LT Aerial Bunched cables

Aerial Bunch Cables For Lt Lines

In the ABC system, the insulated conductors (3 or 4 numbers as required) are twisted around a high strength Aluminium Alloy bare wire, which carries the main weight and also serves as the earth -cum- neutral wire. The bare wire (messenger) may be bare or insulated. The phase conductors are not under tension. The system is very safe and LT faults are practically eliminated consequently, interruptions of supply are minimized and the life of transformers is considerably increased, as these are not subjected to frequent fault as happens with the bear conductors. The problem of tree clearance is also minimized.

ABC Cable constructions is generally and popularly convenient for catering LT power to more number of consumers without any to clumsier requirement of hardware and as such voltage problems are also reduced to notable extent. The phase and street lighting conductors shall be insulated with black weather resistant polyethylene/XLPE suitable for 1100-volt insulation. Cross Linked Polyethylene (XLPE) insulation with colour requirement is also opted by many countries. Due to elimination of insulators and associated hardwares, ABC system is more convenient as compared to overhead LT lines system as conventional electrical requirement of feeding power to LT consumer is fulfilled in better way.

General

The Phase & Street lightening Conductors shall be insulated with Black weather resistant XLPE Insulation 1100V grade. The insulated phase conductors (with additional street lighting conductor, if provided) shall be twisted around the bare aluminium alloy messenger wire, which shall take all the mechanical stress. The messenger wire shall also serve as the earth -cum neutral wire.

Advantage (Abc System)

• All L.T. line faults are practically eliminated, maintaining uninterrupted supply.
• Tripping of Transformers decreases considerably since the line hardly subjected to faults.
• A problem of Tree clearance is totally avoided due to reduction in pole height.
• Insulators are completely eliminated from the insulation of ABC lines.
• The initial cost of laying the line is more or less same as conventional Conductors.
• The Theft of power possibility is reduced substantially since unauthorized tapping of power cannot be done without removing the insulation.
• In remote areas, it is possible to maintain continued power supply with power.
• High capacitance and low inductance leading to low impendence of lines.
• Lower Voltage Drop, Higher Current capacities, vis-à-vis better system stability.
• It can be over hung in dense vegetation and forests.
• Additional connections can be easily and quickly made with hot-line connectors.
• Total lines are reduced and maintenance is very easy. More or less maintence free.
• Multiple circuits of power and telephone cables could be strung in the same set of poles.

1. Scope

• This specification covers the requirements of polyethylene/cross linked polyethylene insulated cables with aluminium conductors twisted over a central bare / insulated aluminium alloy messenger wire for use as overhead distribution feeders.
• The cables covered in this standard are suitable for use on three-phase ac (earthed or unearthed) system for rated voltage upto and including 1100V.
  
  Note:- The cables confirming to his standard may be operated continuously at a power frequency voltage to percent higher than the rated voltage.
   
• The cables covered in this standard are suitable for use where the combination of ambient temperature and temperature rise due to load, including temperature on exposure to direct sunlight results in conductor temperature not exceeding the following.

Type of insulation	Normal Continuous Operation	Short Circuit Operation
Polyethylene	700C	1600C
Cross linked Polyethylene	900C	2500C

2. Aplicable Standards
The rated voltage of the cable shall be 1100volts. Unless otherwise stipulated in this specification, the following standards applicable.

• IS : 1596 1984: Polyethylene insulated cable 1100 volts.
• IS : 8130-1984: Conductors fro insulated cables.
• IS : 6474-1984: Polyethylene insulation of cables.
• IS : 398 -1994: (Part IV) Aluminium alloy conductor.
• IS : 398 1996: (Part III) For ACSR conductor.
• IS : 14255 1995: Arial Bunched Cable Specification
• IS : 7098 (Pt-I) 1988 with latest amendment.

3. Terminology
For the purpose of this standard the following definition to those given in IS 1885 (Part 32) : 1993 shall apply.

3.1 Routine Tests
Test made by the manufacturers on all finished cable lengths to Demonstrate the integrity of the cables.

3.2 Type Tests
Tests required to be made before supply on a general commercial basis on a type of cable in order to demonstrate satisfactory performance characteristics to meet the intended application.

Note : These tests are of such a nature that after they have been made, they need not be repeated unless changes are made in the cable materials of design, which might change the performance characteristics.

3.3 Acceptance Tests
Test carried our on samples taken from a lot for the purpose of acceptance of the lot.

3.4 Optional Tests
Special test to be carried out, when required by agreement between the Purchaser and the supplier.

3.5 Earthed System
All electric system, which fulfills any of the following conditions :

• The neutral point or mid point connection is earthed in such a manner that even fault conditions, the maximum voltage that can between any conductor and earth docs not exceed 80 percent of nominal system voltage
• The neutral point or mid point connection is not earthed but a protective device is installed which automatically cuts our part of the system which accidentally becomes earthed
• In case of ac system only, the neutral point is earthed through an ARC suppression coil with arrangement for isolation within 1 hour of occurrence of the fault provided that total of such periods in a year does not exceed 125 hours.

3.6 Unearthed System
An electric system which does not fulfill the requirements of earthed (see 3.5(a), (b), (c).

Materials

4. Conductor

• The power/outer insulated neutral/ street lighting conductors shall conform to flexibility Class 2 of IS 8130 :1984.
• The messenger (Neutral conductor) or otherwise shall be either stranded circular or compacted circular type and shall have minimum 7 strands. The surface of the conductor shall be smooth.
• 4.3 A protective barrier may be applied between the conductor and insulation, if required. Such barrier, when used, shall be compatible with insulating material and suitable for the operating temperature of the cable.
• 4.4 The size of street lighting conductor shall be (16mm2).
• 4.5 The size of messenger conductor and its breaking load shall be as per Table 1.

Sr. No.	Nominal Cross Sectional Area of Phase	Messenger Conductor
		Nominal Cross Sectional Area	Maximum D.C Resistance at 200C	Minimum Breaking Load
	mm2	mm2	Ohm/km	KN
(1)	(2)	(3)	(4)	(5)
i)	16	25	1.38	7
ii)	25	25	1.38	7
iii)	35	25	1.38	7
iv)	50	35	0.986	9.8
v)	70	50	0.689	14
vi)	95	70	0.492	19.7

• There shall be no joints in any wire of the messenger conductor except those made in the Base rod or wires before final drawing. The direction of outer layer of wires in messenger conductors shall be right hand.

4.7 Core Indentification
The phase conductors shall be provided with one, two or three ridge and outer neutral insulated conductor, if provided, shall have four ridges as shown in Fig. I for quick identification. The street lighting conductor and messenger conductor (if insulated) shall not have any identification mark. Identification by other means, as agreed between the supplier and purchaser, is also permissible.

4.8 Assemby (Laying Up)
Three insulated phase conductors, one insulated neutral conductor (if required) and a street lighting conductor (if required) shall be twisted around the bare (or insulated) as required messenger conductor without fillers with a lay not exceeding 35 times the diameter of the diameter of the insulated phase conductor. The direction of lay shall be right hand.

Phase Conductor & Neutral Conductor

4.9 Phase/Street Lighting Conductor
The conductor shall be of H2 or H4 grade aluminium complying with the Requirements of IS 8130 : 1984

Phase Conductor

• The phase conductor and street lighting conductors shall be insulated with black weather Resistant cross linked polyethylene suitable for 1100V grade. The insulated Conductors shall generally confirm to the standards, applicable standards.
• The phase conductors shall be suitable compacted and the outer diameter shall be within The limits specified.
• The phase conductors shall be provided with one, two and three ridges for quick Indentification.
• The tensile strength of aluminium wire used in the conductors shall not be less the 90N/mm².
• The standard sizes and technical characteristics of the phase and street lighting conductors Shall be as shown in the following table.

Nominal sectional area (mm2)	No. of strands	Max. D.C. resistance at 200C	Insulation Thickness (mm)
16	7	1.91	1.2
25	7	1.2	1.2
35	7	0.868	1.2
50	7	0.641	1.5
70	19	0.443	1.5
95	19	0.32	1.5

Note: - The resistance value given in Col. 3 are the max, permissible.

4.10 Messenger (Neutral Conductor or Otherwise)
The conductor shall be heat- treated aluminium magnesium-silicon alloy wires containing approximate 0.5% magnesium and approximately 0.5% silicon conforming to IS 398 (Part-4): 1979.

• The bare messenger wire shall be generally made of aluminium alloy wire /ACSR confirming to IS to IS: 398 (Part IV) 1994 with latest amendment composed of 7 strands and shall be suitably competed to have smooth surface to avoid damage to the XLPE insulation of the phase conductors twisted around the messenger.
• There shall be no joints in any wire of the stranded messenger conductor except those made in the base rod or wires before final drawing. The number of the insulated Phase conductor in an ABC cable will vary depending on the Specifications and requirement of customer.Whereas, the ABC Cable with a single insulated conductor is called Duplex, the one with two insulated Conductor is called Triplex, and the one with three insulated Conductors is called Quadruple. In addition to this, a street lighting or an emergency service conductor may also be provided public amenities such as street lighting.