Repair works at theoverhead transmission line

REPAIR WORKS AT THE HIGH VOLTAGE LINE UNDER THE TENSION REPLACEMENT OF OVERHEAD GROUND-WIRE CABLE The wide experience in execution of repair operations under tension on the overhead power transmission lines of voltage rating 220 kW and over has been accrued in Russia. Porcelain insulators, in phase bracings of double conductors, vibration dumpers and over are replaced. For each type of work checklists are developed.

From recent time the activity list, which is carried out under the tension, has completed with such actual repair operation as replacement of overhead ground-wire cable. Corresponded procedure, which doesn’t require switching-off overhead transmission lines, was created by professional staff members from Moscow and Novosibirsk.

Aleksey Batrakov, Nicolay Korobkov, Alexander Ovsyannikov, Electrosetservice ENES, OAO Replacement of old overhead ground-wire cable on new or on optical pilot ground cable (OPGC) is very actual for Russia, i.e. on the overwhelming majority of overhead transmission lines old ropes already are used and there is a great demand in laying of optic pilot ground cable. The puller-tensioner complexes are usually operated to allow executes the replacement of old overhead ground-wire cable under the tension.

The replacement of overhead ground-wire cable in traditional technologies carries out on switched off overhead transmission line. For time during execution of works are disconnected as well as crossed overhead transmission lines. Understandably, that this action involves high expenses, and at electrical supply of enterprises with continuous manufacturing circuit and deficiency of reserves of electric power supply (for example industrial complexes of aluminum manufacturing) practically impossible to execute this type of works.

In similar cases the most attractive is the execution of works under the tension on the overhead transmission line.

Pic. 1. Tesmec machine on the equipotential area

Pic. 2. Device for wind around of old ground wire by the special adhesive tape (a) and view of braided rope

FIRST TEST At the end of May team of Electrosetservice has been executed testing replacement one of overhead ground-wire cable on the two chain overhead ground wire transmission line 220 kW under the tension. Old ground wire has been used as a pilot rope. For the time of work execution the automatic rotation switching off device of repaired overhead ground wire transmission line has been disabled. Prior to beginning of rope stringing has been carried out with binocular carefully visual survey of old ground wire. Evident damages on the ground wire weren’t detected.

For stringing of ground wire has been used puller-tensioner machine of Italian Company TESMEC. Puller-tensioner machines provide automatically maintenance of pulling of ground wire and don’t suppose to down movement of ground wire at pulling. Stringing automatically stops in case of excess of adjusted limiting value of pulling. Radio management was applied to increase a safety of operators of puller-tensioner.

Machines were established on the equipotential area in the form of grid with mesh 75.75 mm, executed from steel galvanized rope in diameter 4-5 mm (pic. 1), that provided safety of personnel, serving puller-tensioner, from induced current and in case of short circuit during the work. Ground wire was stringed by aluminum pay-off rollers, having natural metal contact with ground wire and support. Stringing was carried out with release pulling, vertical distance from repaired ground wire till level of near rope at stringing composed 3-4 meters. During of stringing periodically there was snowing, air temperature was a -100C, flaws to 6-7 km/s. At the stringing has burst and one wire of old ground wire has started to fray. At a flaw because of approaching of the end of untressed wire to faze conductor was short circuit with disconnecting of high voltage line. During short circuit on two-three next supports was observed arcing on pay-off rollers. The short circuit place was on distance of 2 km from delivery point 500/220/110 kW. Place of damage of old ground wire has been tightened to support and lashing wire has been executed clamp-on of untressed wire.

PROBLEMS OF WIRES In connection with this incident has been continued development of ground wire replacement technology under the tension. The problem of break off wire, which probably, is available, but is not found at visible inspection or can be appeared in the process of ground wire stringing. For avoidance of further stripping-down already broken wire of old ground wire, which succeed to find out at visible inspection, has been applied special splice cases, which fixed (blocked up) broken wires.

Furthermore, has been decided, that the replaced ground wire before pulldown has to be brained by special (reinforced) adhesive tape, which will not allow to stripping-down to wires, blown out during of the stringing of ground wire process. For the covering of ground wire by adhesive tape has been developed relevant mechanism (pic. 2a) with simple kinematic diagram of torque transmission from supporting travelling wheel to covering mechanism. Construction of mechanism allows moving through connecting clamps, repair shells and untressed wires of ground wire. Moving of mechanism in span of ground wire is carried out from the ground with assistance of isolated ropes or at assistance of radio-controlled tow track.

SAFETY OF CROSS LINES Second problem has been connected with necessity of disconnecting of transit high voltage line, generally, lower voltage class, to all time of rope replacement on repaired high voltage line.

Disconnection of transit high voltage line has involved of damage compensation from distribution of electrical power to the high voltage line holders, that brought to naught economic benefit of the works spent on repaired high voltage lines. For this problem has been established the protection, installed on crossed high voltage lines, which allows to carry out the replacement of ground wire without disconnecting of crossed high voltage lines. Protection is installed under replaced ground wire on cables of repaired high voltage lines (pic. 3). Protection frame allows installing and unloading it under the tension. The tension installing near with the crossing, after by force of isolated ropes strings by the conductor and installs under the crossing. Isolated standing ropes, fixed to anchor, installed on the ground using for prevention of reflex movement of protection by the conductors. Protection establishes original wire screen, restraining for down movement or dropping of ground wire on the crossed high voltage lines at alarm condition during stringing. In case of ground wire broken or at assembly defect of puller-tensioners replaced ground wire or new OPGC falls to the protection, at that crossed high voltage line don’t disconnected and don’t damages.

Protection manufactured from steel strops and capron mesh width 3,5 m with mesh 50.50 mm, strung on lined polymer isolators to conductors of repaired high voltage lines (pic. 4).

Pic. 3. Sample of protection’s installation under the crossed high voltage lines.

Pic. 4. Construction of protection for the crossed high voltage lines.

CONCLUSION In 2008 by developed technology has been led several works by repair of ground wire to OPGC on high voltage line 220 kW with total length approx. 90 km. Among new construction site entered steam Oka crossing of high voltage line 220 kW. Experience of the present development attracted attention of Technical Activities Committee of 78th International Electrotechnical Commission, which continues development of the project of international standard by the present type of work. In fact is that the current foreign technologies of ground wire replacement, which underlined to the base of the draft standard, are more labor intensive. They provide for suspension of roller line on old ground wire, stringing of new OPGC by this roller line assisted isolated rope, overturning of old and new rope and pulling-out of old ground wire, also with using of isolated ropes. Rollers at our technology installed only at the pole arm, and as leader for pulling of new OPGC used old ground wire, that greatly reduce labor contribution and don’t create additional loading on old ground wire. And, certainly, analyst of IEC declared important manufacturing method the taping of old ground wire by adhesive tape and suspension of protections under the crossed high voltage line. All indicated characteristics of the present technology of ground wire replacement has provided the leader position to the technology in the world.

http://www.news.elteh.ru/arh/2008/54/08.php