CA2033410A1 - Powerline monitoring device - Google Patents

Abstract

ABSTRACT
A powerline monitoring device has a single core that can be used to continuously measure current as well as other parameters such as temperature, ambient temperature, phase angle and voltage. The current is measured through the same set of windings that power the device. The device can be mounted on or removed from a powerline while the powerline is activated. Measurements taken by the device are transferred to a receiving station. The device operates from power on the powerline itself and is designed to continue to operate for approximately ten seconds subsequent to complete failure of power in the powerline. The device can operate over a broad range of current in the powerline ranging from 5 amps to 2,000 amps. Previous devices do not operate over a broad range of current or cannot measure current continuously or have two cores or two sets of windings and are relatively expensive or complex to manufacture.

Description

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This invention relates to a powerline ~ ~ -monitoring device and, in particular, a device for ~`
monitoring powerlines in distribution systems b~
measuring one or more of such parameters as current, temperature, ambient temperature, phase angle and voltage for the line in which the monitoring device is installed.
Powerline monitoring devices are known.
However, previous devices are relatively expensive or 10 complex to manufacture; or, they do not operate over a ~-~
broad range of current; or, they cannot measure current continuously; or, they have two cores or two ~ l ~
sets of windings; or, they do not derive power from ~;
the powerline itself. One previous device is lS described in United S~ates Patent No. 4,806,855 naming Murray W. Davis as inventor, being entitled "Sys~em for Rating Electric Power Transmission Lines and Equipment" and being issued on February 21stj 1989. -~
Mechanically, the core of Davis must be changed in size when the device is used with powerlines having different diameters. To design a core that changes in size is relatively expensive and complex. In addition, the core must change size in a manner that the air gaps remain unchanged. The Davis patent suggests a threshold value or current in the powerline between 120 and 150 KA. When the device described in the Davis patent is used to measure current, the power supply transformer for the device ;
cannot be used to monitor the line current because the -30 secondary winding is periodically shorted by the ~ `
switching network. One manner or measuring current that is suggested is to measure the charging time or `
capacitors within the device. Unfortunately, this has - 1 - :

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a disadvantage in that current can no longer be measured after the capacitors have become charged.
Thus, current cannot be measured continuously. As an ~
alternative, it is suggested in the Davis patent that ~ :
a second or additional secondary winding can be added to the core. This additional winding increases the manufacturing costs and the complexit~y of the device. ~;
It is an object of the present invention to provide a powerline monitoring device that is simple ~-and relatively inexpensive to manufacture, that is capable of continuously measuring current within the powerline, that contains a single core containing one set of primary and secondary windings that power the device and also provide means for measuring the current, and that can operate over a broad current range through the powerline.
A powerline monitoring device or mounting on a powerline has a single core with sufficient primary and secondary windings so that the core is not ~!
saturated when operated at a predetermined maximum operating current. There is one set of primary and secondary windings. The core is split and separable so that it can be made to surround said powerline.
The core is connected into an electronic circuit that is contained within a housing. The circuit contains means to control the voltage of the core so that the voltage cannot exceed a predetermined maximum operating voltage o the circuit despite a current level or the occurrence of current surges in said powerline. The electronic circuit is powered from said powerline through said core and said windings.
The circuit contains sensing means for continuously -measuring current in said powerline, said circuit always measuring current. The circuit sometimes - 2 - ;

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contains sensing means to measure one or more other ~ ;
parameters in addition to current, said other parameters being selected from the group of `
temperature, ambient temperature, phase angle and voltage. The circuit is capable of continuously measuring curren~ through the same se~ of windings that power said device. There are means to transfer said measurement to receiving means for said measurement. The~e are clamping means for removably ~;
10 mounting said device on said powerline while said ;
powerline is activated.
In the drawings:
Figure 1 is a front view of a powerline monitoring device;
Figure 2 is an edge view;
Figure 3 is a rear view with a split core in an open position;
Figure 4 is a partial rear view with the ~, split core in a closed position;
Figure 5 is a partial side view of a housing with a cover removed;
Figure 6 is a simplified circuit diagram for one embodiment of the device; and Figure 7 is a block diagram of an electronic circuit of another embodiment of the device.
In Figures 1 and 2, a powerline monitoring device 2 has a,clamp 4, a split core 6, 8 and a housing 10. The clamp 4 is affixed to the core 6, 8 ;~
and to the housing lO by a bracket 12, bolts 14 and nuts 16. The housing lO contains a cover plate 18 which is held in place by screws 20. The clamp 4 is ~-~
conventional and is designed to affix the device 2 to a powerline 22 in such a way that the split core 6, 8 -surrounds the powerline 22 and the powerline can be ; ~-~

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monitored. The clamp 4 can be removably affixed to ;
powerlines of various sizes, while the powerlines are activated, by using a hot stick in th,e opening 24 of ~;
the bolt 26 to turn the bolt 26 in an appropriate direction to either tighten or loosen an arm 28 of the clamp 4 about the powerline 22. The particular clamp shown in the drawings is conventional and is designed -~
for powerlines having a diameter up to a maximum of one inch. For larger powerlines, a larger clamp of the same design or a clamp of a different design will be used.
At a top 30 of the housing 10, ther~ is an antenna 32 to allow signals to be transmitted from the device to receiving means (not shown).
The core 6 has a coil 34 located thereon, -the coil containing one set o~ primary and secondary windings (not shown in Figures 1 and 2).
A portion 8 of the core is pivotally mounted on a bolt 35 and held in place by nuts 36 and a washer 20 38. Springs 40, 42 bias the portion 8 upward into a ~-closed position as shown in Figure 3. ~-In Figure 4, the portion 8 is shown in an open position. When it is desired to mount the device 2 on a powerline, the core is placed in the open position shown in Figure 4. Next, a hot stick (not shown) is used to mount the clamp onto a powerline.
Once the clamp is mounted and the bolt 26 is turned in an appropriate direction to tighten the clamp on the powerline, the core is moved from the open position shown in Figure 4 to the closed position shown in Figure 3 so that the core surrounds the powerline. As soon as the core is moved to the closed position, the monitoring device will be activated and will begin to send signals to a receiving station (not shown). To - 4 ~
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remove the device from a powerline, the opposite procedure is followed. First opening the core to the position shown in Figure 4, thereby deactivating the device and then opening the clamp with a hot stick and removing the device from the powerline.
In Figure 5, the housing 10 is shown with the cover removed. The electronic ci,rcuitry ~not shown) within the housing 10 is completely surrounded by a metal shield 43. Preferably, the metal shield is ~;
a magnetic and conductive metal, for example, tin.
The purpose of the shield 43 is to protect the ~;
circuitry and the processor from magnetic and electrical fields of the powerline. ;~
The housing 10 contains an electronic ;
lS circuit. One embodiment of a circuit is shown in Figure 6.
The core 6 has a primary winding 50 and a secondary winding 52. A centre tap 54 of the secondary winding 52 is connected through a law xesistance resistor 56 to circuit board ground 58.
The monitoring device shown in Figure 5 operates from 5 amps to 2,000 amps and can withstand current surges ;~-from hostile environments. For example, phase to phase or phase to ground short circuits up to 14 KA. ;~
The core and windings supply power to the electronic circuit to make the device operable as well as dividing sensing means for continuously measuring current in the powerline on which the device is ~;
mounted.
Generally, the relationship between the primary current ~Ip) and the secondary current (Is) is as follows~
Ip = KIs where K = Ns ~ Np ' ' :
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Ns is equal to the number of turns on the ;; ;
secondary winding Np is egual to the number of turns on the primary winding.
The voltage produced on the secondary winding will under normal conditions increase to the ~
saturation point of the core. The voltage on the ~, secondary winding in the device 2 is limited to a predetermined maximum. For example, to 5 volts D.C.
Additional voltage appears across the resistor 56 as current in the powerline increases. Voltage across the resistor 56 (Vs6) ~an be calculated as follows~
V56 = IpR56 where ~ s the resistance of the resistor 56.
The resistance of the resistor 56 is low, for example, 5 ohms. As can be seen, the voltage across the resistor 56 is proportional to the primary current or the current through the powerline. This relationship is accurate only so long as the core does not become saturated. ;
On the positive supply side of the ;~
electronic circuit, there is located a zener circuit 60 composed of a 100 ohm resistor 62, a diode 64, a 2S capacitor 66 and a transistor 68. The transistor number is TIP42 and the transistor is heat-sinked to an exterior of the housing. The diode 64 and the capacitor 66 are connected in parallel to one another and are located between the resistor 62 and the transistor 6B. The transistor 68 allows for the dissipation of electrical energy in the form of heat safely to the outside of the housing, which is made of metal and thereby protects the circuitry from current .
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surges in the powerline and maintains the voltage in the electronic circuit at a maximum of 5 volts. ~;~
Still on the positive supply side of the electronic circuit, but beyond the æener circuit 60, 5 there is located a large capacitor 70, preferably ~
having a capacitance of one farad. When the ~ ;
electronic circuit is activated, the capacitor 7 charges and ultimately becomes fully charged. When a complete failure occurs in the powerline so that 10 current no longer flows, the electronic circuit will `
obtain power from the capaci~or 70 and will operate for approximately ten seconds following the complete failure, thereby providing monitoring capability after the failure has occurred. This feature should enable the cause of the failure to be determined more quickly and accurately. Diodes 71, 72 rectify the A.C.
current to D.C. current.
Concerning the negative supply 73, there are two diodes 74, 75 o~f the secondary windlngs 52 which provide D.C. voltage to the negative supply circuitry to -6 volts. An SCR 100 volt crowbar circuit 76 is ~;
connected between the negative supply and the centre `~
tap 54 of the core. The crowbar circuit becomes activated at a particular predetermined voltage level (for example, greater than 2,000 amps) to protect the negative supply from damage during high current surges in the powerline and to reduce the power dissipated through the transistor 68 o~ the zener circuit on the positive supply. The crowbar circuit will only become activated in very high current situations. When activated, the crowbar circuit will short and additional voltage will be dissipated. ;~
- The centre tap 54 is also connected through a peak and hold detector 79 which in turn is connected _ 7 ~

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to a processor 80. Additional protection for the circuit is provided by resistor 77 and diodes 78, which together clamp the voltage in the circuit between a predetermined maximum and m:Lnimum. In S parallel with the detector 79, there :is connected a variable gain 82 and an RMS measurement 84, the RMS -~
also being connected to the processor 80. The peak current in the powerline is measured continuously from the same single set of windings 50, 52 that power the -electronic circuit. The variable gain 82 is controlled by the processor and a voltage measurement resistor 86 is connected to the variable gain 82 so that voltage in the powerline can be measured. The ;
variable gain adjusts automatically under control by the processor to the best range for measurement of both the current and the voltage in the powerline. As the line conditions change, the variable gain also changes so that more accurate measurements can be taken in the particular range of current or voltage actually existing in the powerline. The RMS
measurement 84 is a true RMS chip which is only accurate in a narrow voltage range for both the current or voltage measurements. Variable gain is designed so that the current or voltage measurements that the circuitry is measuring at that time are stepped up or down to the best level at which highest accuracy of the measurement can be made. The true RMS
chip takes any waveform that it receives and converts it to a true RMS D.C. level that is passed on to the 30 A/D converter. ~-In Figure 6, there is shown a block diagram of an electronic circuit with some variations over the ~
circuit shown in Figure 7. The circuit measures the ~ -peak of the sign wave for current to the powerline, ~ ' .: ., - , :: .
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phase angle and voltage. The zener circuit is referred to in the protection block and the SCR
circuit is referred to in the regulation block. The ;~
control contains a transmit~er for transmitting si~nals of the various measurements taken to receiving means, such as a ground station, not shown. The processor contains a frequency dial or dials so that the freguency of a particular device 2 can easily be adjusted by rotating the dial to an appropriate setting. Each device has a separate receiver designated to receive from the transmitter o that device. All of the monitoring devices must transmit ~-at a different frequency to a receiving station so that the signals will not overlap. The housin~
lS contains a light emitting diode (LED), which is visible from the ground when the device is ;~
operational. It should be noted that the voltage is measured by a resistor which is mounted on the monitoring device. One end of the resistor is connected to the circuitry. The other end of the resistor is connected to ground or, if phase to phase voltage is to be measured, to another phase. At either end of the insulator there is located a corona ~ ~ ~
ring and shielding to increase the accuracy o the ~ ~ `
25 voltage measurement. ~ ; ;
The electronic circuit also contains a frequency synthesizer chip in conjunction with the rotary switches for setting the frequency. When the device is activated, the processor reads the desired frequency from the rotary switches and sets the synthesi2er chip to the desired frequency. This ~ -system allows for as many as 256 different frequencies which are easily set manually on site with the aid of a small screwdriver.
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The circuit contains a sleep mode in which all of th~ transmitter circuitry is shut down to conserve energy to allow the capacitors to recharge during low current applications. ~hen sufficient energy is stored in the capacitors, the transmittor section is turned on once again. Under extremely low currents, the data will b~ sent out at one minute intervals rather than continuously as this is usually adequate for most monitoring situations.
The electronic circuitry can also -~
distinguish between faults in the powerline and in-rush currents. An in-rush current lasts for a much shorter time than a fault and the processor can distinguish between them on a time basis.

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Claims (22)

1. A powerline monitoring device for mounting on a powerline, said device comprising:
(a) a single core having sufficient primary and secondary windings so that the core is not saturated when operating at a predetermined maximum operating current, there being one set of primary and secondary windings, said core being split and separable so that it can be made to surround said powerline;
(b) said core being connected into an electronic circuit contained within a housing, said circuit containing means to control the voltage of the core so that the voltage cannot exceed a predetermined maximum operating voltage of the circuit despite a current level as the occurrence of current surges in said powerline;
(c) said electronic circuit being powered from said powerline through said core and said windings;
(d) said circuit containing sensing means for continuously measuring current in said powerline, said circuit always measuring current and sometimes containing sensing means to measure one or more other parameters in addition to current, said other parameters being selected from the group of temperature, ambient temperature, phase angle and voltage, said circuit being capable of continuously measuring current through the same set of windings that powers said device;
(e) means to transfer said measurement to receiving means for said measurement; and (f) clamping means for removably mounting said device on said powerline while said powerline is activated.

2. A device as claimed in Claim 1 wherein the means for controlling the voltage of said core is a zener circuit, said zener circuit containing a transistor that can dissipate unwanted electrical energy in the form of heat.

3. A device as claimed in Claim 2 wherein the zener circuit controls the voltage on the secondary windings through diodes with a centre tap of said secondary winding connected to a low resistance path to ground, any current that would otherwise increase the voltage beyond said predetermined maximum operating voltage being dissipated through said zener circuit and said low resistance path to ground, the current through the zener circuit increasing as the current through the powerline increases.

4. A device as claimed in Claim 3 wherein the device operates so that the core will not become saturated over a range of current within the powerline from approximately 5 amps to approximately 2,000 amps.

5. A device as claimed in any one of Claims 1, 2 or 3 wherein the device is able to detect a fault in the powerline.

6. A device as claimed in Claim 3 wherein the electronic circuit contains a visual indicator mounted in said housing so that said indicator can be viewed externally from a long distance away from the device to indicate that the device is operational.

7. A device as claimed in Claim 4 wherein the zener circuit is on the positive supply and a negative supply of the electronic circuit contains a crowbar circuit connected between the negative unregulated supply and the centre tap of said core, said crowbar circuit protecting the negative supply from damage during very high current surges and reducing the power dissipated by the transistor and power supply of the zener circuit.

8. A device as claimed in any one of Claims 2, 4 or 7 wherein the zener circuit is designed to limit the voltage of the electronic circuit and of the core to substantially 5 volts, thereby controlling the maximum voltage in the electronic circuit at 5 volts.

9. A device as claimed in Claim 4 wherein the electronic circuit contains a multi-gain chip connected to the analogue/digital converter that adjusts the converter in a series of step-ranges in response to variations in current through the powerline, said converter also being connected to a series of RMS chips to take measurements in the various ranges.

10. A device as claimed in Claim 4 wherein the device contains a large capacitor so that the device will continue to monitor the powerline for approximately 10 seconds subsequent to a complete failure of power in the powerline.

11. A device as claimed in any one of Claims 1, 2 or 3 wherein the sensing means for voltage is a resistor surrounded by an insulator with two corona rings surrounding a line of the circuit one ring at each end of said insulator.

12. A device as claimed in Claim 4 wherein the means for transferring the measurements is a transmitter for transmitting the measurements taken by the device to receiving means, said transmitter also being powered by said powerline through said core and said windings.

13. A device as claimed in Claim 12 wherein the transmitter shuts down in order to conserve energy to allow any capacitors in the electronic circuit to recharge during periods of low current in the powerline.

14. A device as claimed in Claim 13 wherein measurements are transmitted at approximately one minute intervals during periods of extremely low current in the powerline in order to conserve energy.

15. A device as claimed in Claim 3 wherein the electronic circuit contains a switch whereby the frequency at which the transmitter will emit a signal can readily be changed by changing said switch.

16. A device as claimed in Claim 10 wherein the capacitor has a size of at least one farad.

17. A device as claimed in Claim 12 wherein the receiving means is connected to a microprocessor to analyze said measurements.

18. A device as claimed in Claim 6 wherein the visual indicator is a light emitting diode.

19. A device as claimed in Claim 9 wherein the analogue to digital converter contains 8 step-up ranges.

20. A device as claimed in any one of Claims 1, 2 or 3 wherein the electronic circuit measures the peak current in the powerline.

21. A device as claimed in Claim 17 wherein the microprocessor distinguishes between faults in the powerline and in-rush currents.

22. A device as claimed in Claim 4 wherein the primary winding is one turn.