Electric overhead cables which are drawn through forests suffer from the fact that the cut outs made for that purpose, so called cable lanes, grow over too quickly. This results in disturbances in the distribution of electricity when the trees or their branches are bent down by snow and ice to contact the cables. The problem can principally be solved by using insulated cables but it is very expensive to replace the many and long existing cables with cables of that kind.

This invention provides a method and a device for insulating overhead cables on the spot by enclosing them with an insulating plastic covering. It is mainly characterized by a carriage which is movable on the cable and which includes means for successively laying a plastic band onto the cable, a heating element for heating the edges of the band and a clamping device for continuously pressing together and welding the heated band edges while enclosing the cable.

In a preferred embodiment the carriage includes a funnel element and a knife for producing the band from a plastic hose which is fed through the funnel element and cut open by the knife. The invention is described below in greater detail with reference to the annexed drawing, which shows the device in a side view and partly in section.

A carriage having a reversed U-shaped section is built-up by two parallel frames 1 which are mutually connected by five transverse beams 3, 4, 5, 6, 7. The distance between the frames is only slightly greater than the diameter of the largest cable to be insulated according to this method with addition for the insulation. Two carrier wheels 8, 9 of the rope disc type are mounted in bearings on fixed shafts between the frames. A heating element 12 with a mirror 13 for mirror welding, a thermostat 14 and an infra-red detector together are carried by two adjustment screws 16, 17, which are passing through each one corresponding threaded hole in the transverse beams 5, 6, and are arranged

between the carrier wheels. The heating element 12 is followed by a cradle 18 comprising bearing for three calibration wheels 20, 21, 22 and is carried by an adjustment screw 19 which passes through a threaded hole in the fifth transverse beam 7. The cradle is rotatable around a shaft and carries at its front end another infra-red detector 23. Below the heating element 12 and the calibration wheels 20, 21, 22 there is a holder 24 which is removably attached to the frame 1 and which carries bearing pins for four lower pressure wheels 25, 26, 27, 28. Below and obliquely behind the heating element there is a support wheel 30 which is adjustably mounted in the vertical direction in the frame 1 by means of an adjustment screw 51 but also is removable therefrom. Behind the support wheel a rocker beam 40, which carries two guide wheels 41, 42, is pivotally mounted on a bolt 33, which over an eccentric 34 with a grip lever 35 is appliably guided from the upper part of the frame 1. Obliquely above and behind the guide wheel 42 a feeder 36 including a funnel element 37 and a knife 38 is pivotally mounted on a bolt 49 which is fixed to the first transverse beam 3 by a thread and two threaded nuts. A replaceable reel for a band 48 which is covered with silica gel, is mounted in the frame 1 above the knife 38. A slide rail 44 which is fastened to the lower part of the frame 1 is shaped as a runner and terminates the device in the downward direction. All details now mentioned are as far as possible made from an aluminium alloy. The function of the method and the device is as follows.

On a straight section which can extend to a few hundred meters, the tying of the electric conductive cable is removed from the isolators of the poles. At the same time a plastic hose, an electric cable 47 and a steel wire is put onto the insulation rails, in parallel to the conductive cable. At the distant end of the section the wire is led over a rope wheel which is attached to the last pole and down to a motorized winch which is anchored to the ground. At the beginning of the section the carriage, which only weighs a few kilograms, is lifted up to the cable. Because of the inverse U-shape of the frame 1 the carriage can hang like a rider over the loosened conducting cable having the

carrier wheels 8, 9 resting thereon. When the carriage is on its place the holder 24 is pushed upwardly such that the pressure wheels 25, 26, 27, 28 with a slight pressure lie against the underside of the cable. Thereafter the plastic hose, here denoted with 50, is pushed in through the funnel element 37 over the knife 38 and via guide wheels 31, 32 cut up to band shape in between the underside of the conducting cable and the support wheel 30. The friction of the hose against the conducting cable holds it maintained in that position while the rocker beam 40 by the grip lever 35 is raised to the shown position and the band 48 is inserted inside the hose 50 above the knife 38. The object of the band 48 is to dry the air inside the insulation. Then the carriage is carefully moved forwards on the cable such a distance that the heating element 12 covers the end portion of the cut hose 50. During this movement a sufficient amount of hose will pass in through the funnel element 37, be cut up by the knife 38 and is split open occasionally by the conducting wire at the guide wheel 41 enough to wriggle it over it. The heating element 12 is adjusted by the adjusting screws 16, 17 to a suitable distance above the conducting wire which is now covered by the cut up plastic hose. The element 12 is put under tension from the ground over the electric cable 47 and will attain a temperature which is controlled by the thermostat 14. The temperature will be about 230°C and is chosen such that the heat radiation which is concentrated to the cut up upper side by the mirror 13, will quickly give the plastic material a temperature which is suitable for welding it together, said temperature also being controlled by the infra-red detector 15. When the plastic material has attained the right temperature the carriage is moved further a distance such that the calibration wheels 20, 21, 22 successively press together and weld the hot hose edges to each other. A suitable pressure is thereby adjusted by means of the adjustment screw 19. As soon as the necessary controls of cutting, wriggling and welding by further movement of the carriage has been completed on the cable, the continuous process may start. For that object the previously mentioned wire which is laid along the conducting cable and fastened to the front end of the carriage and the winch, is started for moving the carriage the chosen

distance with even velocity. That the welding is correct is controlled by the infra-red detector 23 which immediately responds to and issues a signal if instead of the surface of the plastic hose it "sees" the conducting wire. When the carriage passes the insulator rails the slide rail will provide for sufficient lifting so as to allow free passage. After retying of the thus insulated cable the procedure is repeated on a new cable section.

While the device which has been described in detail here uses hose-shaped plastic material for the insulation it is of course also possible to use the same method having plastic material shaped as a band. For that purpose the knife 38 only has to be replaced by a pair of suitably profiled wheels which shape the band to U-shaped section.