Note: Descriptions are shown in the official language in which they were submitted.
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= COMPACT APPARATUS FOR DETECTING FAULTY
COMPOSITE INSULATORS USED ON ELECTRIC
DISTRIBUTION SYSTEMS
BACKGROUND OF THE INVENTION
[001] Composite insulators are sed to mechanically support an electrical
conductor
while electrically insulating the conductor from the grounded structures.
Composite or non-ceramic insulators (NCI) have been widely used on electrical
networks since the 1980s. Composite insulators can be found under multiple
designs, materials and manufacturing processes. They are preferred to ceramic
insulators because of their low weight, low installation cost, higher
resistance,
strength as well as higher contamination resistance due to their hydrophobic
surface.
[002] However, the most important issue that limits the widespread application
of
composite insulators is the issue of assessing their in-service condition
using
actual live line diagnostic methods (LLDM). As reported by the literature [1],
no
single diagnostic technique has yet emerged that can identify all the possible
types of damage that could exist in a composite insulator. This means that a
variety of complementary LLDM and procedures must be employed in order to
identify the absence of critical defects of composite insulators and to carry
out
live line work (LLW) safely on overhead lines equipped with composite
insulators. This fact seems to be a limited factor in the application on
composite
insulator on wide scale.
[003] In order to ensure their safety when performing LLW with composite
insulators,
line men workers need to confirm the electrical integrity of the insulators
for the
duration of their work. For that, there are currently two identified apparatus
which are used by the electrical compagnies all around the word.
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[004] The first method used by the line men to verify the electrical integrity
of the
composite insulators is the apparatus for detecting defective insulators in an
insulating column supporting an electrical conductor in a power circuit line
[2].
Originally developped to identify defective ceramic insulators in a column
made
of a plurality of serially connected insulator members, this apparatus,
commercially called the positron insulator tester, was later adapted for
composite insulators. This apparatus is based on the measurement of the axial
component of the electric field in front of the insulator at the extremity of
the
composite insulator sheds. The apparatus uses a pair of metallic electrodes
which are displaced along the composite insulator. A measure is taken at each
insulator shed extremity in order to record the distribution of the axial
electric
field component of the defective composite insulator. When a conductive defect
is present, the distribution of the axial electric field component measured at
the
extremity of the insulator sheds is modified depending on the position and the
length of the defect. In order to identify the presence of the defect, this
apparatus
proposes two operating modes. The first mode is a Go/ No Go mode which can
detect immediately the presence of a defect closed to the High voltage (HV)
electrode of the composite insulator. However, this function requires the
adjustement of a threshold which must be selected and ajusted by the user on
power-up depending on the power line voltage. The second mode is the
investigation mode which is used to record and display on a Laptop the axial
electric field distribution obtained at the tip of the sheds along the
insulator. The
investigation mode is generally used to validate the alarm obtained with the
Go/
No Go mode. For that, the investigation mode must compare the recorded axial
electric field distribution of the defective composite insulator to a recorded
axial
electric field distribution obtained from a sound insulator. The diagnostic is
done
via a Laptop PC and a specific software which records the data of the
apparatus
via bluetooth link. The Laptop is not intended to be used by the lineperson on
top of the tower and must be used by the supervisor on the ground level.
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However, this apparatus presents some limitations as reported by the
litterature
[1]. The proposed apparatus may not detect low severity defects near the end
fitting of the composite insulators when there are equipped with a corona ring
due to the electric field shielding induced by the corona ring. Also, it was
reported that the use of this apparatus is quite demanding in terms of
time/cost
and expertise as two peoples (the lineman on the tower and the supervisor on
the
ground level) are required to provide a reliable diagnostic of the insulator
integrity and a well trained person to adjust the thresold level of the GO/ NO
GO
mode. Finally, the Go/ NO GO mode does not permit to identify defect at the
grounded end of the insulator as well as the defects at floating potential
positionned in the middle of the insulator.
[005] The second method used by the line person to verify the electrical
integrity of
the composite insulators is the apparatus and method for identifying high risk
non-ceramic insulators with conductive or high permittivity defects [3], also
called polymer insulator tester. The diagnostic method used by this apparatus
consists in submitting the defective composite insulator to a high voltage at
various frequencies for a pre-determined amount of time to determine a
resonance frequency of the defective composite insulator. The measured
resonance frequency obtained for the defective insulator is then compare to a
calibration result set obtained from a sound composite insulator of the same
type
that the potentially defective insulator tested. The high voltage of various
frequency is applied between two electrodes positionned between the insulator
sheds at spaced of about 152 mm. The electrode spacing corresponds to the
section legnth of the insulator which can be tested. This method permits to
detect
high permittivity and conductive defects at any place along the composite
insulator. However, with a weight of 2 kg, this apparatus when mounted on a
hotstick is quite demanding in terms of manipulation for the lineperson
working
on the tower.
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[006] The above-described apparatus and methods of the prior art presents some
additional disadvantages than those mentionned previously. Both of them
required to compare the different measurement obtained on the defective
insulator with a reference measurement taken on a sound insulator of the same
type than the inspected insulator. This implies that the user must be well
trained
in order to provide a reliable calibration of two mentionned apparatus and
consequently to provide a reliable diagnostic of the electrical integrity of
the
composite insulator under test. Also, the two above-described apparatus of the
prior art are not compact in size. Consequently, they are difficult to handle
when
mounted at the extremity of a hotstick. Moreover, due to their size, the
section
closed to the fly end of the composite insulator surrounding by a corona ring
is
not accessible. This can be problematic as this section closed to the HV
electrode of the insulator presents a high probability of internal defects. If
this
section can not be tested, this could represent a life-threatening situation
for the
lineperson. Accordingly, there is a need for an apparatus and method that can
identify electrical integrity of installed polymer insulators
BREF SUMMARY OF THE INVENTION
[007] It is a feature of this invention to provide a novel and compact
apparatus which
substantially overcomes all of the above-mentioned disadvantages of the prior
art, which provides a compact apparatus for identifying high risk defective
composite insulators with conductive or high permittivity defects
independently
of the position of the defects along the composite insulator. The apparatus is
compact, portable, lightweight, able to be used on energized installed
insulators.
The method used by the detector is simple in its concept which does not
require
a calibration on a sound composite insulator in order to provide a reference
measurement. The apparatus provides a simple "Go/No Go" output and a simple
visualization method of the presence of the defect available by the user via a
specific display program compatible with common Cellphone OS technology.
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[008] According to an aspect of the invention, the apparatus has the capacity
to
identify the presence of conductive, semi-conductive or high permittivity
defects, both internal and external without electrical contact with these
defects.
The apparatus is in the form of a circular clamp made of composite insulating
material inside which a plurality of measuring electrodes are equally spaced
around the diameter of the clamp. These measuring electrodes are surrounded by
a coaxial reference electrode at a pre-determined spacing from the measuring
electrodes. The measuring electrodes and reference electrode are positionned
around the core of the composite insulator, between its sheds, and the voltage
of
each measuring electrodes referenced to the reference electrode is obtained
thanks to the electronic measuring and detection system embeded in the
apparatus. The measuring and references electrodes are positionned in a way to
measure an image of the radial electric field component distribution around
the
insulator core.
[009] According to an other aspect of the invention, a method of evaluating
insulators
for defects includes the steps of providing a compact apparatus for
identifying
high risk insulators having a microprocessor, a plurality of uniformly spaced
measuring electrodes, and a reference electrode. The method further includes
the
steps of engaging the uniformly spaced measuring electrodes and reference
electrode around the core of a composite insulator to be tested, measuring the
potential of each measuring electrode referenced to the reference electrode to
determine the magnitude of the radial component of the electric field at each
position of the measuring electrodes, and conducting measurements during a
pre-determined amount of time to detect any distortion in the distribution of
the
radial electric field component around the core of the composite insulator to
be
tested.
[1] F. Schumk, J. Seifert, I. Gutman and A. Pigini, 'Assessment of the
Condition of
Overhead Line Composite Insulators', CIGRE WG B2-214, 2012.
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[2] G. H. Vaillancourt and F. Risk, 'Apparatus for detecting defective
insulators in an
insulating column supporting an electrical conductor in a power line', US
patent
4760343 A, 1988.
[3] A. J. Phillips, M. Major, R. Carlton Lynch, P. N. Beverly and S. H. Moins,
'Apparatus and method for identifying high risk non-ceramic (nci) with
conductive
or high permittivity defects', US 20130043881 Al, 2013.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[010] The subject matter that is regarded as the invention may be best
understood by
reference to the following description taken in conjunction with the
accompanying drawing figures in which:
[011] FIG. 1 illustrates a schematic view of a composite insulator supporting
a HV
electrical conductor of an overhead electric line;
[012] FIG. 2A and 2B present a numerical comparison of the distribution of the
equipotential lines with and without the presence of a semi-conductive
internal
defect closed to the HV metallic electrode of an energised composite insulator
respectively.
[013] FIG. 3A and 3B illustrates a numerical comparison of the distribution of
the
radial electric field lines obtained in the vicinity of the HV electrode of an
energised composite insulator with and without the semi-conductive internal
defect of FIG. 2.
[014] FIG. 4A and 4B presents an example of the distributions of the
normalized axial
and the radial electric field components (in pm.) around the core of the
composite insulator at 3 mm of the surface between the HV electrode and the
first shed obtained with and without the semi-conductive internal defect of
FIG
2 respectively.
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[015] FIG. 5A presents an illustration of an internal defect at the ground
electrode of
the composite insulator and FIG. 5B presents an example of the distributions
of
the normalized axial and radial electric field components (in p.u.) around the
core of the composite insulator at 3 mm of the surface between the HV
electrode
and the first shed obtained with the semi-conductive internal defect of FIG
5A.
[016] FIG. 6 is an example of the perspective view of the apparatus being
installed on
one end of a hotstick and engaged around the envelope between sheds of said
composite insulator;
[017] FIG. 7 is a perspective view of an example of the construction of the
apparatus
with an example of the arrangement of the measuring and reference electrodes
as well as the arrangement of the shielding protection for the electronic
circuit of
measurement, detection and data transmission;
[018] FIG. 8 presents an exemple of experimental results obtained with the
apparauts
of FIG. 7 obtained for an internal conductive defect positionned at the HV end
of a 69 kV composite insulator.
[019] FIG. 9 is a schematic diagram of the measuring, detection and data
transmission
circuits associated with and contained within the apparatus;
[020] FIG. 10 presents an example of the type of display from the electronic
circuit
which permits to visualize the results obtained from FIG. 8.
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DETAILED DESCRIPTION OF THE INVENTION
[021] Referring now to the drawings and more particularly to FIGS. 1, 2 and 3,
there is
shown generally a composite insulator 10 supporting an high voltage (HV)
electrical conductor 11, as used in an overhead electrical line. At each
extremity
of the composite insulator, there is a metallic electrode: the HV electrode 12
which mechinally connect the insulator to the electrical conductor at HV
voltage
and the ground electrode 13 which mechinally connect the composite insulator
to the tower 14 at the ground potential. The composite insulator 10 is formed
of a core 15 made of a fiber glass rod on which is molded the envelop 16 with
the sheds made of composite materail like silicone.
[022] When the HV electrical conductor 11 is energised under HV service
voltage, the
distribution of the equipotential lines 17 that originates on this composite
insulator can be represented numerically by FIG. 2A for a safe insulator. For
the
same composite insulator with a semi-conductive internal defect 18 present
between the core 15 and the envelop 16, numerical simulation permits to show
that the equipotential lines 17 are modified in the vicinity of the internal
defect
18 and closed to the HV electrode 12, as shown in FIG. 2B. When the HV
electrical conductor 11 is energised, an electric field is also present around
the
composite insulator 10. FIG. 3A presents the distribution of the electric
field
lines 19 obtained for a safe composite insulator, in the vincinity of the HV
electrode 12. When a semi-conductive internal defect 18 is present, the
distribution of the electric field lines 19 is significantly pertubed, as
demonstrated by the FIG. 3B, in the vicinity of the position of the internal
defect
18.
[023] The perturbation induced by the internal defect can be clearly
visualized by the
results of FIG. 4A where the distributions of the normalized radial 20 and
axial
21 electric field components were computed between the HV insulator electrode
and the first shed, on a circular line coaxial to the core 15 of the insulator
at 3
mm from the surface of the envelope 16. The results of FIG. 4A clearly
illustrate
. .
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that the presence of the defect leads to a significant perturbation of the
both
radial 20 and axial 21 electric field components. The perturbation induced in
the
radial electric field component 20 corresponds to an increase of about 62%.
This
can be compared to the decrease of 27% obtained for the axial electric field
component 21. The results can be compared to the results of FIG. 4B obtained
without internal defect with a variation of less than 12% and 2% in obtained
in
radial 20 and axial 21 electric field component respectively. The larger
variation
of the radial electric field component 21 is principally due to the presence
of the
energized conductor 11 at the HV electrode 14, as illustrated by FIG. 1. These
results clearly demonstrate that the radial electric field component 20 is
more
sensitive to the presence of the internal defect than the axial electric field
component 21.
[024] When the internal defect 18 is present at the ground electrode 13 of the
composite insulator 10, as illustrated by FIG. 5A, the perturbation induced by
the internal defect on the radial 20 and axial 21 electric field components is
presented on FIG. 5B. The perturbation induced in the radial electric field
component 20 corresponds to an increase of about 56%, which can be compared
to the decrease of 38% obtained for the axial electric field component 21.
These
results demonstrate that the radial electric field component 20 is also more
sensitive to the presence of the internal defect than the axial electric field
component 21.
[025] As demonstrated by the numerical results of FIG. 2 to 5, the measurement
of the
uniformity of the distribution of the radial electric field component 18
around
the surface of the composite insulator between the shed of the envelope 16 can
be a good indication of the presence of an internal defect between the core 15
and the enveloppe 16 of the composite insulator 10 and this, independantly of
the position along the composite insulator 10 of the internal defect 18.
Measuring the uniformity of the radial electric field component 20 around the
_
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surface of the core between the composite insulator sheds is the fundamental
concept of the present invention which general concept is illustrated on FIG.
6.
[026] As illustrated on FIG. 6, the apparatus of the invention has the form of
a circular
clamp 30 which is engaged between the sheds of the composite insulator 10 and
closed on the envelope 16 of the composite insulator in order to perform the
measurement of the radial electric field component distribution. The clamp 30
is
fixed at the end of a hotstick 23 thanks to a joint 22 which permits to orient
the
clamp 30 is several directions. The specific geometry of the clamp, as
presented
in detail in FIG. 7, allows the lineman to easily engage the clamp between the
sheds of the envelope 16 of the composite insulator 10 by applying a pressure
on
the hotstick 23. The compact size and low weight of the clamp allows the
lineman to easily perform measurement at predetermined positions along the
composite insulator 10.
[027] As illustrated by FIG. 7, the apparatus of the invention has the form of
a circular
clamp 30 made of two parts : a fixed part 31 and a moving part 32. The moving
part 32 is attached to the fixed part 31 via a hinge 33 containing a metallic
spring (not represented on the FIG. 7). The metallic spring permits to
maintain
the fixed part 31 and moving part 32 in contact in order to close the clamp 30
on
the envelope 16 of the composite insulator 10 once the clamp 30 is engaged
between the sheds of the composite insulator 10. The extremity of the fixed
and
moving parts 31 and 32 present the same specific turned up geometry permitting
to engage the clamp 30 around the composite insulator envelope 16 when the
lineman applies a force on the opposite end of the hotstick 23. The internal
diameter of the clamp 30 can be adjusted to the diameter betwwen shed of the
composite insulator envelope 16 to ensure that the clamp 30 is well centered
around the composite insulator 10. This also permits to the lineman to
correctly
orient the clamp 30 in a plane perpendicular to the longitudinal axis of the
composite insulator as the joint 22 pivotally connected the clamp 30 to the
hotstick 23 allows several degrees of freedom for the orientation of clamp 30.
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[028] Once the clamp 20 is closed on the envelope 16 between sheds of the
composite
insulator 10, the uniformity of the radial electric field component around the
surface of the envelope can be determined. As illustrated by FIG. 7, the
determination of the uniformity of the radial electric field distribution is
obtained by using a specific arrangement of electrodes 34 and 35. The
measuring electrodes 34 present the same dimension equally spaced on the same
perimeter inside the clamp 30 and axially positionned at the same distance
than
the center of the clamp 30. The reference electrode 35 is composed of two
parts
to permit the opening of the clamp. These two parts are electrically connected
via the electricla link 36. The reference electrode 35 is positionned on a
larger
perimeter than the measuring electrodes 34 and centered with respect to the
center of the clamp 30. In this manner, the distance separated the measuring
electrodes 34 and the reference electrode 35 is exaclty the same. The presence
of
the reference electrode 35 is significant as it permits to provide an uniform
reference potential around the measuring electrodes 34 by uniformise the
radial
component 20 of the electric field distribution around the measuring
electrodes
34 which is not really uniform in the vicinity of the HV electrode 12, as
demonstrated in FIG. 4B.
[029] The number and the size of the measuring electrodes 34 depends
principally on
the diameter of the insulator core. In the example of FIG. 7, the clamp 30
presents a configuration of six measuring electrodes 26. The number of
measuring electrodes 26 can be adjuted to the diameter between sheds of the
composite insulator envelope 26 in order to provide a optimal estimation of
the
radial electric field component distribution 20.
[030] When a conductive or semi-conductive internal defect 18 is present at
the HV
electrode 12 (FIG. 3B) or the ground electrode 13 (FIG. 5A), a local increase
of
the radial electric field component 20 in the vicinity of the internal defect
can be
observed, as demonstrated by FIG 4A and 5B. This increase of the radial
electric
field component 20 leads to an increase of the potential of the measuring
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electrodes 34 situated on and closed to the internal defect position. This
increase
can be observed on the FIG. 8 by the experimental measurements obtained with
a prototype of a clamp 30 containing six measuring electrodes 34, as presented
in FIG. 7. The distribution 39 of FIG. 8 presents the normalized potential
distribution of six measuring electrodes 34 with a peak value obtained for the
measuring electrode 5 which was positionned directly on the internal defect 18
positionned at the HV electrode 12. The distribution 39 can be compared to the
normalized potential distribution 40 obtained for the same position of the
clamp
30 but without internal defect. In presence of an internal defect 18 at the HV
electrode 12, an increase of around 65% is obtained in the normalized
potential
distribution 39, compared to an variation of less than 15% when no internal
defect is present. Such significant increase can then be easily detected in
order
to provide a diagnostic on the presence of a internal defect and, above all,
this
does not require the use of a comparison with any signature or signal
reference
obtained for a sound composite insulator, as used by actual apparatus
presented
in the state of art. The only requirement to provide a simple diagnostic is to
detect the non uniformity of the potential distribution 39 obtained between
the
sheds of the composite insulator 10. This can be achieved in different manners
using several statistical tools like the deviation relative to the average of
potential measurements obtained. For example, in the case of the results
presented on FIG. 8, the maximum deviation obtained is equal to 79% with an
internal defect and less than 13% without defect. In this way, by fixing a
deviation threshold of around 30%, all the deviations greater than this
threshold
correspond to the presence of an internale defect. The indication of the
presence
of an internal defect is provided via a light emitting device indication 38
which
turns red or green dependently if the calculated deviation is greater or lower
than
the fixed threshold value.
[031] The potential of each measuring electrode 34 referenced to the reference
electrode 35 is obtained via the measuring, amplification, signal treatment
and
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detection and transmission electronic system embeded in the clamp 30 which
will be described later. As presented on FIG. 7, the measuring, detection and
transmission electronic system positionned in the outer part of the clamp 30
is
protected from the electric field and partial discharges present around the
composite insulator using a flexible shielding material 37 which acts as a
Faraday cage. In order to match the circular shape of the clamp 30, the
electronic system is obtained using flexible plastic substrate.
[032] FIG. 9 presents the block diagramm of the measuring, amplification,
signal
treatment and detection and transmission electronic system. The potential of
each measuring electrode 34 is measured using the same electronic circuit
associtated to each electrode 34 consisting in: a protection circuit 41, a
programmable gain amplifier/attenuator 42 and a analogic/digital convertor
(ADC) 43. The amplifier/attenuator 43 is controlled via the microcontroller 44
which can automatically adjust the gain to provide the optimal analogic
voltage
of the measuring electrode 34 before its digital conversion by the ADC 43.
Once
digitized, the potential of each measuring electrode 34 is readed by the
microcontroller 44 which computes the deviation or other mathematical tool
relative to the average of the potential measurements of the measuring probes
34
and verify if the value is higher or lower than the fixed thresold. If the
result is
higher, the light emitting device 38 is turned to red which indicates the
presence
of a defect where the clamp 30 is positionned along the composite insulator
10.
In contrary, the light emitting device 38 is turned to green if the value is
lower
than the fixed threshold, which also indicated the presence of an applied
voltage
on the composite insulator. In the same time, the normalized value of each
measuring electrode potential is sent via the wireless communication module 45
to a smart device which can be positionned on the other extremity of the
hotstick
22 in order to provide the lineman with the graphical display of the measuring
electrodes potential, as illustrated by FIG. 10. The measuring, detection and
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transmission electronic system is powered by the module 46 containing
batteries, a charger and a voltage regulator.
[033] FIG. 10A and FIG. 10B present two examples of a display of the potential
distribution obtained for a clamp 30 equipped with six measuring electrodes
34. The
two displays are constitued of the representation of the potential
distribution 39 of the
six measuring electrodes 34 numbered form 1 to 6, a circle 40 representing the
average
of the potential measurements and a circle 41 representing a threshold of 30%.
The
display of FIG. 10A clearly illustrates the presence of an intenal defect at
the HV
electrode positionned on the measuring electrode 5 which presents the higher
potential
value. Moreover, this value exceed the threshold 41 which confirms the
presence of the
internal defect. In the display of FIG. 10B, it can be observed that the
distribution 39 is
quite uniform and does not exceed the threshold 41, meaning that there is not
present of
internal defect where the clamp is positionned. The graphics presented on FIG.
10 can
be displayed using smart devices like tablets or smart phones which can be
linked to the
clamp 30 via wireless communications. These displays will assist the lineman
to
perform the diagnostic of the composite insulator as it permits to the lineman
to judge
of the uniformity of the distribution of potential of the measuring electrodes
34. This is
a diagnotic tool which is complementary to the automatic detection provided by
the
microcontroller 44 and the visual indication 38, then provided a double
verification for
the lineman.
