said at least two locations spaced their respective distance x
i
from said one point, due to external disturbances, are compensated for so that they do not materially affect said value V, so that the value of
∑
i
=
1
n
α
i
dE
i
is sufficiently small, and
x
i
and &agr;
i
are obtained by a method selected from the group consisting of trial-and-error, mathematical or computer modeling.
Preferably x
i
and &agr;
i
are determined using a quadrature method or an integration formula. Preferably the quadrature method is a Gaussian quadrature.
Broadly the present invention relates to an apparatus for measuring voltage comprising an electrically isolating section between a pair of spaced conductors defining opposite ends of said isolating section between which voltage difference is to be measured, at least one electric field sensor which measures electric field at at least one location within said isolating section, said isolating section having a relative dielectric permittivity and geometry which provides sufficient screening of said at least one location from other electric field sources external to the isolating section so that said external electric field sources of practical strength do not materially change said at least one electric field measured at said at least one location.
The present invention relates to an apparatus for measuring voltage comprising an electrically isolating section between a pair of spaced conductors defining opposite ends of said isolating section between which voltage difference is to be measured, at least one electric field sensor which measures electric field at at least one location within said isolating section, said isolating section having a relative dielectric permittivity and geometry which provides sufficient screening of said at least one location from other electric field sources of practical size external to the isolating section so that the error in voltage difference measured under presence of said external sources of electric field is less than 6%.
Preferably, the error in said voltage difference measured is less than 1%, more preferably less than 0.3%.
Broadly the present invention relates to a method and apparatus for measuring voltage comprising an essentially electrically isolating section between a pair of spaced conductors between which voltage difference is to be measured. At least one electric field sensor is positioned within the isolating section. The isolating section has a permittivity and size sufficient to provide screening of the field sensor from other electric field sources external to the isolating section so that the other electric field sources do not materially affect the voltage measurement.
Preferably the electric field sensor is an integrated optics Pockels cell.
Preferably the relative dielectric permittivity of the section is greater than 2, more preferably greater than 20.
Preferably the isolating section is a hollow isolating section in which the electric field sensor is mounted.
Preferably there is one said electric field sensor positioned in said isolating section spaced from one of the conductors a distance of between 25 and 75% of distance L between the pair of conductors.
Preferably there are a plurality of the electric field sensors positioned in the isolating section in spaced relationship along a longitudinal axis of the isolating section between the two conductors.
Preferably the number of electric field sensors in the isolating section is two, a first sensor positioned in said isolating section spaced from the one conductor by a distance of between 50 and 100% of distance L between the pair of conductors and a second electric field sensors positioned in the isolating section spaced from the one conductor by a distance of between 0 and 50% of distance L between the pair of conductors.
Preferably the number of said electric field sensors in the isolating section is three, one positioned in said isolating section spaced from the one conductor a distance of between 70 and 100% of distance L between the conductors, another electric field sensor positioned in the isolating section spaced from the one conductor by a second distance of between 30 and 70% of distance L between the pair of conductors and yet another elect
Chavez Patrick Pablo
Cherukupalli Sudhakar Ellapragada
Jaeger Nicolas August Fleming
Polovick Gregory Samuel
Rahmatian Farnoosh
Brown Glenn W.
NxtPhase Corporation
Rowley C. A.
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