Preformed Armour Rods

• Performed armour rods suitable for ACSR conductors of the required size, diameter and breaking load are provided at all the suspension points of each conductor to minimize the stresses and strains developed in the conductor at suspension supports resulting from static and dynamic loads, such as maximum wind load conditions, aeolin vibrations and sub-span oscillation, slipping of conductor from the clamps as a result of unbalanced conductor tensions in adjustment span and broken wire conditions. They shall also withstand power arcs, chaffing and abrasions from clamps and localised heating effect due to magnetic power losses from clamps as well as copper losses of the conductor covered inside the armour rod and clamps.
• Preformed Armour rods are used as a set composed of 10 or more aluminium cylindrical rods having diameter and length proportional to the conductor diameter. Each rod is preformed in helical shape and has parrot-bill end finish.
• The preformed armour rods are made of aluminium alloy HE-20 or 65032 as per IS : 739-1977 or 6061-T 91 as per Aluminium Association of USA Specification. The aluminium alloy used should be properly heat treated during manufacturing process.

Fig. 15-I

TABLE 15-I

Midspan Compression Joints

• Compression Type joints are used for jointing the length of ACSR Conductors.
• The shape of cross section of sleeves is round before compression and hexagonal after compression.
• The joint consists of two sleeves one for steel portion and the other for Aluminium portion. The steel sleeve is made of mild steel galvanised stainless steel. The Aluminium Sleeve is made out of pure extruded Aluminium Tube of 99.5% purity.

Fig. 15-II

• Technical Particulars :
  • Dimensional details :

TABLE 15-II

Repair Sleeves

• Compression Type repair sleeves are used to repair minor damages on the aluminium strands of the ACSR conductors.
  Repair Sleeves are composed two identical aluminium pieces fitted into each other. They are applied to reinforce a conductor having some of the strands broken or damaged. They are to be compressed by the same die used for the aluminium component of dead end joint for the same conductor. The shape of cross section of the repair sleeves shall be generally round before compression and shall be hexagonal after compression.
• The sleeves shall be manufactured from 99.5% pure extruded aluminium.

Fig. 15-III

• Technical Particulars :

TABLE 15-III

Vibration Dampers

• 4R type Vibration dampers suitable for ACSR conductors shall be provided at all tension and suspension points on each conductor in each span. The dampers shall effectively damp out the vibrations of the conductors. Vibration damper is basically a dissipating machine which transforms the kinetic energy of the Vibrating cable into heat in the messenger cable resulting from interstrand friction of the messenger cable strands.
• The dissipation of the energy is obtained by alternate bending of steel messenger cable connected in the centre to the conductor by means of a suitable clamp and loaded at the extreities with two properly shaped weights. A '4R' damper is a four resonancy system obtained by adopting for the two valves of the damper different mass (placed/attached asymmetrically with messenger cable) and different moment of Inertia of the weights and different length of messenger cables.

Fig.15-IV

• Technical Particulars :
  • Dimension of standard range of '4R' dampers :
    Vibration dampers shall fulfill dimensional requirements as per standard range of dampers mentioned below :

TABLE 15-IV

• Location Chart of the Vibration Dampers

Fig.15-V

Dampers spacing for suspensions string is measured from centre of clamp and for tension string from mouth of dead end clamp.

• Recommended Damper Spacing

TABLE 15-V

Placement chart for the above conductors upto spans of 1200 Metres is given in detail at Table 15-VI on page 102.

Spacer and Spacer Dampers

• In the bundle system configuration of the conductors in EHV class transmission lines, the spacing in the phase sub-conductors is maintained by placing spacers or spacer dampers at appropriate spacing in the span. The proper placement is neccessary to avoid clashing of the sub-conductors during normal as well as under electrical fault conditions. For example in the 400 KV transmission lines, twin bundle of conductors is used per phase. The spacer dampers in addition to maintaining spacing, also act as dampers to restrict the aeolin vibration and sub-span oscillations.

1. Main body.
2. Neoprene bonded cushioned grip/Aluminium alloy grip.
3. Retaining rods (in case of cushioned grip)
   1. Cushioned grip spacers

   

   Fig.15-VI

   1. Rigid Type Spacers

Fig.15-VII

The main body is an aluminium alloy (type LM 6061 or equivalent) tube of suitable length. The grip are fitted by crimping of the ends of the tube. The cushioned grip spacers are used on spacer, whereas rigid grip spacers are used on the jumpers. The cushioned grip is made of neoprene with aluminium inserts embedded in it, whereas rigid grip is made of aluminium alloy. The grip has groove of diameter suitable to the size of conductor. The cushioned grip spacers are provided with retaining rods of aluminium alloy (LM 6061) to provide uniformly distributed stress and also to avoid any pointed stress. The rigid grip have fixing arrangement with bolts, nuts and washers etc.

The spacer dampers normally consist of :

1. Main Body
2. Keepers
3. Arms
4. Rubber bush

Fig.15-VIII

The main body, keeper and arms are made of aluminium alloy gravity die cast. The rubber bush is made of neoprene. The main body and arm at both ends are connected through neoprenes bushes. The arm has groove suitable to the size of conductor. The spacer dampers are fitted on conductors through arms and held with the help off keepers and bolts.

Technical Particulars :

+ 25 mmc) Torsional+ 507.Shore hardness of neoprene65-80 BHN8.UTS of retaining rods35 Kg/mm29.No. of retaining rods8 nos.10.RIV at 266 KV r.m.s.

Not less than 500 microvolts

11.CoronaNot less than 320 KV r.m.s.

(TABLE 15-VI)

For 'Special DEER' being used for 220 KV River Crossings 2 Nos. Vibration dampers are used upto span of 850 metres and 3 Nos. for spans of 850 metres and above. The dampers are used on each side of tower at spacings 0.989 metres, 1.978 metres and 2.9675 metres.