CA1065016A - Sensing electrical parameters inside conductors - Google Patents
Sensing electrical parameters inside conductorsInfo
- Publication number
- CA1065016A CA1065016A CA315,586A CA315586A CA1065016A CA 1065016 A CA1065016 A CA 1065016A CA 315586 A CA315586 A CA 315586A CA 1065016 A CA1065016 A CA 1065016A
- Authority
- CA
- Canada
- Prior art keywords
- conductor
- voltage
- current
- hollow
- temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/142—Arrangements for simultaneous measurements of several parameters employing techniques covered by groups G01R15/14 - G01R15/26
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/58—Testing of lines, cables or conductors
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Current Or Voltage (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Parameters associated with a bus, which may be either an unshielded hollow conductor or a shielded hollow conductor, may be difficult to determine when the bus is carrying large currents at high voltages. An indicator carrying a display is mounted internally to be visible through a window and thereby avoid conductors running from a high voltage region to an external place. Thus tempera-ture of the bus can be determined within the hollow conduc-tor and can be used to activate a display adjacent an opening or window in the conductor. The display may be powered by a power supply mounted within the hollow conduc-tor with the power supply deriving a voltage from longitu-dinally spaced points on the inner surface of the hollow conductor. The current in the hollow conductor may be determined by measuring the IR drop between spaced points on the inner surface of the conductor, measuring the operating temperature of the conductor, determining the resistance from the measured temperature and the temperature/
resistance characteristic, and using the resistance and IR
drop to determine current. Similarly the IX drop can be determined by using a loop enclosing a longitudinally extending portion of the hollow conductor, and this in turn can be used to determine reactance if the current is known.
Parameters associated with a bus, which may be either an unshielded hollow conductor or a shielded hollow conductor, may be difficult to determine when the bus is carrying large currents at high voltages. An indicator carrying a display is mounted internally to be visible through a window and thereby avoid conductors running from a high voltage region to an external place. Thus tempera-ture of the bus can be determined within the hollow conduc-tor and can be used to activate a display adjacent an opening or window in the conductor. The display may be powered by a power supply mounted within the hollow conduc-tor with the power supply deriving a voltage from longitu-dinally spaced points on the inner surface of the hollow conductor. The current in the hollow conductor may be determined by measuring the IR drop between spaced points on the inner surface of the conductor, measuring the operating temperature of the conductor, determining the resistance from the measured temperature and the temperature/
resistance characteristic, and using the resistance and IR
drop to determine current. Similarly the IX drop can be determined by using a loop enclosing a longitudinally extending portion of the hollow conductor, and this in turn can be used to determine reactance if the current is known.
Description
Case 2397 10~0~
This application is a division of Canadian Patent Application Serial No. 247 145 filed March 4, 1976.
This invention relates to the determination of electrical parameters and other parameters in an electrical bus.
For the purpose of this description, electrical bus may be considered to include a hollow conductor or bus which is not shielded along its length and a metal enclosed bus having a hollow central conductor and a surrounding metal enclosure. The central conductor is supported within the metal enclosure by insulators. It is usual to operate the unshielded bus at lower potentials to carry currents of a large magnitude. For example, an unshielded bus might operate at a potential of perhaps 1000 to 5000 volts and could carry currents of the order of a few thousand amperes.
It is usual to use metal enclosed bus at higher potentials where the metal enclosure is grounded and offers protection for the central conductor. For example, a metal enclosed bus might operate at a higher voltage, perhaps of the order of 20 kilovolts (kV) to 230 kV or higher and may carry currents of 5000 to 50 000 amperes or more.
In recent years with the trend to higher voltage, the metal enclosed bus has seen considerable use for conducting electric current for power transmission and distribution.
It is particularly useful at power generating stations where large amounts of power must be handled. It may contain an insulating gas, particularly at higher voltages. It may have means for circulating a gas within the metal enclosure -~
for cooling purposes when large amounts of power are being handled. The present invention is suitable for determining parameters in such metal enclosed bus, although it may also ~, . .
be used to determine parameters in unshielded bus.
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Parameters which may be of interest in the operation or use of an electrical bus include: current I in the bus, the temperature of the bus, the IR drop where R is the resistance of the bus between two longitudinally spaced points. IZ drop where Z is the impedance of the bus between two longitudinally spaced points, (IZ drop has been deter- -mined for bus in the prior art) IX drop where X is the reactance of the bus between two longitudinally spaced points, and the parameters R, X and Z themselves. No simple means has been devised in the past to determine some of these parameters with a desired accuracy. While values for IZ drop have been determined in the past, it has in itself not been of great practical value. There have been a number of attempts made to determine current and to determine temperature and perhaps other parameters. It is, however, quite difficult to determine parameters in a region of high voltage stress and to conduct the signal representing the parameter from that region. Not only do the high voltages cause problems, but the large currents ~
cause heating and create magnetic fields which can inter- ~ ~ -fere with a determination of various parameters.
For example, it is quite common to obtain a tempera- ~ -ture indication on a metal enclosed bus by affixing tempera-ture sensitive patches to the outer surface of the central conductor where the patches are visible from inspection windows. The patches change colour at specific temperatures. ;
This provides a very cheap way of determining if a specific temperature is exceeded. It is however unsatisfactory in that each patch provides an indication of one temperature only. -For another example, it is known in an unshielded bus to have a current transformer surrounding the bus and .- - :, . .
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Case 2397 ~S016 insulated therefrom to obtain an indication of current.
Such current transformers are expensive and bulky and are inconvenient to use, particularly when high voltages are involved and the leads must be run from a high voltage region to a remote region. This type of arrangement has also been used with metal enclosed bus to obtain a current reading. The current transformer is in this arrangement mounted on an insulating bushing surrounding the central conductor and within the metal enclosure. The secondary leads from the current transformer were usually passed to the outside of the metal enclosure through a ring arrange-ment. Metal enclosed bus is usually designed for higher voltages and the voltage gradient between the central conductor and the metal enclosure is usually large. A
current transformer is normally operated at ground potential and it is difficult to prevent flashover and corona problems when a relatively bulky transformer at ground potential is inserted into a bus where there is a large voltage gradient.
In addition, as the bus and enclosure are normally welded together when installed, it is difficult to inspect or repair such a current transformer.
Another prior art arrangement avoids the problem of having a current cransformer within the metal enclosure of a metal enclosed bus. In this arrangement a gap is provided in the metal enclosure and the gap contains in-sulation. A conductor member capable of carrying large currents joins the adjacent ends of the metal enclosure ~ -extending externally over the insulation to form a small loop. A current transformer is positioned over this loop which carries the current in the enclosure of a phase in the system. This current is substantially equal and opposite to the current in the central conductor and con-Case 2397 10~5016 sequently gives a representation of the current in the central conductor. However this arrangement requires a break or gap in the metal enclosure wherever a current reading is desired and this break must not only contain insulation but must be sealed in cases where insulating gap is contained within the metal enclosure. In addition, the metal enclosure may be subjected to fluctuations of current from stray fields originating externally where the central conductor would be shielded from such fluctuations.
Also, arrangements of this nature are relatively expensive.
It is, of course, desirable to obtain a reading of current in a bus as accurately and as economically as possible. Because of the large currents normally handled, small percentage errors can involve considerable amounts of power. It is also desirable to measure or determine the IR drop in a bus during operation so that the resis-tive losses will be known. There have been a number of ways proposed to do this, but none appear to have had the desired accuracy or simplicity. Similarly, it is desirable ~ -to know the IX drop to have a complete understanding of the system, and it appears there have been no prior art arrange-ments which give the desired accuracy and simplicity.
In addition it is desirable to know temperatures at various places on a bus. For example, in an unshielded bus it may be desirable to know the temperature of the bus itself. In a metal enclosed bus it may be desirable to know the temperature not only of the bus or central conduc-tor but perhaps within the central conductor or adjacent the central conductor. It is difficult to determine temperature because the temperature sensitive elements normally provide output voltages as signals which represent temperature. These voltages are many orders smaller than the voltage gradient .
- . .
ase 2397 S0~6 surrounding the central conductor . Small extraneous voltages might be picked up by the wires and affect the accuxacy of the temperature indication. Also, the wires which carry the signals from the sensor would normally be at ground poten-tial. It is not desirable to have wires at ground potential extending through a large voltage gradient. Various ways have been proposed to overcome these problems, for example by using a high frequency carrier signal to carry the temperature signal as a modulation of the carrier. None of these have been completely satisfactory.
It has been discovered that an accurate determination can be made of various parameters of an operating bus by making these determinations in a specific manner and by making the determined values available externally without causing deterioration of the accuracy.
It has been found that by obtaining a voltage reading from longitudinally spaced points within an unshielded bus or within the central conductor of a metal enclosed bus, an accurate determination can be made of IR drop, where R is the resistance of the conductor between the points of measurement. It has been found that by obtaining a voltage reading from a loop extending within the conductor of an unshielded bus or within the central conductor of a metal enclosed bus for a predetermined length, then brought outside the conductor and extended to form the loop, an accurate determination can be made at a break in the loop for the IX
drop where X is the reactance of the portion within the loop. ~;
In an unshielded bus operating at lower voltages it may be feasible to bring the signals representing the parameter externally on a twisted pair of wires without degrading the accuracy. In a metal enclosed bus, in accordance with the invention, values determined within , , - : . .
Case 2397 , - ~ , 50~6 the metal enclosure are made available externally by provi-ding a power supply and a visual display. For example,for values such as IR drop, temperature, or current determined within the central conductor, a display is positioned within the central conductor to be visible through aligned openings in the central conductor and enclosure. The opening in the central conductor is preferably covered with a Farraday screen and the opening in the metal enclosure is sealed with a transparent window. A power supply provides power to operate the display, and if required may also provide power to the temperature sensor or other sensor. In a preferred form the power supply obtains its energizing voltage from a voltage drop between longitudinally spaced points on the inside of the central conductor using leads extending within the conductor to the longitudinally spaced points. A power supply could be energized by IX drop or IZ drop but, while the voltages might be greater, this is not preferred.
Transients are generally reactive in nature and related to frequency and would appear in a voltage for energizing or powering a power supply from IX or IZ drop. It is therefore preferred to power the supply using IR drop which is sub-stantially free of transients. It is also possible to have a supply using batteries. In low voltage systems only, an external or remote power supply is feasihle.
Similarly, for determining IX drop, the voltage drop is normally determined adjacent the outer surface and the display would also be adjacent the outer surface. It will be apparent that the loop could be broken within the conductor and the display would then be within the conductor also. Placing the display within the conductor would, of course, avoid problems which might occur with a display in the high voltage gradient outside. If a power supply is used s Case 2397 ,.
10~01~
to power the display, it is desirable to have the supply inside the hollow conductor whether the display is outside or inside. The supply can thus be energized by IR drop.
The temperature may be determined by using a tem-perature sensitive element or temperature sensor affixed to the main conductor or other place where a temperature determination is required. For example, the temperature sensor could be fixed to this inner surface of the hollow main bus or conductor. A display means, and a power supply to provide power for the display means, are within the conductor so that the display on the display means can be seen through a window or opening in the conductor. The power supply may be as previously mentioned, energized by the IR drop between spaced points on the conductor. The temperature sensor actuates the display to provide an indication of temperature.
The invention also includes a determination of parameters related to the metal enclosure of a metal enclosed bus. The same arrangement will provide a determi-nation of IR drop, and IX drop and knowing R or X, the currentmay be determined. The IR drop is determined using longi-tudinally spaced points within the metal enclosure, and the IX drop is determined using a loop extending internally and externally of a portion of the metal enclosure.
If desired IZ drop may also be determined as is known in the prior art by using longitudinally spaced points on the metal enclosure, externally of the enclosure.
Thus, according to one form of the invention there is provided a method for determining the IR drop in a -~
hollow conductor for carrying a large current where I is the current in the hollow conductor and R is the resistance in the hollow conductor between a first and a second point '' ' .::
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Case 2397 01~;
spaced longitudinally on the conductor, comprising obtaining a voltage representation internally of said hollow conductor between first and second terminal points within said conduc-tor on the inner surface thereof corresponding to said first and second points respectively, displaying the voltage representation obtained on a display means within said conductor, said display being a determination of IR drop, and providing opening means to make the display visible externally.
According to another form of the invention there is provided a method for determining temperature of a hollow conductor for carrying a large current, comprising placing a temperature sensor on the surface of said hollow conductor, connecting said temperature sensor with a display means adjacent said hollow conductor to display a representation of temperature determined, and making said display visible at a region removed from said hollow conductor.
According to another form of the invention there is provided a method for determining current I in a hollow conductor for carrying a large current, comprising, obtain-ing a voltage representation V internally of said hollow conductor between a first and a second terminal point on the inner surface of said hollow conductor, obtaining an indication of temperature from a temperature sensor mounted on the inner surface of the wall of said hollow conductor, determining the resistance R of said hollow conductor from the temperature resistance relationship for said hollow conductor and the temperature from the sensor, for that portion of the hollow conductor between said first and second terminal points, determining the current I from the .:
voltage representation V where V = I R, and displaying the determined value for the current I.
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According to another form of the invention there is provided apparatus for determining the IR drop in a hollow conductor for carrying a large current, where I is the current in the hollow conductor and R is the resistance of the hollow conductor between a first and a second point spaced longitudinally on said hollow conductor, comprising display means mounted within said hollow conductor to the wall of said hollow conductor, said hollow conductor having an opening in said wall, the edges of said opening defining a viewing opening for viewing the display means externally of said hollow conductor, a voltage detector means mounted within said hollow conductor, first and second terminal points on the inner surface of said wall of said hollow conductor at said first and second points respectively, input conductors extending within said hollow conductor and connecting each of said first and second terminal points to said voltage detector means to provide at said voltage detector means a voltage representative of IR drop between said first and second points, said voltage detector means providing a voltage signal representative of said IR drop between said first and second points, and means connecting said voltage detector means and said display means to apply said voltage signal to said display means and actuate said display means responsive thereto to display an indication :~
of IR drop.
According to another form of the invention there is provided apparatus for determining the current I in a hollow conductor having a wall for carrying a large current, said wall having a viewing opening therethrough, comprising a voltage detector means mounted within said hollow conductor, -~
first and second terminal points on the inner surfac~ of said wall forming said hollow conductor spaced longitudinally _ g _ - . . . :.: . .
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Case 2397 ~0~01~
on said conductor, input conductors extending within said hollow conductor connecting said first and second terminal points to said voltage detector to provide a voltage at said voltage detector representing the IR drop between said first and second terminal points, where R is the resistance of said hollow conductor between said first and second terminal points, said voltage between means providing a voltage signal representing said IR drop, a temperature sensor mounted within said hollow conductor to the wall of said hollow conductor to obtain a signal representing the temperature of said hollow conductor, means connecting said voltage sensor to said voltage detector to apply thereto said signal representing the temperature of said conductor, means in said voltage detector means responsive to said temperature signal to provide a signal representing resistance R based on the temperature/resistance relation-ship of said hollow conductor current determining means connected to said voltage detector means to receive said signal representing resistance R and said voltage signal representing said IR drop and providing a signal represen-ting current I, and display means connected to said current determining means for receiving said signal representing current I and responsive thereto to display an indication of said current I, said display means being mounted within said hollow conductor adjacent said opening whereby said display is visible through said opening.
The invention will be described with reference to the accompanying drawings, in which Figure 1, lA and lB are simplified sectional drawings of a portion of an unshielded bus indicating various measurement arrangements, a portion of a metal enclosed bus indicating various arrangements for determining parameters Case 2397 , ~06~~
for the central conductor, and a portion of the metal enclosure of a metal enclosed bus indicating various arrange-ments for determining parameters for the metal enclosure, useful in describing the basic concept of the invention;
Figure 2 is a simplified sectional drawing, partly in block form, showing a portion of a metal enclosed bus with a power supply and a display;
Figure 3 is a simplified sectional drawing, partly in block form, of a metal enclosed bus having apparatus suitable for determining current in the central conductor;
Figure 4 is a simplified sectional drawing, partly in block form, of a metal enclosed bus suitable for deter-mining IX drop in a conductor, and Figure 5 is a schematic circuit diagram of a power supply suitable for use with the invention.
Referring to Figure 1 there is shown a small portion of a bus lOa or hollow conductor lOa which carries a current.
The bus lOa is supported by insulators (not shown). Assuming - ~;
a current is flowing in conductor lOa, there will be a voltage drop which depends on the magnitude of the current and the resistance or impedance involved as is well known in the art. It has been found that by using two terminal points 14 and 15 on the inside of conductor lOa and connec-ting a voltmeter 16 to these terminal points, using conduc-tors 17 and 18 for the connection, that a voltage Vl is obtained where V1 = IR and where I is the current flowing in the conductor lOa and R is the resistance between points -14 and 15. It should be noted that voltmeter 16, conductors 17 and 18, and points 14 and 15 are all within the conductor lOa.
Also, by using a loop formed with conductor 25 extending within conductor lOa and then extending externally , . , : ~ ., .' ` :. ' ,' : ~
Case 2397 ~06~Vl~
as shown, to connect to a voltmeter 26, a voltage V3 can be obtained. The voltage V3 is equal to IX where I is the current flowing in conductor lOa and X is the reactance in that portion enclosed by the loop. The voltmeter 26 may be anywhere in the loop, that is it may be within conductor lOa or externally as shown.
In practice it is desirable to keep equipment or devices within the hollow conductor. This is particularly desirable when the voltage is high. If a piece of equipment, such as a voltmeter or display, is mounted externally it may be affected by the high voltage gradient and also, it may disrupt or interfere with the dielectric effect of the surrounding space.
Also, as is known in the prior art, it is possible to determine IZ. The manner of doing so is included here for completeness. By using two terminal points 20 and 21 on the outer surface of conductor lOa, and connecting a voltmeter 22 to these terminal points using conductors 23 and 24, a voltage V2 is obtained where V2 = IZ and where I
is the current in the conductor lOa and Z is the impedance between terminal points 20 and 21.
Referring now to Figure lA, there is shown a metal enclosed bus arrangement. A hollow central conductor lO
is surrounded by a metal enclosure 11. The enclosure 11 is normally at ground potential and the central conductor lO is supported within enclosure 11 by insulators (not shown). Similar arrangements are shown for obtaining Vl, V2, and V3.
Referring to Figure lB, there is shown a metal enclosed bus with hollow central conductor lO and metal enclosure ll. The structure is the same as that for Figure lA. However in Figure lB it is desired to know Case 2397 . ~
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parameters relating to the metal enclosure. Voltmeter 16a is connected to terminal points 27 and 27a to give voltage reading Vl representing the IR drop in the metal enclosure 11 between points 27 and 27a. Voltmeter 26a is connected in the loop formed by conductor 29 to give voltage V3 repregen-ting the IX drop in the portion of metal enclosure 11 included in the loop.
Also, to complete the description, and voltmeter 22a is connected to terminal points 28 and 28a to give voltage reading V2 representing IZ drop in the metal enclosure 11 between points 28 and 28a.
It will be seen that it is possible to determine resistance, impedance and reactance. If resistance is known, for example, it would be possible to obtain a determination of current from the IR drop. The resistance of conductor 10 changes with temperature. If the temperature could be determined, the voltage Vl (i.e. the IR drop) could be corrected to obtain current. For this reason it is important to know temperature. It is also important to know tempera-ture to ensure operating limits are not exceeded.
As was previously mentioned, it is difficult toobtain temperature readings because the temperature sensor gives small output signals when compared to the voltages on the main conductor or bus. It is difficult to conduct the small voltage signals externally of the high voltage system.
It might be possible to use a battery powered amplifier within the central conductor to amplify signals before conducting them to an outside point. However this would involve problems with battery replacement and would not avoid the difficulties in having wires extending from a region of high potential to a region of low potential. To overcome these problems and difficulties, the present invention ., -Case 2397 ~Ot;~O~t~
provides a power supply which may be mounted within the main conductor, or outside the main conductor and closely adja-cent, energized by the IR drop along the main conductor, and a display visible externally.
Referring to Figure 2, the central conductor 10 has an opening 30 covered by a metal screen 31. The screen 31 does not significantly impede vision but it prevents or inhibits abnormalities in voltage gradient that would otherwise be caused by opening 30. The metal screen is of a type referred to as a "Farraday screen". In a preferred form the screen 31 is a double screen. Opposite the window or opening 30 and aligned therewith is an opening 32 in metal enclosure 11. The opening 32 is covered with a transparent material such as a glass window 33. There is thus a path of vision from outside metal enclosure 11 through window 33 and screen 31 to the interior of central conductor 10.
Mounted within central conductor 10, adjacent opening 30 is a display device 34. The display device 34 may provide a meter type display, but preferably it is a digital display using lighted segmental digits or a binary light display.
A binary light display may, for example, have five separate ~ -lights whose on/off condition forms the binary number. The visual display may be picked up externally of the metal enclosure by an optical device and transmitted optically to a remote location or transformed again to an electrical signal and transmitted to a remote location as an electrical signal for use as a record or transformed to a visual display or both.
A power supply 35 has input conductors 36 and 37 connected to terminal points 38 and 39. The IR drop along conductor 10 provides a voltage to power the supply 35.
Casd 2397 )l6 The input voltage provided by conductors 36 and 37 will vary with the current flowing in central conductor 10. One purpose of power supply 35 is to make use of a wide range of input voltages to provide a satisfactory supply voltage to display device 34 and to associated equipment as required.
The power supply 35 may, for example, provide power for a sensor 40. The sensor 40 may be a temperature sensitive element or it may have inputs for voltage.
Referring now to Figure 3, an arrangement is shown that is quite similar to that of Figure 2 but with a pick up for Vl. Terminal points 41 and 42 are connected by conductors 43 and 44 to a voltage device 45 which determines Vl = IR. The sensor 40' detects the temperature of conductor -10. Knowing the temperature/resistance relationship for conductor 10 and obtaining temperature from sensor 40' will ~
enable a determination of resistance to be made by device ;
45. With resistance known and voltage drop measured, the -current can be determined and displayed by device 34. It will be seen that central conductor 10, between points 41 and 42 may be said to act as its own shunt to give a voltage reading proportional to current.
It will be understood that display device 34 could display both the temperature determined by sensor 40' and the voltage Vl determined by device 45. A current determi-nation could then be made externally if desired.
Referring briefly to Figure 4, there is shown a metal enclosed bus with central conductor 10 and metal -enclosure 11. As in Figures 2 and 3 there is a transparent window 33 in an opening 32 in metal enclosure 11. A voltage sensing and display device 46 is positioned opposite the --window opening 32 and adjacent the outer surface of central conductor 10. The sizes in the drawings are, of course, not Case 2397 l~S~
to scale. The sensing and display device 46 is in practice quite small and flat and would not extend away from the surface of conductor 10 by more than one or two centimetres where the spacing between the central conductor and the metal enclosure 11 might be 20 or more times as large.
Conductor 47 extends from device 46 to opening 50, through opening 50, inside the hollow conductor to opening 51, then back to device 46 to complete the loop. Conductor 47 is kept as close as possible to the outer surface of conductor lO. The voltage picked up by the loop formed by conductor 47 is voltage V3 = IX. This may be displayed by device 46. The simplest form of device 46 is a voltmeter requiring no additional power supply. For more complex arrangements the device 46 may be powered by batteries or by a power supply similar to that described in connection with Figures 2 and 3.
While it is considered that power supplies suitable -for use as the supply 35 described in connection with Figures 2 and 3 and mentioned in connection with Figure 4 could be designed by those skilled in the art, a brief description of a suitable supply will be given with reference to Figure 5 to ensure the description is complete.
Referring now to Figure 5, a typical power supply 35 is shown, suitable for use with the invention. The input conductors 36 and 37 from spaced points on the conductor are shown where they are connected to the supply.
A transformer 53 has its primary winding connected to conductors 36 and 37. The transformer 53 has a center-tapped secondary winding. The center tap is connected to the common conductor 54. The ends of the secondary winding are connected each to a diode 55 and 56. The output of the diodes 55 and 56 is connected to a choke 57. The output . ,~ ., ~ .
Case 2397 ~ ,Of~SO~
from choke 57 has a capacitor 58 connected to a common connection 54. The output of choke 57 is connected to a voltage regulator 59, which may conveniently be a zener diode. The output of the regulator 59 passes through a diode 60, to prevent reverse flow, and a resistor 61 to the output indicated with a plus sign. A rechargeable battery 62 is floated across the output. The power supply 35 is quite conventional and it is believed no further explanation is required.
In practice, the input conductors 36 and 37 might total 150 ft. in length. When the conductor 10 is carrying 15 000 to 30 000 amperes the input voltage thus obtained might then be of the order of 1.35 to 2.7 volts across the primary of transformer 53. The secondary of transformer 53 has a voltage on either side of the center tap between 15 and 30 volts to give a voltage across capacitor 58 of perhaps 20 to 40 volts. This is sufficient for the voltage regulator to provide an output of the order of 12 volts. It will be seen that the power supply will operate down to about half rated current in the central conductor and below that the battery 62 must provide power. The figures given in this paragraph are given only as examples and to provide a better understanding of the power supply. A similar supply could be readily designed for other voltage and currents.
It is believed that the invention in all its forms and variations will be clear from the preceding description.
This application is a division of Canadian Patent Application Serial No. 247 145 filed March 4, 1976.
This invention relates to the determination of electrical parameters and other parameters in an electrical bus.
For the purpose of this description, electrical bus may be considered to include a hollow conductor or bus which is not shielded along its length and a metal enclosed bus having a hollow central conductor and a surrounding metal enclosure. The central conductor is supported within the metal enclosure by insulators. It is usual to operate the unshielded bus at lower potentials to carry currents of a large magnitude. For example, an unshielded bus might operate at a potential of perhaps 1000 to 5000 volts and could carry currents of the order of a few thousand amperes.
It is usual to use metal enclosed bus at higher potentials where the metal enclosure is grounded and offers protection for the central conductor. For example, a metal enclosed bus might operate at a higher voltage, perhaps of the order of 20 kilovolts (kV) to 230 kV or higher and may carry currents of 5000 to 50 000 amperes or more.
In recent years with the trend to higher voltage, the metal enclosed bus has seen considerable use for conducting electric current for power transmission and distribution.
It is particularly useful at power generating stations where large amounts of power must be handled. It may contain an insulating gas, particularly at higher voltages. It may have means for circulating a gas within the metal enclosure -~
for cooling purposes when large amounts of power are being handled. The present invention is suitable for determining parameters in such metal enclosed bus, although it may also ~, . .
be used to determine parameters in unshielded bus.
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Parameters which may be of interest in the operation or use of an electrical bus include: current I in the bus, the temperature of the bus, the IR drop where R is the resistance of the bus between two longitudinally spaced points. IZ drop where Z is the impedance of the bus between two longitudinally spaced points, (IZ drop has been deter- -mined for bus in the prior art) IX drop where X is the reactance of the bus between two longitudinally spaced points, and the parameters R, X and Z themselves. No simple means has been devised in the past to determine some of these parameters with a desired accuracy. While values for IZ drop have been determined in the past, it has in itself not been of great practical value. There have been a number of attempts made to determine current and to determine temperature and perhaps other parameters. It is, however, quite difficult to determine parameters in a region of high voltage stress and to conduct the signal representing the parameter from that region. Not only do the high voltages cause problems, but the large currents ~
cause heating and create magnetic fields which can inter- ~ ~ -fere with a determination of various parameters.
For example, it is quite common to obtain a tempera- ~ -ture indication on a metal enclosed bus by affixing tempera-ture sensitive patches to the outer surface of the central conductor where the patches are visible from inspection windows. The patches change colour at specific temperatures. ;
This provides a very cheap way of determining if a specific temperature is exceeded. It is however unsatisfactory in that each patch provides an indication of one temperature only. -For another example, it is known in an unshielded bus to have a current transformer surrounding the bus and .- - :, . .
.. . . .. . . .
, " , . . ~ :
Case 2397 ~S016 insulated therefrom to obtain an indication of current.
Such current transformers are expensive and bulky and are inconvenient to use, particularly when high voltages are involved and the leads must be run from a high voltage region to a remote region. This type of arrangement has also been used with metal enclosed bus to obtain a current reading. The current transformer is in this arrangement mounted on an insulating bushing surrounding the central conductor and within the metal enclosure. The secondary leads from the current transformer were usually passed to the outside of the metal enclosure through a ring arrange-ment. Metal enclosed bus is usually designed for higher voltages and the voltage gradient between the central conductor and the metal enclosure is usually large. A
current transformer is normally operated at ground potential and it is difficult to prevent flashover and corona problems when a relatively bulky transformer at ground potential is inserted into a bus where there is a large voltage gradient.
In addition, as the bus and enclosure are normally welded together when installed, it is difficult to inspect or repair such a current transformer.
Another prior art arrangement avoids the problem of having a current cransformer within the metal enclosure of a metal enclosed bus. In this arrangement a gap is provided in the metal enclosure and the gap contains in-sulation. A conductor member capable of carrying large currents joins the adjacent ends of the metal enclosure ~ -extending externally over the insulation to form a small loop. A current transformer is positioned over this loop which carries the current in the enclosure of a phase in the system. This current is substantially equal and opposite to the current in the central conductor and con-Case 2397 10~5016 sequently gives a representation of the current in the central conductor. However this arrangement requires a break or gap in the metal enclosure wherever a current reading is desired and this break must not only contain insulation but must be sealed in cases where insulating gap is contained within the metal enclosure. In addition, the metal enclosure may be subjected to fluctuations of current from stray fields originating externally where the central conductor would be shielded from such fluctuations.
Also, arrangements of this nature are relatively expensive.
It is, of course, desirable to obtain a reading of current in a bus as accurately and as economically as possible. Because of the large currents normally handled, small percentage errors can involve considerable amounts of power. It is also desirable to measure or determine the IR drop in a bus during operation so that the resis-tive losses will be known. There have been a number of ways proposed to do this, but none appear to have had the desired accuracy or simplicity. Similarly, it is desirable ~ -to know the IX drop to have a complete understanding of the system, and it appears there have been no prior art arrange-ments which give the desired accuracy and simplicity.
In addition it is desirable to know temperatures at various places on a bus. For example, in an unshielded bus it may be desirable to know the temperature of the bus itself. In a metal enclosed bus it may be desirable to know the temperature not only of the bus or central conduc-tor but perhaps within the central conductor or adjacent the central conductor. It is difficult to determine temperature because the temperature sensitive elements normally provide output voltages as signals which represent temperature. These voltages are many orders smaller than the voltage gradient .
- . .
ase 2397 S0~6 surrounding the central conductor . Small extraneous voltages might be picked up by the wires and affect the accuxacy of the temperature indication. Also, the wires which carry the signals from the sensor would normally be at ground poten-tial. It is not desirable to have wires at ground potential extending through a large voltage gradient. Various ways have been proposed to overcome these problems, for example by using a high frequency carrier signal to carry the temperature signal as a modulation of the carrier. None of these have been completely satisfactory.
It has been discovered that an accurate determination can be made of various parameters of an operating bus by making these determinations in a specific manner and by making the determined values available externally without causing deterioration of the accuracy.
It has been found that by obtaining a voltage reading from longitudinally spaced points within an unshielded bus or within the central conductor of a metal enclosed bus, an accurate determination can be made of IR drop, where R is the resistance of the conductor between the points of measurement. It has been found that by obtaining a voltage reading from a loop extending within the conductor of an unshielded bus or within the central conductor of a metal enclosed bus for a predetermined length, then brought outside the conductor and extended to form the loop, an accurate determination can be made at a break in the loop for the IX
drop where X is the reactance of the portion within the loop. ~;
In an unshielded bus operating at lower voltages it may be feasible to bring the signals representing the parameter externally on a twisted pair of wires without degrading the accuracy. In a metal enclosed bus, in accordance with the invention, values determined within , , - : . .
Case 2397 , - ~ , 50~6 the metal enclosure are made available externally by provi-ding a power supply and a visual display. For example,for values such as IR drop, temperature, or current determined within the central conductor, a display is positioned within the central conductor to be visible through aligned openings in the central conductor and enclosure. The opening in the central conductor is preferably covered with a Farraday screen and the opening in the metal enclosure is sealed with a transparent window. A power supply provides power to operate the display, and if required may also provide power to the temperature sensor or other sensor. In a preferred form the power supply obtains its energizing voltage from a voltage drop between longitudinally spaced points on the inside of the central conductor using leads extending within the conductor to the longitudinally spaced points. A power supply could be energized by IX drop or IZ drop but, while the voltages might be greater, this is not preferred.
Transients are generally reactive in nature and related to frequency and would appear in a voltage for energizing or powering a power supply from IX or IZ drop. It is therefore preferred to power the supply using IR drop which is sub-stantially free of transients. It is also possible to have a supply using batteries. In low voltage systems only, an external or remote power supply is feasihle.
Similarly, for determining IX drop, the voltage drop is normally determined adjacent the outer surface and the display would also be adjacent the outer surface. It will be apparent that the loop could be broken within the conductor and the display would then be within the conductor also. Placing the display within the conductor would, of course, avoid problems which might occur with a display in the high voltage gradient outside. If a power supply is used s Case 2397 ,.
10~01~
to power the display, it is desirable to have the supply inside the hollow conductor whether the display is outside or inside. The supply can thus be energized by IR drop.
The temperature may be determined by using a tem-perature sensitive element or temperature sensor affixed to the main conductor or other place where a temperature determination is required. For example, the temperature sensor could be fixed to this inner surface of the hollow main bus or conductor. A display means, and a power supply to provide power for the display means, are within the conductor so that the display on the display means can be seen through a window or opening in the conductor. The power supply may be as previously mentioned, energized by the IR drop between spaced points on the conductor. The temperature sensor actuates the display to provide an indication of temperature.
The invention also includes a determination of parameters related to the metal enclosure of a metal enclosed bus. The same arrangement will provide a determi-nation of IR drop, and IX drop and knowing R or X, the currentmay be determined. The IR drop is determined using longi-tudinally spaced points within the metal enclosure, and the IX drop is determined using a loop extending internally and externally of a portion of the metal enclosure.
If desired IZ drop may also be determined as is known in the prior art by using longitudinally spaced points on the metal enclosure, externally of the enclosure.
Thus, according to one form of the invention there is provided a method for determining the IR drop in a -~
hollow conductor for carrying a large current where I is the current in the hollow conductor and R is the resistance in the hollow conductor between a first and a second point '' ' .::
, . . - -- .. : ~ . :
- , , ,: - , - : . ~ :.
., - . : : : - :. . ~ . , .:
. . .. . .. . ... . . .
Case 2397 01~;
spaced longitudinally on the conductor, comprising obtaining a voltage representation internally of said hollow conductor between first and second terminal points within said conduc-tor on the inner surface thereof corresponding to said first and second points respectively, displaying the voltage representation obtained on a display means within said conductor, said display being a determination of IR drop, and providing opening means to make the display visible externally.
According to another form of the invention there is provided a method for determining temperature of a hollow conductor for carrying a large current, comprising placing a temperature sensor on the surface of said hollow conductor, connecting said temperature sensor with a display means adjacent said hollow conductor to display a representation of temperature determined, and making said display visible at a region removed from said hollow conductor.
According to another form of the invention there is provided a method for determining current I in a hollow conductor for carrying a large current, comprising, obtain-ing a voltage representation V internally of said hollow conductor between a first and a second terminal point on the inner surface of said hollow conductor, obtaining an indication of temperature from a temperature sensor mounted on the inner surface of the wall of said hollow conductor, determining the resistance R of said hollow conductor from the temperature resistance relationship for said hollow conductor and the temperature from the sensor, for that portion of the hollow conductor between said first and second terminal points, determining the current I from the .:
voltage representation V where V = I R, and displaying the determined value for the current I.
, '' ': ' . " " ' :. ' Case 2397 ~06~0~;
According to another form of the invention there is provided apparatus for determining the IR drop in a hollow conductor for carrying a large current, where I is the current in the hollow conductor and R is the resistance of the hollow conductor between a first and a second point spaced longitudinally on said hollow conductor, comprising display means mounted within said hollow conductor to the wall of said hollow conductor, said hollow conductor having an opening in said wall, the edges of said opening defining a viewing opening for viewing the display means externally of said hollow conductor, a voltage detector means mounted within said hollow conductor, first and second terminal points on the inner surface of said wall of said hollow conductor at said first and second points respectively, input conductors extending within said hollow conductor and connecting each of said first and second terminal points to said voltage detector means to provide at said voltage detector means a voltage representative of IR drop between said first and second points, said voltage detector means providing a voltage signal representative of said IR drop between said first and second points, and means connecting said voltage detector means and said display means to apply said voltage signal to said display means and actuate said display means responsive thereto to display an indication :~
of IR drop.
According to another form of the invention there is provided apparatus for determining the current I in a hollow conductor having a wall for carrying a large current, said wall having a viewing opening therethrough, comprising a voltage detector means mounted within said hollow conductor, -~
first and second terminal points on the inner surfac~ of said wall forming said hollow conductor spaced longitudinally _ g _ - . . . :.: . .
-- , - : ,, : -- : .: :, . :
Case 2397 ~0~01~
on said conductor, input conductors extending within said hollow conductor connecting said first and second terminal points to said voltage detector to provide a voltage at said voltage detector representing the IR drop between said first and second terminal points, where R is the resistance of said hollow conductor between said first and second terminal points, said voltage between means providing a voltage signal representing said IR drop, a temperature sensor mounted within said hollow conductor to the wall of said hollow conductor to obtain a signal representing the temperature of said hollow conductor, means connecting said voltage sensor to said voltage detector to apply thereto said signal representing the temperature of said conductor, means in said voltage detector means responsive to said temperature signal to provide a signal representing resistance R based on the temperature/resistance relation-ship of said hollow conductor current determining means connected to said voltage detector means to receive said signal representing resistance R and said voltage signal representing said IR drop and providing a signal represen-ting current I, and display means connected to said current determining means for receiving said signal representing current I and responsive thereto to display an indication of said current I, said display means being mounted within said hollow conductor adjacent said opening whereby said display is visible through said opening.
The invention will be described with reference to the accompanying drawings, in which Figure 1, lA and lB are simplified sectional drawings of a portion of an unshielded bus indicating various measurement arrangements, a portion of a metal enclosed bus indicating various arrangements for determining parameters Case 2397 , ~06~~
for the central conductor, and a portion of the metal enclosure of a metal enclosed bus indicating various arrange-ments for determining parameters for the metal enclosure, useful in describing the basic concept of the invention;
Figure 2 is a simplified sectional drawing, partly in block form, showing a portion of a metal enclosed bus with a power supply and a display;
Figure 3 is a simplified sectional drawing, partly in block form, of a metal enclosed bus having apparatus suitable for determining current in the central conductor;
Figure 4 is a simplified sectional drawing, partly in block form, of a metal enclosed bus suitable for deter-mining IX drop in a conductor, and Figure 5 is a schematic circuit diagram of a power supply suitable for use with the invention.
Referring to Figure 1 there is shown a small portion of a bus lOa or hollow conductor lOa which carries a current.
The bus lOa is supported by insulators (not shown). Assuming - ~;
a current is flowing in conductor lOa, there will be a voltage drop which depends on the magnitude of the current and the resistance or impedance involved as is well known in the art. It has been found that by using two terminal points 14 and 15 on the inside of conductor lOa and connec-ting a voltmeter 16 to these terminal points, using conduc-tors 17 and 18 for the connection, that a voltage Vl is obtained where V1 = IR and where I is the current flowing in the conductor lOa and R is the resistance between points -14 and 15. It should be noted that voltmeter 16, conductors 17 and 18, and points 14 and 15 are all within the conductor lOa.
Also, by using a loop formed with conductor 25 extending within conductor lOa and then extending externally , . , : ~ ., .' ` :. ' ,' : ~
Case 2397 ~06~Vl~
as shown, to connect to a voltmeter 26, a voltage V3 can be obtained. The voltage V3 is equal to IX where I is the current flowing in conductor lOa and X is the reactance in that portion enclosed by the loop. The voltmeter 26 may be anywhere in the loop, that is it may be within conductor lOa or externally as shown.
In practice it is desirable to keep equipment or devices within the hollow conductor. This is particularly desirable when the voltage is high. If a piece of equipment, such as a voltmeter or display, is mounted externally it may be affected by the high voltage gradient and also, it may disrupt or interfere with the dielectric effect of the surrounding space.
Also, as is known in the prior art, it is possible to determine IZ. The manner of doing so is included here for completeness. By using two terminal points 20 and 21 on the outer surface of conductor lOa, and connecting a voltmeter 22 to these terminal points using conductors 23 and 24, a voltage V2 is obtained where V2 = IZ and where I
is the current in the conductor lOa and Z is the impedance between terminal points 20 and 21.
Referring now to Figure lA, there is shown a metal enclosed bus arrangement. A hollow central conductor lO
is surrounded by a metal enclosure 11. The enclosure 11 is normally at ground potential and the central conductor lO is supported within enclosure 11 by insulators (not shown). Similar arrangements are shown for obtaining Vl, V2, and V3.
Referring to Figure lB, there is shown a metal enclosed bus with hollow central conductor lO and metal enclosure ll. The structure is the same as that for Figure lA. However in Figure lB it is desired to know Case 2397 . ~
~SOlt~
parameters relating to the metal enclosure. Voltmeter 16a is connected to terminal points 27 and 27a to give voltage reading Vl representing the IR drop in the metal enclosure 11 between points 27 and 27a. Voltmeter 26a is connected in the loop formed by conductor 29 to give voltage V3 repregen-ting the IX drop in the portion of metal enclosure 11 included in the loop.
Also, to complete the description, and voltmeter 22a is connected to terminal points 28 and 28a to give voltage reading V2 representing IZ drop in the metal enclosure 11 between points 28 and 28a.
It will be seen that it is possible to determine resistance, impedance and reactance. If resistance is known, for example, it would be possible to obtain a determination of current from the IR drop. The resistance of conductor 10 changes with temperature. If the temperature could be determined, the voltage Vl (i.e. the IR drop) could be corrected to obtain current. For this reason it is important to know temperature. It is also important to know tempera-ture to ensure operating limits are not exceeded.
As was previously mentioned, it is difficult toobtain temperature readings because the temperature sensor gives small output signals when compared to the voltages on the main conductor or bus. It is difficult to conduct the small voltage signals externally of the high voltage system.
It might be possible to use a battery powered amplifier within the central conductor to amplify signals before conducting them to an outside point. However this would involve problems with battery replacement and would not avoid the difficulties in having wires extending from a region of high potential to a region of low potential. To overcome these problems and difficulties, the present invention ., -Case 2397 ~Ot;~O~t~
provides a power supply which may be mounted within the main conductor, or outside the main conductor and closely adja-cent, energized by the IR drop along the main conductor, and a display visible externally.
Referring to Figure 2, the central conductor 10 has an opening 30 covered by a metal screen 31. The screen 31 does not significantly impede vision but it prevents or inhibits abnormalities in voltage gradient that would otherwise be caused by opening 30. The metal screen is of a type referred to as a "Farraday screen". In a preferred form the screen 31 is a double screen. Opposite the window or opening 30 and aligned therewith is an opening 32 in metal enclosure 11. The opening 32 is covered with a transparent material such as a glass window 33. There is thus a path of vision from outside metal enclosure 11 through window 33 and screen 31 to the interior of central conductor 10.
Mounted within central conductor 10, adjacent opening 30 is a display device 34. The display device 34 may provide a meter type display, but preferably it is a digital display using lighted segmental digits or a binary light display.
A binary light display may, for example, have five separate ~ -lights whose on/off condition forms the binary number. The visual display may be picked up externally of the metal enclosure by an optical device and transmitted optically to a remote location or transformed again to an electrical signal and transmitted to a remote location as an electrical signal for use as a record or transformed to a visual display or both.
A power supply 35 has input conductors 36 and 37 connected to terminal points 38 and 39. The IR drop along conductor 10 provides a voltage to power the supply 35.
Casd 2397 )l6 The input voltage provided by conductors 36 and 37 will vary with the current flowing in central conductor 10. One purpose of power supply 35 is to make use of a wide range of input voltages to provide a satisfactory supply voltage to display device 34 and to associated equipment as required.
The power supply 35 may, for example, provide power for a sensor 40. The sensor 40 may be a temperature sensitive element or it may have inputs for voltage.
Referring now to Figure 3, an arrangement is shown that is quite similar to that of Figure 2 but with a pick up for Vl. Terminal points 41 and 42 are connected by conductors 43 and 44 to a voltage device 45 which determines Vl = IR. The sensor 40' detects the temperature of conductor -10. Knowing the temperature/resistance relationship for conductor 10 and obtaining temperature from sensor 40' will ~
enable a determination of resistance to be made by device ;
45. With resistance known and voltage drop measured, the -current can be determined and displayed by device 34. It will be seen that central conductor 10, between points 41 and 42 may be said to act as its own shunt to give a voltage reading proportional to current.
It will be understood that display device 34 could display both the temperature determined by sensor 40' and the voltage Vl determined by device 45. A current determi-nation could then be made externally if desired.
Referring briefly to Figure 4, there is shown a metal enclosed bus with central conductor 10 and metal -enclosure 11. As in Figures 2 and 3 there is a transparent window 33 in an opening 32 in metal enclosure 11. A voltage sensing and display device 46 is positioned opposite the --window opening 32 and adjacent the outer surface of central conductor 10. The sizes in the drawings are, of course, not Case 2397 l~S~
to scale. The sensing and display device 46 is in practice quite small and flat and would not extend away from the surface of conductor 10 by more than one or two centimetres where the spacing between the central conductor and the metal enclosure 11 might be 20 or more times as large.
Conductor 47 extends from device 46 to opening 50, through opening 50, inside the hollow conductor to opening 51, then back to device 46 to complete the loop. Conductor 47 is kept as close as possible to the outer surface of conductor lO. The voltage picked up by the loop formed by conductor 47 is voltage V3 = IX. This may be displayed by device 46. The simplest form of device 46 is a voltmeter requiring no additional power supply. For more complex arrangements the device 46 may be powered by batteries or by a power supply similar to that described in connection with Figures 2 and 3.
While it is considered that power supplies suitable -for use as the supply 35 described in connection with Figures 2 and 3 and mentioned in connection with Figure 4 could be designed by those skilled in the art, a brief description of a suitable supply will be given with reference to Figure 5 to ensure the description is complete.
Referring now to Figure 5, a typical power supply 35 is shown, suitable for use with the invention. The input conductors 36 and 37 from spaced points on the conductor are shown where they are connected to the supply.
A transformer 53 has its primary winding connected to conductors 36 and 37. The transformer 53 has a center-tapped secondary winding. The center tap is connected to the common conductor 54. The ends of the secondary winding are connected each to a diode 55 and 56. The output of the diodes 55 and 56 is connected to a choke 57. The output . ,~ ., ~ .
Case 2397 ~ ,Of~SO~
from choke 57 has a capacitor 58 connected to a common connection 54. The output of choke 57 is connected to a voltage regulator 59, which may conveniently be a zener diode. The output of the regulator 59 passes through a diode 60, to prevent reverse flow, and a resistor 61 to the output indicated with a plus sign. A rechargeable battery 62 is floated across the output. The power supply 35 is quite conventional and it is believed no further explanation is required.
In practice, the input conductors 36 and 37 might total 150 ft. in length. When the conductor 10 is carrying 15 000 to 30 000 amperes the input voltage thus obtained might then be of the order of 1.35 to 2.7 volts across the primary of transformer 53. The secondary of transformer 53 has a voltage on either side of the center tap between 15 and 30 volts to give a voltage across capacitor 58 of perhaps 20 to 40 volts. This is sufficient for the voltage regulator to provide an output of the order of 12 volts. It will be seen that the power supply will operate down to about half rated current in the central conductor and below that the battery 62 must provide power. The figures given in this paragraph are given only as examples and to provide a better understanding of the power supply. A similar supply could be readily designed for other voltage and currents.
It is believed that the invention in all its forms and variations will be clear from the preceding description.
Claims (6)
1. A method for determining current I in a hollow conductor for carrying a large current, comprising obtaining a voltage representation V internally of said hollow conductor between a first and a second terminal point on the inner surface of said conductor, obtaining an indication of temperature from a temperature sensor mounted on the inner surface of the wall of said conductor, determining the resistance R of said conductor from the temperature/resistance relationship for said conductor, and the temperature from the sensor, for that portion of the conductor between said first and second terminal points, determining the current I from the voltage represen-tation V where V = I R, and displaying the determined value for the current I.
2. Apparatus for determining the current I in a hollow conductor having a wall for carrying a large current, said wall having a viewing opening therethrough, comprising a voltage detector means mounted within said hollow conductor, first and second terminal points on the inner surface of said wall forming said hollow conductor spaced longitudi-nally on said conductor, input conductors extending within said hollow con-ductor connecting said first and second terminal points to said voltage detector means to provide a voltage at said voltage detector means representing the IR drop between said first and second terminal points, where R is the resistance of said hollow conductor between said first and second terminal points, said voltage detector means providing a voltage signal representing said IR drop, a temperature sensor mounted within said hollow conductor to the wall of said hollow conductor to obtain a signal representing the temperature of said hollow conductor, means connecting said temperature sensor to said voltage detector means to apply thereto said signal repre-senting the temperature of said conductor, means in said voltage detector means responsive to said temperature signal to provide a signal representing resistance R based on the temperature/resistance relation-ship of said hollow conductor, current determining means connected to said voltage detector means to receive said signal representing resistance R and said voltage signal representing said IR drop and providing a signal representing current I, and display means connected to said current determining means for receiving said signal representing current I
and responsive thereto to the display an indication of said current I, said means being mounted within said hollow conductor adjacent said opening whereby said display is visible through said opening.
and responsive thereto to the display an indication of said current I, said means being mounted within said hollow conductor adjacent said opening whereby said display is visible through said opening.
3. Apparatus as defined in claim 2 and further comprising a metal screen mounted to said wall of said hollow conductor to cover said opening and being substan-tially coextensive with the wall defining said opening, to inhibit distortion of the voltage field in region of said opening.
4. Apparatus as defined in claim 3 in which said metal screen has an inner and an outer layer.
5. Apparatus as defined in claim 2, 3 or 4 and further including power supply means to provide power for said display means, comprising a pair of terminal places on the inner surface of said wall of said conductor spaced longitudinally along said conductor, voltage supply conductors each connecting a respec-tive terminal place to said power supply means to provide thereto a voltage according to the voltage drop between said terminal places, and regulating means to provide a controlled power for said display means.
6. Apparatus as defined in claim 2 3 or 4 in which said hollow conductor is the central conductor of a metal enclosed bus and is surrounded by a metal enclosure concentric with said central conductor, said metal enclosure having an opening therein aligned with said viewing opening in said hollow conductor.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA315,586A CA1065016A (en) | 1978-10-31 | 1978-10-31 | Sensing electrical parameters inside conductors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA315,586A CA1065016A (en) | 1978-10-31 | 1978-10-31 | Sensing electrical parameters inside conductors |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1065016A true CA1065016A (en) | 1979-10-23 |
Family
ID=4112849
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA315,586A Expired CA1065016A (en) | 1978-10-31 | 1978-10-31 | Sensing electrical parameters inside conductors |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1065016A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1992013277A1 (en) * | 1991-01-23 | 1992-08-06 | Abb Patent Gmbh | Current transformer |
| WO1992013278A1 (en) * | 1991-01-23 | 1992-08-06 | Abb Patent Gmbh | Measuring converter at high-voltage potential |
| CN103187159A (en) * | 2011-12-29 | 2013-07-03 | 大连第一互感器有限责任公司 | Gas-sealing and resistance-dividing voltage sensor |
| WO2015135939A1 (en) * | 2014-03-10 | 2015-09-17 | Repl International Limited | Electrical sensor |
-
1978
- 1978-10-31 CA CA315,586A patent/CA1065016A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1992013277A1 (en) * | 1991-01-23 | 1992-08-06 | Abb Patent Gmbh | Current transformer |
| WO1992013278A1 (en) * | 1991-01-23 | 1992-08-06 | Abb Patent Gmbh | Measuring converter at high-voltage potential |
| CN103187159A (en) * | 2011-12-29 | 2013-07-03 | 大连第一互感器有限责任公司 | Gas-sealing and resistance-dividing voltage sensor |
| WO2015135939A1 (en) * | 2014-03-10 | 2015-09-17 | Repl International Limited | Electrical sensor |
| US10514396B2 (en) | 2014-03-10 | 2019-12-24 | Repl International Limited | Electrical sensor attachable to an electrical distribution cable |
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