Types of Conductors :

• In the early days conductor used on transmission lines were usually Copper, but Aluminium Conductors have Completely replaced Copper because of the much lower cost and lighter weight of Aluminium conductor compared with a Copper conductor of the same resistance. The fact that Aluminium conductor has a larger diameter than a Copper conductor of the same resistance is also an advantage. With a larger diameter the lines of electric flux originating on the conductor will be farther apart at the conductor surface for the same voltage. This means a lower voltage gradient at the conductor surface and less tendency to ionise the air around the conductor. Ionisation produces the undesirable effect called corona.
• The symbols identifying different types of Aluminium conductors are as follows:-
  • AAC     : All Aluminium conductors.
  • AAAC   : All Aluminium Alloy conductors
  • ACSR   : Aluminium conductors, Steel-Reinforced
  • ACAR   : Aluminium conductor, Alloy-Reinforced
  
  Aluminium alloy conductors have higher tensile strength than the conductor of EC grade Aluminium or AAC, ACSR consists of a central core of steel strands surrounded by layers of Aluminium strands. ACAR has a central core of higher strength Aluminium Alloy surrounded by layer of Electrical-Conductor-Grade Aluminium.
• The alternate layers of a stranded conductor are spiraled in opposite direction to prevent unwinding and make the outer radius of one layer coincide with the inner radius of the next. Standing provides flexibility for a large cross-sectional area. The number of strands depend on the number of layers and on whether all the strands are of the same diameter. The total number of strands in concentrically stranded conductors, where the total annular space is filled with strands of uniform diameter is 7,19,37,91 or more.

Standard Sizes of Conductor for Lines of Various Voltages:

• The following sizes have now been standardised by CEA for transmission lines of different voltages-

  (i)	For 132 KV lines	:	'Panther' ACSR having 7-strands of steel of dia 3.00 mm and 30-Strands of Aluminium of dia 3.00 mm
  (ii)	For 220 KV lines	:	'Zebra' ACSR having 7-strand of steel of dia 3.18 mm and 54-Strands of Aluminium of dia 3.18 mm.
  (iii)	For 400 KV lines	:	Twin 'Moose' ACSR having 7-Strands of steel of dia 3.53 mm and 54-Strands of Aluminium of dia 3.53 mm.

Special Requirements of Conductors as per UPSEB Specifications :

• No joints are permitted in Steel core as well as in the outer most Aluminium layer of the conductor.
• The composite conductors are subjected to following type tests:-
  • DC Resistance
  • Ultimate Tensile Strength
  • Surface condition Test*                                      *Only for 'Moose' conductor for use on 400 KV lines
  • Corona Test*
  • Radio-Interference Voltage Test.*

All Aluminium Alloy Conductors (AAAC)

• Recently AAAC are being used in some SEBs to overcome menace of pilferage of ACSR and AAC conductors, particularly lower voltage lines. AAAC can not be re-cycled and it does not have any common use for other purposes, as that in case of pure Aluminium.
  AAAC is made out of heat treated Aluminium-Magnesium-Silicon Alloy designed as 64401 T 81 covered under IS:9997:1991 containing 0.6-0.9% Magnesium and 0.5-0.9% Silicon.
• Besides use of AAAC on lower voltage lines from the point of view of avoiding its pilferage, it is also better for use in coastal areas to avoid corrosion problem prevalent in Steel core of ACSR conductors.

Bundled Conductors

• The combination of more than one conductor per phase in parallel suitably spaced from each other used in overhead Transmission Line is defined as conductor bundle. The individual conductor in a bundle is defined as Sub-conductor.
• At Extra High Voltage (EHV), i.e. voltage above 220 KV corona with its resultant power loss and particularly its interference with communication is excessive if the circuit has only one conductor per phase. The High-Voltage Gradient at the conductor in the EHV range is reduced considerably by having two or more conductors per phase in close proximity compared with the spacing between conductor-bundle spaced 450 mm is used in India.
• The three conductor bundle usually has the conductors at the vertices of an equilateral triangle and four conductors bundle usually has its conductors at the corners of a square.
• The current will not divide exactly between the conductor of the bundle unless there is a transposition of the conductors within the bundle, but the difference is of no practical importance.
• Reduced reactance is the other equally important advantage of bundling. Increasing the number of conductor in a bundle reduces the effects of corona and reduces the reactance. The reduction of reactance results from the increased Geometric Mean Radius (GMR) of the bundle.
• Conductors for River Crossing Used in UPSEB :
  For river crossing of 132 KV, 220KV and 400 KV transmission lines, the following conductors are being used in UPSEB:-
  • For 132 KV Lines:
    Special 'Panther' conductor, i.e. one Aluminium layer of ACSR 'Panther' conductor removed having 7-strands of Steel of 3.00 mm dia plus 12-Aluminium strands of 3.00 mm dia.
  • For 220 KV Lines:
    Special 'DEER' conductor, having 17-Strands of Steel of dia 2.69 mm and 12-strands of Aluminium of 4.65 mm dia.
  • For 400 KV Lines: 'Moose' ACSR
• The Technical Particulars of ACSR 'Panther', 'Zebra' and 'Moose' conductors are given in Table  14.1 and that of Special 'Panther' and Special 'Deer' Are given in Table 14.II.