This invention relates to underground electrical power distribution systems, and particularly to underground electrical power distribution cables having concentric neutral wires surrounding the cable construction.
Underground power distribution cables are used extensively to convey electrical power to diverse locations. Typical power distribution cables are characterized by a central conductor surrounded by one or more concentric neutral wires. In some cases, the concentric neutral (“CN”) wires are helically wound around the central conductor. Such concentric neutral wires provide a phase imbalance current return path, and ensure that the outside surface of the cable insulation is at ground potential. In addition, the concentric neutral wires provide a path to ground for any fault currents that might occur such as for example when the cable is struck by lightning, or when an implement, such as a shovel, accidentally cuts into the cable.
Because concentric neutral wires are wound around the outside of power distribution cables, however, they are particularly vulnerable to corrosion, damage, or other harmful effects of the underground environment in which they reside. Indeed, the integrity of such wires may be impaired by moisture, aging, corrosive chemicals, underground mechanical stresses, or the like. Harmful mechanical stresses may include stresses imposed by pressure, freezing and thawing cycles, abrasive elements, pulling through conduit, damage by underground rodents, or the like.
The relative inaccessibility of the cable once it is placed in the ground can be problematic for monitoring and maintaining the cable and its concentric neutrals. Regulations demand that cables with faulty concentric neutrals be replaced, necessitating regular inspection of the power cable. Traditional methods, however, require that portions of the cable be taken out of service for inspection and maintenance. Accordingly, inspection and testing of underground cables and concentric neutrals often occurs less frequently and with higher costs than desired.
In view of the foregoing, what are needed are apparatus and methods to measure currents flowing in concentric neutral wires without interrupting power service. Further what are needed are apparatus and methods to facilitate quick identification and replacement of cables having faulty concentric-neutral wires. Such apparatus and methods are disclosed and claimed herein.
In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific examples illustrated in the appended drawings. Understanding that these drawings depict only typical examples of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:
a is a side view of a sensing device for detecting a faulty concentric neutral wire in a live power distribution cable in accordance with certain embodiments of the invention;
b is an end view of the sensing device of
a is a side view of an alternative embodiment of a sensing device for detecting a faulty concentric neutral wire in a live power distribution cable in accordance with certain embodiments of the invention;
b is an end view of the sensing device of
a is an exemplary plot of measured output of a sensing device in accordance with embodiments of the present invention with all concentric neutral wires intact;
b is an exemplary plot of measured output of a sensing device in accordance with embodiments of the invention where one concentric neutral wire is corroded, cut or not functioning properly;
a is an exemplary fourier transform of the measured output of a sensing device in accordance with embodiments of the present invention with all concentric neutral wires intact; and
b is an exemplary fourier transform of the measured output of a sensing device in accordance with embodiments of the present invention with one concentric neutral wire not functioning properly.
The invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available methods and apparatus for detecting faulty concentric neutral wires in live power distribution cables. Accordingly, the invention has been developed to provide a novel apparatus and method for detecting a faulty concentric neutral wire to facilitate condition-based replacement of a power distribution cable. The features and advantages of the invention will become more apparent from the following description and appended claims and their equivalents, and also any subsequent claims or amendments presented, or may be learned by practice of the invention as set forth hereinafter.
In one embodiment, an apparatus for detecting a faulty concentric neutral wire in a live power distribution cable may include a housing for sliding along a surface of a power distribution cable, a magnetic sensor, and a motion device. The magnetic sensor may be coupled to the housing and configured to detect a magnetic field produced by each concentric neutral wire as the housing moves along the surface of the cable. The motion device may also be coupled to the housing, and may detect motion of the housing relative to the cable.
In another embodiment, a method for detecting a faulty concentric neutral wire in a live power distribution cable may include locating a live power distribution cable having multiple concentric neutral wires associated therewith. A magnetic sensor may slide along a surface of the cable to sense a magnetic field produced by each of the concentric neutral wires. Motion of the magnetic sensor relative to the live power distribution cable may be detected, and data describing the magnetic field and motion may be transmitted to a destination device.
In yet another embodiment, a system for detecting a faulty concentric neutral wire in a live power distribution cable may include a housing, one or more magnetic sensors, a communication device, and a destination device. The housing may be coupled to a surface of a power distribution cable. The magnetic sensors may be coupled to the housing to detect a magnetic field produced by each concentric neutral wire of the power distribution cable. The communication device may communicate data describing the magnetic field to the destination device. The destination device may then receive and analyze the data to identify abnormalities in the magnetic field characteristic of a faulty concentric neutral wire.
It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of apparatus and methods in accordance with the present invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of certain examples of presently contemplated embodiments in accordance with the invention. The presently described embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.
With reference now to
Multiple concentric neutral wires 110 may be substantially evenly spaced to surround and directly contact the outer semiconductive shield 108. In some embodiments, the concentric neutral wires 110 may include copper or aluminum wires helically wound around the outer semiconductive shield 108. In operation, the concentric neutral wires 110 may be at ground potential to protect against large current that might flow if the cable 100 is struck by lightening or accidentally hit or cut with an implement, such as a shovel. In certain embodiments, a polymeric jacket 112 may be extruded over the concentric neutral wires 110 to further insulate and protect the cable 100. The jacket 112 may be made of, for example, linear low density polyethylene, medium density polyethylene, or semi-conductive polyethylene.
Referring now to
In some embodiments, the housing 202 may include one or more substantially transparent regions to facilitate transmission and receipt of optical signals from devices or components contained within the housing 202, as discussed in more detail below. Further, the housing 202 may include one or more regions that are substantially transparent to radio frequency or other communication signals known to those in the art. In certain embodiments, the housing 202 may be substantially hermetically sealed to protect internal components from moisture and other environmental damage.
Internal components may include, for example, a motion device 208 and a magnetic sensor 206. The motion device 208 may detect motion of the housing 202 relative to the power distribution cable 100. For example, in some embodiments the motion device 208 may include an optical or laser source and an optical detector, such that the detector may detect the laser light reflected from the surface of the cable 100 to track linear motion of the device 208 along the surface of the cable 100. Since the motion device 208 may be contained within the housing 202, the motion detected by the motion device 208 may be attributed to the motion of the housing 202 relative to the cable 100. This motion may be communicated from the motion device 208 to a destination device (not shown) to facilitate processing and identification of a faulty concentric neutral wire 110.
One or more magnetic sensors 206 may also be contained within the housing 202 to sense magnetic fields produced by each of the concentric neutral wires 110 as the housing 202 slides along a surface of the cable 100. As shown in
The magnetic sensors 206 may also detect ambient magnetic fields produced by the center conductor 102 and semiconductors 104, 108. Since the magnitude of these ambient magnetic fields is typically the same along a length of the power distribution cable 100, however, such measurements generally do not affect concentric neutral wire 110 testing. In fact, in some embodiments, as discussed in more detail below, an algorithm (such as a fourier transform) may be applied during later processing to highlight only the magnetic fields produced by the concentric neutral wires 110.
In certain embodiments, the magnetic sensor 206 may be a meso-scale or microfabricated piezoelectromechanical current sensor, such that the magnetic field produced by the concentric neutral wire 110 causes a response of the magnetic sensor 206 that is proportional to the strength of the magnetic field. In other embodiments, the magnetic sensor 206 may employ magnetoresistive effects to measure magnetic field strength along one or more orthogonal axes. Such magnetoresistive effects may include, for example, anisotropic magnetoresistance (“AMR”), giant magnetoresistance (“GMR”), and any other magnetoresistive effects known to those in the art. In other embodiments, the magnetic sensor may employ non-piezoelectric and non-magnetoresistive effects, such as the Hall effect.
In some embodiments, the housing 202 may further house a communication device 210, such as a radio chip, to communicate motion and/or magnetic field data from the sensing device 200 to a destination device (not shown). The communication device 210 may communicate with a destination device over a network such as a wi-fi network, a cellular network, a satellite network, a power-line network or any other suitable network known to those in the art. In certain embodiments, the communication device 210 may include a network interface to communicate with such a network. The network interface may enable a wired or wireless connection between the communication device 210 and the network. If wireless communication is used, the communication device 210 may transmit signals over an antenna 220.
The housing 202 may further include a power source 212 to provide power to any or all of the motion device 208, the magnetic sensor 206, and the communication device 210. In certain embodiments the power source 212 may include a battery, or may scavenge energy emitted by the power distribution cable 100. For example, magnetic fields emitted by the power distribution cable 100 may be converted to electrical energy with a transformer, such as one or more conductive loops, or the like. A microprocessor 218 may be provided to control operation of the sensing device 200.
Referring now to
Referring now to
The distance that the housing 202 must travel in an axial direction 300 to enable the magnetic sensor 206 to encounter each of the concentric neutral wires 110 at least once may be easily ascertained based on the diameter of the wires 110 and the distance between adjacent wires 110. Generally, the distance required for a single magnetic sensor 206 to sense each concentric neutral wire 110 may be about a foot and a half. As a result, embodiments of the invention may enable a user to quickly and easily test the power distribution cable 100 to determine the functionality of concentric neutral wires. Advantageously, this testing may occur 110 without disrupting power service. In addition, embodiments of the invention may require temporary access to only one end of the power distribution cable 100, such as that contained within a cable vault, to identify a faulty concentric neutral wire 110. As a result, the condition of the power distribution cable 100 may be easily assessed while avoiding the usual problem of power distribution cable 100 inaccessibility.
Referring now to
One or more magnetic sensors 206 may be integrated into or coupled to the collar 400 along its length to substantially align with one or more concentric neutral wires 110 in a power distribution cable 100. Particularly, as shown in
In certain embodiments, the collar 400 may be substantially fixed with respect to the power distribution cable 100, such that magnetic fields produced by each of the concentric neutral wires 110 may be monitored over an extended period of time. A microprocessor (not shown) may be provided to control operation of the magnetic sensors 206 and sensing device 200.
In other embodiments, the collar 400 may be removably attached to the power distribution cable 100 to obtain magnetic field measurements from each of the concentric neutral wires 110 at specific, discrete times, or as needed. For example, as shown in
In such embodiments, a motion device (not shown) coupled to the housing or collar 400 may detect motion of the collar 400 relative to the power distribution cable 100. The motion device may include, for example, an optical motion detector, a mechanical motion device, a resistive potentiometer, or other suitable position tracking or motion device known to those in the art.
A communication device (not shown) may also be coupled to the housing or collar 400 to communicate data describing the magnetic fields produced by the concentric neutral wires 110 and/or motion of the collar 400 relative to the power distribution cable 100. The communication device may enable communication between the sensing device 200 and a destination device over a network. The network may include, for example, a wi-fi network, a cellular network, a satellite network, a power-line network or any other suitable network known to those in the art.
A power source (not shown) may be coupled to the housing or collar 400 to provide energy for the magnetic sensors 206, motion device, and/or communication device. The power source may include a battery, a device to scavenge energy from the magnetic or electric fields produced by the cable 100, or any other suitable power source known to those in the art.
Referring now to
Specifically, as shown in
In embodiments having multiple magnetic sensors 206, where each magnetic sensor 206 corresponds to a single concentric neutral wire 110, rotating the collar 400 around the power distribution cable 100 may facilitate alignment between each magnetic sensor 206 and a corresponding concentric neutral wire 110, thereby promoting the sensing capability of each sensor 206. In other embodiments having fewer magnetic sensors 206 than concentric neutral wires 110, rotating the collar 400 around the circumference of the power distribution cable 100 may ensure that the magnetic fields produced by each of the concentric neutral wires 110 are sensed at least once.
Referring now to
Data describing the magnetic field sensed may be communicated from the sensing device 200 to a remote destination device 602 by way of a communication device 210 associated with the sensing device 200. In some embodiments, the communication device 210 may be contained within the housing 202, or attached to the housing 202. The communication device 210 may include a radio chip, cable, antenna or the like to communicate radio frequency, wi-fi, power-line or other types of signals to the destination device 602. The destination device 602 may receive and analyze the data to identify abnormalities in the magnetic fields that may indicate a faulty concentric neutral wire 110.
In some embodiments, the sensing device 200 may further include a motion device (not shown) to detect motion of the device 200 relative to the power distribution cable 100. As discussed in more detail above with reference to
As shown in
In one embodiment, the sensing device 200 is substantially permanently attached to the underground power distribution cable 100 to monitor the integrity of the concentric neutral wires 110 over time. The communication device 210 may automatically and/or periodically relay the sensed magnetic fields to a destination device 602 for analysis. In some embodiments, the destination device 602 may similarly relay signals to the sensing device 200 to prompt a reading of the magnetic fields produced by the concentric neutral wires 110.
The destination device 602 may include, for example, a remotely located computer or processing system, a laptop computer, a cell phone, a smart phone, or the like. In some embodiments, the destination device 602 may store measured data from successive sensing operations to monitor progressive degradation of concentric neutral wires 110.
Monitoring concentric neutral wires 110 in this manner may facilitate regular testing and frequent analysis of test results, thereby enabling prompt identification and replacement of a power distribution cable 100 having one or more faulty concentric neutral wires 110. Advantageously, in some embodiments, such monitoring and analysis may occur without requiring repeated human access to and contact with an underground power distribution cable 100 for testing purposes.
a and 7b illustrate examples of data that may be obtained from the sensing device 200 and transmitted to a destination device 602 for analysis.
As shown, the magnetic fields produced by the concentric neutral wires 110 and measured by the sensing device 616 may include a radial component, a circumferential component, and an axial component owing to the helical configuration of the concentric neutral wires 110 around the power distribution cable 100. The magnitude of each of these components may be measured and analyzed with respect to an axial distance the sensing device 200 has traveled along a surface of the power distribution cable 100. Since properly functioning concentric neutral wires 110 are expected to demonstrate similar measurements for similar components, a non-functioning or deteriorating concentric neutral wire 110 may be easily identified by comparison.
For example, as shown in
In some embodiments, a human operator may perform such a comparison to identify a faulty concentric neutral wire 110. In other embodiments, a comparative analysis may be performed automatically or semi-automatically by a processor or destination device 602, as discussed in more detail below.
Referring now to
For example, in one embodiment, the destination device 602 or other processor may apply a fourier transform or other algorithm to the data received from the sensing device 200.
b, on the other hand, depicts an exemplary plot of signal strength and spatial frequency where a defined spike 800 in the data is preceded by a smaller, asymmetric peak 802. This asymmetric peak 802 is clearly distinct from the expected single spike 800 shape. Because of this obvious visual disparity, even an amateur user would likely be alerted to an abnormal reading from the sensing device 200.
Indeed, as shown in
The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described examples are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Number | Date | Country | |
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61351758 | Jun 2010 | US |