Detection of broken conductor events

Abstract

A control system includes: a detection module configured to: analyze a harmonic content metric to determine whether a load break condition exists; if a load break condition exists, compare an amplitude metric of electrical current to an undercurrent specification to determine whether a load loss condition exists; determine whether an electrical system includes one or more broken electrical conductors, where to determine whether the electrical system includes one or more broken conductors, the detection module is configured to determine whether the load break condition and the load loss condition exist at the same time; and if the electrical system includes one or more broken electrical conductors, generating a switch command. The control system also includes a command module configured to: control a switch to stop electrical current flow into the one or more broken conductors in response to the switch command.

Description

[0001] Docket No.: 041-354W01 / P24-1421W001

[0002] DETECTION OF BROKEN CONDUCTOR EVENTS

[0003] CROSS-REFERENCE TO RELATED APPLICATION

[0004] This application claims the benefit of U.S. Provisional Application No. 63 / 679,422, filed on August 5, 2024 and titled DETECTION OF BROKEN CONDUCTOR EVENTS, which is incorporated herein by reference in its entirety.

[0005] TECHNICAL FIELD

[0006] This disclosure relates to detecting broken conductor events in an electrical power distribution network.

[0007] BACKGROUND

[0008] An overhead electrical power distribution network includes overhead electrical conductors that carry electrical current throughout the distribution network. The overhead electrical conductors may be, for example, copper or aluminum wires, metal cables protected by an insulator, or any other mechanism capable of carrying electrical current. The overhead electrical conductors are mounted to various structures in the distribution network and are suspended in the air above ground. For example, the overhead electrical conductors may be mounted to utility poles, frames or other mounting structures in a substation, pylons, or support towers. The support structures are set on the earth or on a foundation that is set into the earth. Mounting the conductor on a structure allows the conductor to be operated safely and away from the public and / or objects that could interfere with the distribution of electricity. Additionally, the structures allow the electrical conductors to be mounted overhead (for example, at least 4.5 meters above the surface below).

[0009] SUMMARY

[0010] In one aspect, a control system includes: a detection module configured to: analyze a harmonic content metric to determine whether a load break condition exists; if a load break condition exists, compare an amplitude metric of electrical current to an undercurrent specification to determine whether a load loss condition exists; determine whether an electrical system includes one or more broken electrical conductors, where to determine whether the Docket No.: 041-354W01 / P24-1421W001 electrical system includes one or more broken conductors, the detection module is configured to determine whether the load break condition and the load loss condition exist at the same time; and if the electrical system includes one or more broken electrical conductors, generating a switch command. The control system also includes a command module configured to: control a switch to stop electrical current flow into the one or more broken conductors in response to the switch command.

[0011] Implementations may include one or more of the following features.

[0012] The harmonic content metric may include an instantaneous change in harmonic content, and to analyze the instantaneous change in harmonic content, the detection module may be configured to compare the difference to an adaptive threshold.

[0013] In some implementations, to determine whether the electrical system includes one or more broken conductors, the detection module is further configured to determine whether there is a time period of a pre-determined duration during which the load break condition and the load loss condition both exist, and the switch command is only generated if the load break condition and the load loss condition both exist over the time period. To determine whether the electrical system includes one or more broken conductors, the detection module may be configured to determine whether the load loss condition occurs after the load break condition, and the switch command is only generated if the load break condition and the load loss condition both exist over the time period and the load loss condition occurs after the load break condition.

[0014] The detection module may be configured to: access measurements of an electrical property of the electrical system, and to determine the harmonic content metric based on the measurements. The measurements of the electrical property of the electrical system may include a time series of measurements of the electrical property; and to determine the harmonic content metric, the detection module may be configured to determine a spectral content of the time series. The harmonic content metric may include a difference between a present value of the harmonic content and an average value of the harmonic content. The measurements of the electrical property of the electrical system may include a plurality of individual measurements of electrical current, each associated with a different time.

[0015] The amplitude metric may include a value of an amplitude of the electrical current, the undercurrent specification includes threshold value, and the load loss condition may exist if the absolute value of the amplitude of the electrical current is less than the threshold value. Docket No.: 041-354W01 / P24-1421W001

[0016] The amplitude metric may include a value of an amplitude of the electrical current, the undercurrent specification may include a range of values that includes zero, and the load loss condition may exist if the value of the amplitude of the electrical current is in the range of values.

[0017] In another aspect, a method of detecting a broken electrical conductor in an overhead electrical power distribution system includes: determining whether a load break condition exists in the overhead electrical power distribution system based on a change in a harmonic content metric associated with the overhead electrical power distribution system; if a load break condition exists, determining whether a load loss condition exists in the overhead electrical power distribution system based on a comparison between an indication of measured current in the overhead electrical power distribution system and an undercurrent specification; and if the load break condition and the load loss condition exist, detecting a broken electrical conductor in the overhead electrical power distribution system.

[0018] Implementations of any of the techniques described herein may include an electrical apparatus, a control system, a system that includes an electrical apparatus and control system, a broken overhead conductor detection module, software stored on a non-transitory computer readable medium that, when executed, monitors and / or analyzes electrical current that flows in the distribution network and determines whether a broken overhead conductor is present, a method, and / or a software upgrade for retrofitting a recloser or protective relay. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

[0019] DRAWING DESCRIPTION

[0020] FIGS. 1A and IB show an example electrical power distribution network.

[0021] FIG. 1C is a block diagram of an example of a switching system.

[0022] FIG. 2 is a block diagram of an example system for controlling the flow of electricity in an electrical power distribution network.

[0023] FIG. 3 is a block diagram of an example of a broken overhead conductor detection module.

[0024] FIG. 4 is a flow chart of an example of a process for detecting a broken overhead conductor event. Docket No.: 041-354W01 / P24-1421W001

[0025] DETAILED DESCRIPTION

[0026] Techniques for detecting a broken conductor event in an electrical power distribution network before the broken electrical conductor reaches the surface below are disclosed.

[0027] Referring to FIGS. 1A and IB, an example electrical power distribution network 100 is shown. The power distribution network 100 distributes electricity from an electrical power source 101 to electrical loads 102 via a distribution path 106. The overhead distribution path 106 includes an overhead conductor 108 mounted to the supports 104 and suspended above a surface 107. The surface 107 is the surface of the earth, a foundation built into the surface of the earth, or a layer or object supported by the surface of the earth. For example, the surface 107 may be a grassy surface, a dirt surface, an asphalt surface, water, or a concrete surface. The supports 104 are any sturdy structure that can hold a power line. The supports 104 may be, for example, utility poles, pylons, mounting structures in a substation, frames, or transmission towers that are secured to the earth.

[0028] The overhead conductor 108 is any electrically conductive path. For example, the overhead conductor 108 may be a transmission line or an electrical cable. Although only one overhead conductor 108 is shown in FIGS. 1 A and IB, the distribution path 106 may include more than one overhead conductor. For example, the distribution path 106 may include an overhead conductor for each phase of a multi-phase distribution path 106 and an additional overhead conductor for a neutral channel.

[0029] Referring also to FIG. 1C, a switching system 105 is controllable to intentionally open or close the distribution path 106. The switching system 105 includes an electrical apparatus 130 and a control system 120 that communicates with the electrical apparatus 130 through a data connection 140. The electrical apparatus 130 is any device capable of controlling and monitoring electricity on the distribution path 106. The electrical apparatus 130 includes an interrupting module 132 that is capable of opening the distribution path 106 to intentionally interrupt the flow of current in the distribution path 106 and closing the distribution path 106 to allow current to flow in the distribution path 106. The electrical apparatus 130 also monitors one or more electrical properties of the electricity that flows in the distribution path 106. For example, the electrical apparatus 130 includes sensor(s) that measure the current, voltage, and / or power on the distribution path 106 at regular time intervals to produce measured data 131. The Docket No.: 041-354W01 / P24-1421W001 electrical apparatus 130 may be a recloser or a switchgear. A vacuum interrupter is an example of a device that may be used as the interrupting module 132.

[0030] The control system 120 is configured to detect a broken overhead conductor event and to deenergize the broken conductor by activating the interrupting module 132. A broken conductor event occurs when an overhead conductor (such as the overhead conductor 108) breaks. FIG. 1 A shows the overhead conductor 108 in an unbroken state. In the unbroken state, the overhead conductor 108 electrically connects the source 101 and the load 102. FIG. IB shows the overhead conductor 108 after a broken conductor event has occurred and the overhead conductor 108 has severed into portions 109a and 109b. The overhead conductor 108 may break in response to, for example, storms, falling debris (for example, falling trees or tree limbs), and / or high winds.

[0031] When the overhead conductor breaks under load, the load 102 is disconnected from the source 101 and an arc 111 forms between the severed portions 109a, 109b. As time passes, the severed portions 109a, 109b continue to fall toward the surface 107 and the arc 111 dies out. After the arc 111 dies out, the amplitude of the current in the broken conductor portion 109a decreases toward zero, resulting in an undercurrent or load loss condition. However, because the source 101 continues to feed the distribution path 106, when the energized portion 109a hits the surface 107, the amplitude of the current in the portion 109a increases again as current flows into the surface 107 and / or objects on the surface 107. This scenario can lead to a high impedance fault and can result in a fire. Additionally, an energized broken overhead conductor can electrocute or otherwise injure people or animals and cause service outages for customers of the power distribution network 100. Thus, broken overhead conductor events reduce the overall reliability and safety of the power distribution network 100.

[0032] On the other hand, the control system 120 detects broken overhead conductor events and activates the current interrupting module 132 to deenergize the broken overhead conductor before it reaches the surface 107. In this way, the control system 120 minimizes the risk of catastrophic failure (for example, fires and / or severe injury) that can result from an energized broken conductor hitting the surface 107. The arcing 111 that occurs when the overhead conductor breaks changes the harmonic content of the current and / or voltage on the distribution path 106. The current that flows in the distribution path 106 is nominally sinusoidal with a frequency at the fundamental frequency (for example, 60 Hertz (Hz)) of the distribution network Docket No.: 041-354W01 / P24-1421W001

[0033] 100. The arcing 111 introduces additional frequencies at multiples of the fundamental frequency (also referred to as harmonics). The additional frequencies change the harmonic content of the electricity in the distribution path 106. The harmonic content at a particular time is a characterization of the amount of current, voltage, and / or power in one or more of the harmonic frequencies at that particular time.

[0034] To determine whether a load break condition is present, the control system 120 analyzes the measured data 131 to assess a change in harmonic content, with greater changes indicating a load break condition. If the control system 120 detects a load break condition, the control system 120 determines whether a load loss condition exists. If a load break condition exists and a load loss condition exists, the control system 120 detects a broken overhead conductor event and activates the current interrupting module 132 to open the distribution path 106 and deenergize the portion 109a before it hits the surface 107.

[0035] Before discussing the control system 120, an overview of the distribution network 100 is provided. The electrical power distribution network 100 may be a multi-phase (for example, three-phase) electrical network that provides electricity to commercial and / or residential customers. The power distribution network 100 may have an operating voltage of, for example, at least 1 kilovolt (kV), up to 38 kV, or higher. The power distribution network 100 may operate at a fundamental frequency of, for example, 50 or 60 Hertz (Hz).

[0036] The power source 101 is any source that is capable of providing alternating current (AC) electrical current and may be a multi-phase power source. For example, the power source 101 may be an electrical generator that converts mechanical power into AC electrical current, a solar or wind farm, or a fossil-fuel based power plant. The electrical loads 102 may be any electrical equipment that receives electricity from the power source 101 and may include, for example, transformers, electrical machinery, motors, power converters, and / or electrical appliances and devices in a residential building, retail establishment, industrial facility, or municipal site.

[0037] Referring to FIG. 2, a block diagram of an example system 205 is shown. The system 205 is used to control the flow of electricity between portions of an electrical power distribution network. For example, the system 205 may be used in the power distribution network 100 (FIGS. 1A and IB) as the system 105.

[0038] The system 205 includes a control system 220, which sends data to and receives data from an electrical apparatus 230 via a data connection 240. The electrical apparatus 230 includes Docket No.: 041-354W01 / P24-1421W001 an interrupting module 232, sensor module 233, a driving module 234, and a communications interface 236. The electrical apparatus 230 may be any type of apparatus that is capable of being controlled to open and close the distribution path 106. For example, the electrical apparatus 230 may be a medium-voltage circuit breaker, a single-phase recloser, a triple single-phase recloser, or a three-phase recloser.

[0039] The data connection 240 may be any communication link capable of transmitting information. The data connection 240 sends information to and receives information from the control system 220. In typical implementations, the data connection 240 is a single control cable connected between the communications interface 236 of the electrical apparatus and the control system 220. The communications interface 236 may be any interface capable of sending data to and receiving data from an input / output interface 224 of the control system 220 via the connection 240.

[0040] The electrical apparatus 230 also includes the interrupting module 232 and the driving module 234, which drives the interrupting module 232 in response to a control signal received from the control system 220 via the data connection 240. The electrical apparatus 230 includes an interrupting module 232 for each phase. Thus, a three-phase apparatus includes three interrupting modules 232 and a one-phase apparatus includes one interrupting module 232. The interrupting module 232 is any mechanism or device that is capable of interrupting (opening) the distribution path 106. For example, the interrupting module 232 may be a vacuum interrupter.

[0041] The electrical apparatus 230 also includes the sensor module 233. The sensor module 233 includes any type of sensor capable of measuring a property of the electricity that flows in the distribution path 106, and the sensor module 233 may include more than one sensor. For example, the sensor module 233 may include one or more current sensors, such as current transformers or Rogowski coils, that sense the amount of current flowing in each phase in the distribution path 106. The sensor module 233 may include voltage sensors and / or power sensors that measure data in the temporal domain. The sensor module 233 may include a spectrum analyzer or other sensor that measures a physical quantity in the frequency or spectral domain. Data 231 representing the measurements collected by the sensor module 233 is provided to the control system 220 via the data connection 240.

[0042] The driving module 234 may include passive and / or active electrical and / or mechanical components that drive the interrupting module 232 to open or close in response to a control Docket No.: 041-354W01 / P24-1421W001 signal from the control system 220. For example, in some implementations, the driving module 234 may include capacitors that provide energy to the interrupting module 232 for closing or opening the contacts. In some implementations, the driving module 234 includes magnets. The driving module 234 may include resistors, inductors, and other passive electronic components. In some implementations, the driving module 234 includes devices that store mechanical energy, such as springs. In some implementations, the driving module 234 includes a motor.

[0043] The system 205 also includes the control system 220. The control system 220 and the electrical apparatus 230 may be physically separated from each other. For example, the electrical apparatus 230 may be mounted near the top of a utility pole or other structure associated with overhead power lines, and the control system 220 may be mounted on the same pole or structure near the ground to facilitate operator access to the control system 220. In another example, the control system 220 may be located at a utility substation control house that is remote from the electrical apparatus 230. Furthermore, the control system 220 may be a mobile device that is separate from the electrical apparatus 230 but is able to connect to the electrical apparatus 230 via the data connection 240. In yet other implementations, the control system 220 is integrated with the electrical apparatus 230 such that the system 205 forms a single, self-contained device. In implementations in which the control system 220 is integrated with the electrical apparatus 230, the control system 220 and the electrical apparatus 230 communicate data via the data connection 240, but the control system 220 and the electrical apparatus 230 are part of the same device and may be received in, for example, a single integrated housing.

[0044] The control system 220 includes a broken overhead conductor detection module 222, an input / output (VO) interface 224, an electronic processor 226, and an electronic storage 228. The broken overhead conductor detection module 222 analyzes current sensed by the sensor module 233 to determine whether an overhead conductor in the distribution path 106 is broken. When a broken overhead conductor is detected, the control system 220 issues a command or control signal to the electrical apparatus 230 to open the interrupting module 232 to isolate the portion of the distribution path 106 that includes the broken overhead conductor. In some implementations, the control system 220 causes a perceivable warning to be presented at the I / O interface 224. FIGS. 3 and 4 discuss an example implementation of the broken overhead conductor detection module 222 in greater detail. Docket No.: 041-354W01 / P24-1421W001

[0045] The I / O interface 224 may be any interface that allows a human operator and / or an autonomous process to interact with the control system 220. The I / O interface 224 may include, for example, a display, a keyboard, speakers, a serial or parallel port, a Universal Serial Bus (USB) connection, and / or any type of network interface, such as, for example, Ethernet. The I / O interface 224 also may allow communication without physical contact through, for example, a wireless communications protocol.

[0046] The I / O interface 224 also may allow the control system 220 to communicate with systems external to and remote from the system 205. For example, the I / O interface 224 may include a communications interface that allows communication between the control system 220 and a remote station 203, or between the control system 220 and an electrical apparatus other than the apparatus 230, through the VO interface 224 using, for example, a Supervisory Control and Data Acquisition (SCAD A) protocol.

[0047] The control system 220 also includes the electronic processor 226 and the electronic storage 228. The electronic processor 226 is one or more processors suitable for the execution of a computer program such as a general or special purpose microprocessor, and any one or more processors of any kind of digital computer. Generally, a processor receives instructions and data from a read-only memory or a random-access memory or both. The electronic processor 226 may be any type of electronic processor, may be more than one electronic processor, and may include a general-purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a field-programmable gate array (FPGA), and / or an application-specific integrated circuit (ASIC). The electronic storage 228 may be volatile memory, such as RAM. In some implementations, the electronic storage 228 may include both non-volatile and volatile portions or components. Examples of electronic storage may include solid state storage, magnetic storage, and optical storage. Solid state storage may be implemented in, for example, resistor-transistor logic (RTL), complementary metal-oxide semiconductor (CMOS), or carbon nanotubes, and may be embodied in non-volatile or volatile random-access memory.

[0048] The electronic storage 228 stores instructions, perhaps as a computer program, that, when executed, cause the electronic processor 226 to perform a process to detect the presence of a broken overhead conductor and to interact with components in the control system 220 (such as the broken overhead conductor detection module 222 and the VO interface 224), the electrical apparatus 230, and / or the remote station 203. Docket No.: 041-354W01 / P24-1421W001

[0049] As discussed above, the electrical apparatus 230 may be, for example, a recloser or a circuit breaker. In implementations in which the electrical apparatus 230 is a recloser 230, the control system 220 is a recloser control 220. In these implementations, the recloser control 220 causes the recloser 230 to open the distribution path 106 when the broken overhead conductor detection module 222 detects a broken overhead conductor. The recloser control 220 also controls the recloser 230 to open or close the distribution path 106 based on other conditions on the distribution path 106.

[0050] In implementations in which the electrical apparatus 230 is a circuit breaker, the control system 220 is a protective relay 220. When the broken overhead conductor detection module detects a broken overhead conductor, the protective relay 220 generates a signal that causes the circuit breaker 230 to open the distribution path 106 to isolate the broken overhead conductor. The protective relay 220 may be located in a substation and may be used to protect any type of electrical equipment.

[0051] FIG. 3 is a block diagram of an example implementation of the broken overhead conductor detection module 222. The broken overhead conductor detection module 222 may be implemented as a collection of machine-executable instructions that are stored on the electronic storage 228. The broken overhead conductor detection module 222 includes a harmonic detection module 350 that analyzes the harmonic content of the data 231. The harmonic detection module 350 may include executable instructions that implement a transformation (such as discrete Fourier transform on a moving time horizon or a wavelet transform) that transforms time domain data into frequency domain data. The frequency domain data describes the frequency content of the time domain data. The harmonic detection module 350 also may pre- process the time domain data prior to transforming the data into the frequency domain data. For example, the harmonic detection module 350 may include a noise removal module, such as a low pass filter or other smoothing technique, to remove noise from the time domain data.

[0052] The harmonic detection module 350 determines a harmonic content metric 351 from the frequency domain data. The harmonic content metric 351 may be, for example, an instantaneous change in the energy at one or more frequencies. The harmonic content metric 351 is provided to a load break detection module 352, which analyzes the harmonic content metric 351 to produce a load break indication 353. The load break indication 353 may be a binary output. In Docket No.: 041-354W01 / P24-1421W001 these implementations, a high value (for example, 1) indicates that a load break condition is present and a low value (for example, 0) indicates that no load break condition is present.

[0053] The broken overhead conductor detection module 222 also includes a load loss detection module 354 that produces a load loss indication 355. The load loss detection module 354 compares measured current in the distribution path 106 to a specification to determine whether a load loss condition exists. A load loss condition exists when the amplitude of the current in the distribution path 106 falls below a pre-defined minimum value or undercurrent specification. The load loss indication 355 may be a binary output. In these implementations, a high value (for example, 1) indicates that a load loss condition is present and a low value (for example, 0) indicates that no load loss condition is present.

[0054] The load loss indication 355 and the load break indication 353 are provided to a logic module 356 that analyzes the load loss indication 355 and the load break indication 353 to produce a broken conductor indicator 357. The logic module 356 includes a set of rules and / or logic to analyze the load loss indication 355 and the load break indication 353 to determine whether a broken overhead conductor event has occurred. For example, the logic module 356 may include a rule that a broken overhead conductor event has occurred when both the load break indication 353 and the load loss indication 355 have a value above a respective threshold. In some implementations, the logic module 356 includes an AND gate that accepts the indications 353 and 355 as inputs and outputs a HIGH when both indications 353 and 355 are HIGH.

[0055] The logic module 356 may include additional rules. For example, the logic module 356 may include a rule that the load break indication 353 and the load loss indication 355 must be above the thresholds (or both HIGH) concurrently during a pre-determined time period and / or that load loss indication 355 occurs after the load break indication 353. In another example, the logic module 356 may include a rule that the load break indication 353 occur before the load loss indication 355 and that the load loss indication 355 persist for a pre-determined time duration for a broken conductor to be present. The pre-determined time duration for the load loss indication 355 depends on characteristics of the monitored overhead distribution path 106, with examples of the characteristics including voltage level, distance of the overhead distribution path 106 from the surface 107, and / or the amount of sag in the overhead distribution path 106. Docket No.: 041-354W01 / P24-1421W001

[0056] The rules and logic implemented by the logic module 354 identify broken overhead conductor events while also avoiding or minimizing false alarms that could be caused by other events that affect the distribution path 106. For example, a fuse blow may produce a fault current and arcing that could change the harmonic content of the electricity on the distribution path 106. However, a fuse blow typically does not produce both a change in the harmonic content and a load loss condition that persist together for more than about a second. Thus, by including a rule in the logic module 356 that the load break indication 353 and the load loss indication 355 must be above the thresholds (or HIGH) concurrently during a pre-determined time period, where the time period exceeds a second, fuse blow events can be distinguished from broken overhead conductor events. In another example, the intentional opening of a recloser may cause arcing and a change in harmonic content. However, even if arcing occurs during the opening, the opening generally causes a load loss condition before the change in harmonic content. Thus, including a rule in the logic module that requires that the load loss condition occur after the change in harmonic content can avoid false detections based on recloser openings. Although avoiding false alarms is generally desirable, the operator of the system 105 and / or the distribution network 100 may decide to accept a higher number of false alarms by selective rule implementation.

[0057] FIG. 4 is a flow chart of a process 400. The process 400 is an example of a process for detecting a broken overhead conductor event. The process 400 may be performed by the broken conductor detection module 222.

[0058] Sensor data 231 is accessed (410). As discussed above, the sensor data 231 includes data from the sensor module 233. The sensor data 231 may be current, voltage, and / or power measurements taken over time. For example, the sensor data 231 may be a time series of discrete current (amplitude and / or phase), voltage (amplitude and / or phase), and / or power measurements of the electricity in the distribution path 106. In this example, the time series includes a value of the measurement for each different time in the time series. The harmonic detection module 350 transforms the time series data into frequency domain data. In some implementations, the sensor data 231 includes data that is already in the frequency domain. For example, in some implementations, the sensor module 233 includes a sensor or data processor that outputs frequency domain data. In these implementations, the harmonic block 350 does not necessarily perform additional transformations on the sensor data 231. Docket No.: 041-354W01 / P24-1421W001

[0059] Regardless of how the frequency domain data is generated, the frequency domain data includes an indication of the amount of electrical energy in the distribution path 106 at the fundamental frequency and at harmonics of the fundamental frequency. The amount of electrical energy may be an amount of current, voltage, or power. Although the frequency domain data includes information about energy at the fundamental frequency and the harmonic frequencies, a subset of frequencies may be used for further analysis. For example, the second, third, and fifth harmonics may be selected.

[0060] The harmonic block 350 outputs the harmonic content metric 351 (420). The harmonic content metric 351 is any type of metric that quantifies a change in harmonic energy in the electricity on the distribution path. The harmonic content metric 351 may be AE, which is determined by subtracting the harmonic baseline reference which could be achieved through smoothing or average of the selected harmonics from the raw total energy of the selected harmonics. The smoothed total energy of the selected harmonics may be determined using a low pass filter or a moving average. The raw total energy of the selected harmonics is the sum of the energy in the frequency domain data at the selected harmonics. The harmonic content metric 351 may be based on harmonics that are at integer multiples of the fundamental frequency and / or based on interharmonics. Interharmonics are at frequencies that are non-integer multiples of the fundamental frequency.

[0061] The harmonic content metric 351 is analyzed at the load break detection module 352 (430). The harmonic content metric (AE) may be analyzed by comparison to a harmonic threshold. The harmonic threshold may be an adaptive harmonic threshold that detects whether the instantaneous variation of AE is abnormal, that is, whether the variance of AE is greater than the average AE variance tracked over time. The AE determined at each time step is stored such that the variance in historical AE can be determined and updated at each time step. The standard deviation could also be achieved through an infinite impulse response (HR) filter of the mean of a locally stored AE variance. In some implementations, the standard deviation (c) of the AE is determined and the adaptive harmonic threshold is set based on the standard deviation. For example, the adaptive harmonic threshold may be a range of values bounded by: (average AE) + / - 3o, where average_AE is the historical average of AE. In this example, if the present harmonic content metric AE is outside of the range of values bounded by (average_AE) + / - 3o, then the present harmonic content metric AE exceeds the threshold. Docket No.: 041-354W01 / P24-1421W001

[0062] Other implementations are possible. For example, the adaptive harmonic threshold may be based on a constant value instead of the standard deviation. In these implementations, values of AE that are not within in a range defined by: (average_AE) + / - C, where C is a pre-defined constant value, exceed the harmonic threshold. In other implementations, a pre-defined, fixed harmonic threshold is used instead of an adaptive threshold.

[0063] The load break detection module 352 outputs the load break indication 353. If the harmonic content metric does not exceed the harmonic threshold, the load break indication 353 is LOW and a load break condition is not present. At (440), the process returns to (410). If the harmonic content metric does not exceed the harmonic threshold, the load break indication 353 is HIGH, and a load break condition is present. At (440), the process 400 continues to (450) and the load loss detection module 354 analyzes the sensor data 231 to determine whether a load loss condition is present. A load loss condition is present if the current on the distribution path 106 drops below a minimum value (an undercurrent specification). For example, the undercurrent specification may be 1 ampere (A) or 0.5 A.

[0064] The sensor data 231 includes current measurements over time (or data from which current amplitude values may be derived). The current measurements are compared to the undercurrent specification. If the absolute value of the magnitude of the measured current does not exceed the undercurrent specification for a pre-determined time period (for example, 100 milliseconds (ms), 200 ms, 1 s, 1.06s, 1.5s, 2s, or at least 10 cycles of the fundamental current), then a load loss condition is detected and the load loss indication 355 is HIGH. At (460), the process 400 advances to (470). In other words, if the undercurrent specification defines a load loss condition as a current with an amplitude between + / -1 A and the pre-determined time period is 100 ms, and the absolute value of the measured current in the distribution path 106 remains at less than 1 A for 100 ms or more, then a load loss condition is detected and the load loss indication 355 is HIGH. If the measured current does not stay below undercurrent specification for the pre-determined time period, then a load loss condition is not detected, the load loss indication 355 is LOW, and, at (460), the process 400 returns to (410).

[0065] The undercurrent specification discussed above is provided as an example, and the undercurrent specification may include different values and / or other parameters. Moreover, the pre-determined time period that may be included in the undercurrent specification can be the same as or similar to the amount of time in which a broken conductor in the overhead Docket No.: 041-354W01 / P24-1421W001 distribution path 106 is expected to hit the surface 107. The pre-determined time depends on the characteristics (for example, voltage, sag, nominal distance from the surface 107) of the overhead distribution path 106. In implementations in which the overhead distribution path 106 is a 11 kV overhead conductor having the lowest sag based on National Electrical Safety Code (NESC) clearance requirements, the pre-determined time is 1.06s.

[0066] When a load loss condition is detected, the process 400 advances to (470), and the load loss and load break conditions are analyzed with the rules of the logic module 356 to determine whether a broken overhead conductor event has occurred (470). The rules of the logic module 356 may include a rule that specifies that both the load break condition and the load loss condition exist at the same time and during a pre-defined time period. The pre-defined time period may exceed one second. In another example, in some implementations, the logic module 356 includes a rule that if load break condition is detected before a load loss condition, the amount of time the load loss condition exists is tracked as a load loss period, and, if the load loss period is more than a predetermined time (for example, 1 ms), a broken overhead conductor event is detected. In this example, if the load loss period is less than the predetermined time, then the rule is not met and a broken overhead conductor event is not detected.

[0067] If the rules of the logic module 356 are met, a broken overhead conductor event is detected at decision block (480), a command to open the interruption module 232 is issued (490). The process 400 ends and may be re-initiated as warranted. If the rules of the logic module 356 are not met at decision block (480), a broken conductor event is not detected, and the process 400 returns to (410) to continue to monitor the overhead distribution path 106.

[0068] Other implementations and variations of the process 400 are possible, and the process 400 may include additional features. For example, in some implementations, the process 400 is performed only in the absence of an overcurrent condition or other fault condition on the overhead distribution path 106.

[0069] These and other implementations are within the scope of the claims.

Claims

Docket No.: 041-354W01 / P24-1421W001WHAT IS CLAIMED IS:

1. A control system comprising: a detection module configured to: analyze a harmonic content metric to determine whether a load break condition exists; if a load break condition exists, compare an amplitude metric of electrical current to an undercurrent specification to determine whether a load loss condition exists; determine whether an electrical system includes one or more broken electrical conductors, wherein to determine whether the electrical system includes one or more broken conductors, the detection module is configured to determine whether the load break condition and the load loss condition exist at the same time; and if the electrical system includes one or more broken electrical conductors, generating a switch command; and a command module configured to: control a switch to stop electrical current flow into the one or more broken conductors in response to the switch command.

2. The control system of claim 1 , wherein the harmonic content metric comprises an instantaneous change in harmonic content, and to analyze the instantaneous change in harmonic content, the detection module is configured to compare the difference to an adaptive threshold.

3. The control system of claim 1, wherein to determine whether the electrical system includes one or more broken conductors, the detection module is further configured to determine whether there is a time period of a pre-determined duration during which the load break condition and the load loss condition both exist, and the switch command is only generated if the load break condition and the load loss condition both exist over the time period.Docket No.: 041-354W01 / P24-1421W0014. The control system of claim 3, wherein to determine whether the electrical system includes one or more broken conductors, the detection module is configured to determine whether the load loss condition occurs after the load break condition, and the switch command is only generated if the load break condition and the load loss condition both exist over the time period and the load loss condition occurs after the load break condition.

5. The control system of claim 1, wherein the detection module is configured to: access measurements of an electrical property of the electrical system, and to determine the harmonic content metric based on the measurements.

6. The control system of claim 5, wherein the measurements of the electrical property of the electrical system comprise a time series of measurements of the electrical property; and to determine the harmonic content metric, the detection module is configured to determine a spectral content of the time series.

7. The control system of claim 6, wherein the harmonic content metric comprises a difference between a present value of the harmonic content and an average value of the harmonic content.

8. The control system of claim 6, wherein the measurements of the electrical property of the electrical system comprise a plurality of individual measurements of electrical current, each associated with a different time.

9. The control system of claim 1, wherein the amplitude metric comprises a value of an amplitude of the electrical current, the undercurrent specification comprises threshold value, and the load loss condition exists if the absolute value of the amplitude of the electrical current is less than the threshold value.

10. The control system of claim 1, wherein the amplitude metric comprises a value of an amplitude of the electrical current, the undercurrent specification comprises a range of valuesDocket No.: 041-354W01 / P24-1421W001 that includes zero, and the load loss condition exists if the value of the amplitude of the electrical current is in the range of values.

11. A method of detecting a broken electrical conductor in an overhead electrical power distribution system, the method comprising: determining whether a load break condition exists in the overhead electrical power distribution system based on a change in a harmonic content metric associated with the overhead electrical power distribution system; if a load break condition exists, determining whether a load loss condition exists in the overhead electrical power distribution system based on a comparison between an indication of measured current in the overhead electrical power distribution system and an undercurrent specification; and if the load break condition and the load loss condition exist, detecting a broken electrical conductor in the overhead electrical power distribution system.

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