WO2021237161A1

WO2021237161A1 - System and methods for detection and mitigation of a power line failure

Info

Publication number: WO2021237161A1
Application number: PCT/US2021/033761
Authority: WO
Inventors: David B. Eisenhaure; James L. Kirtley; Dennis M. Darcy
Original assignee: Eisenhaure David B; Kirtley James L; Darcy Dennis M
Priority date: 2020-05-21
Filing date: 2021-05-21
Publication date: 2021-11-25

Abstract

Rapid detection of power line failures, locating the fault, de-energizing the line, and enabling response teams to rapidly deploy to secure affected areas and extinguish fires is a priority for utility companies. Saving lives, property, and preventing damage to the environment has national urgency, and as the grid ages, power line failures are expected to increase, along with susceptibility to uncontrolled fires. The present disclosure includes determining that a power line has broken and locate where the break occurred. This will be performed by a power line break detector and localizing apparatus. Upon detection of a fault power will be shut off and it will drain the line of stored energy, and then signal a response team that will repair the line and put out any nascent fire thus preventing fire propagation.

Description

SYSTEM AND METHODS FOR DETECTION AND MITIGATION OF A POWER

LINE FAILURE

RELATED APPLICATIONS

[0001] This Application claims benefit of priority to United States Provisional Patent Application Serial Number 63/101,929 filed on May 21, 2020, which is incorporated herein by reference.

BACKGROUND

[0002] Power lines in California owned by Pacific Gas and Electric have ignited an estimated 1,500 fires in the last six years. Due to legal liability for damages from the fires PG&E has filed for bankruptcy and, to prevent more fires, has shut power off for millions of customers for days at a time. Fires are due in no small part to dry wooded areas and the downing of power lines causing sparking, and hot equipment igniting brush fires that rapidly cascade into large wildfires. Data collected by the California State Firefighting Agency, CAL Fire, show a series of 17 fires caused by PG&E scorched 193,743 acres in eight counties, destroying 3,256 structures and killed 22 people.

[0003] Rapid detection of power line failures, locating the fault, de-energizing the line, and enabling response teams to rapidly deploy to secure affected areas and extinguish fires is a priority for utility companies. Saving lives, property, and preventing damage to the environment has national urgency, and as the grid ages, power line failures are expected to increase, along with susceptibility to uncontrolled fires.

When power lines break, they can generate sparks and spots of intense heat that pose a risk for fires starting in wooded areas. The danger was so extreme at times that Pacific Gas and Electric and Southern California Edison turned power off for millions of customers so that the risk of wildfires might be reduced.

SUMMARY OF THE INVENTION

[0004] The embodiment of the present disclosure includes determining that a power line has broken and locate where the break occurred. This will be performed by a power line break detector and localizing apparatus. Upon detection of a fault power will be shut off and it will drain the line of stored energy, and then signal a response team that will repair the line and put out any nascent fire thus preventing fire propagation. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. l is a diagram showing a power-transmission line.

[0006] FIG. 2 is a schematic of the power-transmission line failing and a resultant transient.

[0007] FIG. 3 is a block diagram showing power system arrangement with transient detection sensors.

[0008] FIG. 4 is a block diagram of transient sensor.

[0009] FIG. 5 shows a tone generation and receiving arrangement.

[0010] FIG. 6 is a tone generator detector.

[0011] FIG. 7 Shows a sensor array

[0012] FIG 8 shows a power-line discharge system.

DETAILED DESCRIPTION OF THE EMBODIMENTS

DETECTION

[0013] The first step is the detection of a power line break and localizing the break. In other words, detect that a line has broken and determine where the break occurred. There are a number of methods that are described that may be used by themselves or in combination and make up the power line break detector and localizing apparatus. The first method is called glitch detection. In this application the word glitch is used interchangeably with the word transient.

[0014] FIG.1 shows a typical transmission line 100. In this example, the power is AC and three-phase and without a neutral wire; however, the power transmission could be a four-wire system AC which contains a neutral or it could also be DC transmission. Although it is called a transmission line it could be any line that supplies power over a distance, whether it is a utility transmission line or a distribution line. In the three-phase case, without a neutral, the power is transmitted over power lines 110(1)— (3) where each phase is run separately, 110(1), 110(2), and 110(3). Power originates at a power generation station 120 and is transmitted down the power linesl 10(1)— (3), e.g., to a sub-station 130. The power lines 110(1)— (3) can also be from a sub-station 130 to another substation 130 (not shown). Power can be distributed to power-users via a distribution system. Although, whether in a transmission system or a distribution system the principles presented here are the same and are not limited to just transmission or distribution. GLITCH DETECTION

[0015] FIG. 2 shows the transmission lines 110(1), 110(2), and 110(3). When a transmission line 110(1)— (3) breaks, there is a ‘glitch’ generated that propagates down the transmission linel 10(1)— (3). This ‘glitch’ is a transverse electromagnetic wave that travels at the speed of light. The glitch is shown as 210(1) and 210(2). Each glitch may be detected by an appropriate receiver that is placed at either, or both, ends of the transmission lines 110(1)— (3). The receiver is placed on the transmission lines 110(1)— (3) ahead of interconnection circuitry of the substation (e.g., substation 130), so that circuitry does not attenuate the signal before it can reach a receiver. AC power lines consist of a central steel cable surrounded by a plurality of aluminum wires. Because aluminum has no fatigue limit, the aluminum wires fail first. Once an aluminum wire breaks, an irregular power disruption occurs, causing radio frequency or other frequency signals to run down the line in both directions. Additional aluminum wires continue to break and increase the amount of energy lost and the gap increases, leading to further compromise of the aluminum wire and the cable, and ultimately leading to the line break. The receiving mechanisms that are part of our proposed system would, in addition to detecting returning chirps, detect impending line failures. In addition, the signals from weakening clamps, aggressive trees and other circumstances would be made available to surveillance systems to anticipate impending failures. This information could be used in a variety of ways, including anticipatory shutting down of lines or setting sensitivity of other relays.

[0016] FIG.3 shows a power transmission system where power generation 120 delivers power to a substation 130 using power transmission lines 110(1), 110(2), and 110(3). At each end of the transmission lines 110(1)— (3), there is a glitch detector receiver 310. The glitch detection circuit 310 is at the end of the transmission span but before filters 320 associated with the power generation 120 or substation 130.

FIG. 4 shows a block diagram of glitch detector receiver 310 (or receiver). The glitch detector 310 couples to the power lines via coupling block 410. Coupling block 410 couples the voltage and current. Voltage coupling may be attached via capacitive interconnects and current, sensed via current transformers. A current sense delivers voltage representative of current to a voltage translation circuit 420 that adjusts the value of the voltage suitable for interface to an analog to digital converter 450. The voltage translation circuit 420 may also provide voltage isolation. Current sense 440 is also converted to a suitable voltage for interface to the analog to digital converter 450 allowing the processor to measure the current in the power line. The digital to analog converter (i.e., D/A Converter 450) may have multiple channels or separate converters. The D/A converter 450 may also be a hybrid converter that monitors for a rapid change in voltage or current that represents a glitch and sets an interrupt to a processor 470. The D/A converter 450 is connected to the processor 470 via a data bus 475. The processor 470 may read the contents of the D/A converter 450, as well as the processor may receive an interrupt. The processor can also read and store data to a memory 480 via the data bus 475. There is a time standard 460 that can keep accurate time so that any data received may be time stamped. The processor 470 can communicate to a higher-order processor (not shown) via a communication interface 490 and may communicate via a wired connection or a wireless connection The higher-order processor may be the Supervisory Control and Data Acquisition (SCADA) or it may be communicated directly to an alarm system. The processor may communicate the occurrence of a glitch that represents a line break. Communication of a line break notifies an operator, a person, and may result in dispatching a response team to secure the area of the break and remediate the fault.

TIME STAMPING AT BOTH ENDS OF THE CABLE RUN

[0017] There is a ‘glitch’ received at both ends of the power line (e.g., transmission lines 110(1)— (3)), after a break by the glitch detection circuit 310 at either end of the transmission lines 110(1)— (3). When a glitch is detected the time is read from the time standard 460 and is stored in memory 480, as a glitch event and a time stamp. The time standard 460 may be a cesium time standard. There is a glitch event record recorded, in memory 480, at each end of the transmission lines 110(1)— (3). By reading the two records and comparing the time stamps, a position of the break may be calculated. In other words, the difference in time between the two glitch occurrences will be indicative of where the line broke. For example, if the glitch is received at exactly the same time the break, within the accuracy of the measurement, the break can be calculated to have occurred halfway between the two stations A glitch may travel from where a break occurs, to the glitch detector receiver, at an order of roughly 1 foot per nanosecond. The earlier glitch arrival of x nanoseconds before the later glitch arrival, represents a break that occurs x feet closer to the first receiver. The faster the glitch can be identified and time-stamped, the more accurate the position of the break can be calculated. In other words, if the glitch can be detected and time-stamped within 100 nanoseconds the accuracy of the break can be within 100 feet. Although the diagram in FIG. 4 shows a single phase for simplicity, it monitors all three phases as shown in FIG 3.

TONE DETECTION. [0018] FIG 5. Shows a power generation and substation connected by power transmission lines 110 (l)-(3, and a Tone Generator and receiver 510 at opposite ends of the power transmission line. A pilot tone may be sent down the transmission lines 110(1)— (3) sourced by tone generator 510 and detected at the opposite end by a tone receiver 510. When the pilot tone stops being received, a break in the transmission lines 110(1)— (3) may have occurred. When a transmission lines 110(1)— (3) breaks, a pilot tone may be injected at opposite ends of the transmission lines 110(1)— (3). A break will cause the pilot tone to disappear from each receiver 510 at opposite ends of the transmission lines 110(1)— (3). Noting the time of the disappearance and time stamping the moment of disappearance and comparing the difference in the between the timestamps recorded at each end of the power line may be used to determine the location of the break. That is when each pilot tone is sensed by receivers 510 at the opposite end of the transmission lines 110(1)— (3). A plurality of receivers may be placed at locations along the transmission lines 110(1)— (3). The location of a break may be determined by which receivers no longer sense the tone. When a tone is no longer detected notification may be sent via a wireless connection. Nodes that can sense the tone vs the nodes that can’t sense a tone will give the location of the break. A tone may be sent from both ends of the line. This may be done for each phase of the powerline. A different frequency may be used on each phase and in each direction so that the effect of coupling the signal may be eliminated.

[0019] FIG.6 shows a block diagram of a tone detector and receiver 610. Each transmission line 110(1)— (3) may be electrically coupled to the tone generator 620 and the tone detector 630 through a coupling network 610. The tone generator 620 is set by a digital-to- analog converter 640 or may be controlled directly by the processor 670 through a data bus 675. The processor 670 may set the frequency and tonal characteristics of the tone. A tone may be a and electrical sine wave, square wave, a multi-tone multi frequency signal, or any type of electrical signal. The tone may be detected by the tone detector 630 which interfaces to the line via the coupling 610. The output of the tone detector 630 can be read by the analog-to-digital converter 650. The output of the tone detector 630 may also be directly coupled to the processor 670 through the data bus 675 or may be an interrupt connected directly to the processor 470. When the tone disappears, the event is logged by the processor 670 and time-stamped. When an event occurs at both ends of a transmission line 110(1)— (3), the timestamps of each event can be compared to determine the location of the break. The tone detector and receiver 600 may be placed at multiple points along the transmission lines 110(1)— (3), so that the location of a break may be determined by where along the line the tone is no longer received. A tone detector and receiver 600 may be placed on each tower, for example, and can inject a tone that can be detected at an adjacent tower. Each tone detector and receiver 510 may have a communication module 678 that can interface with the processor 670 to a higher order processor or a SCADA system via a wired or wireless network.

PULSE RANGING

[0020] A pulse or chirp may be injected in to one end of the transmission lines 110(1)— (3) and the reflection of the pulse or chirp may be sensed. The pulse may be in the form of an electrical-frequency pulse. The pulse travels down the line and is reflected by the break or termination at the other end of the transmission line 110(1)— (3). The chirp travels down the transmission line 110(1)— (3) at the determinant speed so that the total round trip time will represent twice the distance. In the event of a break the round-trip time is shorter than without a break. Thus, the round-trip time for the pulse will be used to calculate the length of line from the station to the break. A chirp can originate at either end of the transmission lines 110(1)— (3) or at both ends. So, if chirps are provided from both ends of the line, reflections can determine the length to break from each end. By making the chirps orthogonal they can be used without interfering with each other or their respective detectors. Injecting signals, such as tones or pulses, into transmission lines 110(1)— (3) is described in the following section.

ACOUSTIC CHIRPING

[0021] Similar to an electromagnetic signal, an acoustic tone or pulse may be sent down the transmission lines 110(1)— (3) and detected upon its reflection. Upon a break, the reflected acoustic signal will return sooner than without a break. Also, since the materials making up a transmission line such as 110(l)-(3) have two different materials (e.g., aluminum and steel), two audio pulses can emerge from a single pulse. The difference in time between the acoustic pulses would be determined by the characteristics of the two materials, namely the speed of sound in aluminum and steel. The difference in time between the acoustic pulses may also be affected by temperature. So, the detection of a sound pulse from sensor to sensor along a length of line can infer temperature. So, in addition to breaks, temperature or hot spots may be determined along the length of transmission line between sensors.

[0022] A sensor array can also be used to detect current or voltage with an electric, magnetic, or electromagnetic detector. These sensor packages can be placed at every tower. Each sensor suite can be power from a, e.g., local utility, battery, or even power- scavenge from the lines they are sensing. As with an electric tone, each phase may utilize a different frequency to eliminate the effects of cross coupling. [0023] FIG. 7 is a block diagram of an acoustic sensor array. 700 which contains a clock 710 for accurate time measurement. In some embodiments the clock can be derived from a cesium standard. It also contains a sonic transducer which can detect a sonic signal or inject a sonic signal. It has a controller that containing a processor and a memory as well as a wireless transmitter 730 with an antenna 740 that can communicate with other sensor arrays or with a higher order processor. The acoustic sensor array 700 may contain other sensors such as voltage, current sensors. The acoustic sensor array may be placed at various points along a power transmission line and may inject and/or detect sonic signals. They may inject a sound at each point they are located and measure it at an adjacent or another location. An infrared or IR sensor may be incorporated in the sensor package so that temperature may be measured. The sensor array may contain a combination of any number of sensors.

[0024] All of these sensing techniques may be used singly or in combination.

DISCHARGING THE ENERGY STORED IN THE LINE.

[0025] In addition to determining that a transmission line is broken, it is desirable to disconnect and ground the transmission line so that the transmission line cannot ignite a fire if the transmission line falls on dry brush. If the transmission line is simply disconnected, it may retain charge, or inductively pick up enough power from nearby powerlines, that, when it hits the ground, it could still cause a spark with bad consequences or electrocute repairmen or nearby civilians.

[0026] It is possible to drain that charge before the wire reaches the ground and therefore make it difficult to start a fire.

[0027] FIG.8 shows a transmission line 110 that is connected from generation 120 to a sub station 130. It has a contactor 820 that can disconnect the transmission line 110 from generation 120. It can then connect the transmission line 110 to ground. It may do this through a resistance that is equal to the characteristic resistance of the line 810.

[0028] Upon determining that a break in the transmission line has occurred, the transmission line is disconnected from generation or power feeding the line, and then switched across a load resistor having a value equal to the characteristic impedance of the transmission line. The time to discharge the transmission line, rendering it safe, is determined by the length of the transmission. This amount of time will be short compared with the length of time it takes a wire to fall to the ground. Alternatively the line may be shorted directly to ground.

[0029] When a break occurs, an alarm is generated, that notifies a response team, whose function is to first extinguish any fires that may have started and then to repair the line. The response can be from a truck, car, or even aircraft, such as a helicopter. A drone may be used to deliver fire retardant and to transmit information about the break, as well as assess collateral damage and telemeter information back to a response center.

[0030] Determining a break and locating the break allows a response team to go to the location of the break and secure the area against possible fire.

[0031] Changes may be made in the above methods, devices, and systems without departing from the scope hereof. It should thus be noted that the matter contained in the above description and shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall there between

Combination of Features

[0032] Features described above as well as those claimed below may be combined in various ways without departing from the scope hereof. The following examples illustrate possible, non-limiting combinations of features and embodiments described above. It should be clear that other changes and modifications may be made to the present embodiments without departing from the spirit and scope of this invention:

[0033] (Al) In an embodiment of a first aspect a system for detecting faulty electric-power transmission lines, comprising a power line break detector and localizing apparatus configured to detect and localize a break in an electric power transmission line, a powerline disconnect system that de-energizes the electric power transmission line upon detection of a fault by the fault detection and localization apparatus; and a grounding apparatus coupled to ground and the electric power transmission line upon de-energization of the electric power transmission line by the powerline disconnect system.

[0033] (A2) In the embodiment (Al), wherein the power line break detector and localizing apparatus is a glitch detector.

[0034] (A3) In the embodiment (A2) the detection of a glitch, by the glitch detector, is recorded and time stamped.

[0035] (A4) In the embodiment (A3) wherein the time, of the time stamp, is derived from a cesium time standard. [0036] (A5) In the embodiment (A1)-(A4) wherein the fault is detected on three phases of an AC power line.

[0037] (A6) In the embodiment (Al) wherein the power line break detector and localizing apparatus injects a tone at one end of the electric power transmission line and detects the tone on the other end of the electric power transmission line.

[0038] (A7) In the embodiment (A6) wherein a plurality of tone receivers are placed along the power line.

[0039] (A8) In the embodiment (Al) - (A4) and (A6)- (A7) wherein the electric power transmission line is a DC power line, wherein the fault is detected on the DC power line.

[0040] (A9) In the embodiment (A6) wherein the tone receivers sense partial defects on the power line and is used to alert an operator of imminent failure

[0041] (A10) In the embodiment (Al) wherein the power line break detector and localizing apparatus injects an electrical pulse at one end and records the time for reflect back from the break.

[0042] (Al 1) in the embodiment (Al) wherein the power line break detector and localizing apparatus injects an acoustic pulse and records the time for a reflection.

[0043] (Bl) A method for detecting faulty electric power transmission lines, comprising: detecting a fault in an electric power transmission line determining where the fault occurred disconnecting the electric power transmission line; and connecting the electric power transmission line to a grounding apparatus.

[0044] (B2) in the embodiment (Bl) further comprising detecting a glitch in the electric power transmission lines.

[0045] (B3) in the embodiment (B2) wherein detection of the glitch is recorded and time stamped.

[0046] (B4) in the embodiment (Bl) - (B3) injecting a tone at one end of the electric power transmission line and detecting the tone at the opposite end of the electric power transmission line. [0047] (B5) in the embodiment (Bl) - (B4) wherein tones are injected in a plurality of locations along the electric power transmission line

[0048] (B6) in the embodiment (Bl) -(B5) wherein the tones are of different frequencies.

[0049] (B7) in the embodiment (B 1) further comprising pulsing the electric power transmission line with an electric pulse at one end of the electric power transmission line and detecting the reflection of the pulse back from the break.

[0050] (B8) in the embodiment (B7) further comprising pulsing the electric power transmission line from opposite ends and using pulses that are orthogonal.

[0051] (B8) in the embodiment (Bl) further comprising upon the detection of the fault, an alarm is transmitted to an operator.

Claims

CLAIMS What is claimed is:

1. A system for detecting faulty electric-power transmission lines, comprising: a power line break detector and localizing apparatus configured to detect and localize a break in an electric power transmission line; a powerline disconnect system that de-energizes the electric power transmission line upon detection of a fault by the fault detection and localization apparatus; and a grounding apparatus coupled to ground and the electric power transmission line upon de-energization of the electric power transmission line by the powerline disconnect system.

2. The system of claim 1, wherein the power line break detector and localizing apparatus is a glitch detector.

3. The system of claim 2, wherein the detection of a glitch, by the glitch detector, is recorded and time stamped.

4. The system of claim 3, wherein the time, of the time stamp, is derived from a cesium time standard.

5. The system of claim 1, wherein the fault is detected on three phases of an AC power line.

6. The system of claim 1, wherein the power line break detector and localizing apparatus injects a tone at one end of the electric power transmission line and detects the tone on the other end of the electric power transmission line.

7. The system of claim 6, wherein a plurality of tone receivers are placed along the power line.

8. The system of claim 1, wherein the electric power transmission line is a DC power line, wherein the fault is detected on the DC power line.

9. The system of claim 7 wherein the tone receivers sense partial defects on the power line and is used to alert an operator of imminent failure.

10. The system of claim 1, wherein the power line break detector and localizing apparatus injects an electrical pulse at one end and records the time for reflect back from the break.

11. The system of claim 1, wherein the power line break detector and localizing apparatus injects an acoustic pulse and records the time for a reflection.

12. A method for detecting faulty electric power transmission lines, comprising: detecting a fault in an electric power transmission line; determining where the fault occurred; disconnecting the electric power transmission line; and connecting the electric power transmission line to a grounding apparatus.

13. The method of claim 12, further comprising detecting a glitch in the electric power transmission lines.

14. The method of claim 13, wherein detection of the glitch is recorded and time stamped.

15. The method of claim 12, further comprising injecting a tone at one end of the electric power transmission line and detecting the tone at the opposite end of the electric power transmission line.

16. The method of claim 15 wherein tones are injected in a plurality of locations along the electric power transmission line

17. The method of claim 16, wherein the tones are of different frequencies.

18. The method of claim 12, further comprising pulsing the electric power transmission line with an electric pulse at one end of the electric power transmission line and detecting the reflection of the pulse back from the break.

19. The method of claim 18, further comprising pulsing the electric power transmission line from opposite ends and using pulses that are orthogonal.

20. The method of claim 12, further comprising upon the detection of the fault, an alarm is transmitted to an operator.