U.S. patent application number 16/109922 was filed with the patent office on 2020-02-27 for live urd cable elbow connectivity identification method and apparatus.
The applicant listed for this patent is Gregory Hubert Piesinger. Invention is credited to Gregory Hubert Piesinger.
Application Number | 20200064389 16/109922 |
Document ID | / |
Family ID | 69230373 |
Filed Date | 2020-02-27 |
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United States Patent
Application |
20200064389 |
Kind Code |
A1 |
Piesinger; Gregory Hubert |
February 27, 2020 |
LIVE URD CABLE ELBOW CONNECTIVITY IDENTIFICATION METHOD AND
APPARATUS
Abstract
Methods and apparatus are described to quickly and easily
identify live URD elbow connectivity between junction cabinets in
underground electric utility power distribution circuits so URD
connected elbows can be correctly tagged. A first method segregates
elbows in a cabinet into input elbows from an upstream cabinet,
output elbows to a downstream cabinet, and by phase attribute. A
second method injects a tracer signal into the elbow capacitive
test point of an upstream output elbow and detects the tracer
signal at the elbow capacitive test point of a downstream elbow
capacitive test point to identify connectivity. A third method
compares the output current of an upstream output elbow to that of
the input current of a downstream input elbow to identify
connectivity.
Inventors: |
Piesinger; Gregory Hubert;
(Cave Creek, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Piesinger; Gregory Hubert |
Cave Creek |
AZ |
US |
|
|
Family ID: |
69230373 |
Appl. No.: |
16/109922 |
Filed: |
August 23, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 31/67 20200101;
G01R 31/66 20200101; G01R 31/083 20130101 |
International
Class: |
G01R 31/04 20060101
G01R031/04; G01R 31/08 20060101 G01R031/08 |
Claims
1. A method of identifying elbow connectivity of multiple live URD
power cables between junction cabinets, said method comprising:
measuring voltage phase of each said URD cable in each said
junction cabinet; measuring current phase of each said URD cable in
each said junction cabinet; identifying said elbow as an input
elbow when said current phase is nearly in-phase with said voltage
phase; identifying said elbow as an output elbow when said current
phase is nearly out-of-phase with said voltage phase; and tagging a
said input elbow in a downstream junction cabinet as connected to a
said output elbow in an upstream junction cabinet when said input
elbow and said output elbow have the same phase attribute.
2. A method as claimed in claim 1 additionally comprising measuring
input current of each said input elbow of similar phase attribute
in said downstream junction cabinet; measuring output current of
each said output elbow of similar phase attribute in said upstream
junction cabinet; tagging a said input elbow in a said downstream
junction cabinet as connected to a said output elbow in a said
upstream junction cabinet when downstream said input current in
said input elbow is nearly identical to upstream said output
current in said output elbow; and tagging a said output elbow in a
said upstream junction cabinet as connected to a said input elbow
in a said downstream junction cabinet when upstream said output
current in said output elbow is nearly identical to downstream said
input current in said input elbow.
3. A method as claimed in claim 1 wherein said voltage phase is
measured at elbow test point.
4. A method as claimed in claim 3 wherein said voltage phase is
measured using a voltage input phase identification instrument.
5. A method as claimed in claim 1 wherein said current phase is
measured on said URD cable below said elbow where jacket and
concentric neutrals are stripped back from said URD cable.
6. A method as claimed in claim 5 wherein said current phase is
measured using a current input phase identification instrument.
7. A method as claimed in claim 5 wherein said current phase is
measured using a standard AC current clamp connected to a current
to voltage adapter connected to voltage input phase identification
instrument.
8. A method as claimed in claim 1 additionally comprising
sequentially injecting a tracer signal into each said output elbow
test point of similar phase attribute in said upstream junction
cabinet; sequentially measuring downstream junction cabinet said
tracer signal amplitude of each said input elbow test point of
similar phase attribute as said upstream junction cabinet phase
attribute; and tagging downstream junction cabinet said input elbow
with highest said tracer signal amplitude as connected to said
output elbow in said upstream junction cabinet.
9. A method as claimed in claim 1 additionally comprising
sequentially injecting a tracer signal into each said input elbow
test point of similar phase attribute in said downstream junction
cabinet; sequentially measuring upstream junction cabinet said
tracer signal amplitude of each said output elbow test point of
similar phase attribute as said downstream junction cabinet phase
attribute; and tagging upstream junction cabinet said output elbow
with highest said tracer signal amplitude as connected to said
input elbow in said downstream junction cabinet.
10. A method as claimed in claim 8 wherein said tracer signal is a
direct sequence spread spectrum signal.
11. A method as claimed in claim 9 wherein said tracer signal is a
direct sequence spread spectrum signal.
12. A method of identifying elbow connectivity of multiple live URD
power cables between an upstream junction cabinet and one or more
downstream junction cabinets, said method comprising: measuring
output current of each output elbow in said upstream junction
cabinet; measuring input current of each input elbow in said one or
more downstream junction cabinets; comparing said output current of
each output elbow in said upstream junction cabinet to said input
current of each input elbow in said one or more downstream junction
cabinets; and tagging a said output elbow in said upstream junction
cabinet as connected to a said input elbow in a said one or more
downstream junction cabinets when said output current in a said
output elbow in said upstream junction cabinet is essentially equal
to said input current in a said input elbow in said one or more
downstream junction cabinets.
13. A method as claimed in claim 12 wherein said measuring output
current of each output elbow and said measuring input current of
each input elbow is implemented using a current transformer.
14. A method as claimed in claim 12 wherein said measuring output
current of each output elbow in said upstream junction cabinet
occurs simultaneously.
15. A method as claimed in claim 12 additionally comprising
associating a reference number to each said output elbow in said
upstream junction cabinet; communicating said reference number and
output current of each said output elbow in said upstream junction
cabinet to said one or more downstream junction cabinets; and using
said reference number to identify which output elbow in said
upstream junction cabinet is essentially equal to said input
current in a said input elbow.
16. A method as claimed in claim 15 wherein said communicating is
implemented using either short range radio, cellular modem,
Bluetooth, WiFi, multi-use radio service, or smart phone app.
17. An apparatus for identifying elbow connectivity of live URD
power cables between junction cabinets, said apparatus comprises: a
tracer transmitter configured to generate a tracer signal; a cable
configured to inject said tracer signal into upstream elbow test
point; and a tracer receiver configured to detect said tracer
signal at downstream elbow test point.
18. An apparatus as in claim 17 wherein said cable characteristic
impedance is configured to match said URD power cables
characteristic impedance.
19. An apparatus as in claim 17 wherein said tracer transmitter
additionally comprises an oscillator, said oscillator configured to
generate a high frequency RF signal; a direct sequence PN code
generator, said code generator configured to generate a spread
spectrum signal; and an amplifier, said amplifier configured to
amplify said spread spectrum signal.
20. An apparatus as in claim 17 wherein said tracer receiver
additionally comprises an amplifier, said amplifier configured to
amplify said tracer signal at downstream elbow test point; a
decoder, said decoder configured to decode said tracer signal; and
a display, said display configured to display amplitude of decoded
said tracer signal.
Description
RELATED INVENTION
[0001] The present invention claims priority under 35 U.S.C. .sctn.
119(e) to: "Live URD Cable Elbow Connectivity Identification
"Method and Apparatus" Provisional U.S. Patent Application Ser. No.
62/550,505, filed 25 Aug. 2017 which is incorporated by reference
herein.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates to the field of electric power
distribution networks. More specifically, the present invention
relates to determining the connectivity of Underground Residential
Distribution (URD) power cables.
BACKGROUND OF THE INVENTION
[0003] Electric power distribution networks are used by the
electric utilities to deliver electricity from generating plants to
customers. Although the actual distribution voltages will vary from
utility to utility, in a typical network, 3-phase power at high
voltage (345,000 volts phase-to-phase) is delivered to multiple
transmission substations at which transformers step this high
voltage down to a lower 3-phase voltage (69,000 volts
phase-to-phase). This 69,000-volt 3-phase power then feeds multiple
distribution substations whose transformers further step down the
voltage to the distribution voltage (12,470 volts phase-to-phase)
and separate the power into 3 single-phase feeder cables.
Typically, these 3 feeder cables operate at 7,200 volts
phase-to-ground and are designated as phase attributes A, B, and C.
Each of these 3 feeder cables branch into multiple circuits to
power a plurality of local pole-mounted or pad-mounted transformers
which step the voltage down to a final voltage of 120/240 volts for
delivery to commercial and residential customers.
[0004] In many cases, the final 7,200-volt distribution network
utilizes underground (i.e., buried) cables. These cables are
typically known as Underground Residential Distribution (URD)
cables. Typical URD cables are shown in FIG. 1.
[0005] In a typical URD cable 20, a center conductor 22 is
surrounded by an inner semiconductor sheath 24. Inner semiconductor
sheath 24 serves to relieve electrical stress by spreading out and
making the electrical field more uniform.
[0006] Inner semiconductor sheath 24 is surrounded by an insulator
26. Insulator 26 has significant high-voltage insulating properties
to minimize the overall size of URD cable 20. Typically, insulator
26 is formed of a polymeric material, such as polyethylene.
[0007] Surrounding insulator 26 is an outer semiconductor sheath
28. Like inner sheath 24, outer sheath 28 serves to relieve
electrical stress by making the electrical field more uniform.
Making the electrical field more uniform protects insulator 26,
which would otherwise be more likely to break down.
[0008] Outer semiconductor sheath 28 is surrounded by a shield
formed of a plurality of neutral conductors 30. Neutral conductors
30 together serve as a return line (ground wire) for center
conductor 22. Neutral conductors 30 are surrounded by and embedded
within an insulating jacket 32. However, many older URD cables are
not insulated using insulating jacket 32.
[0009] URD cables 20 are terminated using load break elbows 100
illustrated in FIG. 2. Elbow 100 is composed of insulated material
105 with pulling eye 110. A short length of insulating jacket 32 of
URD cable 20 is removed, neutral conductors 30 are folded back and
twisted together to form grounding wire 125 which is connected to
earth ground. A compression connector 115 is attached to bare
center conductor 22, and inserted into insulated material 105. Male
contact pin 120 is screwed into compression connection 115.
[0010] Most modern elbows also incorporate a capacitive test point
130 covered by removable cap 135. When cap 135 is removed, test
point 130 capacitive couples to center conductor 22 which allows
sensing the voltage of center conductor 22.
[0011] A mating insulated elbow bushing (not shown) is mounted
inside a cabinet. Using an insulated hot stick, a lineman grips the
pulling eye 110 to insert or remove elbow 100 from the cabinet
elbow bushing, thus making or breaking the URD cable circuit.
[0012] A simplified small portion of a typical URD circuit is
illustrated in FIG. 3. Upstream single-phase attribute feeders A,
B, and C branch out using junction cabinet J1. That is, phase A URD
cable elbow E1 is pressed onto bushing B1 which is permanently
mounted in cabinet J1. Bushings B2 and B3 are both also permanently
mounted in cabinet J1 and are connected to B1. Thus, cabinet J1
expands single phase A URD cable into 2 phase A URD cables.
Likewise, phase B and C URD cables are also expanded.
[0013] Also illustrated in FIG. 3 is downstream padmount
transformer cabinet T1 which contains permanently mounted bushings
B4 and B5 which are connected together and to the primary (high
voltage) input of a step-down transformer. The secondary (low
voltage) output supplies the final 120/240 volt power to the
residential customer. A length of URD cable carries power from
upstream junction cabinet J1 to downstream padmount cabinet T1
using elbow E3 connected to bushing B3 in junction cabinet J1 and
elbow E4 connected to bushing B4 in padmount cabinet T1. Another
length of URD cable typically carries power to a second downstream
padmount cabinet (the next one in a long chain of downstream
padmount cabinets) using elbow E5 connected to B5 in padmount
cabinet T1.
[0014] Utilities assign and tag each length of URD cable with a
unique number near the elbow to identify which elbows are connected
to each section of URD cable. This is required so that a lineman
can disconnect the correct elbow if a portion of the URD circuit
must be de-energized. For example, assume the chain of downstream
padmount cabinets after T1 need to be disconnected by pulling elbow
E5 off of bushing B5. If the padmount tags were missing or
incorrectly identified, the lineman might pull elbow E4 which would
disconnect all customers connected to T1.
[0015] Unfortunately over time, equipment failures and new
construction can lead to tagging errors. Utilities would like to
re-confirm URD tagging accuracy, but there is currently no way to
accomplish this short of pulling elbows to determine which elbows
belong to a length of URD cable. Since the URD cables are buried,
they cannot be visually seen where they originate. Although cable
locator equipment can trace URD cables from one cabinet to another,
this equipment cannot identify which elbow connects to the cable
being tracked since both the input and output elbows are connected
together via the two cabinet bushings. For example in cabinet T1,
bushings B4 and B5 connect elbows E4 and E5 together.
[0016] Junction cabinets are implemented each time a URD cable
branch is required. Long chains of padmount transformer cabinets
snake through residential neighborhoods, each serving one or a few
houses. Therefore, URD cable circuits are extensive. Junction
cabinets sometimes contain multiple single phase feeders and some
of the feeders could split into multiple branches going to
additional junction cabinets and to multiple different chains of
padmount transformer cabinets.
[0017] Currently no method or apparatus exists to quickly and
easily identify elbow connectivity on live URD cable circuits so as
to accurately confirm if each elbow tag is either correct or needs
to be re-tagged. Even small and medium size utilities have
thousands or tens of thousands of URD elbows in active service.
Conducting an utility wide elbow connectivity survey today without
better tools and techniques (as disclosed in this patent
application) would be prohibitively expensive and is rarely (if
ever) performed
SUMMARY OF THE INVENTION
[0018] Accordingly, it is an advantage of the present invention
that methods are disclosed for determining the connectivity of live
URD cable circuits.
[0019] It is another advantage of the present invention that
apparatus are disclosed to implement the disclosed methods in an
efficient manner to quickly identify the elbows connected to each
length of live URD cable.
[0020] The above and other advantages of the present invention are
carried out for determining the connectivity of URD cables in an
electric power network operating at a line frequency which is 60
Hertz in the United States (US) and 50 Hertz in many locations
outside the US.
[0021] Three different methods and apparatus are disclosed in the
current invention which, individually or together, ensure that
elbow connectivity identification can be quickly and accurately
performed for all URD circuits.
[0022] The first method identifies input and output elbows in a
cabinet by monitoring each elbow current using an AC current
sensor. If the elbow current is nearly in-phase with the elbow
voltage, the elbow is an input elbow. If the current is nearly
out-of-phase with the elbow voltage, the elbow is an output
elbow.
[0023] The second method injects a tracer signal into an upstream
elbow test point and probes downstream elbow test points for the
tracer signal to indicate which downstream elbow is connected to
the upstream elbow.
[0024] The third method simultaneously measures the current in one
or more upstream elbows. Downstream elbow currents are measured to
find which downstream elbow has nearly identical current as an
upstream elbow. Elbows with nearly identical currents are
identified as being connected.
[0025] Depending on the particular URD circuit, one of these three
methods will be quicker and more effective than the other two
methods. For example, long daisy chains of neighborhood padmounts
on a single phase circuit each contain a single input elbow and a
single output elbow. For this circuit, the first method for
identifying the input and output elbow in each padmount is the
quickest and easiest. The lineman simply moves down the chain to
each padmount and tags its input elbow as connected to the previous
upstream output elbow.
[0026] Other objects and advantages of the present invention will
become obvious as the preferred embodiments are described and
discussed below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 illustrates typical URD cable.
[0028] FIG. 2 illustrates typical URD elbows.
[0029] FIG. 3 illustrates a simplified example of a small portion
of a typical URD circuit.
[0030] FIG. 4 illustrates a block diagram of the first method for
identifying input and output elbows in a junction cabinet.
[0031] FIG. 5 illustrates a typical AC current clamp.
[0032] FIG. 6 illustrates input and output voltage and current
phase in an example junction cabinet.
[0033] FIG. 7 illustrates using a standard line locator to trace
buried URD cable between junction cabinets.
[0034] FIG. 8 illustrates the second method of identifying input
and output elbows in a junction cabinet by injecting a tracer
signal into an elbow test point in one junction cabinet and
detecting it at another elbow test point in a second junction
cabinet.
[0035] FIG. 9 illustrates a block diagram of a tracer transmitter
and receiver.
[0036] FIG. 10 illustrates a block diagram of the third method of
identifying input and output elbows in a junction cabinet by
measuring and comparing URD currents in connected junction
cabinets.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] The first method for identifying input and output elbows in
a cabinet, by monitoring elbow currents is illustrated in FIG. 4.
Input elbow 205 is connected to output elbow 255 through bushings
245 and 250 respectively, which are connected together using bus
bar 247. URD current 270 flows into input elbow 205, through elbow
bushings 245 and 250, and out elbow bushing 255. Current sensor 225
senses current 270 flowing into input elbow 205. Voltage sensor 215
senses AC voltage at test point 210 on input elbow 205. Phase meter
220 compares current sensor 225 phase with voltage sensor 215 phase
and indicates the differential phase on display 230. Likewise,
identical current sensor 260 senses current 270 flowing out of
output elbow 255 (connection to phase meter not illustrated).
Current sensors 225 and 260 are illustrated as using a current
sensing coil of wire which is the method used by virtually all
current sensors.
[0038] Assuming phase meter 220 is initially setup so as to display
current sensor 225 phase as nearly in-phase with voltage sensor 215
phase, then current sensor 260 phase will be displayed as nearly
out-of-phase with voltage sensor 215 phase. This occurs because
current 270 is flowing in the opposite direction through current
sensor 260 compared with the current direction through current
sensor 225. It is well known that reversing current through an AC
current sensor reverses the phase of its AC output signal.
[0039] To measure URD cable 20 center conductor current, current
sensors 225 and 260 must be applied directly below the elbow where
jacket 32 and concentric neutrals 30 are stripped back from URD
cable 20 leaving only outer semicon 28 (refer to FIG. 1). Applying
the current sensor below this stripped back portion, senses the sum
of current flowing in both center conductor 22 and concentric
neutral 30. Concentric neutral 30 is the return path for URD center
conductor 22 supply current. These two currents are essentially
equal and opposite and therefore cancel as is well known by those
skilled in the art.
[0040] FIG. 4 illustrates a generic block diagram of the first
method for identifying input and output elbows by monitoring elbow
current phases. Current sensor 260 could be connected to phase
meter 220. However, applying current sensor 260 is actually not
required. Instead, current sensor 225 can simply sequentially sense
current phase in each elbow. If current sensor 225 phase is
in-phase with voltage sensor 215 phase, the elbow is an input
elbow. If not, the elbow is an output elbow.
[0041] Since the center conductor of both elbows are connected, the
test point voltages on both elbows are essentially the same
amplitude and phase. Therefore, only voltage phase need be sensed
at one test point.
[0042] The best implementation of this first method for identifying
input and output elbows is illustrated in FIG. 4 using current
sensor 225 and alternate block 275 which consists of voltage input
phase identification instrument 240 and current to voltage adapter
235. Voltage input phase identification instrument 240 is described
in commonly owned U.S. Pat. No. 8,570,024 issued Oct. 29, 2013. An
example of a commercial instrument is the Origo Corporation G3
PhaseID System.
[0043] Phase identification instrument 240 is designed to measure
voltage phase on any energized conductor. Adapter 235 allows phase
identification instrument 240 to also measure current phase using a
standard AC current clamp 500 illustrated in FIG. 5, such as a
Fluke i400, as current sensor 225.
[0044] In operation, a lineman squeezes handles 515 together which
opens spring loaded jaws 510 so as to place AC current clamp 500
around stripped back URD cable 28. Leads 520 are plugged into
adapter 235 which in turn is plugged into voltage input phase
identification instrument 240.
[0045] Phase identification instrument 240 reference phase is
initially set to the utility reference phase. Then, AC current
clamp 500 is simply applied to each elbow to determine if the elbow
is an input elbow or output elbow. Typical results are illustrated
in FIG. 6 for a single phase C cabinet containing multiple input
and output elbows. Voltage phase for the entire cabinet is
indicated by the large square. Input elbow current phases are
indicated by small squares and output elbow current phases by
triangles. Note that input elbow current phases are nearly in-phase
with voltage phase and output elbow current phases are nearly
out-of-phase with voltage phase. Current phases will vary slightly
due to differing power factors associated with different elbow
currents.
[0046] This first method for determining elbow connectivity
identification using phase identification instrument 240 is the
optimum and fastest method to use on long daisy chains of padmount
transformers as they snake through neighborhoods since each
padmount contains a single input elbow and a single output elbow.
If one elbow is identified as an input elbow, the other elbow must
be an output elbow and vice versa. A single lineman can simply walk
to the next padmount, open it, measure current phase on one elbow,
tag both elbows, close the padmount, and walk to the next one in
the chain.
[0047] This first method is also optimum for first segregating all
elbows in large cabinets into input elbows and output elbows
associated with each voltage phase attribute A, B, and C, prior to
identifying their upstream sources and downstream destinations.
[0048] The second method for identifying elbow connectivity injects
a tracer signal into an upstream output elbow test point and
searches for that tracer signal on a downstream input elbow test
point. The method is illustrated in FIG. 7 and FIG. 8.
[0049] Currently, the standard method for determining which
downstream cabinets are connected to an upstream cabinet is to use
a line locator. Line locators (also called pipe locators or cable
tracers) are offered by numerous manufacturers and basically all
operate on the same principal. The Utiligard by Subsite Electronics
is a typical example. They are composed of a line locator
transmitter 705 and a line locator receiver 720.
[0050] Line locator transmitter 705 generates a signal typically
around 100 KHz to 200 KHz on signal lead 710 which is connected to
URD cable 20 grounding wire 125 (twisted concentric neutral
conductors 30 as was illustrated in FIG. 2), and its ground wire
715 is connected to a ground rod 718 driven into the earth a few
feet away from grounding wire 125 ground point. This creates a
magnetic field along any metal path. Line locator receiver 720
contains display 725 and is carried by handle 730. It detects the
magnetic field produced by line locator transmitter 705 along any
metal path.
[0051] Although a line locator will track the URD concentric
neutral between output elbow 740 in an upstream cabinet and input
elbow 745 in a downstream cabinet, it also tracks the concentric
neutrals of any other URD cables in the upstream cabinet. Since the
concentric neutrals of all URD cables in a cabinet are connected
together, a line locator will trace the paths of every URD cable in
the cabinet. Even if upstream output elbow 740 is traced to the
correct downstream cabinet, it doesn't indicate the specific input
elbow 745 in that cabinet to which output elbow 740 is
connected.
[0052] FIG. 8 illustrates how the second method for identifying
elbow connectivity solves this problem by using tracer transmitter
870 to inject a high frequency tracer signal into test point 750 of
upstream output elbow 740. Center conductor 805 of coax 855 is
connected directly to test point 750 and its shield is connected
via a short ground wire 865 to URD 20 grounding wire 125 at a point
as close as possible to output elbow 740.
[0053] Maximum tracer signal is injected into test point 750 by
keeping center conductor 805 lead length short, ground wire 865
short, and selecting coax 855 characteristic impedance to match the
URD cable 20 characteristic impedance. More importantly, this coax
to URD connection technique minimizes the stray tracer signal
injected onto any adjacent URD cables. As is well known by those
skilled in the art, maximum injection of high frequency signals
occurs when the connection impedance mismatch is low and minimum
injection occurs when connection impedance mismatch is high.
[0054] The result is that maximum signal will propagate through
upstream output elbow 740 URD cable 20 and into downstream input
elbow 745 test point 735. Only minuscule tracer signal will couple
onto other URD cables in either the upstream or downstream
cabinets. At the downstream cabinet, tracer receiver 875 uses
electric field probe 825 to detect the tracer signal on test point
735 of downstream elbow 745. Although it might be possible to
detect the tracer signal on some other test points in the
downstream cabinet, their amplitudes will be much lower than the
amplitude on test point 735 of connected downstream elbow 745.
[0055] There are numerous techniques available to implement tracer
transmitter 870 and tracer receiver 875. Almost any method of
generating and receiving a signal can be used. The most optimum
technique is illustrated in FIG. 9 in which a direct sequence
spread spectrum tracer signal is used. This is a very common
communication signal used by the global Positioning System (GPS),
Code Division Multiple Access (CDMA) mobile phone systems, and many
other communication systems.
[0056] Tracer transmitter 870 in FIG. 9 creates a spread spectrum
signal using direct sequence pseudo random (PN) code generator 910
clocked by oscillator 905, amplified by amplifier 915, and applied
to elbow test point 750 as was illustrated in FIG. 8.
[0057] Tracer receiver 875 capacitive couples to test point 735.
Spread spectrum tracer signal on test point 735 is amplified using
amplifier 935, decoded in decoder 960, and displayed on display
965. Tracer receiver 875 is a small handheld portable unit that can
be sequentially touched to each cabinet elbow test point to detect
the URD cable energized by tracer transmitter 870.
[0058] Tracer transmitter 870 and tracer receiver 875 illustrated
in FIG. 9 are very generic. Numerous analog and digital techniques
can be used to implement this type of communication system as is
well known by those skilled in the art. The only requirement is
that the frequency, sensitivity, and power of the signal be
adequate to be detected at the downstream cabinet elbow test
point.
[0059] Although this second method was described as connecting the
tracer transmitter to the upstream elbow and detecting the tracer
signal on the downstream elbow, the method will work just as well
when the tracer transmitter is connected to the downstream elbow
and the tracer signal detected on the upstream elbow.
[0060] A more efficient method of using this second method is to
use the first method to segregate all elbows of both upstream and
downstream cabinets into input elbows and output elbows associated
with each voltage phase attribute A, B, and C as was described
before. Assume the upstream cabinet contains a single phase B
output elbow and the downstream cabinet contains multiple phase B
input elbows. Then the tracer signal need only be applied to the
phase B upstream output elbow and searched for on the phase B
downstream input elbows to determine which phase B downstream input
elbow is connected to the phase B upstream elbow.
[0061] Similarly, if the downstream cabinet contains a single phase
B input elbow and the upstream cabinet contains multiple phase B
output elbows, then the tracer signal need only be applied to the
downstream phase B input elbow and searched for on upstream phase B
output elbows to determine which upstream phase B output elbow is
connected to the downstream phase B input elbow. If both upstream
and downstream cabinets contain multiple input or output elbows of
the same phase attribute, then the tracer signal can be
sequentially applied to the elbows to be traced.
[0062] The third method for identifying input and output elbows
simultaneously measures current in upstream and downstream elbow
URD cables. Elbow URD cables with essentially identical currents
are identified as being connected.
[0063] In general, a lineman with a current clamp meter (current
clamp with built-in current display) can be stationed at two
cabinets known to be connected by one or more URD cables. The
upstream lineman attaches his meter to a first elbow and
communicates its current reading to the downstream lineman each
second or so. The downstream lineman uses his current clamp meter
to sequentially measure each elbow current looking for a match.
When a match is found, the upstream and downstream elbows are
tagged as connected.
[0064] Although this technique works, it is terribly slow and
inefficient if multiple elbows are present in one or both cabinets.
It is even more inefficient if multiple downstream cabinets must be
checked to find a connected URD cable. URD currents are statistical
and vary continuously as customers switch on and off various
appliances or when heating and cooling equipment cycles. Therefore,
upstream and downstream current measurements must be nearly
simultaneous.
[0065] The third method for identifying input and output elbows
using an efficient current matching technique is illustrated in
FIG. 10 where short range radio or cellular communication is used
to simultaneous compare upstream and downstream elbow currents.
[0066] Assume the upstream cabinet contains multiple output elbows.
Assume the lineman attaches a current clamp 225 to each of the
output elbow URD cables 28 as was illustrated in FIG. 4. Each
current clamp 225 is plugged into upstream transmitter 602 which
simultaneously measures all current clamp 225 currents using high
speed multiplexer analog-to-digital converter (A/D) 605. These
currents are each integrated over a short period of time (for
example 1 second), formatted and assigned a reference number in
data formatter 620, and transmitted using short range radio or
cellular modem 625.
[0067] Short range radio or cellular modem 635 in downstream
receiver 603 receives upstream current sensor 602 transmission 630.
Downstream lineman attaches his current clamp 225 to an input elbow
URD cable 28, single channel A/D 640 and integrator 645 measures
input elbow URD cable 28 current, comparator 650 compares this
input current against the received list of tagged upstream output
current values from short range radio or cellular modem 635, and
displays matching current upstream reference number on display
655.
[0068] Using this third method, downstream lineman only has to make
one current measurement per input elbow to determine if it is
connected to an upstream cabinet output elbow, and if connected,
immediately know the reference number of the upstream output
elbow.
[0069] This third method is most applicable to large junction
cabinets that contain many (perhaps a dozen or more) elbows and
scant knowledge of which cabinets they come from or go to. The
ability to continuously know the currents of all output elbows can
save hours of searching multiple downstream cabinets and elbows for
a current match.
[0070] The block diagram illustrated in FIG. 10 is very generic.
Any implementation that continuously communicates upstream cabinet
output elbow currents to a lineman checking downstream cabinet
input elbows is acceptable. Depending on range, Bluetooth, WiFi,
cellular, or multi-use radio service (MURS) communications could be
used. A smart phone app could even be written where the upstream
lineman's phone talks to the upstream current senor 602, the
downstream lineman's phone talks to the downstream current sensor
603, and the phones connect with each other over normal cellular
communication.
[0071] Using a sensitive current sensor, it can also be attached to
the complete URD cable 20 in FIG. 1 instead of only around outer
sheath 28 as described in FIG. 4. The sum of center conductor 22
current and concentric neutral 30 current is very low, but seldom
exactly zero due to alternate return current paths on other URD
cables. Although low, it will be identical at all points along a
jacketed URD cable. Therefore, this third method of identifying URD
cables can also be used to identify which of multiple URD cables
exposed in a trench are connected to a particular elbow. This is a
very important benefit as electric utilities have been searching
for a reliable method of identifying URD cables in an open trench
for decades.
[0072] Placing the current sensor around the complete URD cable is
also beneficial in cabinets where an insufficient length of exposed
outer sheath 28 is available below the elbow to accommodate the
current sensor.
[0073] Although the preferred embodiments of the invention have
been illustrated and described in detail, it will be readily
apparent to those skilled in the art that various modifications may
be made therein without departing from the spirit of the
invention.
[0074] For example, for the third method, current sensors other
than the current clamp or current clamp meters described here could
be used. A current transformer (CT) is a type of transformer that
is used to measure AC current. They come in numerous sizes and
styles. Like the current clamps and current clamp meters described
here, they produce an AC current in its secondary which is
proportional to the AC current in it its primary (the wire or
conductor around which it is attached). Almost any primary current
sensitivity required is available. Using a sensitive current
sensor, it could be attached to the complete URD cable 20 in FIG. 1
instead of only around outer sheath 28 as described in FIG. 4, as
was explained earlier.
[0075] In general, examples in this disclosure were described as
using the upstream cabinets as the source and downstream cabinets
as the destination. However, all examples can also use the
downstream cabinets as source and upstream cabinets as
destination.
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