WO2016125028A2

WO2016125028A2 - System for monitoring electrical power transmission line

Info

Publication number: WO2016125028A2
Application number: PCT/IB2016/000394
Authority: WO
Inventors: Vijay Shah; Vivek SIDDHARTH; Hoan Duy Le
Original assignee: Abb Technology Ltd.
Priority date: 2015-02-03
Filing date: 2016-02-03
Publication date: 2016-08-11
Also published as: WO2016125028A8; WO2016125028A3

Abstract

A system for monitoring electrical properties of a power line includes a current sensor with a gapped core and a conductive winding, The system further includes output control circuitry coupled with the current sensor, and including voltage leads configured to provide an output voltage indicative of electrical current through the power line, to an intelligent electronic device (IED). A gas discharge tube is connected to winding leads of the conductive winding and to the output control eirciritry, and activated in response to real or simulated short circuit conditions, to protect the output control circuitry. Related methodology is disclosed.

Description

SYSTEM FOR MONITORING ELECTRICAL POWER TRANSMISSION LINE

TECHNICAL FIELD

[0001] The present disclosure relates generally to monitoring electrical properties of an electrical power transmission line, and more particularly to protecting components of a line monitoring system, from an overvoltage condition, such as a short circuit, via a gas discharge iube (GDT).

BACKGROUND

[0002] Technology for monitorin and control of .electrical power systems, notably electrical power distribution systems, has been of interest for many years. Meeting the demand tor electrical power from customers, system robustness and, particularly in recent years, •efficiency, can all depend on the ability to accurately determine conditions in different parts of an electrical power distribution System essentiall in real time, Certain events can rapidly change local conditions in a power grid, for instance short circuits occurring, in the field. It is well known -that a fallen tree limb, for example, can create a short circuit resulting in a large and rapid rise in electrical current through part^" of a power distribution system. Lightning strikes, power .source switching, and. other events are well known to have often unpredictable and typically undesirable effects on system - peration. If unchecked, such perturbations can damage parts, of an electrical power distribution sy stem, and particularly relatively sensitive m nitoring and control electronics. Interest therefore remains high in improving monitoring instruments and technology in such systems, and increasing resilience. SUMMARY

[0003] In one aspect, a system for monitoring an electrical property of an electrical power transmission line includes a current sensor posiiionabie about the electrical power transmission line, and including a gapped core, and a conductive winding extending about the gapped core so as to inductively couple the current sensor with the electrical power transmission line. The current sensor further includes a first and a second winding lead located at opposite ends of the conductive winding. The system further includes output control circuitry coupled with the current sensor, and including a first and a. second voltage lead, for connecting with an intelligent electronic device (TED), and a plurality of circuit elements structured so as to provide an output voltage across the first and second voltage leads indicative of an electrical current property of the power transmission line. The system further includes a gas discharge tube connected to the first and second, winding leads and to the output control circuitry, such that a voltage across the GDT is dependent upon, an induced voltage in the conductive winding, and the GDT forms an electrical discharge responsive to current spikes in the power transmission line to limit voltage surges to the output control circuitry.

[00041 la another aspect, a mechanism for monitoring an electrical property of an electrical power transmission line includes a current sensor including a gapped core, and a conductive winding extending about the gapped core and having a first winding lead and a second winding lead. The monitoring mechanism further includes a line coupling mechanism structured to inductively couple the current sensor with the power transmission line. The mechanism further includes output control circuitry coupled with the current sensor, and including a first and a second voltage lead, for connecting with an intelligent electronic device (lED), and being structured s© as to provide an output voltage across the first and second voltage leads indicative of an electrical current property of the power transmission line. The mechanism further includes a gas discharge tube (GDT) connected to the first and second winding lead and to the output control circuitry,.

[0005] in still another- aspect, a method of protecting electrical components in a power line monitoring system includes positioning a current sensor having a conductive winding and a gapped core about an electrical power transmission line suc that the conductive winding is inducti vely coupled with the power transmission line, and increasing, electrical, current through the power transmission line, The method further Includes inducing via the increased electrical, current .an increase in voltage across a gas discharge tube (GDT) connected to winding leads of the conductive winding, and activating the GDT in response to the increased voltage. The method still further includes shunting electrical current through an electrical discharge path of the activated GDT^ so as to limit: transmitting voltage pulses to output control circuitry connected to the GDT and .structured to provide an output voltage indicative of electrical current through the power transmission line.

BRIEF DESCRIPTION OF ^"THE DRAWINGS

[0006] FIG. I is a schematic illustration of a system, according to one embodiment;

[0007] FIG. 2 is a circuit diagram schematic of the system of Figure 1 ;

[0008] FIG. 3 is a diagrammatic view, partiall in phantom, of a mechanism, according to one embodiment ;

[0009] FIG. 4 is a partially sectioned side diagrammatic view of the mechanism of Figure^¬ s^'; and

[0010] FIG. 5 is- a -diagrammatic view of short circai t signal characteristics, in an electrical power transmission line.

DETAILED DESCRIPTION OF ILLUSTRATIVE. EMBODIMENTS- [001 1 ] For purposes of promoting, an understanding of the principles of the System For monitoring Electrical Power Transmission Line Having Qvervoltage Protection, reference will now he made to the examples illustrated in the drawings, and specific language will be used, to describe the same, it will nonetheless be understood that no limitation of the scope of the invention is intended by the illustration and description of certain examples of the invention. In addition, any alterations and/or modifications of the illustrated and/or described embodiments) -sire contemplated as being within the scope of the present invention. Further, any other applications of the principles of the invention, as illustrated and/or described herein, as would normally occur to one skilled i the art to which the inventio pertains, are contemplated as being within the scope of the present invention,

[0012} Referring to Figure 1 , there i shown a system. 10 for monitorin electrical properties of an electrical power transmission line 12, such as in an electrical power distribution grid. System 10 includes a current sensor 14 positionab!e about line 10, so as to enable monitoring of an electrical current. roperty such as electrical .current magnitude (Amperes) in line .12, Those skilled in the art will appreciate various reasons wh electrical current, and potentially other properties relating to transmission of -electrical current, are commonly monitored, in certain instances, it is desirable to monitor current to ensure that electrical power is indeed being transmitted, and also to ensure it is being transmitted in an intended manner so that adjustments can. be made if needed. Power sources feeding an electrical power grid are routinely connected, disconnected, or ramped up or ramped down to accommodate changes^' in electrical power demand and to compensate for periods where power generation stations are taken off-line for maintenance, or for a hos of other reasons. Moni toring of electrical current, as well as voltage and other electrical properties relating to current and voltage is used as a way to enable operators to monitor the general state of an electrical power grid, and such monitoring is considered an integral part of modem electrical, power distribution technology. Despite best efforts, there remain instances where impredictable events induce relatively rapid and potentially damaging changes in the magnitude of electrical current a id voltages in a. power transmission, line such as line 12. Since monitoring systems ma include components relatively sensitive to such perturbations, failures of monitoring equipment due to voltage and/or current surges are a relatively common event,

[0013] Each of these types of events has different potential effects on system

components. As will be further apparent .from the following description, system 10 is uniquely configured to protect certain components, in the event of undesired and potentially damaging changes in electrical properties of power line 12, notably those associated with short circuits. While it is contemplated that a principle application of the present disclosure wi 11 he to the high voltage power distribution lines of a public service electrical power grid, it should be appreciated that private institutional power systems and still others may benefit from, application of the materials set forth herein,

[0014] Current sensor 14 includes a gapped core 16, and a conductive winding 20 extending about gapped core 16. Current sensor 14 may also define a gap 1.8 wherein line 12 is received, such that current sensor 14 is inductively coupled with line 12. It can be seen that gap 18 is relatively large, in proportion to the size of the components of current sensor 14, the significance of which will be further apparent from the following description.

[001.5] Current sensor 1 further includes a first winding lead 22 and a second windin lead .24 located at opposite first and second ends 40 and 42 of conductive winding 20. System 10 further includes output control circuitry 26 coupled with current sensor 14, and including a first voltage lead 28 and a second voltage lead 30, for connecting with an intelligent electronic device (FED) 32. Output control circuitry 26 further includes a plurality of circuit elements:, as further discussed herein structured so as to provide an output voltage across first and second voltage leads 28 and 30 which is indicative of an electrical current property such as a magnitude of electrical current in line 12, A signal 36 is shown representing a voltage as might, be observed across leads 22 and 24. Another signal 38, which can be understood as a voltage across leads 28 and 30, is shown as might be interpreted via IED 32.. In a practical implementation strategy, TED 32 could include any of a variety of devices, but will typically include a computer controlled and/or computer operated electronic monitoring mechanism_* typically with a processor and computer readable memory, that receives signal 38 via co tio s with leads 28 and 30, and communicates with other elements of an electrical power distribution system. To this end, IED could be equipped with or connected to transmission equipment that enables wired or wireless communications with a remote server or die like. In any event, it will be appreciated thai a voltage across leads 28 and 30 will typically be proportional to the: current magnitude in line 12, and in one form of a practical implementation strategy may be directly and substantially linearly proportional.

[0016] Surges in current through line 12 can induce surges in voltage in sensor 14, and thus potentially in circuitry 26 and IED 32. Such voltage surges can be sufficient to result in insulation breakdown, damage of components, and potentially failure of system 10 unless some action or hardware to protect against such voltage surges is employed. Those skilled in the art will appreciate that not all voltage surges are the same, and are not experienced the same via eiectrieal circuit components, even where voltage magnitude is identical. In other words, other properties of a voltage surge or impulse such as rise rate, duration, find still other -characteristics can determine whether components will fait

[0017] To protect output circuitry 26, IED 32 and potentially other parts of system 10, a gas discharge tube (GOT) 34 is connected to- first and second winding: leads 22 and 24 and to output control circuitry 26, such that a voltage across GOT 34 is dependent upon an induced voltage in conductive winding 20. GDT 34 forms an electrical discharge- responsive to current spikes in ine 12, to limit voltage surges to output control circuitry 26. Not all current spikes will present the same likelihood of damaging components of system- 10, and therefore GDT 34 is not necessarily activated in response to any particular current- spike in line 1.2 and resultant voltage spike induced in winding 20. Suitable GDT's are commerciall available from Bourns, Inc., or Liltlefuse, for example.

[0018] Referring also now to- Figure 2, there is illustrated a circuit diagram of system 10 shown coupled with line 12, and in particular showing current sensor 14 in non-contact inductive couplin with line 12. Also illustrated in Figure 2 is a voltage sensor 44 including a connecting lead 46 that is in direct contact with line 12. Voltage senso 44 also includes a sensing or monitoring lead 48, and a plurality of in-series cireuii elements structured, to provide an output voltage Vj via monitoring lead 48 that is proportional to a voltage of line 12. The in-series circuit elements may includ a first resistor 52 having relatively high electrical resistance, and suitable voltage rating and power dissipaiion, positioned eleetrically between monitoring lead 48 and connecting lead 46, Sensor 44 may further include a -combination of resistors 54, 56, 58 and 60 in series and having relatively lower resistance, to provide desired ratio of a voltage signal V^'i for the corresponding voltage of line 12 as the primary conductor, and located betwee

monitoring lead 48 and an electrical ground 50. [0019] Also, shown in Figure are a plurality; of circuit elements of output control circuitry 26, including a first resistor 60, a variable resistor 68 to control magnitude of an output, voltag across voltage leads 28 and 30, another resistor 70,. and another variable resistor 72 structured to control phase angle of output voltage V₂. A lurality of capacitors 62, 64, and 66 are provided to provide phase angle shift for voltage V?,. GDT 34 is electrically connected to winding leads 22 and. 24, and. located at entry points to output control circuitry 26. GDT 34 is thus electrically in parallel with conductive winding 20, and also electrically in parallel with each of the circuit elements of output control circuitry 26 that GDT 34 is to protect Positioning GDT 34 as shown has been discovered to provide advantages ove other designs where instead of being positioned at entry point to the circuitry to be protected, a GDT would be positioned elsewhere; however, the present disclosure is. not strictly limited to the Figure 2 embodiment nor to any of the embodiments explicitly discussed herein unless specifically provided to the contrary.

[0020] Referring als now to Figure 3,, ther i shown a mechanism 74 for monitoring an electrical property of an electrieai power transmission line, and including the components of system 10 hut for 1ED 32. Mechanism 74 includes a housing 76, with current sensor 14 and voltage sensor 44 each positioned at least partially within housing 76, Mechanism 74 further includes a connector or port 90 having a plurality of electrical connectors 1 that are structured to connect wit any of a variety of electronic monitoring mechanisms or components, such as an IED, via a cable or the like. Output circuitry 26 is coupled with a printed circuit board or PCB 27, and a second PCB 45 is shown connected: with voltage sensor 44.

[0021 ] Mechanism 74 further includes a line coupling mechanism 78 that includes one or more clamping mechanisms 80, each of which includes: a base 82 and a clamping bar 84 selectively securable to base 82 via a plurality of bolts 86 in the illustrated embodiment. Line coupling mechanism 78 further includes a U-shaped shield 88 which, in conjunction, with, •damping mechanisms 80, forms an open channel 89 that receives an electrical power transmission line for monitoring. The present disclosure is not limited to any particular line coupling mechanism, nor housing configuration., ft is nevertheless contemplated that a design suitable for pole mounting, where housing 76 is positioned upon the top end of a line support pole or the like, provides a practical implementation strategy. In a practical implementation, Some or all of the components of mechanism 78 can be encased withi a resin materi al that cures within a mold.

[0022] Also shown in Figure 3 are certain additional features of curren sensor 14. As noted above, current sensor 14 includes a core 16, Core 16 may include a laminated metal core,- including a plurality of stamped metallic and magnetically permeable layers (not shown). Core 1 may be most magnetically permeable at approximately a specified AC power frequency of the -electrical current through line 12, Core 16 ma further have a generally U-shaped form, including a body 15, and a first limb 17 and. a second limb 1 formed integrally with body 15 to have the general shape of a U, I can be further noted that limbs 17 and 19 are oriented substantially perpendicular to body 15, and substantially parallel to one another. A length of each one of limbs 17 and 19 extending from body 15 to free tips of limbs 17 and 1 9 may be less than, a width of gap 18, Stated another way, gap 18 may have a gap length that is greater than -or equal to lengths of each o -core limbs 17 and .19, It has been discovered that a core having a relatively large gap, such as an air gap as shown, provides a practical implementation strategy, as opposed to closed magnetic cores, o magnetic cores having relatively smaller air gaps. In other embodiments, rather than a U-shape, two I-shaped core pieces might be used,, with a gap separating the core pieces analogous to the gap separating legs of the core as in the illustrated embodiment.

[0023] It can also be seen that conductive winding 20 includes a first coil 21 and a second coil 23. One of the ends of winding 20 is shown via reference numeral 42 in Figure 3. Winding leads 22 and 24, respectively,, connect to opposite end s 40 and 42 of winding 20 as discussed above, it can thus be seen that winding 20 is not continuous about core 16, but instead is comprised of the two separate coils 21 and 23, connected via a part of winding 20 that extends along body 15. It will also be recalled that GDT 34 is connected to winding leads 22 and 24 in a practical implementation strategy at entry points to output control cireuitry 34. Another way to understand this feature is that the electrical connections of GDT 34 to winding 20 are relatively closer to winding 20, as measured along a linear distance of winding leads 22 and 24, tha is output control circuitry 26. If can also be seen that GDT 34 is cormected to a total of one current sensor, and therefore interacts with a total of one core and a total of one winding.

[0024] Referring now to Figure 4, there is shown mechanism 74 as it might appear in a partially sectioned view, and diagrammatic-ally illustrating GDT 34, output control circuitry .26, and certain of the components of mechanism 74 in a sectioned view, it can be seen that housing 76 is formed substantially of one type of a material 92, which, may be a suitable insulating resin matrix material that encases components of system 10. Resin matrix 92 may be structured such that parts of current sensor 20, and potentiall parts or all of clamping mechanism(s) 80 is not encased in resin matri 92. A housing having the form of a shell filled with a matrix, material could be used, as shown, or the housing could consist instead of nothing but the matrix material, having been poured into a mold a d cured, then the mold removed, Suitable resins and curing techniques are known. [0025:] Referring now to Figure 5, there is shown a signal 1 8 representative of a short circuit cufrenl spike that might be experienced b system 10 under the conditions discussed heretn. Signal 1 8 is shown on a graph where the X-axis represents time, and the Y-axis represents current. It can be seen that current resulting from a short circuit has the general form of a symmetrical sine wave with a DC shift. A duration of the short circuit current represented via signal 198 may be about one second, or potentially longer, with the term "about" being understood in the context of conventional numerical rounding. This differs from certain other fault, conditions such a lightning strikes, where the initial rise to maximum voltage of 20-25 kV may occur in 10 microseconds, or less, with the entire duration of the pulse being about 50-70 microseconds, with exponential decay at the end. Standard IEEE€57, 33 defines standard test waves for instrument transformers to be able to withstand without failure, and which may be applied during testing of system 30 or similar systems prior to placing in service, in Figure 5 reference numeral 240 represents the initial value of the DC shift component of signal 1 8. Reference numeral. 230 represents the DC component over time, reference numeral 220 peak short circuit current, and reference numeral 200 represents initial symmetrical short circuit current. A voltage peak shown via reference numeral 210 may be approximately 2765 volts at peak 210, or 1956 V_rms. Voltage at the posi tive: current peak 280 towards the end of signal 1 8 ma be approximatel 1024 V_fOTS or 1448 V_mk. Normal current profile which returns following the short circuit current, such as might be observed under test conditions, is shown via reference numeral 270»

[0026] From the foregoing description it will fee readily apparent that components in system 10 and components coupled with system 10 can be protected from an overvoltage condition arising from a short circuit via GOT 34, and then normal operation restored once the phenomenon giving rise to the overvoltage condition passes. System 10 achieves this aim without the use of expensi ve and bulky high, voltage-tolerant components. As such, many systems now lacking overvoltage protection can be advantageously retrofitted with systems according to the present disclosure. Retrofitting an existing system, or building a new system according to the present disclosure may include positioning a current sensor such as current sensor 14 about an electrical power transmission line such that conductive winding 20 is inductively coupled with the line, and without interrupting electrical current flow through the line. The open, gapped design of core 16 facilitates such coupling. An iED such as IED 32 coupled with current sensor 14 -can thus commence monitoring both current via sensor 15 and voltage i sensor 44 immediately.

[0027] During such monitoring, current spikes of varying nature will inevitably occur.

Certain current spikes may induce voltage pulses in winding 20 that have properties of magnitude or duration, for instance, that are insufficient to trigger activation of GDT 34. Since thermal stress resul ting in damage to components, of circuitry 26 or IED 32 typically requires some time to occur, even where transmitted to circuitry 26 such, voltage pulses tend not to be problematic. When electrical current of sufficient magnitude and duration does occur, then an increase in voltage across GDT 34 sufficient to activate the same will result in formati on of an electrical discharge through GDT 34 that shunts electrical current and clamps voltage at a relatively low level so as to limit voltage pulses to output control circuitry 26,

[0028] in a practical implementation strategy, system 10 may be tested, or a type test eonducted for an example system substantiall identical to system 10, where electrical current is controliably increased under test conditions so as to simulate a short circuit in a power distribution grid that includes a power line with which sensor 14 is coupled. Such a test might be one type of specified short circuit condition test to which system 10 is subjected, with electrical current through the powe line increased to a predefined magnitude and in a predefined way similar to that depicted via Figure 5, and for a relatively longer time duration such as about 1 second to about 3 seconds. In other tests electrical current could be eontrollably Increased for a relatively shorter time duration so as to simulate other conditions, A voltage pulse generated in such other tests might be transmitted to output circuitr 26 without activating GDT 34. As can be expected, overvoltage tests such a short circuit condition tests, lightning strike or switching simulations, or still others will generally represent expected service conditions as specified by applicable standards.

[0029] The present description is for illustrative purposes- onl and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications, might be made to the presently disclosed embodiments without departing from the full and fai scope and spirit of the present disclosure. Othe aspects, features and advantages will be apparent upon an. examinatio of the attached drawings and appended claims.

Claims

CLAIMS What is Claimed is :

1. A system for monitoring .an electrical property of an electrical power transmission line comprising:

a current sensor positionable about the electrical power transmission line, and ine.ln.ding a gapped core, and a conductive winding extending about the gapped core so as to inductively couple the- current sensor with the electrical power transmission line, and the current sensor further includin a first and a second winding lead located at opposite ends of the conductive winding;

output control circuitry coupled with the current sensor, and mc.lud.iiig a first and a second voltage lead, for connecting with an intelligent electronic device (IE0), and plurality of circuit elements, and the output control circuitry being structured so as to provide an output voltage across the first and second voltage leads indicative of an electrical current property of the electrical power transmission line:; and

a gas discharge tube (GDT) connected to the first and second winding leads and to the output control circuitry, such that a voltage across the GDT is dependent upon a induced voltage in the conductive winding, and the GDT forms an electrical discharge responsive to current in the power transmissio line to limit voltage surges to the output control circuitry,

2. The system of claim 1 wherein the GDT is connected to the first and second winding leads at locations .electrically between the output control circuitry and the conductive winding.

3. The system of claim 1 wherein the plurality of circuit elements includes magnitude and phase correction circuit elements.

4. The system of claim 3 further comprising a voltage sensor having a connecting lead for directly connecting to the power transmission line, a monitoring lead, and a plurality of in-series resistors structured to provide an output voltage via the monitoring lead that is proportional to a voltage of the power transmission li e:.

5. The system of claim 1 wherein the gapped core includes a first core limb and a second core limb, and defines a gap extending between the first and second core limbs and having a gap length equal to or greater than lengths of the first and second core limbs,

6. The system of claim 5 wherein the conductive winding includes a first coil extending about the first core limb, and a second coil extending about the second core limb, and the first and second core limbs being substantially parallel.

7. A mechanism for monitoring an electrical property of an electrical power transmission line comprising:

a. curren sensor including a gapped core, and a conductive winding extending about the gapped core and having a first winding lead and a second winding lead;

a line coupling mechanism structured to inductively couple the current sensor with the power transmission line;

output control circuitr coupled with the current sensor, and including a first and a second voltage lead, for connecting with an intelligent electronic device (iED), and being structured so as to provide an output voltage across the first and second voltage leads indicative of an electrical current property of the power transmissio line; and

a gas discharge tube (GDT) connected to the first and second winding leads and to the output control circuitry.

8. The mechanism of claim 7 further comprising, a resin matrix, and. the current sensor being at least partially encased by the resin matrix, and the line coupling mechanism including a clamping element not encased by the resin matrix.

9, The mechanism of claim 7 wherein the output control circuitry includes magnitude and phase correction circuit elements.

10, The mechanism, of claim 7 wherein the gapped core includes a first core limb and a second core limb, and defines a gap extending between the first and second core limbs and having a gap length equal to or greate than lengths of the first and second core limbs.

1 1 , The mechanism of claim_. 7 including a total of one gapped core, and a total of one conductive winding.

12, The mechanism of claim 7 further comprising a voltage sensor at least partially within the housing.

13, A method of protecting electrical components in a power line monitoring system comprising:

positioning -a. current sensor having a. conductive winding and a gapped core about an electrical power transmission line such that the conductive winding is inductivel coupled with the power transmission line;

increasing electrical current through the power transmission line; inducing via the increased electrical current an, increase In voltage across a gas discharge tube (GOT) connected to winding leads of the conductive winding;

activating the GDT in response to the increased voltage; and

shunting electrical current through an electrical discharge path of the activated GDT,. so as to limi transmitting voltage pulses to output control circuitry connected to the GDT and structured to provide an output voltage indicative of electrical current through the power transmission line,

14, The method of claim 13 wherein, increasing electrical current furthe includes control lably increasing the electrical current for a time duration in an over- voltage test so as to simulate a short circuit in a power distribution grid that includes the power transmission line.

15. The method of claim 14 wherein positioning further includes positioning a current sensor having two coils in the conductive winding each extending about the gapped core, and such that the power transmission line is received in a gap extending between the two coils,

16. The method, of claim 14 wherein inducing, the increased voltage includes inducing the increased voltage via electrical connections to the GDT at locations electrically between the conductive winding and tlie output control circuitry.