U.S. patent application number 17/400410 was filed with the patent office on 2022-03-31 for method for isolating a fault and restoring power in an underground radial loop network using fault interrupting switches.
This patent application is currently assigned to S&C Electric Company. The applicant listed for this patent is S&C Electric Company. Invention is credited to Daniel Desmond, John French, Alejandro Montenegro, Michael Quinlan, John Seuss.
Application Number | 20220103010 17/400410 |
Document ID | / |
Family ID | |
Filed Date | 2022-03-31 |
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United States Patent
Application |
20220103010 |
Kind Code |
A1 |
Quinlan; Michael ; et
al. |
March 31, 2022 |
METHOD FOR ISOLATING A FAULT AND RESTORING POWER IN AN UNDERGROUND
RADIAL LOOP NETWORK USING FAULT INTERRUPTING SWITCHES
Abstract
A method for isolating a fault in an underground power
distribution network. The network includes a power line, a
plurality of transformers electrically coupled to and positioned
along the power line, a first end switch connected to one end of
the power line and a second end switch connected to an opposite end
of the power line, where each transformer includes an upstream
switching device and a downstream switching device, and where
source power is provided to both ends of the power line through the
first and second end switches and one of the switching devices is a
normally open switching device. The method includes detecting
overcurrent in the network from the fault, opening certain ones of
the switching devices in response thereto, detecting loss of
voltage as a result of the open switching devices and opening or
closing certain ones of the switching devices to isolate the
fault.
Inventors: |
Quinlan; Michael; (Chicago,
IL) ; Seuss; John; (Washington, DC) ;
Montenegro; Alejandro; (Chicago, IL) ; Desmond;
Daniel; (Chicago, IL) ; French; John;
(Chicago, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
S&C Electric Company |
Chicago |
IL |
US |
|
|
Assignee: |
S&C Electric Company
Chicago
IL
|
Appl. No.: |
17/400410 |
Filed: |
August 12, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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63085441 |
Sep 30, 2020 |
|
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International
Class: |
H02J 13/00 20060101
H02J013/00; H02J 3/00 20060101 H02J003/00 |
Claims
1. A method for isolating a fault in a power distribution network,
the network including a power line, a plurality of transformers
electrically coupled to and positioned along the power line, a
first end switch connected to one end of the power line and a
second end switch connected to an opposite end of the power line,
each transformer including an upstream switching device and a
downstream switching device, wherein source power is provided to
both ends of the power line through the first and second end
switches and wherein one of the switching devices is a normally
open switching device, the method comprising: detecting overcurrent
in the network; opening one or more of the one end switch that is
delivering power to a section of the network that has the fault and
at least one of the switching devices in the section between the
one end switch and the fault; detecting loss of voltage by the
switching devices that are between the fault and the normally open
switching device; closing the switching devices that detect voltage
on their upstream side and do not detect the overcurrent when they
close; closing the normally open switching device if it detects
voltage on its upstream side and does not detect the overcurrent
when it closes; and closing and then opening the switching devices
that detect voltage on their upstream side and detect the
overcurrent.
2. The method according to claim 1 wherein the first and second end
switches are reclosers.
3. The method according to claim 2 wherein the reclosers are
single-phase, self-powered, magnetically actuated reclosers.
4. The method according to claim 1 wherein the upstream switching
device and the downstream switching device in each transformer
share a common control board.
5. The method according to claim 1 wherein the switching devices
are fault interrupting devices.
6. The method according to claim 1 wherein closing and then opening
the switching devices that detect voltage on their upstream side
and detect the overcurrent occurs in less than or equal to 1
current cycle.
7. The method according to claim 1 wherein the power distribution
network is an underground power distribution network.
8. A method for isolating a fault in a power distribution network,
the network including a power line, a plurality of transformers
electrically coupled to and positioned along the power line, a
first recloser connected to one end of the power line and a second
recloser connected to an opposite end of the power line, each
transformer including an upstream switching device and a downstream
switching device, wherein source power is provided to both ends of
the power line through the first and second reclosers and wherein
one of the switching devices is a normally open switching device,
the method comprising: detecting overcurrent in the network from
the fault and then opening the first recloser that is delivering
power to a first section of the network between the first recloser
and the fault; starting a timer in the transformer including the
normally open switching device in response to detecting loss of
voltage when the recloser opens; opening the downstream switching
device in an upstream transformer in the first section in response
to detecting overcurrent and then loss of voltage; opening the
upstream switching device in a downstream transformer in the first
section in response to detecting overcurrent and then loss of
voltage; closing the recloser that opened; detecting voltage on the
upstream side of the upstream transformer when the recloser closes
and opening the downstream switching device in the upstream
transformer in response thereto; detecting voltage on the upstream
side of the downstream transformer when the downstream switching
device closes and closing the upstream switching device in the
downstream transformer in response thereto; detecting overcurrent
downstream of the transformer and locking the downstream switching
device of the downstream transformer open in response thereto;
closing the normally open switching device when the timer expires,
detecting overcurrent from an alternate source as a result of the
fault and opening the normally open switching device; detecting
overcurrent and then loss of voltage by the transformers in a
second section of the network between the fault and the normally
open switching device; opening the downstream switching device in
an upstream transformer in the second section in response to
detecting the overcurrent and then loss of voltage; opening the
upstream switching device in a downstream transformer in the second
section in response to detecting the overcurrent and then loss of
voltage; closing the normally open switching device; detecting
voltage on the upstream side of the downstream transformer when the
normally closed switching device closes and closing the upstream
switching device in the downstream transformer in response thereto;
detecting voltage on the upstream side of the upstream transformer
when the upstream switching device is closed and closing the
downstream switching device in the upstream transformer in response
thereto; and detecting the overcurrent in the upstream transformer
and locking the downstream switching device of the upstream
transformer open in response thereto.
9. The method according to claim 8 wherein the upstream switching
device and the downstream switching device in each transformer
share a common control board.
10. The method according to claim 8 wherein the reclosers are
single-phase, self-powered, magnetically actuated reclosers.
11. The method according to claim 8 wherein the reclosers have a
minimum of a 1.5 current cycle reclosing time.
12. The method according to claim 8 wherein closing and then
opening the switching devices in response to detecting overcurrent
occurs in less than or equal to 1 current cycle.
13. The method according to claim 8 further comprising using a
mechanical handle to open and close the switching devices to reset
the network to an original configuration.
14. The method according to claim 8 wherein the power distribution
network is an underground power distribution network.
15. A method for restoring power from a loss of power event in a
power distribution network where the loss of power event occurs
outside of the network, the network including a power line, a
plurality of transformers electrically coupled to and being
positioned along the power line, a first recloser connected to one
end of the power line and a second recloser connected to an
opposite end of the power line, each transformer including an
upstream switching device and a downstream switching device,
wherein power is provided to both ends of the power line through
the first and second reclosers, the two switching devices closest
to the reclosers are designated head end switching devices and one
of the switching devices is a normally open switching device, the
method comprising: starting a first timer in the transformer that
detects loss of voltage from the loss of power event and has a head
end switching device; starting a second timer in the transformer
that detects loss of voltage from the loss of power event and has
the normally open switching device, where the first timer is
shorter in duration than the second timer; opening the head end
switching device when the first timer expires if the transformer
still detects loss of voltage; and closing the normally open
switching device when the second timer expires.
16. The method according to claim 15 wherein the upstream switching
device and the downstream switching device in each transformer
share a common control board.
17. The method according to claim 15 wherein the reclosers are
single-phase, self-powered, magnetically actuated reclosers.
18. The method according to claim 15 wherein closing and then
opening the switching devices in response to detecting overcurrent
occurs in less than or equal to 1 current cycle.
19. The method according to claim 15 further comprising using a
mechanical handle to open and close the switching devices to reset
the network to an original configuration.
20. The method according to claim 15 wherein the power distribution
network is an underground power distribution network.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority from the
U.S. Provisional Application No. 63/085,441, filed on Sep. 30,
2020, the disclosure of which is hereby expressly incorporated
herein by reference for all purposes.
BACKGROUND
Field
[0002] The present disclosure relates generally to a switching
device that provides fault isolation and restoration in a power
distribution network and, more particularly, to a switching device
that is part of a transformer in an underground residential power
distribution network and that provides fault isolation and
restoration.
Discussion of the Related Art
[0003] An electrical power distribution network, often referred to
as an electrical grid, typically includes a number of power
generation plants each having a number of power generators, such as
gas turbines, nuclear reactors, coal-fired generators,
hydro-electric dams, etc. The power plants provide power at a
variety of medium voltages that are then stepped up by transformers
to a high voltage AC signal to be connected to high voltage
transmission lines that deliver electrical power to a number of
substations typically located within a community, where the voltage
is stepped down to a medium voltage for distribution. The
substations provide the medium voltage power to a number of
three-phase feeders including three single-phase feeder lines that
carry the same current, but are 120.degree. apart in phase. A
number of three-phase and single phase lateral lines are tapped off
of the feeder that provide the medium voltage to various
distribution transformers, where the voltage is stepped down to a
low voltage and is provided to a number of loads, such as homes,
businesses, etc.
[0004] Periodically, faults occur in the distribution network as a
result of various things, such as animals touching the lines,
lightning strikes, tree branches falling on the lines, vehicle
collisions with utility poles, etc. Faults may create a
short-circuit that increases the load on the network, which may
cause the current flow from the substation to significantly
increase, for example, many times above the normal current, along
the fault path. This amount of current causes the electrical lines
to significantly heat up and possibly melt, and also could cause
mechanical damage to various components in the substation and in
the network. Power distribution networks of the type referred to
above often include a number of switching devices, breakers,
reclosers, interrupters, etc. that control the flow of power
throughout the network, and may be used to isolate faults within a
faulted section of the network.
[0005] As part of their power distribution network, many utility
companies employ a number of underground single-phase lateral
circuits that feed residential and commercial customers. Often
times these circuits are configured in a loop and fed from both
ends, where an open location, typically at a transformer, is used
in the circuit to isolate the two power sources. Although providing
underground power cables protects circuits from faults created by
things like storms and vegetation growth, underground cables still
may break or otherwise fail as a result of corrosion and other
things. For a residential loop circuit of the type referred to
above having two power sources, it is usually possible to
reconfigure the open location in the circuit so that loads that are
affected by a fault are fed by the other source and service to all
of the loads is maintained. However, known processes for
identifying the location of a cable failure and the subsequent
reconfiguration of the open location often results in long power
restoration times.
SUMMARY
[0006] The following discussion discloses and describes a method
for isolating a fault in an underground power distribution network.
The network includes a power line, a plurality of transformers
electrically coupled to and positioned along the power line, a
first end interrupter switch connected to one end of the power line
and a second end interrupter switch connected to an opposite end of
the power line, where each transformer includes an upstream
switching device and a downstream switching device, and where
source power is provided to both ends of the power line through the
first and second end interrupter switches and one of the switching
devices is a normally open switching device. The method includes
detecting overcurrent in the network from the fault and then
opening one or more of the one end switch that is delivering power
to a section of the network that has the fault and at least one of
the switching devices in the section between the one end switch and
the fault. The method also includes detecting loss of voltage by
the switching devices that are between the fault and the normally
open switching device, and closing the switching devices that
detect voltage on their upstream side and do not detect the
overcurrent when they close. The method further includes closing
the normally open switching device if it detects voltage on its
upstream side and does not detect the overcurrent when it closes,
and closing and then opening those switching devices that detect
voltage on their upstream side and detect the overcurrent.
[0007] Additional features of the disclosure will become apparent
from the following description and appended claims, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a simplified schematic diagram of a known power
distribution network including an underground residential power
circuit;
[0009] FIG. 2 is an isometric view of a known transformer used in
the circuit shown in FIG. 1;
[0010] FIG. 3 is a simplified schematic diagram of the power
distribution network shown in FIG. 1 where the transformers include
a pair of fault interrupting switching devices;
[0011] FIG. 4 is an isometric view of the transformer shown in FIG.
2 and including the fault interrupting switching devices;
[0012] FIG. 5 is an isometric view of one of the fault interrupting
switching devices separated from the transformer;
[0013] FIG. 6 is a cross-sectional type view of the fault
interrupting switching device shown in FIG. 5;
[0014] FIG. 7 is an isometric view of a sectionalizer switching
device that can be employed in the transformer instead of the fault
interrupting switching devices;
[0015] FIG. 8 is a cross-sectional type view of the sectionalizer
switching device shown in FIG. 7;
[0016] FIG. 9 is a side view of the sectionalizer switching device
shown in FIG. 7 illustrating conductors in the device;
[0017] FIG. 10 is an isometric view of the transformer shown in
FIG. 2 including two of the sectionalizer switching devices shown
in FIGS. 7-9;
[0018] FIG. 11 is a schematic block diagram of a switch assembly
including two of the sectionalizer switching devices sharing a
common control board;
[0019] FIG. 12 is a schematic block diagram of the control board in
the switch assembly;
[0020] FIG. 13 is an isometric view of the transformer shown in
FIG. 10 and including parking stands; and
[0021] FIG. 14 is a simplified schematic diagram of a residential
power distribution network of the type including transformers
having a pair of switching devices that are either fault
interrupting devices or sectionalizer devices, where the network is
used to describe fault isolation and power restoration for
situations where a fault occurs in the network or there is a loss
of voltage upstream of the network.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0022] The following discussion of the embodiments of the
disclosure directed to a switching device that provides fault
isolation and restoration is merely exemplary in nature, and is in
no way intended to limit the invention or its applications or uses.
For example, the switching devices discussed herein have particular
application for use with transformers employed in underground
residential circuits. However, the switching devices may have other
applications.
[0023] This disclosure proposes hardware and algorithms for the
automatic protection, isolation and restoration of underground
residential cable loops and methods to switch cable segments
without handling cable elbows. The system and method provide
automation without communications to a central controller,
automation without having to configure device parameters, such as
IP addresses, even when the automation requires communications
between devices, provides coordinated protection through
communications-less coordination with a recloser, provides for
elimination of load switching and fault making with cable elbows,
and controls packaging that can be replaced and upgraded in the
field as new features become available.
[0024] FIG. 1 is a simplified schematic diagram of a known power
distribution network 10 including an over-head section 12 having a
three-phase feeder 14, or possibly a single-phase feeder, and a
single-phase underground residential loop section 16 including a
single-phase lateral line 18 having one end 22 coupled to the
feeder 14 through a fuse 24 and an opposite end 28 coupled to the
feeder 14 through a fuse 30, where the fuses 24 and 30 may be pole
mounted or pad mounted fuses. Although this embodiment shows the
ends 22 and 28 connected to the feeder 14, in an alternate
embodiment the ends 22 and 28 may be coupled to different feeders.
Further, the ends 22 and 28 would generally be coupled to the same
phase of the feeder 14. The fuses 24 and 30 can be any suitable
switching device for the purposes described herein that disconnects
the line 18 from the feeder 14, such as a fault interrupting device
or reclosing device. The medium voltage provided on the line 18 is
stepped down to a low voltage by a number of transformers suitable
to provide power to a number of loads 34, such as homes. In this
non-limiting embodiment, the circuit 16 includes three transformers
40, 42 and 44 each including a primary coil 46 across which the
medium voltage is applied and a secondary coil 48 that provides low
voltage to a service conductor 50 to which the loads 34 are
coupled. However, as will be appreciated by those skilled in the
art, a typical underground loop circuit of this type will include
several more transformers.
[0025] FIG. 2 is an isometric view of the transformer 40 of the
type that is mounted on a pad (not shown) with the understanding
that the transformers 42 and 44 are the same or similar. The
transformer 40 includes an enclosure 60 that houses the coils 46
and 48 and other electrical components (not shown) of the
transformer 40. A cover 58 of the enclosure 60 is shown in an open
position to expose a panel 62 in the enclosure 60. A connector
bushing 64 extends through the panel 62 that accepts an elbow
connector 66 that connects the line 18 to the primary coil 46 and a
connector bushing 68 extends through the panel 62 that accepts an
elbow connector 70 that connects the line 18 to the primary coil
46. A number of positive and negative 120 V lines 72 and 74 and a
neutral line 76 are connected to the secondary coil 48, extend from
the housing 60 and provide power along the service conductor 50,
where the number of the lines 72 and 74 depends on the number and
type of the loads 34 being serviced by that transformer. A parking
stand 78 is welded to the panel 62 and is a fixture that allows one
of the elbow connectors 66 and 70 to be supported when it is
detached from the bushing 64 or 68 for reasons that will become
apparent from the discussion below.
[0026] Power is provided to both ends 22 and 28 of the line 18 and
as such one of the elbow connectors is disconnected from one of the
transformers 40, 42 or 44 and placed in a bushing (not shown) in
the parking stand 78 while it is hot to electrical separate the
part of the line 18 that receives power from the end 22 and the
part of the line 18 that receives power from the end 28. For
example, the right side of the transformer 40 is disconnected from
the line 18 so that the loads 34 connected to the transformer 40
receive power from the end 22 of the line 18 and the loads 34
connected to the transformers 42 and 44 receive power from the end
28 of the line 18.
[0027] Faults occur even for underground lines from, for example,
deterioration of the cable insulation. If a fault 80 occurs, for
example, in a section 82 of the line 18 between the transformers 42
and 44, the fuse 30 will operate to clear the fault 80 so that
power is prevented from being provided to the loads 34 being
serviced by the transformers 42 and 44. The utility will be
notified of the fault 80 is some manner, such as an automatic
transmission or customer notification, and a procedure is then
implemented by the utility that requires workers to manually
perform a process for restoring power to the loads 34 serviced by
the transformers 42 and 44. For this example, the procedure
requires identifying the location of the fault 80 by driving a
service truck between the fuse 30 and the transformers 40, 42 and
44, disconnecting the line 18 from the transformers 42 and 44 and
closing the fuse 30 to see when the fuse 30 trips and when it does
not. Once the location of the fault 80 is identified, then the
right side of the transformer 42 is disconnected from the line 18
and placed in the parking stand, the left side of the transformer
44 is disconnected from the line 18 and place in the parking stand
and the line 18 is connected to the right side of transformer 40 so
that power is provided from the end 22 of the line 18 to the loads
34 serviced by the transformers 40 and 44 and power is provided
from the end 28 of the line 18 to the loads 34 serviced by the
transformer 42. Such a procedure may take hours to restore power to
the loads 34 serviced by the transformers 42 and 44 even assuming
everything goes smoothly.
[0028] FIG. 3 is a schematic diagram of the network 10 where each
transformer 40, 42 and 44 now includes a pair of fault interrupting
switching devices that provide automatic power restoration to the
loads 34 in response to a fault, as will be described in detail
below. Particularly, the transformer 40 includes a fault
interrupting switching device 90 coupled between the line 18 and
the primary coil 46 and a normally open (NO) fault interrupting
switching device 92 coupled between the line 18 and the primary
coil 46, the transformer 42 includes a fault interrupting switching
device 94 coupled between the line 18 and the primary coil 46 and a
fault interrupting switching device 96 coupled between the line 18
and the primary coil 46, and the transformer 44 includes a fault
interrupting switching device 98 coupled between the line 18 and
the primary coil 46 and a fault interrupting switching device 100
coupled between the line 18 and the primary coil 46. Instead of
putting the elbow connector at the right side of the transformer 40
in the parking stand 78, the switching device 92 is opened.
Additionally, the fuses 24 and 30 have been replaced with
single-phase, self-powered, magnetically actuated reclosers 86 and
88.
[0029] FIG. 4 is an isometric view of the transformer 40 now shown
with the switching devices 90 and 92 in place. Particularly, the
switching device 90 is coupled to the bushing 64 and the elbow
connector 66 and the switching device 92 is coupled to the bushing
68 and the elbow connector 70.
[0030] FIG. 5 is an isometric view and FIG. 6 is a cross-sectional
view of the switching device 90 separated from the transformer 40.
The device 90 includes an outer grounded enclosure 102 having a
special configuration to hold the various components therein. A
mounting plate 104 is secured to the enclosure 102 and provides an
interface to mount the device 90 to the panel 62. A transformer
interface 106 extends from the enclosure 102 and is configured to
be electrically coupled to the bushing 64 and a load-break
connector interface 108 extends from the enclosure 102 and is
configured to be electrically coupled to the elbow connector 66. A
manual operating handle 110 allows the device 90 to be manually
opened and closed, if necessary.
[0031] The enclosure 102 defines an internal chamber 112 in which
is configured the various components of the device 90. Those
components include a vacuum interrupter 116 having a vacuum housing
120 defining a vacuum chamber, a fixed upper terminal 122 extending
through a top end of the housing 120 and into the vacuum chamber
and a movable lower terminal 126 extending through a bottom end of
the housing 120 and into the vacuum chamber, where a bellows (not
shown) allows the movable terminal 126 to slide without affecting
the vacuum in the vacuum chamber. The upper terminal 122 goes into
the page and is connected to the transformer interface 106 and the
lower terminal 126 is connected to the load-break interface 108
through a flexible connector 134. A high impedance resistive
element 130 is helically wound around the housing 120 and is
connected to the upper terminal 122 at one end to provide a current
flow for energy harvesting purposes when the vacuum interrupter 116
is open. A Rogowski coil 136 or other current sensor, well known to
those skilled in the art, is wrapped around the terminal 126 and
measures current flow by means of the voltage that is induced in
the coil 136 being proportional to the rate of change of current
flow. It is noted that the switching device 90 including the vacuum
interrupter 116 can have other designs consistent with the
discussion herein.
[0032] The movable terminal 126 is coupled to a rod 138 that is
coupled to a plate 140, which in turn is coupled to an actuator
assembly 142 having an electromagnetic actuator 144 and an opening
spring 146, where other compliance springs (not shown) may also be
included. The actuator assembly 142 can be any suitable actuator
system for the purposes described herein and may, for example,
include an armature that is moved by an opening coil to open the
vacuum interrupter 116 and is moved by a closing coil to close the
vacuum interrupter 116, where the armature and a stator provide a
magnetic path for the flux produced by the coils. The coils are
de-energized after the actuator 144 is moved to the open or closed
position, and permanent magnets (not shown) are used to hold the
armature against a latching surface in the open or closed position.
The operating handle 110 is connected to a rod 150, which is
coupled to the rod 138. When the handle 110 is rotated in the
clockwise or counter-clockwise direction, the rod 150 moves up or
down to manually open or close the vacuum interrupter 116. The
vacuum interrupter 116, the Rogowski coil 136 and the actuator
assembly 142 are all at medium voltage potential, and as such are
encapsulated in an insulating material 152, such as an epoxy, that
fills most of the chamber 112.
[0033] An electronics control board 160 is provided within the
chamber 112 and includes various electrical components, such as a
microprocessor, etc., where the board 160 is powered through the
vacuum interrupter 116 when it is closed and through the high
impedance element 130 when the vacuum interrupter 116 is open. More
particularly, current flows through the lower impedance vacuum
interrupter 116 when it is closed and not through the element 130,
but flows through the element 130 when the vacuum interrupter 116
is open. Current flow through the element 130 provides power to
operate the electronics on the board 160 and operate the actuator
assembly 142 to close the vacuum interrupter 116. A high voltage
capacitor 164 and an energy storage capacitor 166 are electrically
coupled to the board 160. One side of the capacitor 164 is coupled
to the board 160 at high voltage and the opposite side of the
capacitor 164 is coupled to the grounded enclosure 100, which
provides a constant impedance and current that allows voltage
measurements. When the vacuum interrupter 116 is closed the
capacitor 164 provides a constant current that is used to power the
board 160, operate the actuator 144 and charge the storage
capacitor 166. When the vacuum interrupter 116 is open and current
is flowing through the element 130 if it is available the capacitor
164 also provides a constant current that is used to power the
board 160, operate the actuator 144 and charge the storage
capacitor 166. The energy stored in the storage capacitor 166 can
be used when the vacuum interrupter 116 is open or closed depending
on what power is available through the vacuum interrupter 116 or
the element 130. A dielectric material 168 that takes the shape of
its container and sets, such as epoxy, potting, silicone foam or
gel, etc., is provided in the chamber 110 to electrically isolate
the high voltage on the electronics board 160 with the grounded
enclosure 100. Because the vacuum interrupter 116, the actuator
assembly 112 and the control board 160 all operate at the line
voltage and thus have a floating reference potential, the device 90
can be made smaller than otherwise would be possible since these
components do not need to be electrically isolated.
[0034] If the fault 80 occurs in the section 82 of the line 18
between the transformers 42 and 44, the devices 94 and 96 detect
overcurrent and will open and interrupt the flow of current. The
devices 98 and 100 will see loss of voltage, will not detect
overcurrent and will open. A fault hunting algorithm is then
performed to isolate the fault and restore power to the loads 34,
as described below. The device 94 will detect voltage on its source
side, but no voltage on its downstream side and will close after a
period of time, and since it does not detect fault current will
remain closed. At about the same time, the device 92 will detect
voltage on its primary source side, but no voltage on its alternate
source side and will close, and since it does not detect fault
current will remain closed. When the device 94 closes, the device
96 will detect voltage on its upstream source side and no voltage
on its downstream side and will close, but will detect fault
current, and will immediately open within, for example, one current
cycle time. At the same time, when the device 92 closes, the device
100 will detect voltage on its downstream side, but no voltage on
its upstream side and will close, and since it does not detect
fault current will remain closed. When the device 100 closes, the
device 98 will detect voltage on its upstream source side and no
voltage on its downstream side and will close, but will detect
fault current, and will immediately open. Thus, the fault 80 is
isolated between the devices 96 and 98 and power is restored to all
of the loads 34, where the process will take less than a
minute.
[0035] Fault interrupting switching devices of the type just
described can be complex devices that measure voltage, which
requires a reference potential. A utility may want to employ less
expensive or less sophisticated switching devices, such has
sectionalizers, that do not provide fault interrupting and may not
include voltage sensors and can only measure current. A
sectionalizer is generally a self-contained, circuit-opening device
used in combination with source-side protective devices, such as
reclosers or circuit breakers, to automatically isolate faulted
sections of an electrical distribution network. Sectionalizers are
typically distributed between and among the reclosers to provide a
system for isolating smaller sections of the network in response to
a fault. Sectionalizers rely on observing a sequence of fault
currents and/or the presence and absence of voltage either to
indicate the presence of a fault or count the number of reclosing
attempts, and then perform circuit isolation sectionalizing when
the maximum number of reclosing attempts has been reached. Existing
power distribution circuit sectionalizers detect the passage of
fault currents, including both the initial fault event and
subsequent recloser-initiated events, as part of more elaborate
fault isolation and restoration processes. These processes may
include counting discrete intervals of fault current passage, or
counting discrete intervals of voltage presence and absence. In the
cases where the particular device is not able to measure voltage,
the fault location and isolation schemes discussed above can be
augmented using a revised fault location and isolation scheme
proposed below.
[0036] For the fault interrupting switching devices discussed
above, each of the devices included its own electronics board that
operated at a floating potential relative to the line voltage. In
an alternate embodiment, the electronics are removed from the
devices and provided as a single electronics unit for both of the
devices in each of the transformers 40, 42 and 44, where the
electronics unit operates at ground potential. In this embodiment,
the devices can operate as fault interrupting devices or
sectionalizers. As used herein, sectionalizers detect overcurrent,
but do not provide reclosing, increase a count each time they
detect loss of voltage during a fault clearing operation, and lock
open if their count has reached a predetermined value and no
current is flowing through the device in response to receiving a
message. Capacitors are used for voltage sensing and power line
communications.
[0037] FIG. 7 is an isometric view and FIG. 8 is a cross-sectional
view of a switching device 180 that can be configured to provide
both fault interrupting and sectionalizing, where sectionalizing
for this discussion is similar to the traditional sectionalizer
with some differences. The device 180 includes an outer enclosure
182, a transformer interface 184, a load-break connector interface
186 and a manual handle 188 configured in a similar manner as the
device 90 and operating in a similar manner. The components within
the enclosure 182 are encapsulated within an insulating medium 190,
such as an epoxy, where many of the components are conductors
operating at the medium voltage potential. FIG. 9 is a side view of
the switching device 180 with the outer enclosure 182 and the
insulating medium 190 removed to show the conductors.
[0038] The switching device 180 includes a vacuum interrupter 196
having a vacuum enclosure 198 defining a vacuum chamber 200, an
upper fixed terminal 202 extending through the enclosure 198 and
into the chamber 200 and having a contact 204 and a lower movable
terminal 206 extending through the enclosure 198 and into the
chamber 200 and having a contact 208, where a gap 210 is provided
between the contacts 204 and 208 when the vacuum interrupter 196 is
open. A bellows 212 allows the movable terminal 206 to move without
affecting the vacuum integrity of the chamber 200. The movable
terminal 206 is coupled to a drive rod 214 that is coupled to an
actuator assembly 216 of the type discussed above for opening and
closing the vacuum interrupter 196. In this design, the actuator
assembly 216 is insulated and not at the line potential. As above,
the details of the vacuum interrupter 196 are merely for
illustrative purposes in that other designs will be applicable.
[0039] A cup-shaped conductor 220 is provided around a top end of
the enclosure 198 and is electrically coupled to the fixed terminal
202 and to an elbow conductor 222 that is electrically coupled to
the connector interface 186. An hour glass or cylindrical shaped
conductor 224 is provided around a bottom end of the enclosure 198
and is electrically coupled to the movable terminal 206. The
cup-shaped conductor 220 includes an orifice 228 that accepts an
end 230 of an elbow conductor 232 in an electrically coupled
slidable engagement so that the elbow conductor 232 can slide
relative to the cup-shaped conductor 220 and still maintain
electrical contact therewith. The conductor 224 includes an orifice
234 that accepts an end 236 of a rod conductor 238 in an
electrically coupled slidable engagement so that the conductor 238
can slide relative to the conductor 224 and still maintain
electrical contact therewith, where the conductor 238 is part of a
cylindrical transformer conductor 240 that is electrically coupled
to the transformer interface 184. The elbow conductor 222 is
coupled to the cup-shaped conductor 220 in the same manner.
Therefore, when the conductors 220, 222, 224, 232 and 238 are
placed in a mold (not shown) and heated insulating material is
injected around them, the conductors 220, 222, 224, 232 and 238 are
able to slide relative to each other as the insulating material
cools and shrinks without affecting the electrical connections.
[0040] The elbow conductor 232 is also electrically coupled to one
end of a pair of capacitors 242 and 244 and a conductor 246 is
electrically coupled to an opposite end of the capacitors 242 and
244, where the end of the capacitors coupled to the elbow conductor
232 is at line potential and the end of the capacitors 242 and 244
coupled to the conductor 246 is at or near ground potential, and
thus provide stable voltage coupling for power line communications
signals, provide voltage coupling for voltage sensing, help
determine power flow direction and help determine the distance to a
fault.
[0041] FIG. 10 is an isometric view of a transformer 250 that is
similar to the transformer 40 except that the switching devices 90
and 92 have been replaced with switching devices 252 and 254 that
are identical and are the same as or similar to the device 180,
where like elements are identified by the same reference number.
The conductors in both of the devices 252 and 254 are connected to
a common control unit 256 that controls both of the devices 252 and
254, where the control unit 256 is mounted to the panel 62. In this
embodiment, the control unit 256 is powered by 120 V ac from the
lines 72 and 74 through lines 258.
[0042] FIG. 11 is a schematic block diagram of a switch assembly
260 including a switch circuit 262 representing the switching
device 252, a switch circuit 264 representing the switching device
254 and a control board 266 representing the control unit 256. The
circuit 262 includes a vacuum interrupter 268, an actuator 270, a
Rogowski coil 272 and a capacitor 274 and the circuit 264 includes
a vacuum interrupter 276, an actuator 278, a Rogowski coil 280 and
a capacitor 282 operating as discussed above. The circuit 262
includes a limit switch 284 and the circuit 264 includes a limit
switch 286 that tell the control board 266 which position the
device 188 on each of the devices 258 and 252 currently holds.
Voltage sensing is accomplished by the coupling capacitors 274 and
282 that provide a constant current to a resistor (not shown) in
the control board 266 and the voltage is measured across the
resistor. The control board 266 is powered by a 120 Vac source 290
from the secondary coil 48 and a 9V dc battery 292, and may provide
signals to a communications device 294, such as a utility
radio.
[0043] The control board 266 can be configured with any suitable
components and software that perform any desired function
consistent with the discussion herein. FIG. 12 is a schematic
diagram of the control board 266 showing one non-limiting example.
The control board 266 includes a microcontroller 300 that receives
the various inputs, performs the various algorithms and provides
the various outputs. Signals are received from and provided to
various elements with respect to the microcontroller 300. These
elements include measured voltages for both of the switching
circuits 262 and 264 at boxes 302 and 304, respectively, high gain
at box 306 for the Rogowski coils 274 and 280, low gain at box 308
for the Rogowski coils 274 and 280, ultra-gain at box 310 for the
Rogowski coils 274 and 280, and a modem 312 that provide signals to
an analog-to-digital (ADC) converter 314. Further, the elements
include handle position at box 316 that links up with the limit
switches 284 and 286, a ferroelectric random access memory (FRAM)
318, a relay 320 and a crystal oscillator 322. The elements further
include an insulated gate bipolar transistor (IGBT) module 326, a
half-wave rectifier 328 and voltage converters 330, 332, 334, 336
and 338.
[0044] By employing the switching devices in connection with the
transformers as discussed above, the known parking stand 78 may be
obscured and not usable, i.e., blocked by the control unit 256,
which may not be acceptable. FIG. 13 is an isometric view of the
transformer 250 including various embodiments for attaching
auxiliary parking stands thereto. Specifically, the transformer 250
includes parking stand units 350, 352 and 354 mounted to an edge
360 of the enclosure 60 to which the cover 58 is secured. The unit
350 includes a mount 364, the unit 352 includes a mount 366 and the
unity 354 includes a mount 368 that are configured to receive the
elbow connector 66 or 70 when it is detached from the load-break
connector interface 186. Thus, when the cover 58 is lifted, the
technician can secure one or more of the units 350, 352 and 354 to
the edge 360 using, for example, securing mechanisms 370 or
372.
[0045] FIG. 14 is a simplified schematic diagram of a residential
power distribution network 400 similar to the network 10. The
network 400 includes two single-phase, self-powered, magnetically
actuated reclosers 402 and 404 connected to the same or different
feeders (not shown), i.e., at a head end of the network 400, an
underground distribution line 406 and ten transformers 408, 410,
412, 414, 416, 418, 420, 422, 424 and 426 coupled along the line
406 in the manner discussed above. The transformer 408 includes
switching devices 430 and 432, the transformer 410 includes
switching devices 434 and 436, the transformer 412 includes
switching devices 438 and 440, the transformer 414 includes
switching devices 442 and 444, the transformer 416 includes
switching devices 446 and 448, the transformer 418 includes
switching devices 450 and 452, the transformer 420 includes
switching devices 454 and 456, the transformer 422 includes
switching devices 458 and 460, the transformer 424 includes
switching devices 462 and 464, and the transformer 426 includes
switching devices 466 and 468. The switching device 448 is normally
open to provide electrical isolation between the source ends of the
network 400.
[0046] The network 400 will be used below to describe fault
isolation and power restoration processes when a fault 398 occurs
in the line 406 between the transformers 410 and 412 or there is a
loss of voltage upstream of the network 400, where each of the
switching devices 430-466 is similar to the switching device 180
and operate as fault interrupting devices or as sectionalizers that
do not provide fault interrupting. For the discussion below, any
reference to detecting overcurrent, detecting loss of voltage,
starting timers, sending messages, etc. in the transformers or the
switching devices is performed by the shared control unit 256 for
the switching devices in the transformer.
[0047] For the fault interrupting embodiment, if the fault 398
occurs in the line 406, the network 400 operates to isolate the
fault and restore power as follows. In order for the fault
isolation and power restoration to be performed by the network 400
using the fault interrupting switching devices, the reclosers 402
and 404 need to have a minimum 1.5 power frequency cycle recloser
trip. When the fault occurs, the recloser 402 will open, the
transformers 408 and 410 will log the overcurrent event and in
response to detecting loss of voltage a timer will start in the
transformer 416, which will eventually be used to open the normally
closed device 448. In response to detecting the overcurrent
followed by loss of voltage, one fault interrupter in each of the
transformers 408 and 410 will open. The recloser 402 will then
close in the reclosing operation after 1.5 cycles, and the
transformer 408 will detect voltage on the upstream side of the
device 432 and it will close. When the device 432 closes, the
transformer 410 will detect voltage on the upstream side of the
device 434 and it will close. When that happens, the transformer
410 detects overcurrent again due to the fault on the adjacent
segment and determines the fault must be on its downstream side,
and thus causes the device 436 to lock open to isolate the fault.
When the timer in the transformer 416 expires, the normally open
switching device 448 is closed and in response to the transformer
416 detecting overcurrent now from the recloser 404 side of the
line 406, the normally open switching device 448 will immediately
open and clear the fault current, but the recloser 404 will not
open because its trip time is 1.5 cycles. The transformers 412 and
414 detect the overcurrent followed by loss of voltage, and thus
the now downstream device 438 in the transformer 412 and the now
upstream device 444 in the transformer 414 are opened. The normally
open switching device 448 is then closed, and the transformer 414
will detect voltage on the upstream side of the device 444 and it
will close. When the device 444 closes, the transformer 412 will
detect voltage on one side of the device 438 and it will close.
When that happens, the transformer 412 detects overcurrent again
and determines the fault must be on its downstream side, and thus
causes the device 438 to lock open and isolate the fault on the
original upstream side. In this scenario, it would be required that
a worker reset the original configuration of the network 400 when
the fault is fixed using the manual handle 188 on the appropriate
switching devices 430-466.
[0048] For the loss of voltage scenario upstream of the network
400, the devices 430 and 466 are designated "head end" devices. If
loss of voltage occurs upstream of the recloser 402, the
transformers 408, 410, 412, 414 and 416 detect the loss of voltage,
and a timer is started in the transformer 408 because it has the
head end switching device 430 and a timer is started in the
transformer 416 because it has the normally open switching device
448, where the timer in the transformer 408 is shorter than the
timer in the transformer 416. When the timer in the transformer 408
expires and loss of voltage is still detected, the head end
switching device 430 will open to isolate the source at the
recloser 402 from the recloser 404, which gives the system time to
clear faults upstream of the recloser 402. The timer in the
transformer 416 will then expire and the device 448 will close,
which will provide power from the recloser 404 to all of the
transformers 408-416. In this embodiment, the head end switching
device 430 becomes the normally open switching device. In this
scenario, it would be required that a worker reset the original
configuration of the network 400 when the source voltage returns
using the manual handle 188 on the appropriate switching devices
430-466.
[0049] For the sectionalizer embodiment, if the fault occurs in the
line 406 between the transformers 410 and 412, the network 400
operates to isolate the fault and restore power as follows. In this
design, the protection settings in the reclosers 402 and 404 do not
need to be modified so that, for example, they have a 1.5 minimum
trip cycle time, but can be set in any suitable manner. The
recloser 402 detects the overcurrent and opens in a fault clearing
process, and the switching devices 430, 432, 434 and 436 detect the
overcurrent, but do not have fault interrupting capability, and
detect the loss of voltage when the recloser 402 opens. The
switching devices 438, 440, 442, 444 and 446 do not detect the
overcurrent, but do detect loss of voltage, and thus the
transformers 412 and 414 start a timer in response thereto, where
the transformer 416 does not start a timer because it has the
normally open switching device 448. The recloser 402 then closes as
part of the fault clearing process, detects the overcurrent again
and opens again. In response to detecting overcurrent and then loss
of voltage a second time, the downstream devices 432 and 436 in the
transformers 408 and 410, respectively, open, and the transformers
408 and 410 send a power line carrier "clear to close" message on
the line 406 to their immediate upstream transformer to close their
downstream switching device if they detected overcurrent, and thus
the device 432 closes, but the device 436 remains open because the
transformer 410 did not receive the clear to close message. The
transformer 408 does send the message upstream, but since there is
not a switching device upstream to receive the message nothing
happens in response thereto. This allows all of the devices 430-466
to be the same without the need to provide any in-field
configuration of the devices 430-466 when they are installed. The
recloser 402 then operates a third reclosing sequence test, and
since the device 436 did not receive the clear to close message and
is open, the recloser 402 does not detect overcurrent and remains
closed, and power is restored between the recloser 402 and the
transformer 410. The recloser 402 will then reset all of its
protection timings, which do not need to be coordinated with the
devices 430-446.
[0050] Subsequently, the timers operating in the transformers 412
and 414 will expire and since they detected loss of voltage, but
did not detect overcurrent and did not receive a clear to close
message, they know that they are downstream of the fault or a loss
of voltage event. In response to this the upstream devices 438 and
442 in the transformers 412 and 414, respectively, will open and
the transformers 412 and 414 will send a clear to close message to
their immediate downstream transformer that includes a unique
communications (com) ID generated at runtime. The device 446 is not
opened because the transformer 416 knows that it has the normally
open device 448. The transformer 412 did not receive a clear to
close message so the device 438 remains open and the fault is
isolated between the transformers 410 and 412. The transformer 414
does receive the clear to close message from the transformer 412 so
the device 442 is closed, and the transformer 416 receives the
clear to close message from the transformer 414, but since it knows
that it has the normally open device 448 and the device 446 is
still closed, it starts a timer, which allows the system time to
make sure the fault is isolated. When the timer in the transformer
416 expires, the device 448 is closed, and power is restored to the
transformers 412, 414 and 416 from the recloser 404. The part of
the line 406 between the transformers 410 and 412 will then likely
be repaired. When workers arrive at the transformers 410 and 412,
they will use the manual lever 188 to lock out the devices 436 and
438 and prevent them from opening.
[0051] If power is lost upstream of the recloser 402, the
transformers 408, 410, 412, 414 and 416 will go through the process
discussed above where they do not detect overcurrent, but do detect
loss of voltage. When that occurs, the transformers 408, 410, 412,
414 and 416 start timers and when the timer expires, the upstream
devices 430, 434, 438 and 442 in the transformers 408, 410, 412 and
414, respectively, open and a clear to close message is sent
downstream from the transformer 408 to the transformer 410, from
the transformer 410 to the transformer 412, from the transformer
412 to the transformer 414 and from the transformer 414 to the
transformer 416, along with a unique comID generated at run time in
the message. Each time a transformer receives a comID it resends
the comID to its downstream transformer so that all of the comIDs
are accumulated in the transformer 416. The messages cause the
devices 434, 438 and 442 to close, but the device 430 remains open
because it didn't receive a clear to close message and as a result
will isolate the network 400. The device 448 does not immediately
close because it is subject to the timer in the transformer 416,
and when the timer expires it will close and re-energize all of the
transformers 408-416 from the recloser 404.
[0052] When power is restored to the recloser 402, it is desirable
to return the network 400 to its normal state. For the
sectionalizer embodiment, when the transformer 408 detects the
return of voltage on its upstream side it will transmit a message
along with its comID down the line 406 to the transformer 416 to
return to the normal state. The comIDs are used to identify the
transformers 430-446 as they relay messages from transformer to
transformer so that messages are not sent to the transformers 418,
420, 422, 424 and 426 that are not affected by the loss of voltage.
The transformer 416 then knows to open the device 448, where power
is lost between the transformers 408 and 416, and not to send the
message further downstream. The device 430 is then closed to
restore power.
[0053] The foregoing discussion discloses and describes merely
exemplary embodiments of the present disclosure. One skilled in the
art will readily recognize from such discussion and from the
accompanying drawings and claims that various changes,
modifications and variations can be made therein without departing
from the spirit and scope of the disclosure as defined in the
following claims.
* * * * *