NZ613474B2 - An ac or dc power transmission system and a method of measuring a voltage - Google Patents
An ac or dc power transmission system and a method of measuring a voltage Download PDFInfo
- Publication number
- NZ613474B2 NZ613474B2 NZ613474A NZ61347412A NZ613474B2 NZ 613474 B2 NZ613474 B2 NZ 613474B2 NZ 613474 A NZ613474 A NZ 613474A NZ 61347412 A NZ61347412 A NZ 61347412A NZ 613474 B2 NZ613474 B2 NZ 613474B2
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- New Zealand
- Prior art keywords
- optical
- minimum distance
- power transmission
- transmission system
- electrical conductor
- Prior art date
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- 230000005697 Pockels effect Effects 0.000 claims description 11
- 239000003989 dielectric material Substances 0.000 claims description 8
- LWIHDJKSTIGBAC-UHFFFAOYSA-K Tripotassium phosphate Chemical compound [K+].[K+].[K+].[O-]P([O-])([O-])=O LWIHDJKSTIGBAC-UHFFFAOYSA-K 0.000 claims description 6
- 229910000160 potassium phosphate Inorganic materials 0.000 claims description 3
- 235000019798 tripotassium phosphate Nutrition 0.000 claims description 3
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- GNSKLFRGEWLPPA-ZSJDYOACSA-M potassium;dideuterio phosphate Chemical compound [K+].[2H]OP([O-])(=O)O[2H] GNSKLFRGEWLPPA-ZSJDYOACSA-M 0.000 description 2
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/24—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/24—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices
- G01R15/241—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using electro-optical modulators, e.g. electro-absorption
- G01R15/242—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using electro-optical modulators, e.g. electro-absorption based on the Pockels effect, i.e. linear electro-optic effect
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/24—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices
- G01R15/247—Details of the circuitry or construction of devices covered by G01R15/241 - G01R15/246
Abstract
The present invention relates to an AC or DC power transmission system. The system comprises a first electrical conductor, a second electrical conductor and an insulating space there between. The system further comprises an electric field measurement device comprising the following components being mounted in optical continuation: a first optical fibre being connected to a light source, a first optical lens, a circular polarization filter, a crystal rod having electro-optical properties, a linear polarization filter, a second optical lens, and a second optical fibre being connected to a light detection unit. The electric field measurement device is located adjacent the first electrical conductor and defines a first minimum distance between the crystal rod and the first electrical conductor and a second minimum distance between the crystal rod and the second electrical conductor. The second minimum distance is at least 10 times larger than the first minimum distance. mounted in optical continuation: a first optical fibre being connected to a light source, a first optical lens, a circular polarization filter, a crystal rod having electro-optical properties, a linear polarization filter, a second optical lens, and a second optical fibre being connected to a light detection unit. The electric field measurement device is located adjacent the first electrical conductor and defines a first minimum distance between the crystal rod and the first electrical conductor and a second minimum distance between the crystal rod and the second electrical conductor. The second minimum distance is at least 10 times larger than the first minimum distance.
Description
An AC or DC power ission system and a method of measuring a
voltage
The present invention relates to an AC or DC power transmission system, a
method of measuring a voltage and a method of calibrating a voltage
measurement system.
The power industry has a need for monitoring the condition of power
transmission systems. For these purposes, it has been known to make current
measurements using only optical technology. One example of such optical
current sensors utilizing the y effect is described in the applicant's own
international application WO/2004/099798. In a Faraday effect current sensor,
the polarization plane of a polarized incident light undergoes a rotation, which is
a function of the magnetic field created by the electric current to be ed.
Such Faraday effect current s have the advantage over generally known
Rogowski coils and similar ic current s that they may be constructed
entirely from dielectric materials and may thus be d in locations where a
very high electric field is present.
It has also been known to carry out voltage measurements using an optical
sensor. This may be achieved by utilizing the Pockels effect, which is an optical
effect in anisotropic crystals. In a voltage sensor utilizing the Pockels , the
zation plane of incident light passing through the crystal undergoes a
rotation if there is an electric field applied over it. The main principle of such
Pockels effect voltage s thus resembles the principle of the above
mentioned Faraday effect current sensor, namely that the induced electric field
over the sensor element gives rise to a small variation in the polarization of the
light going h the sensor. This variation can be measured and from such
measurements the electric field strength may be derived. From the derived
ic field strength at the location of the sensor, the voltage on the wire may
be determined.
There are several advantages of using an optical voltage , the first being
simplicity. The optical voltage sensor is comprised of few parts and hence is easy
to assemble. Further, the measured signal is solely optical so that there is no
electrical noise induced in the measurement. Yet r, there is no electrical
connection between the conductor to be measured and the ground like in a
conventional voltage r. Such electrical connection may cause problems
such as a short circuit.
The physics behind the optical voltage sensor is based on the Pockels effect,
which was discovered in the late 19th century. It has since been used in various
known optical s such as Q—switches and Chlrped pulse amplification. The
effect is expressed in the linear term of the following equation:
1 1
—2—-l—7‘E+RE2
n 710
wherein E is the electric field. n, no, r and R are all tensors, respectively
describing the refractive index, the ordinary refractive index, the linear and
quadratic electro-optic coefficient. If E is applied correctly with respect to the r
tensor (the crystal) and the quadratic term is neglected, n will become non—
symmetric, thus giving rise to birefringence. This means that light sees a
different refractive index depending on the orientation of the polarization with
respect to the r tensor.
In known optical voltage sensors, the crystals which exhibit the Pockels effect
have electrodes attached to them and have a predetermined trajectory for light
passing h. The above configuration is generally known as a Pockels cell
and functions as a voltage-controlled wave plate. Such configurations are usecl in
various prior art publications. One e includes an IEEE ation titled
“230 kV Optical Voltage Transducer Using a Distributed Optical Electric Field
Sensor " by P. P. Chavez, F. Rahmatian and N. A. F. Jaeger. The
proposed sensor system uses a Pockels effect crystal located within an insulating
section between line voltage and ground. The full line voltage thus is applied
over the s cell, which at least for medium e and above requires a
high insulation level.
US 6,285,182 discloses an electro-optic voltage sensor having no need for a
ground reference. However, the voltage sensor still needs metallic electrodes in
the vincinity of the Pockels l. EP 0338542 discloses a similar electro~optic
voltage sensor using a Pockels sensor and capacitive e divider d
within a common housing. Thus, only AC e is measureable.
Further prior art describing the use of Pockels cells voltage sensors located
within an insulating section for measuring the voltage on high voltage lines, or
similar technologies, are among others: US 6,380,725, US 5,029,273, US
,635,831, US 6,388,434, US 6,946,827, US 6,411,077, JP 64,
WO2009/138120, US 483, US 6,492,800, US 7,769,250, US 7,057,792,
US 6,353,494, JP 2005315815, JP 03044563, WOOD/13033, EP 0011110, US
4253061, W098/13698, CA 2,289,736 and GB 1353543.
Using a conventional Pockels cell configuration as described above has the
disadvantage that metallic electrodes need to be attached adjacent the crystal
within the voltage sensor. For high e or medium voltage purposes, this
necessitates a large amount of insulation, resulting in a very large voltage
sensor. Furher, since metallic objects are located wihtin a high electric field,
there is a risk of insulation failure and a dielectric breakdown within the voltage
sensor. Such dielectric failures would result in the immediate e of the
‘15 voltage sensor and possibly in an interruption of the power transmission system.
It would therefore be an age to have a voltage sensor with no odes
attached to the crystal. Thus, it is the object of the t invention to provide
s and systems for ing the voltage of a conductor without the
involvement of any metallic materials other than the conductor itself.
It is an object of preferred embodiments of the present invention to address
some of the aforementioned disadvantages. An additional or alternative object
is to at least provide the public with a useful choice.
The above need and the above object together with numerous other needs and
objects, which will be t from the below detailed description, are according
to a first aspect of the present invention obtained by an AC or DC power
transmission system sing a first electrical conductor, a second electrical
conductor and an insulating space between the first electrical conductor and the
second electrical conductor, the power transmission system further comprising
an electric field measurement device, the electric field measurement device
comprising:
a housing made of dielectric al and defining a first Open end
and a second open end opposite the first open end,
a first opticai fibre being ted to a light source,
a first optical lens being mounted in the housing at the first open
end and in optical continuation of the a first optical fibre,
a circular polarization filter mounted in the g in l
uation of the first optical lens,
a crystal rod received in and encapsulated within the housing in
optical continuation of the circular polarization filter, the crystal rod being made
of a material having electro—optical properties,
a linear polarization filter mounted in the g in optical
continuation of the crystal rod, preferably oriented 45° relative to the induced
optical axis of the crystal rod,
a second optical lens mounted in the housing at the second open
end in optical continuation of the linear polarization filter, and
a second l fibre in optical continuation of the second optical
lens, the second optical fibre being connected to a light detection unit, the
eiectric field measurement device being d adjacent the first electrical
conductor within the insulating space and defining a first minimum distance
between the l rod and the first electrical conductor and defining a second
minimum distance between the crystal rod and the second electrical tor,
the second minimum distance being at least 10 times larger than the first
minimum distance, such as 100 times, preferably 1,000 times, more preferred
,000 times, most preferred 0 times.
The term "comprising" as used in this specification and claims means "consisting
at least in part of". When interpreting statements in this specification and claims
which include the term "comprising", other features besides the features
prefaced by this term in each statement can also be present. Related terms
such as ise" and ised" are to be interpreted in similar manner.
In the present context, the applicant has surprisingly found that even if the
ground reference is located remote from the energized conductor, the electric
field strength in a very close proximity to the conductor is sufficient to produce a
measurabie retardance in a crystal exhibiting the Pockels effect. The present
system has the additional advantage over some prior art systems that both AC
and DC may be measured. The ude of the intended current of the power
transmission system is typically at least from a few Ampere up to several
hundreds or thousands of Amperes.
The electric field measurement device may constitute a voltage sensor for
ing the voltage of the first electrical conductor ve to the second
electrical conductor. The insulating space between the first electrical tor
and the second electrical conductor may be tuted by a gas such as air, or a
solid insulator such as an insulator made of glass, porcelain or polymeric
materials.
The housing of the ic field measurement device is typically made of
polymeric al such as plastic. It should preferably be opaque to prevent any
ambient light from the outside to influence the measurement. The light source is
typically constituted by a light—emitting diode or laser which is optically
connected to the first optical lens by the first l fibre. The optical fibre
ensures that no substantial amount of light is lost between the light source and
the first l lens. In this way, the light source may be located at a distant
location, i.e. in a voltage measurement module easily accessible to maintenance
staff. The first optical lens is used for collimating all of the incoming light from
the first optical fibre s the circular polarization filter. The circular
polarization filter causes the incoming light to be circularly polarized before
entering the crystal rod. The crystal rod has electro-optical properties exhibiting
the Pockels effect so that when the crystal rod is exposed to an electric field, the
incoming light experiences retardance. Depending on how the crystal is cut and
the direction of the incoming light, the crystal may be oriented in any ion
relative to the electric field d by the first tor and generated by the
current. Typically, however, the crystal will be oriented either parallel or
perpendicular to the electric field from the first electrical conductor. The length
of the crystal rod is typically between 5mm and 20mm. The material used may
be e.g. KD*P (DKDP, potassium dideuterium phosphate). When leaving the
crystal rod, and in case an electric field is applied, the outgoing light has been
retarded so that the circular polarization is turned into elliptical polarization. A
last linear polarization filter is typically oriented at 45° to the induced optical axis
in the crystal rod, which means parallel or perpendicular to the major axis of the
ellipse. The ude of the light leaving the linear polarization filter thus
corresponds to the electric field th at the location of the crystal rod. The
value of the electric field strength at the location of the crystal rod may be
translated into a voltage of the first conductor. Since the linear polarization filter
will allow 50% of the light to pass when the first conductor is grounded, i.e. the
light leaving the crystal rod remains circularly polarized, positive and negative
voltages may be distinguished as either an increase or a decrease in light. The
light g the linear polarization filter is ted by a second optical lens and
via a second optical fibre led to a light detection unit detecting the light intensity
of the light leaving the optical voltage sensor. The relative value of the light
emitted by the light source and the light detected by the light ion unit
corresponds to the voltage of the first conductor.
The crystal rod of the electric field ement device should be positioned in a
fixed on close to the first conductor. The ic field measurement device
should be placed in a position exhibiting an electric field, such as between a
power line and the ground, and not encapsulated inside the first conductor,
between two conductors exhibiting the same electrical potential or within a
metallic object. For high accuracy, the distance between the crystal rod and the
first tor shouid be as small as possibie. The minimum distance between
the crystal rod and the second electrical conductor should exceed the distance
between the crystal rod and the first electrical conductor at least 10 times,
preferably 100 times or more.
In a further ment according to the first aspect, the first electrical
conductor comprises an overhead line or a metallic object electrically connected
to an overhead line. The sensor may be placed either close to a metal plate of
the same potential as the conductor of interest or on the conductor . The
conductor is typicaily an overhead line.
In a further embodiment according to the first aspect, the second electrical
conductor comprises a metallic object being insuiated in relation to the first
electrical conductor. The second conductor may be e.g. a power line having a
voltage, frequency or phase angle different from the first conductor.
In a further embodiment ing to the first aspect, the second electrical
conductor constitutes the ground. Further, the second tor may constitute
a ground reference such as a metallic pylon supporting one or more power lines,
or the ground surface below an overhead line.
In a further ment according to the first aspect, the first electrical
conductor of the power transmission system has a rated voltage of between
0,1kV and 1000kV, preferably n 1kV and SOOkV, more preferred between
SW and IOOkV, most preferred between 10kV and SOkV. The power
transmission system is intended for power transmission voltages of at least
0,1kV and above. Typical power transmission voltages range between 1kV and
SOOkV for both AC and DC.
In a further ment according to the first aspect, the crystal rod is being
exposed to an ive electric field strength of between 1*104 V/m and 1.2"‘108
V/m, preferably between 1*10S V/m and 1.2”‘107 V/m, when the power
’15 transmission system is being operated at its rated voltage. The above ranges
define typical electric field strengths within which the present voltage sensor is
capable of delivering te measurements.
In a r embodiment according to the first aspect, the first minimum
distance is between 0,1mm and 100mm, preferably between 1mm and 10mm.
For high accuracy of the voltage measurement, the voltage sensor should be
positioned as close as le to the first conductor, where the electric field
strength is high in comparison to a more distant location.
In a further embodiment according to the first aspect, the second minimum
distance is between 0,1m and 100m, preferably between 1m and 10m. The
voltage sensor should be positioned as far as possible from the second tor
in order to have no influence on the voltage measurement. The second
conductor may, as explained above, be tuted by another power line, the
ground, or a grounded object.
In a further ment according to the first aspect, the light path through the
l rod is oriented ntially parallel to the electric field at the first
conductor, or alternatively, the light path through the crystal rod is oriented
substantially perpendicular to the electric field at the first conductor. By orienting
the crystal rod_substantia|ly perpendicular to the electric field, the crystal rod
may be oned closer to the conductor. However, by orienting the crystal rod
substantially parallel to the electric field, a smaller and thus less complex and
less costly crystal may be used.
In a further embodiment according to the first aspect, the circular polarization
filter consists of a quarter-wave plate and a linear polarizer. In a preferred
embodiment, the linear polarizer and the quarter-wave plate are made from a
single sheet in order to minimize light losses. atively, the linear polarizer
and the quarter-wave plate constitute two separate parts. The linear polarizer
and the r-wave plate should be oriented in such a way that the light first
enters the linear polarizer and subsequently the quarter-wave plate.
In a r embodiment according to the first aspect, the crystal rod, preferably
made of potassium phosphate, exhibits the Pockels effect. Potassium phosphate
is a preferred material as it exhibits a high birefringence when applying an
ic field, which is characteristic of the Pockels effect.
In a further embodiment according to the first aspect, the electric field
measurement device r comprises:
a first sealing means for sealing the first end of the housing, the
first sealing means having an aperture for receiving the first optical fibre,
a first fixture means for ng the first optical fibre to the housing,
a first reception part being attached to the first optical lens and
adapted for receiving the first fixture means,
a second fixture means for fixating the second optical fibre to the
housing,
a second reception part being attached to the second l lens
and adapted for receiving the second fixture means,
a second sealing means for sealing the second end of the housing,
the second sealing means having an aperture for receiving the second optical
fibre, and
a first and a second lid fixated to the first and second end,
tively, of the housing, the first and second lid including an aperture for
receiving the first and second optical fibre, respectively. By using a fixture
means for fixating the optical fibre and a reception part attached to the optical
lens for receiving the fixture means, the l fibre may be optimally positioned
with respect to the optical lens when assembling the optical voltage sensor in the
field without access to high precision equipment. In this way, the loss of light
intensity may substantially be avoided. Further, the sealing means and the lids
prevent moisture from ng the housing, making the optical voltage sensor
weather-proof.
In a further ment according to the first aspect, the housing is made of
polymeric material, such as plastic. c is preferred since it is durable and
constitutes a tric material which does not influence the electric field.
Further, plastic may be made essentially opaque for preventing any ambient
light from entering the crystal rod, thereby bing the ement results.
The above need and the above object together with numerous other needs and
objects, which will be evident from the detailed description below, are according
to a first aspect of the t invention obtained by a method of measuring a
voltage of a first electrical conductor in relation to a second electrical conductor
spaced apart from the first electrical conductor by an insulating space, the
method comprising providing an electric field measurement device, the electric
field measurement device comprising:
a housing made of dielectric material and defining a first open end
and a second open end opposite the first open end,
a first optical fibre being connected to a light source,
a first optical lens being mounted in the housing at the first open
end and in optical continuation of the first optical fibre,
a circular polarization filter mounted in the housing in optical
uation of the first optical lens,
a crystal rod received in and encapsulated within the housing in
l continuation of the circular polarization , the crystal rod being made
of a material having electro-optical properties for causing retardance,
a linear polarization filter mounted in the housing in optical
continuation of the crystal rod,
a second optical lens mounted in the g at the second open
end in optical continuation of the linear polarization filter, and
a second optical fibre in optical continuation of the second optical
lens, the second optical fibre being connected to a light detection unit, the
method further comprising the following steps:
positioning the electric field measurement device nt the first
‘10 electrical conductor within the insulating space so that a first minimum distance
defined between the crystal rod and the first electrical conductor is at least 10
times larger than a second minimum distance defined between the crystal rod
and the second electrical conductor, such as 100 times, preferably 1000 times,
more preferred 10,000 times, most preferred 100,000 times, and
‘15 detecting a relative retardance between light emitted by the light
source and Eight ed by the light detection unit.
The above need and the above object er with numerous other needs and
objects, which will be evident from the detailed description below, are according
to a first aspect of the present invention obtained by a method of ating an
electric field measurement device included in a power transmission system, the
power transmission system comprising a first electrical conductor having a
known voltage, a second ical conductor having another known voltage and
an insulating space between the first electrical tor and the second
electrical tor, the electric field ement device comprising:
a housing made of dielectric al and defining a first open end
and a second open end opposite the first open end,
a first optical fibre being connected to a light source,
a first optical lens being mounted in the housing at the first open
end and in optical uation of the first optical fibre,
a circular zation filter mounted in the housing in optical
continuation of the first optical lens,
a crystal rod received in and encapsulated within the housing in
optical continuation of the circular polarization filter, the crystal rod being made
of a material having electro~optical properties for causing retardance,
a linear polarization filter mounted in the housing in l
continuation of the crystal rod,
a second optical lens mounted in the housing at the second open
end in optical continuation of the linear polarization filter, and
a second optical fibre in optical continuation of the second optical
lens, the second optical fibre being connected to a light detection unit, the
electric field measurement device being located adjacent the first electrical
conductor within the insulating space and defining a first minimum distance
between the crystal rod and the first electrical conductor and defining a second
minimum distance n the crystal rod and the second electrical tor,
the second minimum distance being at least 10 times larger than the first
minimum distance, such as 100 times, preferably 1000 times, more preferred
,000 times, most preferred 0 times,
the method comprising the steps of:
detecting a ve retardance between light emitted by the light
source and light detected by the light detection unit, and
calculating a calibration constant based on the ve retardance
and the known voltages.
It is evident from the above that the methods according to the second and/or
third aspects may be used in combination with the system according to the first
.
In a preferred embodiment, the ting space constitutes a gas insulated
space, such as a space filled by N2, SF6 or, preferably, atmospheric gas.
Typically, the first electrical conductor tutes an overhead line and the
insulated space will consequently constitute atmospheric gas. The ic field
measurement device may thus be located adjacent the first electrical conductor
without compromising the electrical insulation properties of the insulating space.
It is contemplated that other gaseous matter may be used for the insulating
space, such as N2 or SFe insulating gas.
Brief description of the gs
Fig 1 shows the working principle of the electric field measurement device,
Fig 2 shows possible positions of the voltage sensor relative to the power line,
Fig 3 shows a power line and voltage sensor holder,
Fig 4 shows a high voltage pylon and a voltage sensor,
Fig 5 shows an alternative holder and insulator,
Fig 6 shows an alternative e sensor,
Fig 7 shows the results of a first proof of concept experiment,
Fig 8 shows the results of a second proof of concept experiment, and
Fig 9 shows the results of a third (solid line) and fourth (dashed line) proof of
concept experiment.
Detailed description of the drawings
Fig 1A shows a sectional view of a first embodiment of an ic field
measurement device constituting a voltage sensor 10 according to the t
invention. The main principle of the e sensor 10 is the Pockels technology.
The e sensor 10 is basically a phase retarder with a retardance
proportional to an applied electric field. The working principle of the voltage
sensor 10 is as follows: Light generated by a light source 12, e.g. a laser or LED,
is led through a first optical fibre 14 to a sensor housing 16. The sensor housing
16 ses a c casing with the first optical fibre 14 ng at one end of
the housing 16 and a second optical fibre 18 leaving the opposite end of the
housing 16. The second optical fibre 18 is connected to a photo detector 20,
comprising e.g. a photo diode. Both optical fibres 14, 18 couple into respective
lenses 22, 24 which collimate the light through the center of the housing 16. In
the housing 16, the incoming light is focused by the first lens 22 to pass through
the interior components of the voltage sensor 10. The light path is d as
being along the Z-axis. All optical parts of the sensor are placed perpendicular to
the light path (hence in the XY—plane). The interior of the housing 16 is
comprised of three parts: a sheet constituting a circular polarizer 26, an electro-
optical crystal 28 and a linear zer 30. The circular polarizer 26 is in turn
made up of a linear polarizer and a quarter-wave plate. The light travels through
all parts, i.e. all parts are positioned in optical continuation. The circular polarizer
26 is cut from a sheet and must be placed in the sensor so that the light enters
3O first the linear polarizer, then the quarter-wave plate. The circular zer 26
makes the incoming light circularly polarized. After passing the circular polarizer
26, the light passes through the electro—optical crystal 28, made of e.g. KD*P
(DKDP, potassium dideuterium phosphate), in which the optical axis, induced by
the electric field, is arranged in the XY-plane. When ted to an electric field,
the electro-optica] crystal 28 causes a change of polarization of the incoming
circularly polarized light into elliptically polarized light. Finally, the light passes
through a linear polarizing filter 30 oriented at a 45° angle to the induced optical
axis of the eiectro-optical crystal 28. The linear polarizing filter 30 will allow
more or less light to pass h, depending on the ellipticity of the polarization
of the incoming light, which ellipticity in turn depends on the strength of the
electric field subjected to the electro—optical crystal 28.
Fig 18 shows a graph describing the polarization of the light after passing the
linear polarizer of the circular polarizer 26 of the voltage sensor 10 of Fig 1A.
rized light from the light source enters the linear polarizer of the circular
polarizer 26 of the voltage sensor 10, which linear polarizer makes the light
ly polarized with an angle of 45° to the x—axis.
Fig 1C shows a graph describing the polarization of the light after passing the
r-wave plate of the circular polarizer 26 of the voltage sensor 10 of Fig 1A.
The quarter—wave plate introduces a 90° phase shift between the light’s E-field
component along the x-axis and the light’s E-field component along the y-axis,
thus making the light circularly polarized.
Fig 1D show two respective graphs describing the zation of the light after
g the o—optical crystal 28, which have been cut so that when an
electric field is applied over the crystal 28, the induced optical axis is in the xy-
plane. When the circularly polarized light enters the l 28 and an electric
field is applied onto the crystal 28, the phase shift between the light’s E~fie|d
component parallel and perpendicular to the induced optical axis is slightly
increased, as shown in Fig 1D, or slightly decreased, as show in Fig 1E,
depending on the direction of the applied electric field. The circular polarization
of the incoming light is thus squeezed from a circle, shown in full, into an ellipse,
shown as a dashed line, which ellipse is oriented either 45° or —45° to the optical
axis, depending on the ion of the applied field. A higher applied electric
field yields a greater ellipticity.
The azimuthal on of the crystal with respect to the circular polarizer 26 is
inconsequential, as the resulting s polarization is circular, which is
azimuthally symmetric. In effect, a circular polarizer is a 90° phase retarder. The
electro-optical crystal, preferably a KD*P crystal, is oriented so that an electric
field applied parallel to the light path induces an l axis perpendicular to the
light path. This phenomenon is called Pockels effect. This will induce a phase
retardance between linearly polarized light perpendicularly and parallel to this
axis:
nmgv
Ago =
wherein Atp is the difference in phase between light polarized perpendicularly
and el to the optical axis, r is the linear electro—optical cient, A is the
vacuum wavelength of the light and V is the electric potential over the crystal.
The already circularly polarized light will thus experience a further phase
retardance depending on the strength and direction of the electric field. This will
make the polarization state of the light elliptical, with the long axis being either
45° or -45° to the optical axis in the crystal as shown in Figs 1D and 1E (the
d optical axis is orientated along the y-axis).
The dotted line shown is the state of the light as it exits the sensor, after g
the linear polarizing filter 30. A longer clotted line, as in Fig 1D, means higher
amplitude of the light wave, which in turn means higher light intensity. A shorter
dotted line, as in Fig 1E, means lower amplitude of the light wave, which in turn
means lower light intensity. So there is a correlation between the strength and
direction of the applied electric field and the resulting light intensity. This
variation can be measured by the photo detector, eg. a light-sensitive diode,
and can be translated into the voltage of the conductor to be measured.
The last linear polarizing filter 30, which the light enters uent to the
crystal 28, is a polarizer oriented at a 45° angle to the induced i axis. The
last zer 30 is also cut from a sheet and must be ed at 45° to the
induced opticai axis in the l 28. In the present case, the filter is rotated
45° rclockwise. The curve shows the light polarization state after it has
passed this last polarizer. If no field is applied over the crystal 28, half of the
incident iight is allowed through the last filter (under ideal circumstances with no
iight loss except from polarization effects). If the ellipse is “stretched” along the
polarizer, as in Fig 113, more than half of the light is allowed through, as
indicated by the line. Whereas, if it is “squeezed”, less than half the light is
allowed through. Hence a higher electric field resuits in a bigger stretch/squeeze
of the ellipse, which gives a higher resulting light variation from half intensity.
This is the main principle of the sensor.
In the present context, the half intensity of the incoming light may be
designated DC light. The overlying light variation from the polarization effects
may be designated AC light, since it is a result of the AC e applied to the
conductor the potential of which is to be measured. The AC light signal is in the
present context very small compared to the DC light signal, and thus the DC
light may be ed away from the total signal in the electronics leaving only the
AC light signal. The amplitude of the AC light can then be calibrated so that it
translates into the amplitude of the voltage of the conductor the sensor is
ed to.
Fig 1F shows the light intensity as a function of retardance ( I = Io sin2(tp) ) of
the light after passing the last linear polarizing filter 30 of the e sensor 10
of Fig 1A. The reason for using a ar polarizer instead of just a linear
polarizer can be seen when g at Fig 1F. If there were no retardance prior
to the crystal 28, the variation in intensity, due to the AC field over the crystal
28, would be around zero, which is where the derivative of the intensity function
is at its minimum. This wouid also mean that there is no difference in light
intensity between a positive and a negative field, thus making phase
determination difficult. By moving the “zero voltage” point to correspond to a 90°
retardance bias, two ages will become apparent: Firstly, there is an obvious
difference between positive and negative applied electric fields, and secondly,
the function around the “zero voltage”, i.e. at the half intensity of the incoming
light, is approximately linear, resulting in a m sensitivity to retardance
variation around the “zero voltage”. In the figure, this area has been encircled.
Fig 2A shows a first embodiment describing a possible positioning of the voltage
sensor 10. The voltage sensor 10 is positioned adjacent an overhead line
constituting an electrical power line 32, e.g. a high voltage line. The ground is
designated the reference numeral 34. The electric field lines are shown between
the power line 32 and the ground 34. The ic field must be applied in
parallel to the light path through the l 28. The voltage sensor 10 is placed
so that the electro-optical crystal 28 of the voltage sensor 10 is located as close
to the power line 32 as possible. The distance between the electro-optical crystal
28 and the power line 32 has been designated A, and the distance between the
optical l 28 and the ground 34 has been designated B. The ce B is at
least 10 times longer than the distance A. The electric field strength at the
crystal 28 adjacent the power line 32 is approximately linear and decreases
quadratically to the distance from the power line 32.
Fig 28 shows a second embodiment describing a possible positioning of the
voltage sensor 10. It is also possible to cut the crystal 28 in such a way that
both the current path and the field will lie at a 90° angle to the direction of light
through the crystal 28. This has the advantage that it is easier to place the
crystai close to the power line without the lens and fibre being in the way.
Fig 2C shows a third ment describing a possible positioning of the voltage
sensor 10. It is also possible to cut the l 28 in such a way that the field will
lie at a 90° angle to the direction of light through the crystal 28, while the
current path lies parallel to the light through the crystal 28. This embodiment
has the advantage that it is easier to place the crystal 28 close to the power line
without the lens and fibre being in the way. Also it is easier to boost the
sensitivity by increasing the length of the l 28.
Fig 20 shows a fourth embodiment describing a possible oning of the
e sensor 10. It resembles Fig 2C, but further es a plate 36 for
holding the voitage sensor 10. The plate 36 may be made of conducting
material, Le. a metal or a dielectric material such as plastic. Using a metal for
the plate causes the plate 36 to assume the same potential as the power line 32.
The voltage sensor 10 may be constructed in such a way that the fibre 14 and
the lens (not shown here) pass through a hole in the metal plate 36 which has
the same electric potential as the tor. The plate 36 may thus be used for
allowing the crystal 28 to be located even closer to the conductor than otherwise
possible, thereby minimizing the distance A.
Fig 2E shows a fifth embodiment describing a possible positioning of the voitage
sensor 10. It resembles Fig 28, but further includes a piate 36’ for holding the
voltage sensor 10. The upper part of the plate 36’ constitutes a hook-shaped
member which is used for grabbing the power line 32, either temporarily or
permanently.
Fig 2F shows a sixth ment describing a possible positioning of the voltage
sensor 10. It resembles Fig 2A, but further includes a plate 36" for holding the
voltage sensor 10.
Fig 2G shows a seventh ment describing an alternative placement of the
voltage sensor 36 above the power line 32. The present ment resembles
Fig 2C, but is as such ible with the other above mentioned embodiments.
Since the outwardly projecting electric field lines will, adjacent to the conductor,
form a linear field around the conductor 32, it is not required to on the
voltage sensor 10 immediately below the power line 32. Any position around and
adjacent the conductor 32 is allowable. The electric field lines will initially project
outwards, evenly distributed around the conductor, before eventually going
towards the ground. Therefore, in the present ment, the electric field
lines will go upwards through the crystal 28 of the voltage sensor 10 before
bending towards the ground.
Fig 3A shows a perspective view of a voltage sensor holder 38 being attached to
a power line 32. The power line holder 38 is made of metal and comprises a
snap holder 40 and a screw holder 42. The snap holder 40 is held by a hinge 4S
and loaded by a spring (not shown). The screw holder 42 comprises a threaded
rod 44. The threaded rod 44 is located in a threaded receptacle 46. A handle 48
for turning the ed rod 44 and thereby either fixating or releasing the screw
holder 42 is attached to the end of the threaded rod 44 facing away from the
power line 32. A fixation spacer 50 is attached to the end of the threaded rod 44
facing towards the power line 32. The fixation plate 36 provides a larger fixation
area to fixate the power line 32 in a secure position. The fixation spacer 50 may
preferably be slightly undulated, corresponding to the outer surface of the power
line 32. By turning the handle 48 ise, the power line 18 may be firmly
fixated to the power line holder. Consequently, by turning the handle 48
anticlockwise, the power line 18 may be released.
The voltage sensor holder 38 r comprises an extension 52 and an
elongated rod 54 ed to the extension and opposite the remaining part of
the voltage sensor holder 32. The voltage Sensor 10 is attached to the elongated
rod 54. Since the e sensor holder 38 is made of metal, the elongated rod
will have the same potential as the power line 32.
Fig 3B shows a side view of a voltage sensor holder 38 being attached to a
power line 32, similar to the already shown holder of Fig 3A.
Fig 4 shows a high voltage pylon 56 ing multiple power lines 32, 32’, at
least some of which operate at different voltages, frequencies and/or phase
angles with respect to one another. The design of the pylon shown in Fig 4 is
only to be ued as an example and may vary depending on national and
local circumstances. The power lines 32 are separated from the grounded pylon
56 by insulators 58. The electro-optical crystal (not shown) of the voltage sensor
defines a minimum distance A to the power line 32. An electric field is
established from the power line 32 to the grounded pylon 56, to another power
line 32' which operates at another voltage, frequency and/or phase angle, and to
the ground 34. The electro- optical l (not shown) of the voltage sensor 10
defines a minimum distance Bl to the high voltage pylon 56 which is a ground
reference, a minimum distance 82 to another power line 32’ which operates at
another e, frequency and/or phase angle, and a minimum distance B3 to
the ground 34 surface on which the high voltage pylon 56 is located. Depending
on the ion and location of the voltage sensor 10, any of Bl, 82 or BB may
be the minimum distance. Typically, as shown, the voltage sensor 10 is located
close to the pylon and preferably near the insulator 58, and the distance Bl will
be the minimum distance. However, in case the voltage sensor 10 is located in
n two pylons 56, the minimum distance 82 or B3 to either another power
line 32’ or the ground will be smaller than the minimum distance Bl to the pylon
Fig 5A shows a combined tor and voltage measurement system. In a
l embodiment, a hollow insulator 58’ is coupled to a voltage sensor holder
38' made of dielectric material. The voltage sensor holder is in principle r
to the holder 38 of Fig 3A, but in on comprises a hollow loop 60 and a
hollow cylindrical base 62 attached to the hollow loop 60. The hollow cylindrical
base 62 has a circular opening 64 for accessing the inner space defined by the
hollow cylindrical base 62 and the hollow loop 60. The hollow loop 60 is attached
to the hollow cylindrical base 62 on the closed side opposite the circular opening
64. The power line holder 38 may be used to fixate the t measurement
system to the power line 32 in a flexible way. The power line 32 comprises an
elongated wire or a set of wires having a diameter of approximately 10 mm. For
normal air-insulated overhead applications, the power line 32 does not have any
insulating coating. The power line 32 may also comprise a set of thinner wires
bundled together. The power line 32 is made of a metal having excellent current-
conducting capabilities, typically aluminium, alternatively copper. A spacer 50
made of soft material such as plastic or rubber may be used to avoid direct
contact between the holder 38’ and the power line 32. The hollow loop 60, the
hollow cylindrical base 62 and the power line holder 38’ are made of a dielectric
material with sufficient rigidity to withstand many years of rs use. Such
material may e.g. be a composite polymeric material.
A voltage sensor 10 is located in a specific measurement position 10’ (dashed
line) inside the hollow loop 60. The voltage sensor comprises a small and
elongated cylinder made of plastic material and has a size fitting inside the
hollow loop 60. The specific measurement position is defined at a position
osed and perpendicular to the power line 32 so that the electric field lines
in the direction of the light beam through the voltage sensor 10 are maximized.
The voltage sensor 10 is fixated in the specific measurement position by a
fixation part 66. The on part 66 ses a flexible rod 68 and a gripping
member 70. The ng member 70 is ed to the flexible rod 68 and
comprises two claws ng the voltage sensor 10 and holding it in a secure
position. The flexible rod 68 is substantially ht in its relaxed state. By
positioning the flexible rod 68 inside the hollow loop 60, the flexible rod 68 will
assume a substantially bent state, thereby applying a friction force on the inner
wall of the hollow loop 60. The distance of the rod 68 will position the voltage
sensor 38 in the measurement position. The fibres 14, 18 are odated
inside the hollow loop 60. The optical fibre has a limited flexibility and may break
or be damaged when subject to a high bending force or curvature. The curvature
of the hollow loop 60 should not extend the maximum allowed curvature of the
optical fibres 14, 18. The fibres 14, 18 are preferably encapsulated in rubber,
plastic or the like. The hollow loop 60 must be made of a non-conducting
material to prevent it from shielding the sensor 10 from the electric field.
Fig SB shows a high voltage pylon 56 including a holder 38’ and hollow insulator
58' as bed above. The holder 38' is mounted on the hollow insulator 58' so
that the optical fibres 14, 18 may be led though the tor 58'. In this way,
the voltage sensor 10 and the optical fibres 14, 18 are well protected from wind
and weather. The optical fibres 14, 18 may be led via the pylon 56 to the base of
the pylon 56.
Fig 6A is a cross-sectional View of a second embodiment of a voltage sensor 10”
which is particularly adapted for outdoor use. The voltage sensor 10” comprises
an oblong housing 16' defining a first and an opposite second end designated
16” and 16’” respectively. At the first end 16” of the housing 16’ a first sealing
72 is mounted, the first sealing 72 having an aperture for receiving a first optical
fibre 14’. A first fibre fixture 74 is mounted in the housing 16’. The first fibre
fixture 74 has an re for receiving the opticai fibre 14’. A first optical lens
22 has a first receiving section 76 for ing the optical fibre 14’ and the first
fibre fixture 74. A circular polarization filter 26’ is d in optical
continuation of the first optical lens 22’. A crystal rod 28’ of electro-optical
material is located in optical continuation of the circular polarization filter 26’. At
‘10 the opposite end of the crystal rod 28’ a linear polarization filter 30’ is mounted
in optical continuation thereof. A second optical iens 24’ is d in optical
continuation of the second polarizatiOn filter 30’. The second optical lens 24’
includes a second receiving section 78 for receiving a second fibre e 80. A
second sealing 82 having an aperture for receiving a second l fibre 18’ is
iocated in optical continuation of the second fibre fixture 80.
Two optical fibres 14’, 18’ are inserted through the first and second seaiing 72,
82 into the first and second fibre fixtures 74, 80, respectively. The optical fibres
14’, 18’ are ically fixated to the housing 16’ by means of two sensor lids
84, 86, respectiveiy. The sensor lids 84, 86 fixate the fibres 14’, 18’ and seal the
voltage sensor 10”.
Fig 68 is a schematic perspective View of a voltage sensor 10’, illustrating a
groove 90 in the housing 16’ extending paraliel to the l rod 28’. The groove
90 may have a planar bottom wall or alternatively a rounded bottom wall for
improving the fixation of the voltage sensor 10’ to an electrical conductor. The
groove 90 is incorporated in the housing in order to bring the crystal rod 28’ as
close to the power line as possible and has the further advantage of fixating the
voltage sensor 10’ at a 90° angle with respect to the power line. The groove 90
may be of arbitrary length, but is preferably of the same iength as the crystal
rod 28’ or shorter.
Fig 6C is a schematic ctive View of a voltage sensor 10’ illustrating the
housing 16’ which may further comprise a set of wings 88 for mounting the
voltage sensor 10’ to a power line by plastic strips or other fastening means. The
al used for the g 16’ and lids 84, 86 is preferably a plastic material
capable of withstanding temperature ranges from -40 to 150°C and having
electrical ting properties. The material is preferably non—permeable to light
in the 400 to 1000 nm range. Materials having the above-mentioned properties
may be piastic materials such as Ultem or Peek. The fixation wings 88 may be
incorporated in a geometrical expansion of the groove 90 (not shown).
The l voltage sensor according to the present invention is very compact
and may advantageously be integrated in an optical voltage module (not shown)
which generates an analogue voltage over e.g. a CAN bus in an existing LV or
MV module. Hence, there is no need for specific changes to ng modules and
measurement setups.
Proof of concept
Fig 7 shows the s of the first proof of t experiment. The x—axis is the
applied voltage (in volts) and the y-axis is an arbitrary value representing the
measurement. In the first experiment, a sensor was built to be compatible with a
DISCOS® Opti module, which is a commercially avaiiable current ement
module produced by the applicant company. Thus the onic measurement
hardware, as well as the fibres and lenses, are ail commercially available. The
sensor house, electro-opticai glass rod and polarization filters in the normal
DISCOS® current sensor were replaced by a different custom-designed voltage
The first step of the proof of concept was to perform theoretical calculations to
check the feasibility of the present system and method. A computer program
was made, based on Jones a, which program can simulate the polarization
state of light passing though different media. The minimum current which is
detectable in a commercially ble optical current sensor module is
approximately 1A. The simulator was used to calculate the change in light
intensity resulting from 1A AC using the commercially ble current sensor
module. Subsequently it was determined which voltage was needed to be applied
to a voltage sensor in order to achieve the same light intensity change. The
result of the simulation was that a 1V signal from the voltage sensor
corresponded to a current signal of 50A. This means that a minimum voltage of
20mV is detectable, which is extremely sensitive, considering that the typically
voltages within the technical field of power distribution are many kV.
The i setup had the lens with the incoming light from a light—emitting
diode entering the sensor in one end. The light then traversed i eiements
(filters as weil as the crystal) before exiting into the other lens which focused the
light into the fibre, leading it back to a photo diode. The first filter was a linear
polarizer; the next a quarter-wave plate; then the light entered the KD*P crystal
and finally a second polarizer (also referred to as the analyzer). Electrodes were
also inserted on each side of the crystal, generating an electric field over the
crystal parallel to the light trajectory. This is calied a longitudinal sensor or
longitudinal setup, because the electric field is parallel to the light trajectory.
The first sensor used polaroid s cut from a sheet similar to the ones used in
the t sensor. The half—wave plate used was of extremely high precision
and was acquired from the company BBT. The electro~optical crystals were
acquired from the company EKSMA. Such crystals may be specifically grown and
cut ing to specifications. The dimensions of the crystals used were (x,y,z)
= (1,1,2) cm, with the z-axis being parallel to the light trajectory. The crystal
was cut so that an electric field applied along the z-axis induced a i axis
along the x—axis (thus making it a longitudinal sensor). The electrodes were thin
copper plates, each with a hole in the middle to allow the sensor and the light to
pass through.
The fibre was connected to the above mentioned DISCOS® Opti module, which
is a current sensor, and ements were taken with a graphical PC tool
known as nTM. The result of the first experiment is shown in the graph in
Fig 7.
As can be seen from Fig 7, one applied Volt reads almost as one Ampere signal
from a current . The results are well within the sensitivity of the
equipment used, albeit not quite as good as theoretically predicted when using
the above mentioned software. The pancy in relation to the theoretically
predicted results may be explained by the fact that quite a large amount of light
was lost in the filters.
It was discovered that the length of the crystal along the light path was
inconsequential, as the increase in retardance clue to length was cancelled out by
the decrease in the electric field due to the increased distance between the
electrodes on either side of the crystal. However, a shorter crystal has other
advantages such as reduced loss of light and reduced cost. So the next sensors
were made with 5mm long crystals. Further, it was discovered that modern 3D
glasses, such as the ones used in cinemas for viewing 30 movies like the well-
known movie Avatar, are in fact circular polarizers. Hence it was possible to
replace the first polarizer filter and the ive r—wave plate by a single
film cut from such 3D glasses. The polarizing film used in the 3D glasses is also
commercially available in the form of sheets.
Fig 8 shows the results of the second proof of concept experiment. The x-axis is
the applied voltage and the y-axis is the ement. In the second
experiment, a combined first polarizer filter and quarter-wave plate was used.
This resulted in a lower loss of light compared to using a separate poiarizer filter
and quarter-wave plate.
In order to achieve a maximized E-field over the electro-optical l, the
voltage should be applied to ng electrodes located on each side of the
crystal and constituting ground and line voltage, respectively. However, any
conductor radiates an electric field, and close to the conductor the electric field
strength can be quite intensive. Since it is possible to measure a potential drop
over the crystal of only a couple of volts, a wire of 10 kV will also be measurable,
even though there may be several meters to the nearest ground.
Fig 9 shows the result of two measurements made very close to the conductor.
The x-axis is the d voltage (in W) and the y—axis is an arbitrary value
representing the measurement. The solid line in Fig 9 shows the results of a
voltage measurement in which the sensor points away from the conductor at a
distance of about 2 cm. The results show that the voitage is certainly
eable even in case the ground is located at a distant location. r,
3O this approach makes the voltage sensor more susceptible to the E— field from
neighboring phases in a three—phase system, which neighboring phases must of
course not influence the measurement. However, the field strength drops
proportionally to the reciprocal of the squared distance, and as the neighboring
conductor is at least about 100 times r away from the sensor than the
tor to be ed and the field vector of the neighboring phase is
typically at an angle to the crystal, the effect of the neighboring phase may be
neglected.
The next phase was to build an all—optical combined sensor. For the attempt a
standard overhead DISCOS® Outdoor Combined Sensor was used. Two fibres
were pulled through the top part of the sensor, one of which went to the current
sensor aiso placed in the top part. The other fibre went all the way through the
top part to the e sensor which was placed just under the top part. The
voltage sensor was placed so that light pointed away from the conductor, which
was parallel to the ic field radiated by the conductor. An empty insulating
tube was attached to the the sensor's bottom, which was a metal plate
ted to the ground potential. This created a more powerful and
neous field inside the tube (in which the sensor was placed). The result
is shown by the dashed line in Fig 9.
The measurement by the overhead sensor was carried out without the bottom
plate being grounded. However, connecting the plate gave only a small change
in signal, possibiy due to the relatively large length of the tube (28 cm) and thus
distance to the grounded bottom. This does give some support to the idea that
the close field is indifferent to the far away geometry, thus eliminating the
necessity of a ground tion in the sensor, even if there are other phases in
the vicinity. Later calculations have confirmed that the close proximity field is in
fact almost independent of nearby wires of different potential.
The specifications of the proposed all-optical combined sensor can easiest be
described by comparing them to the DISCOS outdoor ed sensor. The
specifications of the former are very similar to the latter, with some key
differences.
Specification of the prototype:
Voltage range: 100 V — 500.000 V. The lower voltage can be as low as about 1
V, but this will require electrodes being attached on either side of the sensor,
which will lower the max voltage.
Estimated accuracy: 2%. The ion in light intensity is much like that caused
by the current sensor, and the electronics will be very (or maybe y)
similar, hence the accuracy will likely be about the same.
Material of conductor: preferably aluminum, copper or any other tive
material
Operational temperature: —40°C to 75°C
Weight: ~ 500 9
Expected lifetime: 50 years
Reference numerals with reference to the figures:
Claims (40)
1. An AC or DC power ission system comprising a first electrical conductor, a second electrical conductor and an insulating space between said first electrical conductor and said second electrical conductor, said power transmission system further comprising an electric field measurement device, said electric field measurement device comprising: a housing made of dielectric material and defining a first open end ‘10 and a second open end opposite said first open end, a first optical fibre being connected to a light source, a first optical lens being mounted in said housing at said first open end and in optical uation of said first optical fibre, a circular polarization filter mounted in said housing in optical 15 continuation of said first optical lens, a crystal rod received in and encapsulated within said housing in optical continuation of said circular zation filter, said crystal rod being made of a material having electro-optical properties, a linear polarization filter mounted in said g in optical 20 continuation of said crystal rocl, a second optical lens mounted in said housing at said second open end in optical continuation of said linear polarization filter, and a second optical fibre in optical continuation of said second optical lens, said second optical fibre being connected to a light detection unit, said 25 electric field measurement device being located adjacent said first electrical conductor within said insulating space and defining a first m ce between said crystal rod and said first ical conductor and defining a second minimum ce between said crystal rod and said second electrical conductor, said second minimum distance being at least 10 times larger than said first 30 minimum ce.
2. The power transmission system according to claim 1, n said second minimum distance is at least 100 times larger than said first minimum distance.
3. The power transmission system according to claim 1, n said second minimum distance is at least 1000 times larger than said first minimum distance.
4. The power transmission system according to claim 1, wherein said second minimum distance is at least 10,000 times larger than said first minimum distance.
5. The power transmission system according to claim 1, wherein said 10 second m distance is at least 0 times iarger than said first minimum distance.
6. The power transmission system according to claim 1, wherein said first eiectrical conductor comprises an overhead line or a metallic object 15 electrically connected to an overhead line.
7. The power transmission system according to any one of the preceding claims, wherein said second electricai conductor comprises a metallic object being insulated in relation to said first electrical tor.
8. The power transmission system according to any one of the preceding , wherein said second electrical tor constitutes the ground. 25
9. The power transmission system according to any one of the preceding ciaims, wherein said first electrical conductor of said power transmission system has a rated voltage of between 0,1kV and 1000kV.
10. The power transmission system according to any one of claims 1—8, 30 wherein said first electrical conductor of said power transmission system has a rated voltage of nlkv and SOOkV.
11. The power transmission system ing to any one of claims 1-8, wherein said first electrical conductor of said power transmission system has a 35 rated voltage of between SW and 100kV.
12. The power transmission system according to any one of ciaims 1-8, wherein said first electrical conductor of said power transmission system has a rated voltage of between 10kv and SOkV.
13. The power transmission system according to any one of the preceding claims, wherein said crystal rod is being exposed to an effective electric fieid strength of between 1"‘104 V/m and l.2"‘108 V/m when said power transmission system is being operated at its rated voltage. ‘10
14. The power transmission system according to any one of claims 1- 12, wherein said crystal rod is being exposed to an effective electric fieid strength of between 1*105 V/m and 1.2”‘107 V/m when said power transmission system is being operated at its rated voltage.
15 15. The power transmission system according to any one of the ing claims, wherein said first minimum distance is between 0,1mm and 100mm.
16. The power transmission system according to any one of the 20 preceding claims 1—14, wherein said first minimum distance is n 1mm and 10mm.
17. The power transmission system according to any one of the preceding claims, n said second minimum distance is between 0,1m and 25 100m.
18. The power transmission system according to any one of the ing claims 1—16, n said second minimum distance is between 1m and 10m.
19. The power transmission system according to any one of the preceding claims, wherein the light path through said crystal rod is oriented substantially parallel to the electric field at said first tor, or alternatively, wherein the light path h said crystal rod is oriented ntially 35 perpendicular to the electric field at said first conductor.
20. The power transmission system according to any one of the preceding , wherein said ar polarization filter consists of a quarter- wave plate and a linear polarizer.
21. The power transmission system according to any one of the preceding claims, wherein said crystal rod exhibits the Pockels effect.
22. The power ission system according to claim 21, wherein said crystal rod is made of potassium phosphate. 10
23. The power ission system according to any one of the ing claims, wherein said electric field measurement device further comprises: a first sealing means for sealing said first end of said housing, said first sealing means having an aperture for receiving said first l fibre, 15 a first fixture means for fixating said first optical fibre to said housing, a first reception part being attached to said first optical lens and adapted for receiving said first fixture means, a second fixture means for fixating said second optical fibre to said 20 housing, a second reception part being attached to said second optical lens and adapted for ing said second fixture means, a second sealing means for sealing said second end of said housing, said second sealing means having an aperture for ing said second optical 25 fibre, and a first and a second lid fixated to said first and second end, respectively, of said g, said first and second lid including an aperture for respectively receiving said first and second optical fibre. 3O
24. The power transmission system according to any one of the preceding claims, wherein said housing is made of polymeric al, such as piastic.
25. A method of measuring a voltage of a first eiectrical conductor in 35 relation to a second electrical conductor spaced apart from said first electrical conductor by an insulating space, said method comprising providing an electric field measurement device, said electric field measurement device comprising: a housing made of dielectric material and defining a first open end and a second open end opposite said first open end, a first optical fibre being connected to a light source, a first optical lens being mounted in said g at said first open end and in optical continuation of said a first optical fibre, a circular polarization filter mounted in said housing in optical continuation of said first l lens, a crystal rod received in and encapsulated within said housing in optical continuation of said ar polarization filter, said crystal rod being made 10 of a material having electro-opticai properties, a linear polarization filter mounted in said housing in optical continuation of said crystal rod, a second optical lens mounted in said housing at said second open end in optical continuation of said linear polarization filter, and 15 a second l fibre in l continuation of said second optical lens, said second optical fibre being connected to a light detection unit, said method further sing the following steps: positioning said electric field measurement device adjacent said first electrical conductor within said insulating space so that a first minimum distance 20 defined between said crystal rod and said first electrical conductor is at least 10 times larger than a second minimum distance defined between said crystal rod and said second ical conductor, and detecting a ve retardance between light d by said light source and light detected by said light detection unit.
26. The method of claim 25 wherein said second minimum distance is at least 100 times larger than said first minimum distance.
27. The method of claim 25 wherein said second minimum ce is 30 at least 1000 times larger than said first minimum distance.
28. The method of claim 25 wherein said second minimum distance is at least 10,000 times larger than said first minimum distance. 35
29. The method of claim 25 wherein said second minimum distance is at least 100,000 times larger than said first minimum distance.
30. A method of calibrating an electric field measurement device included in a power transmission system, said power transmission system comprising a first electrical conductor having a known voltage, a second electrical conductor having another known voltage and an insulating space between said first ical conductor and said second electrical conductor, said electric field measurement device comprising: a housing made of dielectric material and ng a first open end and a second open end opposite said first open end, a first optical fibre being connected to a light , 10 a first optical lens being mounted in said housing at said first open end and in optical continuation of said first optical fibre, a circular polarization filter mounted in said housing in optical continuation of said first optical lens, a crystal rod received in and encapsulated within said housing in 15 optical continuation of said ar polarization filter, said crystal rod being made of a material having eiectro—optical ties, a linear polarization filter mounted in said housing in optical continuation of said crystal rod, a second optical lens mounted in said housing at said second open 20 end in optical continuation of said linear polarization filter, and a second optical fibre in optical continuation of said second optical lens, said second l fibre being connected to a light detection unit, said electric field measurement device being located adjacent said first ical conductor within said insulating space and defining a first minimum distance 25 between said crystal rod and said first electrical conductor and defining a second minimum distance between said crystal rod and said second electrical conductor, said second minimum distance being at least 10 times larger than said first minimum distance, said method sing the steps of: 30 ing a relative retardance between light emitted by said light source and light detected by said light detection unit, and calculating a calibration constant based on said relative rotation and said known voltages. 35
31. The method of claim 30 wherein said second minimum distance is at least 100 times larger than said first minimum distance.
32. The method of claim 30 wherein said second minimum distance is at least 1000 times larger than said first minimum distance.
33. The method of claim 30 wherein said second minimum distance is at least 10,000 times larger than said first minimum distance.
34. The method of claim 30 wherein said second minimum ce is at least 100,000 times larger than said first minimum distance. 10
35. The power transmission system according to any one of the claims 1—24, wherein said insulating space constitutes a gas insulated space.
36. The power transmission system of claim 35, wherein said gas insulated space is a space filled by one of N; or SFa. 15
37. The power transmission system of claim 35, wherein said gas insulated space is a space filled by heric gas.
38. An AC or DC power transmission system substantialty as herein bed with reference to any embodiment shown in the accompanying 20 drawings.
39. A method of measuring a e substantially as herein described with reference to any embodiment shown in the accompanying drawings. 25
40. A method of calibrating an electric fieid measurement device included in a power ission system, said method substantially as herein described with reference to any embodiment shown in the accompanying drawings. WO 98099
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP11151637.3 | 2011-01-21 | ||
EP11151637A EP2479581A1 (en) | 2011-01-21 | 2011-01-21 | An AC or DC power transmission system and a method of measuring a voltage |
PCT/EP2012/050615 WO2012098099A1 (en) | 2011-01-21 | 2012-01-17 | An ac or dc power transmission system and a method of measuring a voltage |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ613474A NZ613474A (en) | 2014-07-25 |
NZ613474B2 true NZ613474B2 (en) | 2014-10-29 |
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