U.S. patent application number 14/869387 was filed with the patent office on 2016-01-21 for leakage current sensor for suspension type insulator.
The applicant listed for this patent is Electric Power Research Institute, Inc.. Invention is credited to Christiaan Stephan Engelbrecht, Robert Carlton Lynch, J. Mark Major, Andrew John Phillips.
Application Number | 20160018455 14/869387 |
Document ID | / |
Family ID | 48694328 |
Filed Date | 2016-01-21 |
United States Patent
Application |
20160018455 |
Kind Code |
A1 |
Phillips; Andrew John ; et
al. |
January 21, 2016 |
LEAKAGE CURRENT SENSOR FOR SUSPENSION TYPE INSULATOR
Abstract
A sensor apparatus for detecting leakage current in a
suspension-type insulator of an electrical power system includes: a
housing having a first half of a leakage current sensor contained
therein; a door pivotally connected to the housing by a hinge, and
having a second half of the leakage current sensor contained
therein, the door pivotable about the hinge between an open
position in which the first and second halves of the leakage
current sensor are separate from each other, and a closed position
in which mating surfaces of the first and second halves of the
leakage current sensor join together to define a closed perimeter;
and a clamping mechanism connected to the housing comprising a
first jaw and a second jaw, wherein the jaws are moveable between
an open position and a closed position.
Inventors: |
Phillips; Andrew John;
(Harrisburg, NC) ; Engelbrecht; Christiaan Stephan;
(Ede, NL) ; Major; J. Mark; (San Antonio, TX)
; Lynch; Robert Carlton; (Fuquay-Varina, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Electric Power Research Institute, Inc. |
Charlotte |
NC |
US |
|
|
Family ID: |
48694328 |
Appl. No.: |
14/869387 |
Filed: |
September 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13728462 |
Dec 27, 2012 |
|
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14869387 |
|
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|
61580808 |
Dec 28, 2011 |
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Current U.S.
Class: |
324/551 |
Current CPC
Class: |
G01R 15/186 20130101;
G01R 31/50 20200101; G01R 31/085 20130101 |
International
Class: |
G01R 31/02 20060101
G01R031/02; G01R 31/08 20060101 G01R031/08 |
Claims
1. A sensor apparatus for detecting leakage current in a
suspension-type insulator of an electrical power system, the
apparatus comprising: a housing having a first half of a leakage
current sensor contained therein; a door pivotally connected to the
housing by a hinge, and having a second half of a leakage current
sensor contained therein, the door pivotable about the hinge
between an open position in which the first and second halves of
the leakage current sensor are separate from each other, and a
closed position in which mating surfaces of the first and second
halves of the leakage current sensor join together to define a
closed perimeter and; a clamping mechanism connected to the housing
comprising a first jaw and a second jaw, wherein the jaws are
moveable between an open position and a closed position.
2. The apparatus according to claim 1, wherein: the first jaw is
supported by a first arm; the second jaw is supported by a second
arm; a first threaded collar is connected to the first arm; a
second threaded collar is connected to the second arm; and a bolt
mechanism is disposed in threaded engagement with the first and
second arms.
3. The apparatus according to claim 2, wherein the bolt mechanism
includes first and second opposing bolts coupled together at their
ends by a coupling.
4. The apparatus according to claim 2, wherein the first and second
jaws include a plurality of apertures for receiving a fastener
therethrough.
5. The apparatus according to claim 1, further including a hot
stick adapter mounted to the housing.
6. The apparatus according to claim 1, further including a fastener
for securing the door in the closed position.
7. The apparatus according to claim 1, further including an
electronics module configured to receive a signal from the leakage
current sensor and a communications system operable to wirelessly
transmit the signal to an external receiver.
8. The apparatus according to claim 1, wherein the leakage current
sensor is operable to generate an analog signal proportional to a
received leakage current.
9. The apparatus according to claim 1, wherein the leakage current
sensor includes a current transformer having: a ferrite core having
windings wrapped therearound; and a metal housing around the
ferrite core and windings to shield the current transformer from
magnetic fields, wherein the metal housing includes a slot
extending along an inner surface thereof.
10. A method of detecting leakage current in a suspension-type
insulator of an electrical power system, the method comprising:
installing a grounded end fitting of the insulator in the apparatus
of claim 7; conducting a leakage current from a grounded end
fitting of the insulator through a current transformer of the
leakage current sensor; generating an analog signal proportional to
the leakage current flowing through the current transformer; using
the electronics module to receive the analog signal and convert the
analog signal to a digital value; and using the communications
system to wirelessly transmit the digital value to an external
receiver.
11. The method according to claim 10, further including the step of
using the electronics module to assign the digital value to one of
a plurality of bins based on a magnitude of the digital value,
wherein each of the plurality of bins represents a predetermined
range of magnitudes of leakage current.
12. The method according to claim 11, further including the step of
incrementing the assigned bin each time a digital value is assigned
to the bin.
13. The method according to claim 10, further including the step of
using the electronics module to detect a peak value of the analog
signal at a first interval.
14. The method according to claim 13, further including the step of
using the electronics module to convert the peak value to the
digital value.
15. The method according to claim 10, wherein the step of
installing the grounded end fitting includes the steps of: moving
the door of the apparatus to an open position; moving the jaws to
an open position; receiving the grounded end fitting between the
jaws and moving the jaws to the closed position, such that the jaws
clamp onto the grounded end fitting and secure the sensor apparatus
to the insulator; and moving the door to the closed position and
securing the door in the closed position.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to the monitoring of
leakage currents in a transmission system and, more particularly,
to a sensor for accurately detecting and monitoring leakage current
in suspension type insulators.
[0002] In many countries, including the US, wood is utilized as
part of the line insulation to improve the basic insulation level
(BIL) of the line, as it has been recognized that the lighting
performance of transmission lines can be improved by utilizing the
wood support or pole. This has, however, not been without problems
as there were, and still are, many instances of fires of the wood
poles and cross arms caused by low frequency leakage current and
sparking on the wood from sources such as leakage current due to
insulator contamination despite mitigation measures being
taken.
[0003] Insulators installed on transmission and distribution
systems are exposed to contamination, for example from marine salt,
road salt, and industrial pollutants. This contamination can result
in flashover of the insulator, usually under light wetting
conditions, e.g. condensation, when the salts and water mix to
become a conductive electrolyte. Flashover is a problem in that it
results in an outage which interrupts power to a utility company's
customers.
[0004] When the salts on the surfaces of an insulator become wet
they form an electrolyte which is conductive. Since the one end of
the insulator is energized, and the other end is grounded, currents
flow along the insulator surfaces. If these currents are large
enough, arcing will occur (called dry band arcing). This arcing
will either extinguish or grow to result in a flashover. The
magnitude of leakage currents that occur under dry band arcing
conditions provide an indication of the risk of the insulator
flashing over. If insulators are at risk of flashover due to
contamination build-up, utilities can wash the insulators or take
other measures, such as redirect power to other transmission and
distribution assets.
[0005] In addition when composite (also called polymer or
non-ceramic) or coated insulators are used the leakage currents and
arcing on the surface can degrade the rubber material. By
monitoring the leakage currents an indication can be obtained as to
the level of degradation.
[0006] Some commonly used mitigation measures are listed below;
however, none of these mitigation measures provide a means for
monitoring and pinpointing potential leakage current problems so
that a utility company can take preventative measures.
[0007] 1. Wrapping metal bands around the wood pole and connecting
it to the insulator hardware. This method has the advantage that
the reduction in the "insulated" wood path lengths (used as
improvement for the BIL) is limited. The conductor material used
for this purpose should be compatible with other hardware not to
cause corrosion.
[0008] 2. A small guard electrode, in the form of a coach screw or
a multi-spiked plate (e.g. gang-nail), is fastened to the wood
outside the rain shadow area and bonded to the insulator hardware.
This method has a minimal effect on the BIL of the structure.
[0009] 3. Application of conducting paint to cover the high
resistance zones around metal to wood interfaces. This method has a
minimal effect on the BIL of the structure.
[0010] 4. Bonding of the insulator hardware together with a
conductor. The intension with this bond wire is to "balance" the
leakage current so that only a small residual current will flow in
the pole. There are two variants to this scheme: [0011] (a) The
insulator bases are connected together but not grounded. The ground
lead terminates some distance away to realize the required BIL
phase-to-ground for induced lightning surges. [0012] (b) The
insulator bases can be bonded together and connected to ground. In
this case the wood is not utilized anymore as part of the line
insulation against lightning. Also here it is important that the
material of the bond wire is selected to be compatible with the
other hardware used to prevent corrosion.
[0013] 5. An extension of the previous method is to use steel
cross-arms to bond the insulator bases together. The steel
cross-arm can either be grounded or be left floating depending on
whether or not the utility wants wood as part of the line
insulation for lightning performance.
[0014] 6. Finally the insulators used can be upgraded to those with
an improved contamination performance. For example porcelain
insulators can be replaced by hydrophobic silicone rubber composite
insulators. Other options include regular insulator cleaning or the
application of silicone grease to insulators.
BRIEF SUMMARY OF THE INVENTION
[0015] These and other shortcomings of the prior art are addressed
by a leakage current monitoring system that continuously monitors
and reports potential leakage current issues to allow an action to
be taken to mitigate any potential problems that may arise from the
leakage current.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] 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:
[0017] FIG. 1 is a schematic side view of a portion of a utility
pole carrying a suspension-type insulator and a sensor unit
constructed according to an aspect of the present invention;
[0018] FIG. 2 is a perspective view of the sensor unit shown in
FIG. 1;
[0019] FIG. 3 is another view of the sensor unit shown in FIG.
1;
[0020] FIG. 4 is a view of the sensor unit of FIG. 1 with a cover
removed to show the internal components;
[0021] FIG. 5 shows a door of the sensor unit of FIG. 1; and
[0022] FIG. 6 is a block diagram showing the operation of the
sensor unit of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Referring now to the drawings, wherein identical numerals
indicate the same elements throughout the figures, FIG. 1
schematically depicts an insulator 10 which is suspended from a
cross-arm 11 of a utility pole 12 and which supports an electrical
conductor 13. The insulator 10 is a known suspension-type insulator
having a generally cylindrical exterior shape with an upper end or
grounded end fitting 14 and a lower end 16 connected to the
electrical conductor 13, and is made from an electrically
insulating (i.e., non-electrically-conductive) material. An
exemplary sensor unit for accurately detecting and monitoring
leakage currents according to an embodiment of the invention is
mounted on the upper end 14 and shown generally at reference
numeral 20.
[0024] In summary, the sensor unit 20 is an RF sensor which
attaches to the insulator's grounded end 14, measures the leakage
current flowing in the insulator 10, processes the current and
assigns them to specific ranges. The sensor unit 20 then transmits
the information wirelessly to either a local base station or a
handheld device.
[0025] Referring to FIGS. 2 and 3, the sensor unit 20 includes a
housing 21 for containing a leakage current sensor 22 and
electronic module 70 (shown in FIG. 4), a door 23 hinged to the
housing 21 to allow the sensor unit 20 to be positioned onto the
insulator 10, and a clamping mechanism 24 for clamping the sensor
unit 20 to the insulator 10. The housing 21 is a metal housing
which encloses the sensor unit's functional components (described
in detail below) and protects them from electromagnetic
influences.
[0026] The door 23 is pivotally hinged to the housing 21 at hinge
26 to allow the door 23 to pivot away from the housing 21 to an
open position and allow the sensor unit 20 to be installed on the
insulator 10. Fastener 27 secures the door 23 to the housing 21 in
a closed position once the sensor unit 20 has been installed. A hot
stick adapter 28 is connected to the housing 21 and positioned next
to fastener 27 to allow a user to use a hot stick for placement of
the sensor unit 20 on the insulator 10. The hinge 26 is resistive
in nature so that it moves freely, making it easier for the
installer--especially under live line conditions.
[0027] Clamping mechanism 30 is secured to the housing 21 and
includes first and second adjustable clamping jaws 31 and 32
connected to first and second pivotable arms 33 and 34,
respectively. The jaws 31 and 32 are used to mechanically attach
the sensor unit 20 to the grounded end 14 of the insulator 10 and
are adjustable to account for different insulator end fitting
diameters. As shown in FIG. 2, the jaws 31 and 32 include apertures
36 for receiving fasteners therethrough and to allow for adjustment
of the jaws 31 and 32 with respect to arms 33 and 34. The jaws 31
and 32 are adjusted by removing fasteners 37, moving the jaws 31
and 32 relative to arms 33 and 34 until a desired aperture 36
(representative of a specific diameter) aligns itself with
apertures in the arms 33 and 34. The fasteners 37 are then
re-installed through the apertures in the arms and apertures 36 to
secure the jaws 31 and 32 in position. As illustrated, the jaws 31
and 32 have a V or U shaped profile for mating engagement with the
grounded end 14 of the insulator 10.
[0028] The jaws 31 and 32 are moved between opened and closed
positions by a bolt mechanism 40 connected to threaded collars 41
and 42 disposed at an end of the arms 33 and 34, respectively. The
bolt mechanism 40 includes a pair of opposing bolts 43 and 44
coupled together at their ends by a coupling 46. Each of the bolts
43, 44 extend through a respective one of the threaded collars 41,
42. As the bolts 43 and 44 are turned, the threaded collars 41 and
42 move along the length of the bolts 43 and 44, which in turn
causes the arms 33 and 34 to move about pivots 47 and 48 such that
they move the jaws 31 and 32 between opened and closed positions.
The key feature of the bolt mechanism 40 is that it allows a user
to turn either one of the bolts 43, 44 to open and close the jaws
31 and 32, thereby eliminating any issues with the user being on a
specific side of the sensor unit 20. When installing the sensor
unit 20 onto the grounded end fitting 14, the door 23 and jaws 31,
32 are moved to the open position for receiving the end fitting 14.
The jaws 31, 32 are then moved to the closed position to clamp onto
the end fitting 14. With the sensor unit 20 firmly clamped to the
end fitting 14, the door 23 is then moved to the closed position
and secured in place by fastener 27.
[0029] Referring to FIG. 4, the leakage current sensor 22 includes
a toroidal current transformer 50 with a frequency response from
<5 Hz to >100 kHz and a sensitivity of lower than 10 mA. The
transformer 50 is formed by a leakage current toroidal ferrite core
51 and winding 52 wound around the core 51 with multiple turns. The
core 51 is formed of two halves 51A and 51B so that it can surround
the grounded end 14 of insulator 10. When the two halves 51A and
51B of the core 51 are put together, the voltage output from the
windings 52 is proportional to the current flowing through the
middle of the core 51.
[0030] A sheet metal housing 53 (steel which is ferromagnetic for
magnetic field shielding) surrounds the core 51. As shown, the
housing 53 is also formed by two halves 53A and 53B to surround
respective core halves 51A and 51 B. The metal housing 53 is split
along an inside with a metal slot 54, See FIG. 5, so that the core
51 can still couple with a magnetic field from current flowing in
an insulator's metal end fitting. This enables the core 51 to be
shielded from stray magnetic fields which are not due to current
flowing through an insulator end fitting but still measure the
currents flowing through the insulator metal end fitting. This is
very important as there are large magnetic fields due to the
currents flowing in the conductors which are energized at ends of
the insulators.
[0031] As shown in FIG. 5, core 51B and housing 53B are installed
in the door 23 so that the sensor unit 20 can be installed in the
field on insulators without removing them from service. The core
51B and housing 53B are connected to a plate 56 which is connected
to the door 23. The plate 56 is moveable relative to the door 23
and is biased towards the housing 21 by springs 57 and 58 to ensure
that mating surfaces 59 and 60 of cores 51A and 51B are properly
mated together. The mating surfaces 59 and 60 of the cores 51A and
51B are machined with key patterns so that alignment is ensured
between the two cores. Alignment is vital so that the unit
consistently measures the leakage currents flowing through the end
fitting of the insulator, and it reduces the influence of stray
magnetic fields.
[0032] Referring again to FIG. 4, an output 61 from the sensor 22
operably connects the sensor 22 to the electronics module 70. The
electronics module 70 is imbedded in potting compound to protect it
from both environmental and electromagnetic influences and includes
analog, digital, and radio frequency (RF) electronics which
function to receive, process, and store signals from the sensor 22,
to receive external commands, and to transmit data to an external
source. The electronics module 70 may include, for example, a
printed circuit board incorporating analog, digital and/or
radio-frequency ("RF") electronic components or may incorporate
discrete components and/or one or more microprocessors.
[0033] In addition to the electronics module 70, the housing 21
includes an electric power source for the electronics module 70,
such as the illustrated batteries 72. The housing 21 also includes
one or more RF antennas 63 which protrude from the exterior of the
housing 21 and are used to transmit signals generated by the
electronics module 70 to a remote receiver (not shown), and/or to
receive RF signals from a remote receiver (not shown). The sensor
unit 20 incorporates a communication system that may be based on
the IEEE 805.15.4 architecture. The communication protocol is
customized to allow two-way communications.
[0034] In the illustrated example, one or more
magnetically-operated switches 71 are mounted inside the housing 21
and coupled to the electronics module 70. The switches 71 may be
tripped by placing a magnet in the near vicinity of the switch 71
on the outside of the housing 21. In the illustrated example, the
sensor unit 20 may include a power switch which toggles the sensor
unit 20 between the on and off state, and a reset switch which
signals the sensor unit 20 to erase any stored data.
[0035] The electronics module 70 may include a temperature sensor,
in order to assist in assessing condensation conditions. The
electronics module 70 may also include a 3D accelerometer, in order
to assess whether the insulator or structure is experiencing
vibration issues.
[0036] The operation of the electronics module 70 and the sensor
unit 20 will now be described with reference to the block diagram
in FIG. 6. In block 200, the electronics module 70 uses a peak
detect circuit of a known type to measure and hold a voltage signal
from the sensor assembly described above. The voltage signal is
proportional to the highest leakage current measured in a
predetermined first time interval, e.g. 60 seconds. This peak
detect circuit is reset at the first interval, e.g. 60 seconds,
based on a digital signal from the microprocessor. At block 202, an
Analog to Digital (A/D) converter (which may be part of a
microprocessor of the electronics module 70) measures the value
from the peak detect circuit, repeating as the first interval. At
block 204, the microprocessor evaluates the digital value and
assigns the value to membership in a category or "bin". The bin
represents a range in which the measured value lies. For example,
there may be six numbered bins which account for different leakage
current magnitudes. Examples of two different settings for the
leakage current threshold for the bins are listed in Table 1 below,
in which "regular" indicates a classification that is relatively
less sensitive to leakage currents and "sensitive" indicates a
classification that is relatively more sensitive to leakage
currents.
TABLE-US-00001 TABLE 1 CURRENT RANGE, CURRENT RANGE, BIN REGULAR
SENSITIVE NUMBER (PEAK mA) (PEAK mA) 1 0-10 0-1 2 10-20 1-2 3 20-50
2-5 4 50-200 5-20 5 200-500 20-50 6 500+ 50+
[0037] The electronics module 70 maintains a counter for each of
the bins. When the digital value is assigned to a bin, the counter
for that bin is incremented (see block 206). At block 208, the
number of counts in each bin is then transmitted using RF to a
remote receiver. The transmission repeats at a second interval
which is preferably shorter than the first interval described
above.
[0038] The sensor unit 20 only stores the statistical parameters
(i.e. the bin counts) of the leakage current peaks that occur. No
other leakage current parameters need be recorded. Using the
communications system described above, a remote user can reset the
bins or change the ranges of the bins remotely.
[0039] The sensor unit 20 also keeps track of the time since the
last reset. This limits the data message sent by the device to the
bare minimum. It also limits the internal circuit complexity and
power consumption for the device. Based on the battery
characteristic and low power consumption of the sensor unit 20,
battery life is estimated at more than 10 years.
[0040] The sensor units 20 can be employed in different modes. For
example, when installed on transmission lines the sensor units 20
may be polled a only few times per year when line maintenance crews
do inspections or maintenance, for example using handheld receivers
(not shown).
[0041] Alternatively, in substations or on specific transmission
line structures a more sophisticated approach may be followed. A
dedicated base station system (not shown) installed at the
substation/structure would poll the nearby sensor units 20 at a
short time interval. This base station stores leakage current data
together with weather parameters from attached sensors. The data is
then transmitted from the base station using a variety of methods
including the use of GPRS modems or connecting to a utility data
management system. The data is stored and processed on a remote
server. Alarms can be generated based on algorithms and data can be
viewed using visualization tools.
[0042] If the leakage current characteristics of the insulators are
known, alarms can be generated automatically based on preset
leakage current alarm levels. Warnings or alarms can be raised to
initiate insulator maintenance (e.g. washing) if certain pre-set
leakage current thresholds are exceeded. Leakage current
information can also be used select appropriate mitigation
measures.
[0043] It should be noted that the sensor units 20 are connected
between the insulator and the grounding system. With this
configuration the insulator leakage current is directly shunted to
ground and it will therefore not pass through the wood cross arm.
The leakage currents measured can however be used to raise warnings
that conditions and insulator contamination levels are sufficiently
high to cause wood pole fires.
[0044] The sensor unit 20 described above has several advantages.
The sensor units 20 are suitable for wide spread deployment which
makes them practical for installations on overhead lines and
substations. Some of the specific advantages of the sensor are low
cost; absence of wiring to either power the sensor unit 20 or
communicate with the sensor 20, leading to improved reliability
compared to wired units; the ability to quickly deploy many sensor
units 20; on-board processing of data, providing a user with
processed information on which he can make a decision; and a
combination of analog and digital electronics, ensuring that no
current pulses are ever missed, as compared to previous
technologies that used digital measurement only.
[0045] The foregoing has described a sensor apparatus for detecting
and monitoring leakage current in suspension type insulators. While
specific embodiments of the present invention have been described,
it will be apparent to those skilled in the art that various
modifications thereto can be made without departing from the spirit
and scope of the invention. Accordingly, the foregoing description
of the preferred embodiment of the invention and the best mode for
practicing the invention are provided for the purpose of
illustration only and not for the purpose of limitation.
* * * * *