US20220103010A1 - Method for isolating a fault and restoring power in an underground radial loop network using fault interrupting switches - Google Patents
Method for isolating a fault and restoring power in an underground radial loop network using fault interrupting switches Download PDFInfo
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- US20220103010A1 US20220103010A1 US17/400,410 US202117400410A US2022103010A1 US 20220103010 A1 US20220103010 A1 US 20220103010A1 US 202117400410 A US202117400410 A US 202117400410A US 2022103010 A1 US2022103010 A1 US 2022103010A1
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- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
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- H02H3/06—Details with automatic reconnection
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- H—ELECTRICITY
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- H02H3/42—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to product of voltage and current
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- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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- H01H33/38—Power arrangements internal to the switch for operating the driving mechanism using electromagnet
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- H02H3/02—Details
- H02H3/04—Details with warning or supervision in addition to disconnection, e.g. for indicating that protective apparatus has functioned
- H02H3/042—Details with warning or supervision in addition to disconnection, e.g. for indicating that protective apparatus has functioned combined with means for locating the fault
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- H02J13/00016—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment using a wired telecommunication network or a data transmission bus
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- H02J13/00032—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for
- H02J13/00036—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for the elements or equipment being or involving switches, relays or circuit breakers
- H02J13/0004—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for the elements or equipment being or involving switches, relays or circuit breakers involved in a protection system
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- H02H7/266—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving switching on a spare supply
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/18—Systems supporting electrical power generation, transmission or distribution using switches, relays or circuit breakers, e.g. intelligent electronic devices [IED]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/20—Systems supporting electrical power generation, transmission or distribution using protection elements, arrangements or systems
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S40/00—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them
- Y04S40/12—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them characterised by data transport means between the monitoring, controlling or managing units and monitored, controlled or operated electrical equipment
- Y04S40/124—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them characterised by data transport means between the monitoring, controlling or managing units and monitored, controlled or operated electrical equipment using wired telecommunication networks or data transmission busses
Definitions
- 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.
- An electrical power distribution network 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° 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.
- 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.
- 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.
- FIG. 1 is a simplified schematic diagram of a known power distribution network including an underground residential power circuit
- FIG. 2 is an isometric view of a known transformer used in the circuit shown in FIG. 1 ;
- 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;
- FIG. 4 is an isometric view of the transformer shown in FIG. 2 and including the fault interrupting switching devices;
- FIG. 5 is an isometric view of one of the fault interrupting switching devices separated from the transformer
- FIG. 6 is a cross-sectional type view of the fault interrupting switching device shown in FIG. 5 ;
- 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;
- FIG. 8 is a cross-sectional type view of the sectionalizer switching device shown in FIG. 7 ;
- FIG. 9 is a side view of the sectionalizer switching device shown in FIG. 7 illustrating conductors in the device
- 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 ;
- FIG. 11 is a schematic block diagram of a switch assembly including two of the sectionalizer switching devices sharing a common control board;
- 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.
- 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.
- 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 .
- 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 .
- 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 .
- 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.
- 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
- 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.
- 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.
- 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
- 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 .
- 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 .
- 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 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.
- 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 .
- 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 .
- 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.
- 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 .
- 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 .
- 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.
- 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.
- the device 96 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.
- 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.
- the fault location and isolation schemes discussed above can be augmented using a revised fault location and isolation scheme proposed below.
- each of the devices included its own electronics board that operated at a floating potential relative to the line voltage.
- 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.
- the devices can operate as fault interrupting devices or sectionalizers.
- 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.
- 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.
- the details of the vacuum interrupter 196 are merely for illustrative purposes in that other designs will be applicable.
- 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.
- 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.
- 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.
- 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 .
- the control unit 256 is powered by 120 V ac from the lines 72 and 74 through lines 258 .
- 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.
- FIG. 13 is an isometric view of the transformer 250 including various embodiments for attaching auxiliary parking stands thereto.
- 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
- 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 .
- 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 .
- 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
- 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 .
- 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.
- 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.
- the network 400 operates to isolate the fault and restore power as follows.
- the reclosers 402 and 404 need to have a minimum 1.5 power frequency cycle recloser trip.
- 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 .
- 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.
- the transformer 410 will detect voltage on the upstream side of the device 434 and it will close.
- 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.
- the normally open switching device 448 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.
- 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 .
- the head end switching device 430 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 .
- the network 400 operates to isolate the fault and restore power as follows.
- 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.
- 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 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.
- 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.
- 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.
- 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.
- a transformer 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 .
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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.
Description
- 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.
- 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.
- 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° 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.
- 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.
- 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.
- 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.
- Additional features of the disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
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FIG. 1 is a simplified schematic diagram of a known power distribution network including an underground residential power circuit; -
FIG. 2 is an isometric view of a known transformer used in the circuit shown inFIG. 1 ; -
FIG. 3 is a simplified schematic diagram of the power distribution network shown inFIG. 1 where the transformers include a pair of fault interrupting switching devices; -
FIG. 4 is an isometric view of the transformer shown inFIG. 2 and including the fault interrupting switching devices; -
FIG. 5 is an isometric view of one of the fault interrupting switching devices separated from the transformer; -
FIG. 6 is a cross-sectional type view of the fault interrupting switching device shown inFIG. 5 ; -
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; -
FIG. 8 is a cross-sectional type view of the sectionalizer switching device shown inFIG. 7 ; -
FIG. 9 is a side view of the sectionalizer switching device shown inFIG. 7 illustrating conductors in the device; -
FIG. 10 is an isometric view of the transformer shown inFIG. 2 including two of the sectionalizer switching devices shown inFIGS. 7-9 ; -
FIG. 11 is a schematic block diagram of a switch assembly including two of the sectionalizer switching devices sharing a common control board; -
FIG. 12 is a schematic block diagram of the control board in the switch assembly; -
FIG. 13 is an isometric view of the transformer shown inFIG. 10 and including parking stands; and -
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. - 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.
- 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.
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FIG. 1 is a simplified schematic diagram of a knownpower distribution network 10 including an over-headsection 12 having a three-phase feeder 14, or possibly a single-phase feeder, and a single-phase undergroundresidential loop section 16 including a single-phaselateral line 18 having oneend 22 coupled to thefeeder 14 through afuse 24 and anopposite end 28 coupled to thefeeder 14 through afuse 30, where thefuses ends feeder 14, in an alternate embodiment theends ends feeder 14. Thefuses line 18 from thefeeder 14, such as a fault interrupting device or reclosing device. The medium voltage provided on theline 18 is stepped down to a low voltage by a number of transformers suitable to provide power to a number ofloads 34, such as homes. In this non-limiting embodiment, thecircuit 16 includes threetransformers primary coil 46 across which the medium voltage is applied and asecondary coil 48 that provides low voltage to aservice conductor 50 to which theloads 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. -
FIG. 2 is an isometric view of thetransformer 40 of the type that is mounted on a pad (not shown) with the understanding that thetransformers transformer 40 includes anenclosure 60 that houses thecoils transformer 40. Acover 58 of theenclosure 60 is shown in an open position to expose apanel 62 in theenclosure 60. Aconnector bushing 64 extends through thepanel 62 that accepts anelbow connector 66 that connects theline 18 to theprimary coil 46 and aconnector bushing 68 extends through thepanel 62 that accepts anelbow connector 70 that connects theline 18 to theprimary coil 46. A number of positive and negative 120V lines neutral line 76 are connected to thesecondary coil 48, extend from thehousing 60 and provide power along theservice conductor 50, where the number of thelines loads 34 being serviced by that transformer. Aparking stand 78 is welded to thepanel 62 and is a fixture that allows one of theelbow connectors bushing - Power is provided to both
ends line 18 and as such one of the elbow connectors is disconnected from one of thetransformers parking stand 78 while it is hot to electrical separate the part of theline 18 that receives power from theend 22 and the part of theline 18 that receives power from theend 28. For example, the right side of thetransformer 40 is disconnected from theline 18 so that theloads 34 connected to thetransformer 40 receive power from theend 22 of theline 18 and theloads 34 connected to thetransformers end 28 of theline 18. - Faults occur even for underground lines from, for example, deterioration of the cable insulation. If a
fault 80 occurs, for example, in asection 82 of theline 18 between thetransformers fuse 30 will operate to clear thefault 80 so that power is prevented from being provided to theloads 34 being serviced by thetransformers 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 theloads 34 serviced by thetransformers fault 80 by driving a service truck between thefuse 30 and thetransformers line 18 from thetransformers fuse 30 to see when thefuse 30 trips and when it does not. Once the location of thefault 80 is identified, then the right side of thetransformer 42 is disconnected from theline 18 and placed in the parking stand, the left side of thetransformer 44 is disconnected from theline 18 and place in the parking stand and theline 18 is connected to the right side oftransformer 40 so that power is provided from theend 22 of theline 18 to theloads 34 serviced by thetransformers end 28 of theline 18 to theloads 34 serviced by thetransformer 42. Such a procedure may take hours to restore power to theloads 34 serviced by thetransformers -
FIG. 3 is a schematic diagram of thenetwork 10 where eachtransformer loads 34 in response to a fault, as will be described in detail below. Particularly, thetransformer 40 includes a fault interruptingswitching device 90 coupled between theline 18 and theprimary coil 46 and a normally open (NO) fault interruptingswitching device 92 coupled between theline 18 and theprimary coil 46, thetransformer 42 includes a fault interruptingswitching device 94 coupled between theline 18 and theprimary coil 46 and a fault interruptingswitching device 96 coupled between theline 18 and theprimary coil 46, and thetransformer 44 includes a fault interruptingswitching device 98 coupled between theline 18 and theprimary coil 46 and a fault interruptingswitching device 100 coupled between theline 18 and theprimary coil 46. Instead of putting the elbow connector at the right side of thetransformer 40 in theparking stand 78, the switchingdevice 92 is opened. Additionally, thefuses reclosers -
FIG. 4 is an isometric view of thetransformer 40 now shown with theswitching devices device 90 is coupled to thebushing 64 and theelbow connector 66 and theswitching device 92 is coupled to thebushing 68 and theelbow connector 70. -
FIG. 5 is an isometric view andFIG. 6 is a cross-sectional view of theswitching device 90 separated from thetransformer 40. Thedevice 90 includes an outer groundedenclosure 102 having a special configuration to hold the various components therein. A mountingplate 104 is secured to theenclosure 102 and provides an interface to mount thedevice 90 to thepanel 62. Atransformer interface 106 extends from theenclosure 102 and is configured to be electrically coupled to thebushing 64 and a load-break connector interface 108 extends from theenclosure 102 and is configured to be electrically coupled to theelbow connector 66. Amanual operating handle 110 allows thedevice 90 to be manually opened and closed, if necessary. - The
enclosure 102 defines aninternal chamber 112 in which is configured the various components of thedevice 90. Those components include avacuum interrupter 116 having avacuum housing 120 defining a vacuum chamber, a fixedupper terminal 122 extending through a top end of thehousing 120 and into the vacuum chamber and a movablelower terminal 126 extending through a bottom end of thehousing 120 and into the vacuum chamber, where a bellows (not shown) allows themovable terminal 126 to slide without affecting the vacuum in the vacuum chamber. Theupper terminal 122 goes into the page and is connected to thetransformer interface 106 and thelower terminal 126 is connected to the load-break interface 108 through aflexible connector 134. A high impedanceresistive element 130 is helically wound around thehousing 120 and is connected to theupper terminal 122 at one end to provide a current flow for energy harvesting purposes when thevacuum interrupter 116 is open. ARogowski 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 thecoil 136 being proportional to the rate of change of current flow. It is noted that the switchingdevice 90 including thevacuum interrupter 116 can have other designs consistent with the discussion herein. - The
movable terminal 126 is coupled to arod 138 that is coupled to aplate 140, which in turn is coupled to anactuator assembly 142 having anelectromagnetic actuator 144 and anopening spring 146, where other compliance springs (not shown) may also be included. Theactuator 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 thevacuum interrupter 116 and is moved by a closing coil to close thevacuum 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 theactuator 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. Theoperating handle 110 is connected to arod 150, which is coupled to therod 138. When thehandle 110 is rotated in the clockwise or counter-clockwise direction, therod 150 moves up or down to manually open or close thevacuum interrupter 116. Thevacuum interrupter 116, theRogowski coil 136 and theactuator assembly 142 are all at medium voltage potential, and as such are encapsulated in an insulatingmaterial 152, such as an epoxy, that fills most of thechamber 112. - An electronics control
board 160 is provided within thechamber 112 and includes various electrical components, such as a microprocessor, etc., where theboard 160 is powered through thevacuum interrupter 116 when it is closed and through thehigh impedance element 130 when thevacuum interrupter 116 is open. More particularly, current flows through the lowerimpedance vacuum interrupter 116 when it is closed and not through theelement 130, but flows through theelement 130 when thevacuum interrupter 116 is open. Current flow through theelement 130 provides power to operate the electronics on theboard 160 and operate theactuator assembly 142 to close thevacuum interrupter 116. Ahigh voltage capacitor 164 and anenergy storage capacitor 166 are electrically coupled to theboard 160. One side of thecapacitor 164 is coupled to theboard 160 at high voltage and the opposite side of thecapacitor 164 is coupled to the groundedenclosure 100, which provides a constant impedance and current that allows voltage measurements. When thevacuum interrupter 116 is closed thecapacitor 164 provides a constant current that is used to power theboard 160, operate theactuator 144 and charge thestorage capacitor 166. When thevacuum interrupter 116 is open and current is flowing through theelement 130 if it is available thecapacitor 164 also provides a constant current that is used to power theboard 160, operate theactuator 144 and charge thestorage capacitor 166. The energy stored in thestorage capacitor 166 can be used when thevacuum interrupter 116 is open or closed depending on what power is available through thevacuum interrupter 116 or theelement 130. Adielectric material 168 that takes the shape of its container and sets, such as epoxy, potting, silicone foam or gel, etc., is provided in thechamber 110 to electrically isolate the high voltage on theelectronics board 160 with the groundedenclosure 100. Because thevacuum interrupter 116, theactuator assembly 112 and thecontrol board 160 all operate at the line voltage and thus have a floating reference potential, thedevice 90 can be made smaller than otherwise would be possible since these components do not need to be electrically isolated. - If the
fault 80 occurs in thesection 82 of theline 18 between thetransformers devices devices loads 34, as described below. Thedevice 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, thedevice 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 thedevice 94 closes, thedevice 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 thedevice 92 closes, thedevice 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 thedevice 100 closes, thedevice 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, thefault 80 is isolated between thedevices loads 34, where the process will take less than a minute. - 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.
- 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 -
FIG. 7 is an isometric view andFIG. 8 is a cross-sectional view of aswitching 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. Thedevice 180 includes anouter enclosure 182, atransformer interface 184, a load-break connector interface 186 and amanual handle 188 configured in a similar manner as thedevice 90 and operating in a similar manner. The components within theenclosure 182 are encapsulated within an insulatingmedium 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 theswitching device 180 with theouter enclosure 182 and the insulatingmedium 190 removed to show the conductors. - The
switching device 180 includes avacuum interrupter 196 having avacuum enclosure 198 defining avacuum chamber 200, an upperfixed terminal 202 extending through theenclosure 198 and into thechamber 200 and having acontact 204 and a lowermovable terminal 206 extending through theenclosure 198 and into thechamber 200 and having acontact 208, where agap 210 is provided between thecontacts vacuum interrupter 196 is open. A bellows 212 allows themovable terminal 206 to move without affecting the vacuum integrity of thechamber 200. Themovable terminal 206 is coupled to adrive rod 214 that is coupled to anactuator assembly 216 of the type discussed above for opening and closing thevacuum interrupter 196. In this design, theactuator assembly 216 is insulated and not at the line potential. As above, the details of thevacuum interrupter 196 are merely for illustrative purposes in that other designs will be applicable. - A cup-shaped
conductor 220 is provided around a top end of theenclosure 198 and is electrically coupled to the fixedterminal 202 and to anelbow conductor 222 that is electrically coupled to theconnector interface 186. An hour glass or cylindrical shapedconductor 224 is provided around a bottom end of theenclosure 198 and is electrically coupled to themovable terminal 206. The cup-shapedconductor 220 includes anorifice 228 that accepts anend 230 of anelbow conductor 232 in an electrically coupled slidable engagement so that theelbow conductor 232 can slide relative to the cup-shapedconductor 220 and still maintain electrical contact therewith. Theconductor 224 includes anorifice 234 that accepts anend 236 of arod conductor 238 in an electrically coupled slidable engagement so that theconductor 238 can slide relative to theconductor 224 and still maintain electrical contact therewith, where theconductor 238 is part of acylindrical transformer conductor 240 that is electrically coupled to thetransformer interface 184. Theelbow conductor 222 is coupled to the cup-shapedconductor 220 in the same manner. Therefore, when theconductors conductors - The
elbow conductor 232 is also electrically coupled to one end of a pair ofcapacitors conductor 246 is electrically coupled to an opposite end of thecapacitors elbow conductor 232 is at line potential and the end of thecapacitors 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. -
FIG. 10 is an isometric view of atransformer 250 that is similar to thetransformer 40 except that theswitching devices devices device 180, where like elements are identified by the same reference number. The conductors in both of thedevices common control unit 256 that controls both of thedevices control unit 256 is mounted to thepanel 62. In this embodiment, thecontrol unit 256 is powered by 120 V ac from thelines lines 258. -
FIG. 11 is a schematic block diagram of aswitch assembly 260 including aswitch circuit 262 representing theswitching device 252, aswitch circuit 264 representing theswitching device 254 and acontrol board 266 representing thecontrol unit 256. Thecircuit 262 includes avacuum interrupter 268, anactuator 270, aRogowski coil 272 and acapacitor 274 and thecircuit 264 includes avacuum interrupter 276, anactuator 278, aRogowski coil 280 and acapacitor 282 operating as discussed above. Thecircuit 262 includes alimit switch 284 and thecircuit 264 includes alimit switch 286 that tell thecontrol board 266 which position thedevice 188 on each of thedevices coupling capacitors control board 266 and the voltage is measured across the resistor. Thecontrol board 266 is powered by a 120Vac source 290 from thesecondary coil 48 and a9V dc battery 292, and may provide signals to acommunications device 294, such as a utility radio. - 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 thecontrol board 266 showing one non-limiting example. Thecontrol board 266 includes amicrocontroller 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 themicrocontroller 300. These elements include measured voltages for both of the switchingcircuits boxes box 306 for the Rogowski coils 274 and 280, low gain atbox 308 for the Rogowski coils 274 and 280, ultra-gain atbox 310 for the Rogowski coils 274 and 280, and amodem 312 that provide signals to an analog-to-digital (ADC)converter 314. Further, the elements include handle position atbox 316 that links up with thelimit switches relay 320 and acrystal oscillator 322. The elements further include an insulated gate bipolar transistor (IGBT)module 326, a half-wave rectifier 328 andvoltage converters - 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 thetransformer 250 including various embodiments for attaching auxiliary parking stands thereto. Specifically, thetransformer 250 includesparking stand units edge 360 of theenclosure 60 to which thecover 58 is secured. Theunit 350 includes amount 364, theunit 352 includes amount 366 and theunity 354 includes amount 368 that are configured to receive theelbow connector break connector interface 186. Thus, when thecover 58 is lifted, the technician can secure one or more of theunits edge 360 using, for example, securingmechanisms -
FIG. 14 is a simplified schematic diagram of a residentialpower distribution network 400 similar to thenetwork 10. Thenetwork 400 includes two single-phase, self-powered, magnetically actuatedreclosers network 400, anunderground distribution line 406 and tentransformers line 406 in the manner discussed above. Thetransformer 408 includes switchingdevices transformer 410 includes switchingdevices transformer 412 includes switchingdevices transformer 414 includes switchingdevices transformer 416 includes switchingdevices transformer 418 includes switchingdevices transformer 420 includes switchingdevices transformer 422 includes switchingdevices transformer 424 includes switchingdevices transformer 426 includes switchingdevices switching device 448 is normally open to provide electrical isolation between the source ends of thenetwork 400. - The
network 400 will be used below to describe fault isolation and power restoration processes when afault 398 occurs in theline 406 between thetransformers network 400, where each of the switching devices 430-466 is similar to theswitching 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 sharedcontrol unit 256 for the switching devices in the transformer. - For the fault interrupting embodiment, if the
fault 398 occurs in theline 406, thenetwork 400 operates to isolate the fault and restore power as follows. In order for the fault isolation and power restoration to be performed by thenetwork 400 using the fault interrupting switching devices, thereclosers recloser 402 will open, thetransformers transformer 416, which will eventually be used to open the normally closeddevice 448. In response to detecting the overcurrent followed by loss of voltage, one fault interrupter in each of thetransformers recloser 402 will then close in the reclosing operation after 1.5 cycles, and thetransformer 408 will detect voltage on the upstream side of thedevice 432 and it will close. When thedevice 432 closes, thetransformer 410 will detect voltage on the upstream side of thedevice 434 and it will close. When that happens, thetransformer 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 thedevice 436 to lock open to isolate the fault. When the timer in thetransformer 416 expires, the normallyopen switching device 448 is closed and in response to thetransformer 416 detecting overcurrent now from therecloser 404 side of theline 406, the normallyopen switching device 448 will immediately open and clear the fault current, but therecloser 404 will not open because its trip time is 1.5 cycles. Thetransformers downstream device 438 in thetransformer 412 and the nowupstream device 444 in thetransformer 414 are opened. The normallyopen switching device 448 is then closed, and thetransformer 414 will detect voltage on the upstream side of thedevice 444 and it will close. When thedevice 444 closes, thetransformer 412 will detect voltage on one side of thedevice 438 and it will close. When that happens, thetransformer 412 detects overcurrent again and determines the fault must be on its downstream side, and thus causes thedevice 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 thenetwork 400 when the fault is fixed using themanual handle 188 on the appropriate switching devices 430-466. - For the loss of voltage scenario upstream of the
network 400, thedevices recloser 402, thetransformers transformer 408 because it has the headend switching device 430 and a timer is started in thetransformer 416 because it has the normallyopen switching device 448, where the timer in thetransformer 408 is shorter than the timer in thetransformer 416. When the timer in thetransformer 408 expires and loss of voltage is still detected, the headend switching device 430 will open to isolate the source at therecloser 402 from therecloser 404, which gives the system time to clear faults upstream of therecloser 402. The timer in thetransformer 416 will then expire and thedevice 448 will close, which will provide power from therecloser 404 to all of the transformers 408-416. In this embodiment, the headend switching device 430 becomes the normally open switching device. In this scenario, it would be required that a worker reset the original configuration of thenetwork 400 when the source voltage returns using themanual handle 188 on the appropriate switching devices 430-466. - For the sectionalizer embodiment, if the fault occurs in the
line 406 between thetransformers network 400 operates to isolate the fault and restore power as follows. In this design, the protection settings in thereclosers recloser 402 detects the overcurrent and opens in a fault clearing process, and theswitching devices recloser 402 opens. The switchingdevices transformers transformer 416 does not start a timer because it has the normallyopen switching device 448. Therecloser 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, thedownstream devices transformers transformers line 406 to their immediate upstream transformer to close their downstream switching device if they detected overcurrent, and thus thedevice 432 closes, but thedevice 436 remains open because thetransformer 410 did not receive the clear to close message. Thetransformer 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. Therecloser 402 then operates a third reclosing sequence test, and since thedevice 436 did not receive the clear to close message and is open, therecloser 402 does not detect overcurrent and remains closed, and power is restored between therecloser 402 and thetransformer 410. Therecloser 402 will then reset all of its protection timings, which do not need to be coordinated with the devices 430-446. - Subsequently, the timers operating in the
transformers upstream devices transformers transformers device 446 is not opened because thetransformer 416 knows that it has the normallyopen device 448. Thetransformer 412 did not receive a clear to close message so thedevice 438 remains open and the fault is isolated between thetransformers transformer 414 does receive the clear to close message from thetransformer 412 so thedevice 442 is closed, and thetransformer 416 receives the clear to close message from thetransformer 414, but since it knows that it has the normallyopen device 448 and thedevice 446 is still closed, it starts a timer, which allows the system time to make sure the fault is isolated. When the timer in thetransformer 416 expires, thedevice 448 is closed, and power is restored to thetransformers recloser 404. The part of theline 406 between thetransformers transformers manual lever 188 to lock out thedevices - If power is lost upstream of the
recloser 402, thetransformers transformers upstream devices transformers transformer 408 to thetransformer 410, from thetransformer 410 to thetransformer 412, from thetransformer 412 to thetransformer 414 and from thetransformer 414 to thetransformer 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 thetransformer 416. The messages cause thedevices device 430 remains open because it didn't receive a clear to close message and as a result will isolate thenetwork 400. Thedevice 448 does not immediately close because it is subject to the timer in thetransformer 416, and when the timer expires it will close and re-energize all of the transformers 408-416 from therecloser 404. - When power is restored to the
recloser 402, it is desirable to return thenetwork 400 to its normal state. For the sectionalizer embodiment, when thetransformer 408 detects the return of voltage on its upstream side it will transmit a message along with its comID down theline 406 to thetransformer 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 thetransformers transformer 416 then knows to open thedevice 448, where power is lost between thetransformers device 430 is then closed to restore power. - 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.
Claims (20)
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.
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CA3130298A CA3130298A1 (en) | 2020-09-30 | 2021-09-09 | Method for isolating a fault and restoring power in an underground radial loop network using fault interrupting switches |
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US20220102961A1 (en) | 2022-03-31 |
CA3130310A1 (en) | 2022-03-30 |
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US11811213B2 (en) | 2023-11-07 |
US11563318B2 (en) | 2023-01-24 |
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