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Patent 2401771 Summary

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(12) Patent: (11) CA 2401771
(54) English Title: ELECTRO-OPTIC VOLTAGE SENSOR
(54) French Title: VOLTMETRE ELECTRO-OPTIQUE
Status: Expired
Bibliographic Data
(51) International Patent Classification (IPC):
  • G01R 29/00 (2006.01)
  • G01R 19/00 (2006.01)
  • G01R 29/08 (2006.01)
(72) Inventors :
  • WOODS, GREGORY K. (United States of America)
  • RENAK, TODD W. (United States of America)
(73) Owners :
  • LOCKHEED IDAHO TECHNOLOGIES COMPANY (United States of America)
(71) Applicants :
  • LOCKHEED IDAHO TECHNOLOGIES COMPANY (United States of America)
(74) Agent: SMART & BIGGAR
(74) Associate agent:
(45) Issued: 2008-09-30
(22) Filed Date: 1996-12-05
(41) Open to Public Inspection: 1997-06-19
Examination requested: 2002-10-02
Availability of licence: N/A
(25) Language of filing: English

Patent Cooperation Treaty (PCT): No

(30) Application Priority Data:
Application No. Country/Territory Date
08/569,338 United States of America 1995-12-08
08/750,152 United States of America 1995-12-11

Abstracts

English Abstract

An electro-optic voltage sensor for achieving voltage measurement without significant error contributions from neighboring conductors or environmental perturbations. The voltage sensor includes a transmitter (1), a sensor (4), a detector (43, 44) and a processor (62). The transmitter (1) produces a beam of electromagnetic radiation which is routed into a sensor (4). Within the sensor (4), the beam undergoes the Pockels electro-optic effect. The electro--optic effect produces a modulation of the beam's polarization, which is in turn converted to a pair of independent conversely-amplitude-modulated signals, from which the voltage of the E-field is determined by the processor (62). The use of converse AM signals enables the signal processor (62) to better distinguish signal from noises. The sensor (4) converts, the beam by splitting the beam in accordance with the axes of the beam's polarization state (an ellipse whose ellipticity varies between -1 and +1 in proportion to voltage) into at least two AM signals. These AM signals are fed into a signal processor (62) and processed to determine the voltage between ground conductor and the conductor (2) on which voltage is being measured.


French Abstract

Un voltmètre électro optique pour mesurer la tension sans contribuer à des erreurs significatives provenant de conducteurs se trouvant à proximité ou de perturbations environnementales. Le voltmètre comporte un émetteur, (1), un capteur (4), un détecteur (43, 44) et un processeur (62). L'émetteur (1) produit un faisceau de radiation électromagnétique qui est acheminé dans un capteur (4). € l'intérieur du capteur (4), le faisceau subit l'effet électro-optique linéaire ou effet Pockels. L'effet électro optique produit une modulation de la polarisation du faisceau, qui à son tour est convertie en une paire de signaux indépendants à modulation d'amplitude inverse, à partir desquels la tension du champ électrique est déterminée par le processeur (62). L'utilisation de signaux à modulation d'amplitude inverse permet au processeur de signaux (62) de mieux distinguer les signaux des bruits. Le capteur (4) convertit le faisceau en le fractionnant en fonction des axes de son état de polarisation (une ellipse dont le caractère elliptique varie entre 1 et +1 en fonction de la tension) dans au moins deux signaux de modulation d'amplitude. Ces signaux de modulation d'amplitude sont acheminés dans un processeur de signaux (62) et traités pour déterminer la tension entre le conducteur mis à la terre et le conducteur (2) sur lequel la tension est mesurée.

Claims

Note: Claims are shown in the official language in which they were submitted.



28

CLAIMS:


1. A sensor head for use in combination with at least
one beam of electromagnetic radiation for detecting presence
and magnitude of electric field and voltage, said sensor

head comprising:


polarizing means for polarizing said at least one
beam such that said at least one beam comprises at least two
beam components in at least two orthogonal planes;


transducing means configured for disposition in an
electric field, but out of contact with electrical
conductors generating said electric field, and for receiving
said at least one beam from said polarizing means and
inducing a first differential phase shift of the beam
components which varies in magnitude in response to the
magnitude of an electric field; and


first reflecting means for receiving said at least
one beam from said transducing means and reflecting said
beam back into said transducing means.


2. The sensor head as in claim 1, wherein the sensor
head further comprises: quarter wave retarding means for
biasing the beam's polarization such that zero electric
field magnitude on the transducer corresponds to a circular
polarization state.


3. The sensor head as in claim 1, wherein said first
reflecting means comprises a material having at least one
surface, a reflective coating disposed on at least one
surface of said reflecting means wherein said reflective
coating accomplishes reflection of said beam.


4. The sensor head as in claim 2, wherein said
quarter wave retarding means resides within said first


29

reflecting means, said first reflecting means further
comprising:


phase shifting means for shifting the phase of at
least one of said beam components to thereby achieve a
second differential phase shift between said beam components
of one-quarter of a wavelength, said quarter wavelength
shift comprising at least a single order shift.


5. The sensor head as in claim 2, wherein said
quarter wave retarding means comprises:


a quarter wave plate disposed at a point within a
path of said beam following said polarizing means for
shifting the phase of at least one of said beam components
one-quarter of a wavelength, said quarter wavelength shift
comprising at least a single order shift.


6. The sensor head as in claim 1, wherein said
transducing means further comprises a Pockels transducing
material.


7. The sensor head as in claim 6, wherein said
Pockels transducing material is a material selected from a
group consisting of:


Lithium Niobate (LiNbO3),

Ammonium Dihydrogen Phosphate (NH4H2PO4),
Ammonium Dideuterium Phosphate (NH4D2PO4),
Potassium Dideuterium Phosphate (KD2PO4),
MgO-doped Lithium Niobate (MgO-LiNbO3),
Lithium Tantalate (LiTaO3),

Electro-optic polymers, and
Organic material.


8. The sensor head as in claim 1, wherein said sensor
head further comprises:


30

translucent means disposed between the polarizing

means and the transducing means for receiving said at least
one beam from said polarizing means and transmitting said
beam to said transducing means.


9. The sensor head as in claim 8, wherein said
translucent medium further comprises a material that is
substantially non-birefringent and nonconductive.


10. The sensor head as in claim 1, wherein said sensor
head further comprises:


beam separation means for separating the beam
components corresponding to a major axis and a minor axis of
a polarization ellipse of said at least one beam, forming at
least two signals therefrom.


11. The sensor head as in claim 10, wherein said
sensor head further comprises:


translucent means disposed between the transducing
means and the separation means for receiving said at least
one beam from said transducing means and transmitting said
beam to said separation means.


12. The sensor head as in claim 10 wherein said at
least two signals comprise independent converse amplitude-
modulated signals.


13. The sensor head as in claim 9 wherein said
translucent means comprises at least one material selected
from a group consisting of: fused quartz, fused silica, and
nonconductive translucent media.


14. The sensor head as in claim 9 wherein said
translucent means comprises at least one fiber selected from


31

a group consisting of: collimator-coupled low-birefringence
fiber and polarization-maintaining optic fiber.


15. A sensor head for use in combination with at least
one beam of electromagnetic radiation for detecting
magnitude of an electric field, said sensor head comprising:

polarizing means for polarizing said at least one
beam such that said at least one beam comprises at least two
beam components in at least two orthogonal planes;

transducing means configured for disposition in an
electric field, but out of contact with electrical
conductors generating said electric field, and for receiving
said at least one beam from said polarizing means and
inducing a differential phase shift of the beam components
which varies in magnitude in response to the magnitude of an
electric field; and

first reflecting means for receiving said at least
one beam from said polarizing means and reflecting said beam
into said transducing means.


16. The sensor head as in claim 15, wherein the sensor
head further comprises:


quarter wave retarding means for biasing the
beam's polarization such that zero electric field magnitude
on the transducing means corresponds to a circular
polarization state.


17. A sensor head for use in combination with at least
one beam of electromagnetic radiation for detecting
magnitude of an electric field, said sensor head comprising:


32

polarizing means for polarizing said at least one
beam such that said at least one beam comprises at least two
beam components in at least two orthogonal planes;

transducing means configured for disposition in an

electric field, but out of contact with electrical
conductors generating said electric field, and for receiving
said at least one beam from said polarizing means and
inducing a differential phase shift of the beam components
which varies in magnitude in response to the magnitude of an
electric field;


beam separation means for receiving said at least
one beam and separating the beam components and forming at
least two signals therefrom; and


first reflecting means for receiving said at least
one beam from said transducing means and reflecting said
beam into said beam separation means.



18. The sensor head as in claim 17, wherein the sensor
head further comprises:


quarter wave retarding means for biasing the
beam's polarization such that zero electric field magnitude
on the transducing means corresponds to a circular
polarization state.


19. A method for detecting magnitude of an electric
field using at least one beam of polarized electromagnetic
radiation having at least two beam components propagating in
at least two orthogonal planes, comprising the steps of:


(a) imposing an electric field upon at least one
transducing means by disposing said at least one transducing
means into an apparatus containing electric flux
proportional to voltage, wherein said at least one


33

transducing means is out of contact with electrical
conductors generating said electric field;


(b) passing said beam through said at least one
transducing means;


(c) inducing a differential phase shift between
the beam components when said beam passes through said
transducing means in said electric field, said differential
phase shift indicating a presence and a magnitude of said E-
field;


(d) reflecting said beam after said beam has
passed through the transducing means with a reflective
means, so that said beam is directed back into the

transducing means, thereby causing said beam to reenter the
transducing means;


(e) separating beam components into at least one
pair of converse amplitude modulated (AM) signals, said AM
signals corresponding to a major axis and a minor axis of
said beam's polarization ellipse, whose ellipticity

modulates between -1 and +1 in proportion to voltage,
wherein an intensity along the minor axis modulates
conversely to an intensity along the major axis;


(f) transmitting said AM signals, whereby the
electric field magnitude (and hence voltage) can be
ascertained.

Description

Note: Descriptions are shown in the official language in which they were submitted.



CA 02401771 2002-10-02

1
ELECTRO-OPTIC VOLTAGE SENSOR
BACKGROUND OF THE INVENTION
1. The Field of the Invention.
The present invention pertains generally to the
field of voltage sensors and more particularly to a
voltage sensor system which utilizes the Pockels
electro-optic effect to measure voltage.

2. The Background Art.
High-accuracy measurement of high voltage has
traditionally been accomplished using iron-core ferro-
magnetic potential transformers. These devices have
substantially limited dynamic range, bandwidth,
linearity, and electrical isolation. During
electrical fault conditions these transformers can
conduct dangerous levels of fault energy to downstream
instrumentation and personnel, posing an additional
liability.
A variety of optic sensors for measuring voltage
have been developed in attempts to offer the power
industry an alternative to the conventional
transformer technology. Generally, these voltage
sensor systems require that direct electrical contact
be made with the energized conductor. This contact is
made necessary by the use of a voltage divider which
is utilized to connect the sensing element with the
energized conductor on which a measurement is to be
made. Direct electrical contact with the conductor


CA 02401771 2002-10-02

2
may alter or interrupt the operation of the power
system by presenting a burden or load.
In addition to the disadvantages associated with
direct electrical contact with the energized
conductor, prior art voltage sensor systems are
typically bulky, particularly in extremely high
voltage applications. This is true because the size
of the voltage divider required is proportional to the
voltage being measured. The size of such systems can
make them difficult and expensive to install and house
in substations.
Many prior art sensors are based upon the
electrostrictive principle which utilize
interferometric modulation principles. Unfortunately,
interferometric modulation is extremely temperature
sensitive. This temperature sensitivity requires
controlled conditions in order to obtain accurate
voltage measurements. The requirement of controlled
conditions limits the usefulness of such systems and
makes them unsuited for outdoor or uncontrolled
applications. In addition, interferometric modulation
requires a highly coherent source of electromagnetic
radiation, which is relatively expensive.
open-air E-field based sensors have also been
developed, but lack accuracy when used for measuring
voltage because the open-air E-field used varies with
many noisy parameters including ambient dielectric
constant, adjacent conductor voltages, moving
conductive structures such as passing vehicles, and
other electromagnetic noise contributions.
Systems which utilize mechanical modulation of
the optical reflection within an optic fiber have also
been developed. Among other drawbacks, the reliance
of such systems on moving parts is a significant
deterrent to widespread use.
It would therefore be an advantage in the art to
provide a system which does not require direct


CA 02401771 2002-10-02

3
electrical contact with the energized conductor, is
compact, operates in a variety of temperatures and
conditions, is reliable, and is cost effective.

OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the present
invention to provide an electro-optic voltage sensor
system which does not require contact with a
conductor.
It is a further object of the present invention
to provide such an electro-optic voltage sensor system
which is capable of use in a variety of environmental
conditions.
It is a still further object of the present
invention to provide such an electro-optic voltage
sensor system which can be employed to accurately
measure high voltages without use of dedicated voltage
division hardware.
It is an additional object of the present
invention to provide such an electro-optic voltage
sensor system which minimizes the electronics needed
for implementation.
It is a further object of the present invention
to provide a sensor system capable of being integrated
with existing types of high voltage power transmission
and distribution equipment so as to reduce or
eliminate the need for large stand-alone voltage
measurement apparatus.
It is yet another object of the present invention
to provide a sensor system capable of being integrated
with existing types of power transmission and
distribution equipment.
These and other objects of the present invention
will become more fully apparent from the following
description and appended claims or may be learned by
the practice of the invention as set forth herein.


CA 02401771 2002-10-02

4
While the present invention is described in terms
of a sensor system, it is to be understood that the
subject apparatus and method may be used in any field
of electrical or optical application. Those having
ordinary skill in the fie:L:d of this invention will
appreciate the advantages of the invention, and its
application to a wide variety of electrical uses.
The above objects and others not specifically
recited are realized in a specific illustrative
embodiment of an Electro-Optical Voltage Sensor System
whereby one may measure the voltage difference (or
electrical potential difference) between objects or
positions. Voltage is a function of the electric
field (hereinafter "electric field" shall be indicated
"E-field") and the geometries, compositions and
distances of the conductive and insulating matter.
Where, as in the present invention, the effects of an
E-field can be observed, a voltage measurement can be
calculated.
The invention employs a transmitter, a sensor, a
detector, and a signal processor. The transmitter
produces a beam of electromagnetic radiation which is
routed into the sensor. Although this electromagnetic
radiation used in the present invention can comprise
any wavelengths beyond the visible spectrum, the term
"light" will be used hereinafter to denote
electromagnetic rad_iation for the purpose of brevity.
The beam undergoes polarization before it undergoes an
electro-optic effect in transducer material which is
included in the sensor. Tn the polarized beam, the
light has at least two components which propagate
along at least two orthogonal axes, thus forming at
least two orthogonal planes within the beam. The
electro-optic effect occurs when the sensor, and in
particular the transducer material, is placed in an E-
field, and is observable as a differential phase shift
of the orthogonal beam components (the two components


CA 02401771 2006-12-15
68483-34D

are shifted in opposite directions). The planes of
propagation are the object of the differential phase shift,
also called phase modulation. The differential phase shift
causes a corresponding change in the beam's polarization.

5 The polarization change is in turn converted into a set of
amplitude modulated (AM) signals of opposing polarity that
are transmitted out of the sensor. The detector converts
the set of optical AM signals into electrical signals from
which the voltage is determined by the signal processor.

The sensor processes the beam by splitting the
beam in accordance with the components of the orthogonal
polarization planes into at least two AM signals. In the
preferred embodiment, these AM signals are then converted
into digital signals, fed into a digital signal processor

and mathematically processed into a signal proportional to
the voltage which produced the E-field.

In a preferred embodiment of the sensor, the beam
is routed through the transducer material along an initial
axis and then reflected by a retroreflector back along a

second axis generally parallel to the initial axis.
In accordance with an aspect of the present
invention, there is provided a sensor head for use in
combination with at least one beam of electromagnetic
radiation for detecting presence and magnitude of electric

field and voltage, said sensor head comprising: polarizing
means for polarizir.ig said at least one beam such that said
at least one beam comprises at least two beam components in
at least two orthogonal planes; transducing means configured
for disposition in an electric field, but out of contact

with electrical conductors generating said electric field,
and for receiving said at least one beam from said


CA 02401771 2006-12-15
68483-34D

5a
polarizing means and inducing a first differential phase
shift of the beam components which varies in magnitude in
response to the magnitude of an electric field; and first
reflecting means for receiving said at least one beam from

said transducing means and reflecting said beam back into
said transducing means.

In accordance with another aspect of the present
invention, there is further provided a sensor head for use
in combination with at least one beam of electromagnetic

radiation for detecting magnitude of an electric field, said
sensor head comprising: polarizing means for polarizing said
at least one beam such that said at least one beam comprises
at least two beam components in at least two orthogonal

planes; transducing means configured for disposition in an
electric field, but out of contact with electrical
conductors generating said electric field, and for receiving
said at least one beam from said polarizing means and
inducing a differential phase shift of the beam components
which varies in magnitude in response to the magnitude of an

electric field; and first reflecting means for receiving
said at least one beam from said polarizing means and
reflecting said beam into said transducing means.

In accordance with another aspect of the present
invention, there is further provided a sensor head for use
in combination with at least one beam of electromagnetic

radiation for detecting magnitude of an electric field, said
sensor head comprising: polarizing means for polarizing said
at least one beam such that said at least one beam comprises
at least two beam components in at least two orthogonal

planes; transducing means configured for disposition in an
electric field, but out of contact with electrical
conductors generating said electric field, and for receiving
said at least one beam from said polarizing means and


CA 02401771 2006-12-15
68483-34D

5b
inducing a differential phase shift of the beam components
which varies in magnitude in response to the magnitude of an
electric field; beam separation means for receiving said at
least one beam and separating the beam components and

forming at least two signals therefrom; and first reflecting
means for receiving said at least one beam from said
transducing means and reflecting said beam into said beam
separation means.

In accordance with another aspect of the present
invention, there is further provided a method for detecting
magnitude of an electric field using at least one beam of
polarized electromagnetic radiation having at least two beam
components propagating in at least two orthogonal planes,
comprising the steps of: (a) imposing an electric field upon

at least one transducing means by disposing said at least
one transducing means into an apparatus containing electric
flux proportional to voltage, wherein said at least one
transducing means is out of contact with electrical
conductors generating said electric field; (b) passing said

beam through said at least one transducing means; (c)
inducing a differential phase shift between the beam
components when said beam passes through said transducing
means in said electric field, said differential phase shift
indicating a presence and a magnitude of said E-field; (d)

reflecting said beam after said beam has passed through the
transducing means with a reflective means, so that said beam
is directed back in.to the transducing means, thereby causing
said beam to reenter the transducing means; (e) separating
beam components into at least one pair of converse amplitude

modulated (AM) signals, said AM signals corresponding to a
major axis and a minor axis of said beam's polarization
ellipse, whose ellipticity modulates between -1 and +1 in
proportion to voltage, wherein an intensity along the minor


CA 02401771 2006-12-15
68483-34D

5c
axis modulates conversely to an intensity along the major
axis; (f) transmitting said AM signals, whereby the electric
field magnitude (and hence voltage) can be ascertained.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and
advantages of the invention will become apparent from a
consideration of the subsequent detailed description
presented in connection with the accompanying drawings in
which:

FIG. 1 is a diagram of the electro-optical voltage
sensor system shown in a generalized high voltage
application scenario. The diagram was made in accordance
with the principles of the present invention.

FIG. 2 is a diagram of an alternative embodiment
of the electro-optical voltage sensor system (in the same
generalized application scenario) made in


CA 02401771 2002-10-02
6

accordance with the principles of the present
invention.
FIG. 3 is a diagram of the light polarizing beam
splitter of FIGS. 1 and 2.
FIG. 4 shows a partially sectioned side view of a
collimator of FIG. 2 and also FIGS. 7 and 8, below.
FIG. 5 is a diagram of one embodiment of the
transducer of FIGS. 1 and 2, wherein transducing
material in only one orientation is shown.
FIG. 6 is a diagram of one embodiment of the
transducer in FIGS. 1 and 2, wherein transducing
material in two orientations is shown.
FIG. 7a is a top-down schematic view of one
embodiment of the sensor head of FIG. 2.
FIG. 7b is a top-down schematic view of one
embodiment of the sensor head of FIG. 2.
FIG. 7c is a top-down schematic view of one
embodiment of the sensor head of FIG. 2.
FIG. 8 is a top-dowri schematic view of one
embodiment of the sensor head of FIG. 1.
FIG. 9 is a cross-sectional, schematic view of
one embodiment of the E-f:ield originator of FIGS. 1
and 2, as a shielded joint.
FIG. 10 is a top perspective, partially schematic
view of one embodiment of the E-field originator of
FIGS. 1 and 2, as a terminator.
FIG. 11 is a cross-sectional side view of one
embodiment of the E-field. originator of FIGS. 1 and 2,
as a bushing.
FIG. 12 is a sectional, partially schematic, side
view of one embodiment of the E-field originator of
FIGS. 1 and 2, as a shielded bus or shielded cable.
FIG. 13 is a sectional, partially schematic, side
view of one embodiment of the E-field originator of
FIGS. 1 and 2, as a gas or oil-insulated switchgear.


CA 02401771 2002-10-02

7
FIG. 14 is a sectional, partially schematic, side
view of one embodiment of the E-field originator of
FIGS. 1 and 2, as a duct-enclosed bus.
FIG. 15 is a side view of one embodiment of the
E-field originator of FIGS. 1 and 2, as a clamp-on
apparatus.
FIG. 16 is an alternative embodiment of the
electro-optical voltage sensor of FIG. 1 having a
current detector.
DETAILED DESCRIPTION
A preferred embodiment in accordance with the
present invention is illustrated in FIG. 1, which is a
diagram of the electro-optical voltage sensor system.
There is shown a transmitter 1, which is a
transmitting means that transmits a beam of
electromagnetic radiation (the beam is not shown in
FIG. 1 but generally designated as 12 elsewhere) and a
sensing means, shown in FIG. 1 as a sensor head 4. In
the preferred embodiment the beam is routed from the
transmitter 1 to the sensor head 4 by a polarization
maintaining (PM) fiber 18. In an alternative
embodiment the PM fiber 18 is replaced by low-
birefringence fiber. Another alternative embodiment
whose cost/performance characteristic may be quite
different and better suited to certain applications,
entails replacement of the PM fiber 18 by single-mode
or multi-mode optic fiber. The PM fiber 18 directs
the beam from the transmitter 1 into the sensor head
4. Optical signals are :routed from the sensor head 4
by a pair of either single-mode or multi-mode optical
fibers, shown as 37 and 38. The optical fibers 18,
37, and 38 electrically isolate the sensor head 4 from
the transmitter 1 and the rest of the detection
system, providing further protection to personnel and
equipment from the dangers of high voltage systems.


CA 02401771 2002-10-02

8
The sensor head of the preferred embodiment of
FIG. 1 is shown in greater detail in the top-down
schematic view of FIG. 8, where the preferred
embodiment of the sensor head is generally depicted at
4. The sensor head 4 comprises a polarizer 6, a
translucent medium 13, a transducer 5, a retro-
reflector generally depicted at 10, a polarizing beam
splitter 80 and beam reflector 14. A collimator 26 is
connected to the PM fiber 18 and transmits the beam 12
from the PM fiber 18 into the polarizer 6. The
polarizer 6 polarizes the beam 12 when the beam 12 is
transmitted from the collimator 26; thus, the
polarizer 6 polarizes the beam 12 if the beam 12 is
not polarized when it is transmitted from the
collimator 26, or re-polarizes the beam 12 if the beam
12 is polarized when it is transmitted from the
collimator 26. As a practical matter, the polarizer 6
could be eliminated or placed anywhere between the
transducer 5 and the transmitter of the beam 12,
including anywhere along the PM fiber 18. In an
alternative embodiment the PM fiber 18 can be aligned
with sufficient precision with respect to the optical
axes of the transducing medium, to perform the
function of (and eliminate the need for) the polarizer
6. The beam 12 passes f:rom the polarizer 6 through
the translucent medium 13 and into the transducer 5.
The translucent medium 13 comprises a non-conductive,
non-birefringent material, such as fused quartz or a
similar substance, which provides a pathway for the
beam from the polarizer 6, which is preferably
situated outside the E-field, to the transducer 5,
which must reside within the E-field. The source of
this E-field will be discussed shortly.
When the transducer 5 (also called the
transducing medium) is in a non-zero E-field (not
shown) it induces a"differential phase shift" to
orthogonal beam components of the beam 12 through the


CA 02401771 2002-10-02

9
Pockels electro-optic effect, which will now be
explained. In the polarized beam 12 the light has at
least two components which propagate along at least
two orthogonal planes, respectively, thus forming at
least two orthogonal planes within the beam 12. The
phase of the components in each plane of propagation
are the object of a shift:, relative to the phase of
the component in the other plane, in the transducer S.
The Pockels electro-optic: effect, which takes place in
transducer 5, changes the relative phases of the beam
components by altering their respective velocities,
and is observed in Pockels transducing crystals and
similar media. The magnitude of the phase shift,
called the "differential phase shift", is proportional
to the magnitude of the E-field. Thus, the Pockels
electro-optic effect is observed as a "phase
differential shift" of the orthogonal beam components
which is proportional to the magnitude of the E-field.
Due to the fixed coaxial structure of the devices in
which the sensor head is to be installed, the
magnitude of the E-field is proportional to the
voltage. Therefore, the differential phase shift is
proportional to (and can be used to measure) the
voltage of the E-field between energized conductor and
ground conductor.
In the preferred embodiment, the transducer 5, or
transducing medium, comprises a material which
exhibits the Pockels electro-optical effect. In the
present invention the transducer 5 is preferably
Lithium Niobate (LiNbO3) Pockels, although other
materials, such as Ammonium Dihydrogen Phosphate
(NH4H2P04 ) , Ammonium Dideuterium Phosphate (NI-i9D2P04 ) ,
Potassium Dideuterium Phosphate (KDzP04), MgO-doped
Lithium Niobate (MqO-LiNbO3), electro-optic polymers,
organic materials, and others may be used.
The phase shift between orthogonal components
further manifests itself as ai7 alteration of the


CA 02401771 2002-10-02

beam's polarization. Therefore, the beam may be
considered either to be a differential phase shifted
signal or an optical polarization modulation signal.
The polarization modulation signal is used in the
5 present invention because it can be detected using
low-cost, components that are less susceptible to
temperature, mechanical perturbations, and optical
incoherence than those components that would be
required to sense the differential phase shift
10 directly.
In the practice of the present invention, the
sensor head 4 or the trarisducer 5 may be encased in a
dielectric buffering material, not shown, to smooth
the transition geometry between the permittivity of
the transducer 5 and the permittivity of the
surrounding media, which in most cases will be an
insulator. The dielectric buffering material promotes
uniformity in the E-field, particularly around the
edges of the transducer 5. This enhances uniform
phase shift in the beam 12 passing through the
transducer 5, and minimizes voltage stress on the
materials in and surrounding the sensor head 4 as
well, thereby increasing the probable maximum
operating lifetime of the entire system.
After the beam 12 has passed sequentially through
the polarizer 6 (FIG. 8), translucent medium 13 and
transducer 5, it enters into the retro-reflector 10.
The retro-reflector 10 comprises a reflector material
9 which induces the beam to reflect and causes a
quarter-wave retarding of: the beam 12. The quarter-
wave retarding property of the reflector material 9
induces a 1/4 wavelength shift in the orthogonal
planes of the beam 12. 7'he 1/4 wavelength shift can
be achieved by reflection of the beam 12 alone, if the
material 9 is non-birefringent; alternatively, the
material 9 can comprise birefringent reflector


CA 02401771 2005-06-28
68483-34D

11
material wherein the properties of the material help achieve
the shift.

If a reflector material 9 having birefringence is
used, the phase shifting occurs when orthogonal components
S of the electromagnetic waves of the beam are shifted (here
by 1/4 a wave length) with respect to one another. This
birefringence, which is inherent in some materials, is not
dependant upon the E-field. In the preferred embodiment, a
reflector material 9 is used which exhibits a reflection-
induced retardation to differentially shift the relative
phases of the beam components in orthogonal planes in the
beam 12 by n/2 radians. The polarization of the beam 12
incident upon the retro-reflector 10 depends upon the
E-field present when the beam 12 makes a first pass through
the transducer 5. If there is an E-field present then there
will be some differential phase shift already present in the
beam 12.

In some embodiments, the n/2 retardation within
the retro-reflector 10 may be used to bias the sensor's
overall resultant polarization such that zero E-field (and
hence zero voltage) corresponds to circular-polarized light,
as no differential phase shift is induced upon the beam 12
by the transducer S. However, due to the location of the
retro-reflector 10 in the sensor head 4, if the transducer 5
is in a non-zero E-field and induces a differential phase
shift in the beam 12, then the retro-reflector 10 will not
convert light from linear to circular-polarization, rather
it will induce elliptical-polarization upon the beam 12,
whose ellipticity will vary in proportion to the voltage.
While laser light is used in the preferred embodiment, other
forms of electromagnetic radiation could also be used in the
practice of the invention.


CA 02401771 2005-06-28
68483-34D

11a
The reflection of the beam 12 in the retro-
reflector 10 is in accordance with the principle of the
angle of incidence being the same as the angle of


CA 02401771 2002-10-02

12
reflection. In the practice of the preferred
embodiment of the present invention, the retro-
reflector 10 is configured to cause a 180 change in
the direction of the beam 12, thereby sending the beam
back into the transducer S. Upon each reflection, a
beam 12 may be induced to undergo a 1/8 wave length
phase shift to produce a total of 1/4 wave phase
shift, as in the preferred embodiment. One skilled in
the art could further induce a 1/4 wave length shift
in beam 12 by combining reflection and birefringence.
When the beam 12 reenters the transducer 5, it
undergoes further phase shift from the Pockels
electro-optic effect. As shown in FIG. 8, the beam 12
then passes through the translucent medium 13 and
enters into the polarizing beam splitter 80.
In the polarizing beam splitter 80, (also called
an analyzer in the art), the beam 12 is separated in
accordance with the respective axes of its
polarization ellipse into AM signals 35 and 36. The
said polarization ellipse will exhibit an ellipticity
ranging between -1 and +1, in proportion to voltage at
any given time. Those skilled in the art will note
that an elliptic polarization whose ellipticity ranges
between -1 and +1 can be described as ranging from a
linear polarization along one axis to a linear
polarization along a second axis perpendicular to the
first axis, wherein the point at which ellipticity
equals 0 corresponds to circular polarization. As
shown in FIG. 3, the major and minor axes of the
polarization ellipse of beam 12 can be represented by
two orthogonal components, indicated generally at 83.
The beam splitter= 80 then separates the beam 12 into
two components 84 and 85 which comprise the
intensities along each of the two axes of the
polarization ellipse shown as orthogonal components
83. The intensity of beam components 84 and 85 will
modulate conversely to one another in response to


CA 02401771 2002-10-02

13
modulations in the ellipticity of the beam's
polarization. The beam components 84 and 85 are two
AM signals shown as 35 and 36, respectively, which are
routed as shown in FIG. 1 into photo-detectors 43 and
44, respectively.
The AM signals 35 and 36 are then passed by
collimators 27 and 28, shown in FIG. 8, and routed
through multi-mode or single-mode optic fibers 37, 38.
A beam reflector 14 may be used to aid in routing the
AM signals 35 and 36.
As shown in FIG. 1, first and second routing
means, shown as optic fibers 37 and 38, are used to
route the AM signals 35 and 36 from the sensing means
into the detecting means. First the AM signals 35 and
36 are routed into the photodetectors 43 and 44
through the first and second routing means, shown as
the first and second translucent fibers 37 and 38,
respectively. In the preferred embodiment the first
and second translucent fibers 37 and 38 comprise at
least one optic fiber, wherein the optic fiber is
selected from the group consisting of: a single-mode
optic fiber, and a multi-mode optic fiber. In the
photodetectors 43 and 44 the AM signals 35 and 36
become electrical signals 45 and 46. The electrical
signals 45 and 46 are routed into a signal processor
62, the final component of the detecting means,
wherein a desired E-field characteristic is
determined, particularly that of voltage.
To determine the voltage in the practice of the
preferred embodiment of the present invention the
signal processor 62 is designed to sample each AM
signal at substantially regular intervals and
substantially simultaneous times, process the signals
to produce a display signal (not shown) which is then
displayed on a readable display such as: digital,
hardcopy, video, software, computer memory displays or
an audible indicator.


CA 02401771 2002-10-02

14
While it is possible to actually measure the
relative phases of the orthogonal components of the
beam 12 after exiting the transducer, the relative
phase shift can also be derived from the intensities
of the AM signals 35 and 36 shown in FIG. 8 without
using complex and costly approaches as involved in
direct phase measurements. Therefore, in the
present invention, when the two AM signals 35 and 36
are separated from a single differential phase shifted
signal using a properly oriented polarizing beam
splitter 80, the beam's polarization state is analyzed
to obtain AM intensity signals. The AM signals 35 and
36 extracted from the beam's polarization state by the
splitter 80 are transmitted to and used in the signal
processor 62 where their complementary nature
facilitates rejection of common mode noise and
minimizes effects of temperature dependent intrinsic
birefringence that may reside in the transducing
medium or other optical components within the system.
This feature of the present invention substantially
enhances accuracy and practicality of the system and
represents an additional advancement over much of the
prior art. The signal processor 62 performs these
functions while converting the received AM signals 35
and 36 into a single, highly accurate voltage
measurement. In addition to measuring the voltage of
a device, the invention rnay be used in conjunction
with a device for measuring current to provide
information regarding power, power factor angle, and
energy on the conductor of interest.
As mentioned, each AM signal, 35 and 36 (FIG. 8)
is converted by a photo-detector 43 and 44 (FIG. 1)
into a electrical signal 45 and 46 (FIG. 1) which can
be processed by the signal processor 62. The photo-
detector comprises an optic-to-electronic conversion
means for converting said AM signals into analog
electronic signals. Preferably, the analog electronic


CA 02401771 2002-10-02

signals comprise low-level analog voltage signals or
current signals.
In the preferred embodiment of the present
invention the electrical signals 45 and 46 are
5 electronic signals transmitted to the signal processor
62 which correspond to the intensity of the AM signals
35 and 36. Thus, in the practice of the present
invention, a series of AM signals are manipulated by
the signal processor 62, as each of the electrical
10 signals 45 and 46 corresponds to intensity of each AM
signal 35 and 36. The electrical signals 45 and 46
are sampled by the signal processor 62 at regular
intervals and substantially simultaneously with one
another. The sampled signals are the instantaneous
15 intensity for each AM signal, 35 and 36. These
intensity signals will be discussed below as (A) and
(B), respectively.
In the signal processor 62 (FIG. 1) the
instantaneous intensity signal for each beam component
is sampled sequentially and stored, thereby forming a
data base of stored sigrials which represents each AM
signal over time. The stored signals are then
converted into a displayable signal regarding the
voltage of E-field at the transducer 5 (FIG. 8).
In the preferred embodiment signals are
manipulated in the following manner. First, an
average intensity for each independent amplitude
modulated signal is calculated. This is done by
summing the instantaneous intensities of the signals
which have been sampled over a pre-determined time
interval and dividing by the number of samples taken
in the interval. In the preferred invention this is
accomplished by taking the average of the signals over
time for each beam component by summing the signals of
each beam component and dividing the sum by the number
of signal samples taken.


CA 02401771 2002-10-02

16
Mathematically, the average intensity for the AM
signal (A) is expressed as follows:

(Z/L) E Ai
i-n-L

where the average intensity is (a), the instantaneous
AM signal is (Ai), the number of samples is (L), the
samples are taken and stored at uniform time intervals
(i), and the average is calculated using samples
between present time index n and past time index (n-
L). Similarly, the average intensity for the AM
signal (B) is expressed as follows:

B = (1/L) E Bi
i-n-L

where the average intensity is (s), the instantaneous
AM signal is (B;), with the other values being as
above.
Next, an adjusted instantaneous intensity for
each signal is found by comparing the most recent
instantaneous signal intensity with the average signal
intensity of the corresponding AM signal. Thus, for
the beam component corresponding to AM signal (A), the
adjusted instantaneous intensity (In) is:

In = A-At,

Where at (An) is the instantaneous intensity of AM
signal (A) at the present time index. Similarly, for
AM signal (B), the adjusted instantaneous intensity
(Jn) iS.

Jn = B-Bn

Where (Bn) is the instantaneous intensity of signal (B)
at the present time. It will be recognized by those


CA 02401771 2002-10-02

17
skilled in the art that because signals (A) and (B)
each represents a different axis on the polarization
ellipse, their amplitudes will change in opposite
directions from one another for a given change in
polarization. Thus where the intensity of one signal
increases there will be a decrease of intensity of
equal magnitude in the other signal. Therefore, the
adjusted instantaneous intensity signals (In) and (J,)
must be computed as indicated above in order to
preserve sign.
The adjusted average instantaneous intensity
signal for both signals (A) and (B) compensates for
any temperature induced birefringence that may exist
within the transducer. Temperature induced
.15 birefringence causes a change in the intensity of the
AM signals over time, as the transducer heat or cools.
The variation in the intensity due to temperature-
dependant intrinsic birefringence of the transducer
appears as a modulation or variation in the average
intensity. Thus, by comparing the instantaneous
intensity with the average intensity of the signals,
and deducting the average intensity from the
instantaneous intensity, temperature induced
variations of the signal due to the birefringence in
the transducer are compensated for in the adjusted
instantaneous intensity signals (I,,) and (Jõ) .
An additional manipulation of the adjusted
instantaneous intensity signals (I,,) and (Jõ)
compensates for intensity fluctuations and other
common mode noise. This is accomplished by comparing
the average of the adjusted instantaneous intensity
signals (Ii) and (J;) for the signals (A) and (B) .
This comparison entails calculating the average
between (In) and the sign-reversed value of (Jn).
K. = (In_J,,Z
2
This average (Kr,) is directly proportional to the
voltage. This is so because the Pockels electro-optic


CA 02401771 2002-10-02

18
effect induces a differential phase shift in the
orthogonal planes of the beam 12 (FIG. 8) which is
directly proportional to the E-field, and the E-field
is directly proportional to voltage. Thus, for a
sampling of interest (n), the average instantaneous
intensity signal (Kn) for the signals (A) and (B) is
directly proportional to the actual instantaneous
voltage (Võ) between energized conductor and ground,
varying only by a scaling constant (k).
VR = kKn = k I- J
2
The scaling constant (k) is determined by
applying a precisely known voltage to the device of
interest and adjusting the scaling constant (k) until
the value measured as the actual instantaneous voltage
(V,,) is equivalent to the precisely known voltage being
applied. In a typical general application of the
present invention, shown in FIG. 1, the sensor head 4
is placed in an insulator 50 between a conductor 52
and a grounded conductor 48. When voltage is applied
to the conductor 52 an E-field is created between the
conductor 52 and the grounded conductor 48, in the
insulator 50. Determination of the scaling constant
(k) is accomplished by applying a precisely known
voltage to the conductor 52. Once the scaling
constant (k) is known the electro-optical voltage
sensor system may be operated to determine additional
actual instantaneous voltages applied to conductor 52.
An alternative embodiment in accordance with the
present invention is illustrated in FIG. 2, which is a
diagram of the electro-optical voltage sensor system.
Wherever practicable, components in the alternative
embodiment which are equivalent those discussed above
have the same reference numbers. In this embodiment
there is shown a transmitter 1, which comprises a
laser (not shown), a polarizer 6, and a wave plate 9.
The laser emits an electromagnetic radiation beam 12.
The electromagnetic radiation beam 12 passes first


CA 02401771 2002-10-02

19
through a polarizer 6 and then a wave plate 9,
producing a polarized beam 12 which may be circular-
polarized. The beam 12 enters into a PM optic fiber
18 through a collimator 20. The PM optic fiber 18 may
further comprise a low-birefringence optic fiber. The
optic fiber 18 routes the beam 12 to a sensor head
generally designated at 16. It is important to note
that the sensor head 16 in this alternative embodiment
shown in FIG. 2 differs from the sensor head 4 of the
preferred embodiment shown in FIG. 1.
The detector generally depicted at 8, as shown in
FIG. 2, comprises a polarizing beam splitter 80, at
least two photo-detectors 43, 44, a signal processor
62. The beam 12 is routed from the sensor head 16
through another PM optic fiber 19 through a collimator
23 and into the polarizing beam splitter 80. Again,
as shown in FIG. 3, the polarizing beam splitter 80
separates the polarized beam 12 in accordance with the
respective separate wave components propagating in the
orthogonal axes of the polarization ellipse into AM
signals 35, 36. In the embodiment shown in FIG. 2,
the AM signals 35, 36 which are analog optic signals,
are routed through multi-mode or single-mode optic
fibers 37, 38 to the photo-detectors 43, 44.
The photo-detectors convert the AM signals 35, 36
into electrical signals 45, 46 which can be analyzed
in the signal processor 62.
Prior to discussing the sensor head 16, consider
the collimators 20, 21, 22, 23, 24, 25 in FIGS. 2, 7a,
7b, and 7c and collimators 26, 27 and 28 in FIG. 8,
which each are generally represented by the collimator
29, shown in FIG. 4. Generally, a collimator 29
comprises a lens 30 and a transparent end 31 which can
pass a beam 12 into or out of the core 32 of an optic
fiber 40. A collimator used to couple light into the
core of an optic fiber is sometimes also referred to
as a"coupler" in the art, but the term "collimator"


CA 02401771 2002-10-02

is used herein for simplicity. In the preferred
embodiment, the optic fiber 40 is a PM optic fiber 18,
which may also take the form of low-birefringence
fiber.
5 Referring to FIGS. 7a, 7b, and 7c, these
alternative embodiments of the sensor head 16 comprise
a transducer 5 and a reflector 17. In FIG. 7a the
beam 12 enters into the sensor head 16, through a
collimator 21 which is attached to a PM fiber 18. The
10 beam 12 then passes through the transducer 5 and upon
being reflected by a beam reflector 17 enters into a
second collimator 22. The second collimator 22 is
connected to an optical fiber 19 by which the beam 12
is routed away from the sensor head 16. In this
15 embodiment (and that in F'IG. 7b), the beam only passes
through the transducer once.
Similarly, in the practice of the alternative
embodiment of FIG. 7b, the beam 12 enters into the
sensor head 16, through a collimator 21 which is
20 attached to a PM fiber 18, following which it is
reflected by the beam reflector 17 into the transducer
5. The beam 12, after passing through the transducer
5 would enter into a second collimator 22 connected to
an optical fiber 19 and be routed away from the sensor
head 16.
Likewise, in the practice of the alternative
embodiment of FIG. 7c, the beam 12 enters into the
sensor head 16, following which it travels through the
transducer 5. The beam 12 is then reflected by the
beam reflector 17 back through the transducer 5, and
into a second collimator 22 connected to an optical
fiber 19. The beam 12 is then routed away from the
sensor head 16.
In the embodiments of FIGS. 1 and 2, the sensor
heads 4 and 16 each have a cross-sectional area of
only approximately fifty millimeters squared (50 mm2)
or less, and a length of approximately twenty five


CA 02401771 2002-10-02

21
centimeters (25 cm) or less, depending upon the
particular apparatus in which the sensor head is
embedded.
There are two alternative embodiments of the
transducer 5 which vary according to intrinsic
birefringence. The first embodiment of the transducer
5, as shown in FIG. 5, is particularly appropriate
where the transducer material 5 does not exhibit
intrinsic birefringence along the propagation axis,
shown as z. The beam 12 propagates along axis z. The
transducer 5 in the presence of the E-field 90 causes
differential phase modulation in the orthogonal planes
of the beam 12. The embodiment shown in FIG. 5 is
preferred where the transducer 5 exhibits no
intrinsic birefringence. It is desirable to avoid
intrinsic birefringence, as it is typically
temperature dependant.
The second embodiment for the transducer 5 which
exhibits intrinsic birefringence is shown in FIG 6.
Here, the transducer 5 and a second transducer 11,
have matched intrinsic birefringence to one another
along the propagation axes, shown as y'. The
transducer 5 is aligned with the second transducer 11
such that the optic axes y' are rotated ninety degrees
(180 ) with respect to one another. The E-field 90,
aligned along the z axes, achieves a reverse polarity
in the second transducer 11. The orientation of the
beam 12 with respect to the optic axes y' is preserved
by the rotation of the beam 12 by ninety degrees (900).
This rotation of the orientation is achieved by
placement of a 90 polarization rotator 7 between the
first transducer 5 and the second transducer 11. This
configuration achieves cancellation of the effects of
intrinsic temperature dependant birefringence, while
yielding a differential phase shift in each transducer
5, 11. Thus, in this enibodiment, the beam 12 goes
through the transducer 5 to the 90 polarization


CA 02401771 2002-10-02

22
rotator 7, and thence through the second transducer
11.
There are a number of expressions of the E-field
originator 96 which will now be discussed. The first,
shown in FIG. 9, is a shielded joint 100. A shielded
joint 100 is used to connect shielded conductors 52 to
one another, and may take the form of either a splice
or pre-molded connector. In the preferred embodiment
the two conductors 52 connected to one another are
each enclosed within insulation 50, around which is a
semi-conducting jacket 109 and a cable ground shield
111. Around the conductor connecting means 104 is a
layer of shielded joint insulation 108 and a joint
ground shield 102. The joint ground shield 102 is
supported in place by the end caps 115. A ground
shield connector 113 can be used to maintain a common
ground potential upon the cable ground shields 111 and
the joint ground shield 102. The cable ground shields
111 are electrically connected by conductive wire 106
attached to ground shield connector 113.
Alternatively, the cable ground shields 111 can be
physically connected to the joint ground shield 102 at
the intersection points without use of a ground shield
connector 113 or conductive wire 106. The sensor head
4 is disposed between the joint ground shield 102 and
the conductor connecting means 104. The optical
fibers 18, 37, 38, route the beam to and from the
sensor head 4. The E-field of interest, and into
which the sensor head 4 is introduced, arises between
the joint ground shield 102 and conductor connecting
means 104 when an electric voltage is present upon the
conductor connecting means 104.
Another expression of the E-field originator 96
is the terminator 118 shown in FIG. 10. In the
preferred embodiment showing a terminator 118, a
conductor 52 is enclosed within insulation 50 forming
a transition span. The insulation 50 is enclosed


CA 02401771 2002-10-02

23
within a voltage gradient control means 120. A cable
ground shield 111 may partially enclose the voltage
gradient control means 120. The sensor head 4 is
disposed between the conductor 52 and the voltage
gradient control means 120. Optical fibers 18, 37, 38
route the beam to and from the sensor head 4. The E-
field of interest, and into which the sensor head 4 is
introduced, arises between conductor 52 and the
voltage gradient control means 120 when a voltage is
present upon the conductor 52.
Another expression of the E-field originator 96
of FIGS. 1 and 2 is the through-hole insulator 124,
here shown as a transforrner bushing in FIG. 11. In
the preferred embodiment showing a through-hole
insulator 124, a conductor 52 is enclosed within
insulation 50, which is enclosed within a grounded
conductor 48. The through-hole insulator shown here
as a transformer bushing has a mounting flange 126 for
mounting the bushing and creepage distance skirts 128
which extend from the grounded conductor 48. The
sensor head 4 is disposed between the conductor 52 and
the grounded conductor 48. Optical fibers 18, 37, 38
route the beam to and from the sensor head 4. The E-
field of interest, and into which the sensor head 4 is
introduced, arises between the conductor 52 and the
grounded conductor 48 when a voltage is present upon
the conductor 52.
Another expression of the E-field originator 96
of FIGS. 1 and 2 is the shielded cable or bus 129,
shown in FIG. 12. in the preferred embodiment of a
shielded cable or bus 129, a conductor 52 is enclosed
within insulation 50, which is enclosed within a
grounded conductor 48. The sensor head 4 is disposed
between the conductor 52 and the grounded conductor
48. Optical fibers 18, 37, 38 route the beam to and
from the sensor head 4. The E-field of interest, and
into which the sensor head 4 is introduced, arises


CA 02401771 2002-10-02

24
between the conductor 52 and the grounded conductor 48
when a voltage is present upon the conductor 52.
Whereas FIG. 12 shows a bus having a round cross-
section, an alternative and equivalent embodiment
comprises a rectangular (or square) cross-section.
Another expression of the E-field originator 96
shown in FIGS. 1 and 2 is the gas or oil-insulated
switchgear 132, shown in FIG. 13. In the preferred
embodiment showing a gas or oil-insulated switchgear
132, a conductor 52 is enclosed within gas or oil
insulation 134, by a grounded conductive or semi-
conductive containment means 140 for containing the
gas or oil insulation. The sensor head 4 is disposed
between the conductor 52 and the grounded containment
means 140. Optical fibers 18, 37, 38 route the beam
to and from the sensor head 4. The E-field of
interest, and into which the sensor head 4 is
introduced, arises between the conductor 52 and the
grounded containment means 140 when a voltage is
present upon the conductor 52.
Another expression of the E-field originator 96
is the duct-enclosed bus 142, shown in FIG. 14. In
the preferred embodiment of a duct-enclosed bus 142, a
conductor 52 is enclosed within insulation 50 of
sufficient thickness to minimize possibility of flash-
over. The insulated bus is enclosed within a grounded
duct or other grounded at least semi-conducting means
144. Those skilled in the art will appreciate that by
the term "at least semi-conducting", it is meant all
semi-conducting and conducting means, by which the bus
can be grounded. The sensor head 4 is disposed
between the conductor 52 and the grounded semi-
conducting means 144. Optical fibers 18, 37, 38 route
the beam to and from the sensor head 4. The E-field
of interest, and into which the sensor head 4 is
introduced, arises between the conductor 52 and the


CA 02401771 2002-10-02

grounded semi-conducting means 144 when a voltage is
present upon the conductor 52.
Another expression of the E-field originator 96
is the clamp-on apparatus 147, shown in FIG: 15. In
5 the preferred embodiment of the clamp-on apparatus, a
conductor 52 is enclosed within a coaxial conductive
grounded surrounding means 149. In the practice of
the invention, the conductor 52 is preferably a
nonshielded transmission line, a nonshielded cable, or
10 a nonshielded bus. The conductor 52 is separated from
the conductive grounded surrounding means 149 by
insulated standoff means 151. The sensor head 4 is
disposed between the conductor 52 and the coaxial
conductive grounded surrounding means 149. Optical
15 fibers 18, 37, 38 route the beam to and from the
sensor head 4. The E-field of interest, and into
which the sensor head 4 is introduced, arises between
the conductor 52 and the coaxial conductive grounded
surrounding means 149 when a voltage is present upon
20 the conductor 52.
FIG. 16 is an alterriative embodiment of the
electro-optical voltage sensor of FIG. 1, having a
current detector 153 disposed substantially in common
with the sensor head. The current detector 153
25 detects the current, not shown, passing through the
conductor 52 by detecting the magnetic field, not
shown, associated with the current. The current
detector provides a current signal, not shown, which
is routed through a current signal routing member 156
to the signal processor 62. In one embodiment the
optical current signal routing member 156 consists of
optic fiber, photodetection rneans, and electrical
connecting means, none of which are shown. Where
voltage (V) and current (I) are known, the power (P)
can be determined by the signal processor by
multiplying the current (I) by the voltage (V) as
follows:


CA 02401771 2002-10-02

26
P=IV
A combination of at least two sensors of the
present invention may be used to achieve a line-to-
ground voltage measurement on separate conductors of a
multi-source system. "Multi-source system" is meant a
to include both a multi-phase as well as a multi-line
system. In such a system, line-to-ground measurements
may also be used to calculate line-to-line voltages
through simple subtraction of line-to-ground values.
The present invention represents a significant
advance over the prior apparatus, methods and art of
voltage measurement. The present invention does not
require any additional electronics to bias the
transducing material to determine voltage, such as a
voltage divider. Voltage is determined in the present
invention by utilizing the E-field that exists within
many types of devices to transmit and distribute
power, often these power distribution devices are co-
axial, which simplifies the application of the present
invention. The E-field, which is proportional to
voltage, is used to bias a transducing element in
order to induce a differential phase shift in the
orthogonal planes of the beam, which as modulated
optic signals, is proportional to voltage.
It is noted that many of the advantages of the
present invention accrue due to the simplified
structure of the sensor head, which is sufficiently
small so as to be conveniently installed in devices in
which E-fields arise, or built in as part of a sensor.
Although the prior art apparatus and methods for
voltage measurement have attempted to use the electro-
optical effect in materials having either a Pockels or
Kerr coefficient, they have typically required a
separate compensator crystal with a known reference
voltage or a separate voltage divider directly
connected to the energized conductor in order to make


CA 02401771 2002-10-02

27
a voltage measurements. The result has been devices
which were bulky and required additional electronics
for measuring the known reference, or required extra
hardware presenting size, weight, expense,
reliability, and other problems.
By using the sensor head of the present
invention, which may be installed or built into the
described voltage transmission and distribution
apparatus, voltage measurement is achieved without the
use of a large, dedicated, stand-alone voltage
division device. Real estate within Power substations
is at a premium, thus this sensor system offers a
substantial economic advantage due to space savings.
In addition, contact with the energized conductor is
substantially reduced and in most cases altogether
eliminated with the practice- of the present invention.
This is advantageous, as an energized conductor can
present significant life and health risks among other
hazards where high voltages are involved. Further,
the practice of the present invention does not
interfere with the apparatus being measured, and
avoids various other problems associated with the use
of the voltage dividers in the prior art.
Those skilled in the art will appreciate from the
preceding disclosure that the objectives stated above
are advantageously achieved by the present invention.
It is to be understood that the above-described
arrangements are only illustrative of the application
of the principles of the invention. Numerous
modifications and alternative arrangements may be
devised by those skilled in the art without departing
from the spirit and scope of the present invention and
the appended claims are intended to cover such
modifications and arrangements.

Representative Drawing
A single figure which represents the drawing illustrating the invention.
Administrative Status

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Administrative Status

Title Date
Forecasted Issue Date 2008-09-30
(22) Filed 1996-12-05
(41) Open to Public Inspection 1997-06-19
Examination Requested 2002-10-02
(45) Issued 2008-09-30
Expired 2016-12-05

Abandonment History

There is no abandonment history.

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Request for Examination $400.00 2002-10-02
Registration of a document - section 124 $50.00 2002-10-02
Application Fee $300.00 2002-10-02
Maintenance Fee - Application - New Act 2 1998-12-07 $100.00 2002-10-02
Maintenance Fee - Application - New Act 3 1999-12-06 $100.00 2002-10-02
Maintenance Fee - Application - New Act 4 2000-12-05 $100.00 2002-10-02
Maintenance Fee - Application - New Act 5 2001-12-05 $150.00 2002-10-02
Maintenance Fee - Application - New Act 6 2002-12-05 $150.00 2002-10-02
Maintenance Fee - Application - New Act 7 2003-12-05 $150.00 2003-11-12
Maintenance Fee - Application - New Act 8 2004-12-06 $200.00 2004-09-16
Maintenance Fee - Application - New Act 9 2005-12-05 $200.00 2005-09-15
Maintenance Fee - Application - New Act 10 2006-12-05 $250.00 2006-09-18
Maintenance Fee - Application - New Act 11 2007-12-05 $250.00 2007-09-20
Maintenance Fee - Application - New Act 12 2008-12-05 $250.00 2008-05-23
Final Fee $300.00 2008-07-15
Maintenance Fee - Patent - New Act 13 2009-12-07 $250.00 2009-11-10
Maintenance Fee - Patent - New Act 14 2010-12-06 $250.00 2010-11-17
Maintenance Fee - Patent - New Act 15 2011-12-05 $450.00 2011-11-17
Maintenance Fee - Patent - New Act 16 2012-12-05 $450.00 2012-11-15
Maintenance Fee - Patent - New Act 17 2013-12-05 $450.00 2013-11-14
Maintenance Fee - Patent - New Act 18 2014-12-05 $450.00 2014-11-14
Maintenance Fee - Patent - New Act 19 2015-12-07 $450.00 2015-11-13
Owners on Record

Note: Records showing the ownership history in alphabetical order.

Current Owners on Record
LOCKHEED IDAHO TECHNOLOGIES COMPANY
Past Owners on Record
RENAK, TODD W.
WOODS, GREGORY K.
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.
Documents

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Document
Description 
Date
(yyyy-mm-dd) 
Number of pages   Size of Image (KB) 
Description 2002-10-02 30 1,422
Claims 2006-12-15 6 209
Description 2006-12-15 31 1,440
Representative Drawing 2002-11-14 1 7
Cover Page 2002-12-20 1 45
Representative Drawing 2006-06-20 1 10
Claims 2002-10-02 6 206
Drawings 2002-10-02 8 121
Abstract 2002-10-02 1 33
Claims 2005-06-28 6 248
Description 2005-06-28 31 1,457
Cover Page 2008-09-16 1 48
Correspondence 2002-10-17 1 42
Assignment 2002-10-02 2 119
Correspondence 2002-11-15 1 13
Correspondence 2003-01-07 1 16
Fees 2002-12-05 2 88
Prosecution-Amendment 2004-12-29 2 52
Prosecution-Amendment 2005-06-28 12 539
Prosecution-Amendment 2006-06-15 3 88
Prosecution-Amendment 2006-12-15 15 560
Prosecution-Amendment 2007-05-10 1 39
Correspondence 2008-07-15 1 38