WO1999022432A1

WO1999022432A1 - Device for de-icing a live conductor

Info

Publication number: WO1999022432A1
Application number: PCT/CA1998/000974
Authority: WO
Inventors: Marc-André Allaire; Jean-Louis Laforte
Original assignee: Allaire Marc Andre; Laforte Jean Louis
Priority date: 1997-10-24
Filing date: 1998-10-16
Publication date: 1999-05-06
Also published as: CA2219449A1

Abstract

The invention concerns a device and a method for de-icing a live conductor (12) which consists in: first detecting the presence of ice in the surroundings of the conductor (12) by means of a sensor (32) and then in emitting, by radio wave, a triggering signal to a source of electromagnetic pulses (28) located in the proximity of the conductor (12). The source (28) then produces electromagnetic pulses which circulate in one or pairs (14) of conductor wires (16, 18) coiled along and around the live conductor (12). The electromagnetic repelling power to which conductor wires (16, 18) are subjected when a current flows through them causes them to move, thereby breaking the ice formed on the live conductor (12) and causing it to fall.

Description

DEVICE FOR DEFROSTING A CONDUCTIVE LIVE

FIELD OF THE INVENTION

The present invention relates to devices for removing snow or ice that can accumulate on electric lines or cables, and relates more particularly to a device for deglazing a live overhead conductor of power transmission and distribution lines. electric.

HISTORY OF THE INVENTION

In cold regions, structural tubular elements, regardless of their shape, i.e. rectangular, square or circular, are often exposed to precipitation of atmospheric ice, such as hard frost, sleet and sticky snow. The accumulation of ice on these elements can cause mechanical overloads which will deform them, even going so far as to produce mechanical failures which are sometimes catastrophic. No method to minimize the accumulation of ice on such structural elements has been used until now, particularly in the case of live overhead conductors in which a very high electric current flows. In addition, the absence of electrical insulation on these conductors complicates the application of an icebreaking system.

US Patent 4,690,353 (HASLIM), US Patent 5,411,121 (LAFORTE et al.) And Canadian Patent Application No. 2,211,034 (ALLAIRE et al.) Filed on August 1, 1997 describe devices or systems using electromagnetic pulses high intensity to break the ice.

In the case of HASLIM, the system is applicable to flat surfaces, and was developed to remove ice on an aircraft wing. Electromagnetic pulses are injected into a double thin copper tape placed (inserted) in a rubber film. In the case of LAFORTE et al., The device is applicable to stranded conductors, such as a stranded cable. To break the ice, electromagnetic pulses are injected into some of the integrated insulated conductors in the last stranded layer of the cable. These conductive wires are insulated for this purpose during the manufacture of the cable.

The Canadian patent application in the name of ALLAIRE et al. describes a device for deicing an elongated structural element with a closed contour, comprising at least one pair of preformed electrically conductive wires for winding, one next to the other, along and around the structural element following a substantially helical trajectory, while substantially matching the outline of the structural element with a predetermined clearance between the conductive wires and the structural element. The lead wires have first ends for receiving electromagnetic pulses, and second ends opposite the first ends. The conductive wires are of a size to withstand a current causing, between the conductive wires of the pair, a repulsion having an intensity capable of breaking ice or frost on the structural element by a distancing of the conductive wires one of the other in response to repulsion. The conductive wires have properties of rigidity and elasticity such that they regain their shape around the structural element after the separation caused by the repulsion. The device also comprises means for electrically connecting the second ends of the conductive wires of the pair together, and means for electrically isolating the conductive wires of the pair from each other and from the structural element. This patent application mentions the possibility of using such preformed electrical wires for de-icing live conductors, but without however describing an automated system making it possible to carry out this application.

The publication "An Investigation of Power Line De-lcing by Electro-Impulse Methods", published in the journal IEEE Transaction on Power Delivery, Vol. 4, No. 3, July 1989 on behalf of EGBERT et al., Describes a test with a conductor

ACSR wrapped in rubber bands containing flexible copper strips in which electromagnetic pulses have been injected. In this experiment, the rubber bands surrounding the conductor did not have an adequate shape and the copper strips, too thin, did not offer sufficient mechanical resistance to break the ice, so that under the effect of the impulses, the he envelope was deformed rather than breaking the ice, the mechanical resistance of the copper blades being weaker than that of the ice. As the authors point out at the conclusion of the experiment, the use of this type of covering cannot effectively deglaze the closed surface of a conductor.

SUMMARY OF THE INVENTION

The invention relates to a device for deicing a live conductor in which an electric current flows. The device comprises at least one pair of electrically conductive wires wound, one next to the other, along and around the live conductor following a substantially helical path. The lead wires of the pair have first ends for receiving electromagnetic pulses and second ends electrically connected together. These conductive wires are electrically isolated from each other and from the live conductor. The device also comprises a source of electromagnetic pulses electrically connected to the first ends of the pair of conductive wires, and means for supplying the source of electromagnetic pulses with a supply current produced from the electric current flowing in the conductor under voltage. The device further comprises detection means for detecting an ice formation in an environment occupied by the live conductor, and a communication system having a first component associated with the detection means for sending a trigger signal when the ice formation is detected in the environment of the live conductor, a second component associated with the source of electromagnetic pulses to receive said trigger signal, and means for transmitting the trigger signal from the first to the second component.

The invention also relates to a device for deicing a transmission line comprising at least one bundle, each bundle comprising a plurality of live conductors in which an electric current of the same phase flows, the device comprising at least one pair of coiled electrically conductive wires. , one next to the other, along and around each live conductor following a substantially helical path. The lead wires of the pair have first ends to receive pulses electromagnetic and second ends electrically connected together. These conductive wires are electrically isolated from each other and from live conductors. The device further comprises a source of electromagnetic pulses for each beam, electrically connected to the first ends of the pairs of conductive wires wound around each of the live conductors included in the beam. The device also comprises means for supplying each source of electromagnetic pulses with a supply current produced from an electric current flowing in one of the live conductors included in the bundle with which the source of electromagnetic pulses is associated, and detection means for detecting ice formation in an environment occupied by the transmission line. A communication system is also included in the device, this communication system having a first component associated with the detection means for sending a trigger signal when the formation of ice is detected in the environment of the transmission line, a second component. associated with each source of electromagnetic pulses to receive said trigger signal, and means for transmitting the trigger signal from the first to each second component.

The invention further relates to a device for deicing a transmission line comprising a plurality of live conductors in which an electric current of different phases flows, the device comprising at least one pair of coiled electrically conductive wires, one next to the other, along and around each live conductor following a substantially helical path. The lead wires of the pair have first ends for receiving electromagnetic pulses and second ends electrically connected together. These conductive wires are electrically isolated from each other and from live conductors. The device also comprises a source of electromagnetic pulses for each live conductor, electrically connected to the first ends of the pairs of conductive wires wound around the corresponding live conductor. Means for supplying each source of electromagnetic pulses with a supply current produced from an electric current flowing in the live conductors are also included in the device. This device further comprises detection means for detecting an ice formation in an environment occupied by the transmission line, and a communication system having a first component associated with the detection means for sending a trigger signal when the ice formation is detected in the environment of the transmission line, a second component associated with each source of electromagnetic pulses to receive said trigger signal, and means for transmitting the trigger signal from the first to each second component. Finally, the invention relates to a method for deglazing a live conductor in which an electric current flows, comprising the steps of: detecting ice formation in an environment occupied by the live conductor; sending a trigger signal to an electromagnetic pulse source by a radio wave when the formation of ice in the environment occupied by the live conductor is detected; receive the trigger signal; supplying current to the source of electromagnetic pulses; and applying electromagnetic pulses between first ends of at least one pair of electrically conductive wires wound, one next to the other, along and around the live conductor following a substantially helical path, the conductive wires the pair having second ends electrically connected together, the conductive wires being electrically isolated from each other and from the live conductor. The device according to the present invention is particularly well suited to overhead conductors of high voltage lines while the line is under tension and very high currents are flowing there. It also has the advantage of being autonomous and completely automated. It can also be installed on both existing and future lines. BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood on reading the non-restrictive description which follows of a preferred embodiment thereof, made with reference to the appended drawings in which:

Figure 1 is a side view of a live conductor along and around which is wound the pair of conductive wires of a device according to the present invention;

Figure 2 is a side view of the source of electromagnetic pulses of the device according to the invention, this source being supplied from the current flowing in the live conductor;

Figure 3 appearing on the same board as Figure 1 is a side view showing the connection of the electromagnetic source to the first ends of a pair of conductive wires; Figure 4 is a diagram of an ice detector that can be used in the device according to the invention;

Figure 5 shows a receiving antenna mounted on the source of electromagnetic pulses;

Figure 6 is a perspective view of a pylon supporting three bundles of four conductors according to an example of application of the present invention;

Figure 7 is a side view of an electromagnetic pulse source connected to four bundled conductors according to the application example shown in Figure 6;

Figure 8 is a front view of the source shown in Figure 7; Figure 9 is a side view of a junction of conductive wires at their second ends electrically connected together; and

Figure 10 is a side view of a welded junction of conductive wires passing over a spacer according to an example of application of the present invention. DETAILED DESCRIPTION OF THE PREFERRED ACHIEVEMENTS

The device according to the invention as illustrated in the accompanying drawings is intended to deglaze a live conductor 12 in which an electric current flows. With reference to FIG. 1, the device comprises at least one pair 14 of electrically conductive wires 16 and 18 wound, one next to the other, along and around the live conductor 12 following a substantially helical path, the lead wires 16 and 18 of the pair 14 having first ends 20 and 22 for receiving electromagnetic pulses and second ends 24 and 26 electrically connected together, the conductive wires 16 and 18 being electrically isolated from each other and of the live conductor 12.

This device is used to deglaze the live conductor 12 by means of electromagnetic pulses. The de-icing capacity comes from the conductive wires 16 and 18 which are preformed and arranged in pairs 14 around the live conductor 12. In each pair 14, these wires are arranged so as to be adjacent to each other and to this that the direction of the current in one wire 16 is opposite to the current flowing in the other wire 18. In this way, when a current is injected into the pair 14 of conducting wires 16 and 18 in the form of electromagnetic pulses a repulsive force proportional to the square of the current and inversely proportional to the distance between the two wires 16 and 18 will be produced between them. A fairly strong current for a fraction of a second will thus cause the two wires 16 and 18 to move, and the ice that may have accumulated on the live conductor 12 will be broken by this movement.

The conductor wires 16 and 18 are preferably preformed to be wound along the live conductor 12, as described in the Canadian patent application by Allaire et al. A conductive aluminum alloy of great mechanical strength can be used for their manufacture (for example the grade 6021 T83). They are covered with an insulating material, preferably a plastic material also of great mechanical resistance. The dimensions of the conducting wires 16 and 18 are chosen so as to maximize the current pulse while breaking the glass without permanently deforming under the temperature conditions likely to be encountered. It is understood, however, that the present device can also be used in conjunction with a system for deicing a g conductor by electromagnetic pulses different from that described by Allaire et al., such as for example the system which is the subject of American patent 5,411,121 (LAFORTE).

Referring to Figures 2 and 3, it is shown that the device according to the present invention comprises a source of electromagnetic pulses 28, electrically connected to the first ends 20 and 22 of the pair 14 of conductive wires 16 and 18. The source d electromagnetic pulses 28 is preferably installed under the live conductor 12 and is capable of generating pulses of very high intensity. The device also comprises means for supplying the source of electromagnetic pulses 28 with a supply current produced from the electric current flowing in the live conductor 12. The supply of the pulse source 28 from the conductor to 12 allows the use of the high voltage system without having to electrically isolate the pulse source 28 and the conductor 12 from ground. Preferably, as shown in FIG. 2, these means comprise a current transformer 30 fixed to the live conductor 12 and electrically connected to the source of electromagnetic pulses 28. A current transformer suitable for this application is for example described in the reference WILDI, THÉODORE, "Électrotechnique", 2nd edition, Les Presses de l'Université Laval, Éditions ESKA (1994) pp 434-437.

The source of electromagnetic pulses 28 is preferably composed of one or more capacitor units which are charged at the voltage required to obtain in the pair or pairs 14 of conductive wires 16 and 18 pulses of an approximate duration from 1 to 3 milliseconds and a current peak of about 6 to 8 kiloamps. The discharge of the capacitors is controlled using power modules made up of thyristors connected in series. The source 28 has a number of power modules equal to the number of pairs 14 of conductive wires 16 and 18 which it supplies. A microcontroller can also be included to manage the power modules. It is preferable to minimize as much as possible the weight and dimensions of the pulse source 28, and to assemble its components in a sealed container of cylindrical shape. The latter can be oriented so as to minimize aerodynamic drag and corona discharge.

The device according to the present invention also comprises detection means for detecting ice formation in an environment occupied by the live conductor 12. Preferably, these means comprise an ice detector 32 of a type already known and used in the industry, for example described in the article "Wind tunnel evaluation of a rime metering device using a magnetostrictive sensor", (published in Atmospheric research 36 (1995) 287-301). Figure 4 shows such a detector 32, which can be installed on the ground near the live conductor 12 to be deglazed. The detector 32 comprises a detector element 34 operating according to the principle of magnetostriction. An oscillator 36 causes the detector element 34 to oscillate at a nominal frequency in the absence of ice or condensation on the external surface of the detector element 34. When there is deposition of ice, frost or any other form of adherent precipitation on the external surface of the detector element 34, the mass of the latter increases and causes it to oscillate at a modified frequency lower than the nominal frequency. It is this change in frequency which makes it possible to identify the atmospheric conditions which may make it necessary to de-ice the power lines.

The device according to the present invention further comprises a communication system having a first component associated with the detection means for sending a trigger signal when the formation of ice is detected in the environment of the live conductor, a second component associated with the electromagnetic pulse source 28 for receiving said trigger signal, and means for transmitting the trigger signal from the first to the second component. Ideally, the communication is done by radio link, thus avoiding all the problems of earthing the components of the communication system. In this application the first component of the communication system is thus a radio transmitter 38, associated with the detector 32 as shown in Figure 4 the second component of the communication system is an antenna 40, as shown in Figure 5. The antenna is preferably hemispherical in shape. In use, de-icing a live conductor 12 in which an electric current flows, comprises the following steps. Ice formation is detected in an environment occupied by the live conductor 12, for example using a magnetostrictive detector as described above. A trigger signal is then sent to an electromagnetic pulse source 28 when the formation of ice in the environment occupied by the live conductor 12 is detected. Preferably this signal is transported by a radio wave. The trigger signal is received by an antenna 40 attached to the source 28. This source 28 must be supplied with current, preferably from the live conductor 12 using a current transformer installed on the latter. Finally, electromagnetic pulses, produced by the source 28, are applied between first ends 20 and 22 of at least one pair 14 of electrically conductive wires 16 and 18 wound, side by side, along and around of the live conductor 12 as described above.

The device according to the invention has been applied to the deicing of a single live conductor 12, but this device is also applicable to the deicing of electric lines comprising more than one live conductor 12. We can for example consider a transmission line comprising three conductors of different phases; due to the insulation problems between each phase, a source 28 must be used for each of the live conductors 12. Thus, three different pulse sources 28 must be used to deglaze all the conductors 12 of this type of transmission line . The same ice detector 32 can however be used to detect the formation of ice in the environment of the power line and send a trigger signal to each of the three sources 28.

The present invention can also be applied to deicing a transmission line comprising at least one beam, each beam comprising a plurality of live conductors in which a current of the same phase flows. Referring to Figures 6 to 10, we can see by way of example a pylon 42 supporting a power transmission line 46 of 735 kilovolts. In this example, the line comprises three bundles 44 each comprising four conductors under voltage 12 of the same phase. The same source of electromagnetic pulses 28 can be used for all the conductors 12 of the same beam 44, since they all have the same phase. Three sources 28 are therefore used for this line 46 fixed on the pylon 42 under each of the beams 44. The sources 28 are fixed under the insulators 48 supporting the conductors 12.

Figure 6 shows the pylon 42 and its environment. The same ice detector 32 is installed on the ground near the pylon 42, and is used to detect the presence of ice in the environment of the line 46 and send a trigger signal to the three sources 28. Figures 7 and 8 show from the front and from the side a pulse source 28 as installed under the insulators 48. The supports 50 and 52 allow the source 28 to be attached to the insulators 48. The first support 50 consists of a plate supported by the insulators 48 by means of the fixing rod 54 and the ring 56. The geometry of the fixing rod 54 and the ring 56 is chosen to standardize the electric field at the points of attachment of the conductors 12 to the insulators 48. The source 28 is cylindrical in shape and is placed horizontally so as to minimize the strong electrical gradients existing near the conductors 12. Fasteners 58 and 64 connect the connection cables 60 and 62 of the source 28 to the first bo uts 20 and 22 of each of the pairs 14 of conductive wires 16 and 18.

Figure 9 shows the welded insulation joints 66 made to join and insulate the second ends 24 and 26 of the conductive wires 16 and 18. In this example, the joints 66 are placed on the conductors 12 midway between two pylons 42 ; in this way, the electromagnetic pulses produced by each source 28 serve to deglaze the conductors over half their length.

FIG. 10 shows an attachment joint 68 made to join two parts of conductive wires 16 or 18 when the latter must pass over a spacer 70. This junction is generally carried out by welding, but a compression joint could also to be used. Changes and modifications to the embodiments described can be made without departing from the scope or spirit of the invention. The scope of the invention is considered to be limited only by the scope of the appended claims.

Claims

1. A device for deglazing a live conductor (1 2) in which an electric current flows, the device comprising at least one pair (14) of electrically conductive wires (16, 18) wound, one next to the other, along and around the live conductor (12) following a substantially helical path, the conductor wires (16, 18) of the pair (14) having first ends (20, 22) for receiving electromagnetic pulses and second ends (24, 26) electrically connected together, the conductive wires (16, 18) being electrically isolated from each other and from the live conductor (12), a source of electromagnetic pulses (28) being electrically connected to the first ends (20, 22) of the pair (14) of conductive wires (1 6, 18); the device being characterized in that it further comprises: means for supplying the source of electromagnetic pulses (28) with a supply current produced from the electric current flowing in the live conductor (12); detection means for detecting ice formation in an environment occupied by the live conductor (12); and a communication system having a first component associated with the detection means for sending a trigger signal when the formation of ice is detected in the environment of the live conductor (12), a second component associated with the source of electromagnetic pulses (28) for receiving said trigger signal, and means for transmitting the trigger signal from the first to the second component.

2. A device according to claim 1, characterized in that the source of electromagnetic pulses (28) comprises: at least one unit of capacitors; at least one output unit per unit of capacitors, each output unit being connected to a pair (14) of conductive wires (16, 18); and a power module for each output unit, each power module comprising a plurality of thyristors connected in series and controlling a discharge of the corresponding capacitor unit to produce electromagnetic pulses in the connected conductor wires (1 6, 1 8) to the output unit.

3. A device according to claim 1 or 2, characterized in that the means for supplying a supply current to the source of electromagnetic pulses (28) comprise a current transformer (30) fixed to the live conductor (1 2 ) and electrically connected to the source of electromagnetic pulses (28).

4. A device according to any one of claims 1 to 3, characterized in that the detection means comprise a detector element (34) operating according to the principle of magnetostriction, the detector element having an external surface, an oscillator (36 ) oscillating the sensor element (34) at a nominal frequency in the absence of ice on said outer surface, the presence of ice on the outer surface increasing the mass of the sensor element (34) and causing it to oscillate at a modified frequency lower than the nominal frequency.

5. A device according to any one of claims 1 to 4, characterized in that the first component of the communication system is a radio transmitter (38), the second component of the communication system is an antenna (40), and the means for transmitting the trigger signal is a radio wave.

6. A device according to claim 5, characterized in that the antenna (40) is of hemispherical shape.

7. A device according to any one of claims 1 to 6, characterized in that the source of electromagnetic pulses (28) supplies pulses having a duration of approximately 1 to 3 milliseconds and a current peak of approximately 6 to 8 kiloamperes, in the conducting wires (1 6, 1 8).

8. A device for deicing a transmission line (46) comprising at least one beam (44), each beam (44) comprising a plurality of live conductors (12) in which an electric current of the same phase flows, the device comprising: at least one pair (14) of electrically conductive wires (1 6, 1 8) wound, one next to the other, along and around each live conductor (1 2) following a substantially trajectory helical, the conductive wires (1 6, 1 8) of the pair (14) having first ends (20, 22) for receiving electromagnetic pulses and second ends (24, 26) electrically connected together, the conductive wires (1 6, 1 8) being electrically isolated from each other and from live conductors (1 2); a source of electromagnetic pulses (28) for each beam (44), electrically connected to the first ends of the pairs (1 4) of conductive wires (1 6, 1 8) wound around each of the live conductors (1 2) included in the bundle (44); the device being characterized in that it further comprises: means for supplying each source of electromagnetic pulses (28) with a supply current produced from an electric current flowing in one of the live conductors (1 2 ) included in the beam (44) with which the source of electromagnetic pulses (28) is associated; detection means for detecting ice formation in an environment occupied by the transmission line (46); and a communication system having a first component associated with the detection means for sending a trigger signal when ice formation is detected in the environment of the transmission line (46), a second component associated with each pulse source electromagnetic (28) for receiving said trigger signal, and a means for transmitting the trigger signal from the first to each second component.

9. A device for deicing a transmission line comprising a plurality of live conductors (1 2) in which an electric current of different phases flows, the device comprising: at least one pair (14) of electrically conductive wires (1 6, 18) wound, one next to the other, along and around each live conductor (1 2) following a substantially helical path, the conductive wires (1 6, 1 8) of the pair (1 4 ) having first ends (20, 22) for receiving electromagnetic impulses and second ends (24, 26) electrically connected together, the conductive wires (1 6, 1 8) being electrically insulated from each other and live conductors (1 2); a source of electromagnetic pulses (28) for each live conductor (1 2), electrically connected to the first ends (20, 22) of the pairs (1 4) of conductive wires (1 6, 1 8) wound around the conductor under corresponding voltage (1 2); the device being characterized in that it further comprises: means for supplying each source of electromagnetic pulses (28) with a supply current produced from an electric current flowing in the live conductors (1 2) ; detection means for detecting ice formation in an environment occupied by the transmission line; and a communication system having a first component associated with the detection means for sending a trigger signal when the formation of ice is detected in the environment of the transmission line, a second component associated with each source of electromagnetic pulses (28 ) to receive said trigger signal, and means for transmitting the trigger signal from the first to each second component.

1 0. A device according to claim 8 or 9, characterized in that each of the sources of electromagnetic pulses (28) comprises: at least one unit of capacitors; at least one output unit per unit of capacitors, each output unit being connected to a pair (14) of conductive wires (1 6, 18); and a power module for each output unit, each power module comprising a plurality of thyristors connected in series and controlling a discharge of the corresponding capacitor unit to produce electromagnetic pulses in the conductor wires (1 6, 1 8) connected to the output unit.

1 1. A device according to any one of claims 8, 9 or 10, characterized in that the means for supplying a supply current to each source of electromagnetic pulses (28) comprise a current transformer (30) fixed to a conductor energized (12) and electrically connected to the source of electromagnetic pulses (28).

1 2. A device according to any one of claims 8 to 1 1, characterized in that the detection means comprise a detector element (34) operating according to the principle of magnetostriction, the detector element (34) having an external surface , an oscillator (36) oscillating the detector element (34) at a nominal frequency in the absence of ice on said external surface, the presence of ice on the external surface increasing the mass of the detector element (34) and causing it to oscillate at a modified frequency lower than the nominal frequency.

1 3. A device according to any one of claims 8 to 12, characterized in that the first component of the communication system is a radio transmitter (38), each second component of the communication system is an antenna (40), and the means for transmitting the trigger signal is a radio wave.

14. A device according to claim 1 3, characterized in that the antenna (40) is of hemispherical shape.

1 5. A device according to any one of claims 8 to 14, characterized in that each source of electromagnetic pulses (28) supplies pulses having a duration of approximately 1 to 3 milliseconds and a current peak of approximately 6 to 8 kiloamperes, in the conducting wires (1 6, 1 8) to which the source of electromagnetic pulses (28) is electrically connected.

1 6. A method for deglazing a live conductor (1 2) in which an electric current flows, characterized in that it comprises the steps of: detecting ice formation in an environment occupied by the live conductor (1 2 ); sending a trigger signal to a source of electromagnetic pulses (28) by a radio wave when the formation of ice in the environment occupied by the live conductor (1 2) is detected; receive the trigger signal; supplying current to the source of electromagnetic pulses (28); and applying electromagnetic pulses between first ends (20, 22) of at least one pair (14) of electrically conductive wires (1 6, 1 8) wound, side by side, along and around of the live conductor (1 2) following a substantially helical path, the conductive wires (1 6, 1 8) of the pair (14) having second ends (24, 26) electrically connected together, the conductive wires (1 6 , 1 8) being electrically isolated from each other and from the live conductor (1 2).