Patent Application
20180233895
This invention relates generally to apparatus for sensing, isolating and de-energizing a downed alternating current electric utility primary distribution circuit conductor which has developed into a high impedance fault which overcurrent protection devices or high impedance detection systems have been unable to clear. This dangerous condition may occur at any location on an electrical utility distribution circuit due to lack of conductivity of the earth in the fault current return path. In some instances, the line impedance due to the distance of the ground fault from the substation source combined with high fault impedance at the wire down location may limit the ground fault current to a value less than the normal actual load current at this location. There is a need for a fault isolating package that has no limitation on distance limits or fault current value.
A type of high impedance fault condition may also occur when a high voltage primary conductor is downed, poorly grounded and the primary conductor is back fed through a wye-delta secondary 3 phase power bank providing a dangerous high voltage condition, yet insignificant fault current. In this latter situation, the delta connected windings of three single phase transformer windings of different phases provide an induced transformed source of a low level back fed fault current and a dangerous high voltage condition on the downed primary conductor.
The frequent occurrence of live downed high voltage primary conductors is directly related to the high incidence of variable high impedance ground fault return paths. This variable ground fault impedance is directly related to the various withstand voltages of a wide range of values of impedances in the variable grounding material. The withstand voltage, measured in volts per inch across the material under stress, may vary over a period of time as high voltage is maintained at the fault by the downed wire. This variation in the material withstand voltage is dependent upon both material type and its moisture content. A breakdown by the line to ground fault voltage of the earth material into carbon paths, which is leakage fault current seeking return paths to the power source, is one impedance progression which occurs until the high impedance ground resistance collapses and the full available fault current occurs. Carbon paths may develop, either directly through the material or via a circuitous exterior path. A poorly developed carbon path may also result in re-establishing a high impedance because the downed conductor can move (dance) as the fault current begins to flow, landing on another highly non-conducive medium, permitting the downed high voltage live wire condition to persist with high impedance to ground.
The present invention, more specifically, is directed to an electrical safety device capable of detection, processing and isolating a high impedance, low fault current disposed in the main circuit or in a remote branch, or tap, of an electrical power distribution circuit. This inventive fault elimination arrangement employs only those components within the faulted section, and does not impact the overall control and/or operation of the electrical power distribution protection system. In addition, surge arrestors are connected to a driven ground located on the same pole as the arrestors, with ground rod resistance limited to no more than 5 ohms on the distribution system per National Safety Code requirements.
High impedance, low current faults, such as a downed distribution line conductor in an electric utility distribution network which is contacting a poor conductive earth composite, have proven to be difficult to isolate with present technology. Conventional overcurrent protection devices, both at the source and at strategic circuit locations, use the combined relationship of fault current magnitude and time duration to clear faults associated with downed grounded high voltage conductors. A particularly difficult situation for detecting a high impedance fault in an electrical distribution system incorporating a live conductor downed, but intact, where the conductor is grounded through a poor conducting medium such as sand, rock, concrete, snow, blacktop or a dead tree. The variable ground fault impedance may approach infinity with an equivalent fault current value of zero amps
For reliability purposes, it is common electric utility practice to install downstream circuit reclosers, expulsion fuses or sectionalizers at all taps to the main stem distribution circuit. These protection devices function to locally isolate faulted circuit portions in the smallest segments possible, in order to maintain normal service to the balance of customers on that same circuit. These downstream overcurrent protection devices are designed to be time coordinated with each other and with the main circuit breaker in order to automatically isolate dangerous conditions located throughout the distribution circuit.
Present applied overcurrent protection devices are, however, unable to distinguish low fault currents (high impedance faults) from normal load currents because trip settings for these devices are typically set at 125 to 250 percent of maximum estimated peak load current. These standard tripping current levels are selected to minimize inadvertent tripping due to transient causes. Isolating devices with more sensitive protection have recently been introduced, but still require a certain minimum value of fault current and have no automated means of clearing for a zero current flow. A hazardous condition for the public is created when energized high voltage conductors fall to the ground or come in contact with a high impedance fault current return path, and the overcurrent protection system fails to de-energize the conductor. Physical contact with an energized distribution primary conductor by any conducting body may cause serious injury or death due to electric shock. Numerous fatalities and serious injuries occur annually in the United States due to inadvertent contact with live down power distribution conductors. Experience has shown that these conditions occur more frequently at distribution level voltages of 15 KV and below, which is the predominant primary distribution voltage range in the United States. The current National Electrical Safety Code limits the maximum allowed ground rod resistance to 5 ohms or less when measured with a ground resistance meg to multi-ground requirements for electrical distribution.
Referring to
The invention disclosed and claimed in U.S. Pat. No. 9,136,692 (hereinafter “the '692 patent”) overcomes the aforementioned limitations of the prior art by sensing the combination of loss of voltage on the load side of a downed conductor and comparing it with live voltage on the source side of the same downed wire. Applicant's U.S. Pat. No. 9,385,522, which was filed as a divisional application based upon the '692 patent, is also involved with a downed wire in an electrical power distribution system. The disclosure and claims of the '692 patent are hereby incorporated in the present application by reference. This downed wire constitutes a very high impedance fault characterized by a limited fault current typically below the tripping value of the associated fault isolating device. The detection, isolation and de-energization of the downed or damaged live conductor is analyzed and controlled by a host computer through remote tripping of an associated isolation device. This process functions automatically and serves as a backup to a conventional overcurrent protection system for de-energizing high impedance electrical distribution primary faults, while permitting normal service to continue on the unaffected remainder of the power distribution circuit. As shown in
The present invention addresses this complex and expensive approach to detecting, isolating and eliminating a high impedance fault in a branch tap 62 of an overhead distribution primary circuit 56 by localizing both the polling of both SM'S (“out of service signals” and “in service signals”), plus analyzing the coded signals with proprietary software and subsequently applying a bolted ground fault on the isolating device. The electrical equivalent circuit of this operation is paralleling a bolted phase to ground minimal impedance with the high impedance downed wire conductor, resulting in increased fault current to trip the isolating device. The present invention also addresses this approach with a locally installed compound device which monitors out of service slave smart meter RF signals and if a downed wire condition is analyzed, applies a bolted ground fault to the same primary fault isolator which was unable sense and clear the high impedance fault downed wire condition due to a fault current value less than the sensing value. Accordingly, there is a need for quickly and safely detecting, isolating and clearing of a high impedance fault such as a downed electric utility high voltage primary distribution circuit conductor using a low cost, locally controlled spring-loaded earth grounding device to operate the primary tap isolating device.
Accordingly, it is an object of the present invention to minimize (out of service) signal data processing time and safely detect, isolate and de-energize an AC electric utility primary distribution circuit conductor in a multi-tap, or multi-branch, electric power distribution network using only the effected tap, or branch, for isolation and protection of the power distribution network without involving other standard portions of the distribution network's fault analysis and isolation package.
It is another object of the present invention to provide for the automatic detection, isolation and shutdown of a high impedance, low fault current in a high voltage electrical power distribution network comprised of plural independent and separate branches, or taps, using only the circuitry of the faulted branch, or tap, and not any portion of the non-faulted branches or of the electric power distribution circuit itself, to minimize SM out of service (O/S) signal data handling, to more efficiently, faster, more simply and safely automatically detect, isolate and shutdown the high impedance, low fault current in the effected high voltage tap.
It is a further object of the present invention to locally detect, isolate and shutdown a high impedance, low fault current which occurs in a remote branch, or tap, of a multi-branch electric power distribution network which remains undetected by an automated overcurrent isolating device.
A still further object of the present invention is to detect, isolate and neutralize a high impedance, low current fault in one of plural branches, or taps, of a plural branch electric power distribution network by directly accessing and isolating the downed high voltage conductor, and neutralizing the fault without involving other distribution system components not directly involved with the faulted conductor.
The present invention contemplates an arrangement in an electrical distribution system for identifying, isolating and clearing a live high voltage wire down in any one of plural feeder taps, the arrangement comprised of one or more father smart meters (FSM) disposed in each of the taps and coupled to each of plural slave smart meters in a respective one of said taps, wherein each of said one or more FSM's is adapted to (1) receive downstream loss of voltage signals and in service coded signals from each of the other master and or slave smart meters to which the FSM is coupled, and (2) and form a HIFIS (High Impedance Fault Isolation System) polling and logging with an RF LAN antenna and receiver and logging the coded slave SM in service or (out of service) signals, for analysis by the microprocessor combined with a compliant IEEE STANDARD 802.16 chip. Positive analysis of the coded signal data associated with a downed wire by the above mentioned chip, results in the microprocessor closing a normally open relay contact in the fire door sensor electrical circuit, which applies 120 volts to melt the fire door sensor releasing a coiled earth grounded spring; and the grounded spring applies earth ground to the load side of a high voltage distribution system isolator (expulsion fuse, recloser or sectionalizer) which clears the fault and de-energizes the live primary downed wire.
The appended claims set forth those novel features which characterize the invention. However, the invention itself, as well as further objects and advantages thereof, will best be understood by reference to the following detailed description of a preferred embodiment taken in conjunction with the accompanying drawings, where like reference characters identify like elements throughout the various figures, in which:
Referring to
Attached to a second cross member 123 on the electric pole 124 is a primary tap fuse isolator 201 and a trouble primary tap 202 which was previously formed with and attached to a now broken primary wire 203 which includes a high impedance fault 126. Trouble primary tap 202 represents a portion of the primary tap which is still electrically alive. Attached to the trouble portion of the primary tap 202 is a serially coupled combination of a first transformer 204 and a first fuse 204a. The combination of the first transformer 204 and first fuse 204a is also coupled to the radial arrangement of a first smart meter (SM) 204a, a second smart meter (SM) 204b, and a father (master) smart meter (FSM) 204d.
The distal end of the primary tap, or open wire, 203 is electrically dead and no longer carries electric current sourced by its normal primary circuit. Primary open wire 203 is illustrated disconnected from trouble primary wire, or tap, 202 and is attached to second and third combinations of a second transformer 222 and a second fuse 222a and a third transformer 223 and a third fuse 223a which are coupled in parallel respectively to fourth through sixth smart meters (SM's) 222b, 222c and 222d and to seventh through ninth smart meters 223b, 223c and 223d (SM's).
In this arrangement, FSM 204d receives out of service (O/S) signals from all of the aforementioned SM's plus live voltage status signals from SM'S 204a and 204b. HIFIS 300 is associated with a fuse or recloser 201 which is positioned on the second cross member 123 attached to the electric pole 124. HIFIS 300 is equipped with a Local Area Network (LAN) antenna receiver which polls the incoming voltage signals from SM 222 and analyzes the data using an IEEE STANDARD 802.16 compliant chip as described below.
The electrical pole's second cross member 123 also supports the lead 126 to a 120 volt source and an earth grounded connection lead 128 (shown in dotted line form), both connected to the HIFIS 300 pole-mounted monitor with a ground resistance of no more than 5 ohms. Having referenced all of the external connections and the source of the coded signal data, the operation of the single phase utility overhead distribution circuit tap 200 and associated High Impedance Fault Isolation System (HIFIS) 300 will now be described. The pole mounted HIFIS 300 case contains the LAN antenna with receiver, polling the associated SM coded signals of both o/s and in service data to the main tap FSM 204d.
Referring to
Referring to
Referring to
The process starts at step 100 upon connection of the high impedance fault isolation system (HIFIS) to a source of 120 volt power for initiating installation of the high impedance fault isolation system at the primary tap. At step 110X, the HIFIS is energized to accept entry of all associated smart meter (SM) identification data required for processing of the chip in microprocessor 301. All of the associated data for the incorporated smart meters is then entered for analysis by the computer chip software at step 100X. In step 100Y, geographical location data for all of the aforementioned smart meters is then entered for the protected tap circuit, including the SM at the distal end of the primary tap. After initial installation of the HIFIS, a time delay is entered at step 105 before line voltage status is first checked on the local HIFIS protected tap associated SM's. The program then at step 110 every five seconds checks the secondary voltage of each SM and transmits this data to the father smart meter (FSM) 204d which is monitored by the associated local HIFIS. With a voltage level of 85 volts established as an out of service voltage (0/S), the program at step 115 then checks for a change in the secondary voltage value. If at step 115, it is determined that there has not been a change of voltage to a value less than 85 volts, the program returns to step 110 and continues every five seconds to check if there has been a change in secondary voltage value to a value less than 85 volts. If at step 115 a change of secondary voltage to a value less than 85 volts is detected, the program proceeds to step 120 where the SM which detected a loss of voltage provides a loss of voltage signal (O/S) to the FSM 204d which is logged in and stored by the HIFIS microprocessor. The program then proceeds to step 130 where this loss of voltage data is stored for analysis by the software chip 303. Also at this step, a pre-specified time delay of 45 seconds minimum is initiated before an analysis is initiated on each received SM O/S signal. During this time delay period, all SM O/S signals are logged in with the time of day. After the passage of the aforementioned pre-specified time delay, the HIFIS monitor checks the main source side FM 206c shown in
If at step 140 the HIFIS monitor determines that the main feeder has an entire circuit outage, the program proceeds to step 145A and then to step 150, whereupon the HIFIS takes no further action. The program then proceeds to step 160 where the FM notifies the dispatcher of possible operation of the substation circuit breaker and provides the circuit number indicating the location of the affected substation circuit breaker.
If at step 140, the HIFIS monitor determines that the main feeder SM 206c is alive and that only the tap is out of service, the program proceeds to step 170 for confirming that the main feeder is alive. The program then proceeds to step 175 where the HIFIS analyzes the status of all tap isolator load side SM voltages. If at step 180, the HIFIS determines that an isolator device has tripped an over current operation, the HIFIS takes no action. The program then proceeds to step 188 and leaves the isolator status open. The program then proceeds to step 190 where the FMS notifies the dispatcher of normal overcurrent trip operation on the tap isolator and provides the geographical location number of the affected circuit. The operating program, or embedded software, within HIFIS chip 303 then proceeds to step 145c with reference to
With reference to
While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the relevant arts that changes and modifications may be made without departing from the invention in its broader aspects. Therefore, the aim in the appended claims is to cover all such changes and modifications that fall within the true spirit and scope of the invention. The matters set forth in the foregoing description and accompanying drawings are offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.
