Medium Voltage Power Cables Aerial Bundle Cable 3X70 50mm2 Alu 12 / 20kV Unipolar MT Cable

1.1. MATERIALS AND CONSTRUCTION

1.1.1. General

Only compatible materials that are suitable for the specified service conditions shall be used in the construction of the cables.

1.1.2. Phase Cores

• Each core of the aerial bundled cable shall be suitable for use in a system operating voltage of 11,000V 50Hz.
• The conductor shall be made from hard drawn, circular, stranded and compacted plain aluminum conductor as per IEC 60228.
• The conductor screen shall consist of an extruded layer of semi-conducting compound, applied to each conductor direct, in the same operation as the application of the dielectric and of the core screen. The outer surface of the conductor screen shall be in continuous adherent contact with the inner surface of the dielectric. The screen shall be readily removable from the conductor and it shall have a thickness of at least 0.5mm.
• The insulation (dielectric) shall consist of an extruded sheath of cross-linked polyethylene (XLPE). The nominal thickness of the dielectric shall conform to Table 2 (the thickness of screening materials shall not be included in the measured dielectric thickness).
• A dielectric screen consisting of a semi-conducting core screen, bedding tape and metallic screen shall be applied to each core.

• The core screen shall consist of an extruded layer of semi-conducting compound, applied in intimate contact with the dielectric of each core, in the same operation as the application of the conductor screen and the dielectric. The layer shall be continuous and uniform in quality and shall be removable without causing damage to the dielectric. It shall have a thickness of at least 0.5mm.
• A semi-conducting bedding tape shall be applied over the semi-conducting core screen.
• The metallic screen shall consist of annealed copper tape helically applied over the bedding tape. The metallic screen shall be electrically continuous and any joints shall be made in an acceptable, workmanlike manner and so finished that no sharp edges or protrusions remain. The copper tape shall be applied with a minimum overlap of 15%.
• The metallic screen shall be suitably water blocked.
  • The outer sheath shall be extruded PVC, black and ultra-violet protected for operation in direct sunlight.

• Supporting Catenary
  • The supporting catenary shall consist of stranded galvanized steel wires. Galvanizing of the wires shall comply with the requirements of IEC 60888 for class 1.
  • The lay of the wires shall be right-hand (Z) with lay ratio not less than 10 and not more than 14.
  • The covering shall be PVC applied by forced extrusion to provide a smooth outer finish, and shall be ultra-violet protected for operation in direct sunlight.

  • Table 1: Supporting Catenary

    Catenary Size, mm²		50	70
    Number of Wires		7	7
    Wire Size (diameter), mm		3.00	3.60
    Minimum Tensile Strength of each Wire, kN		9.26	13.13
    Elongation at break, minimum %		3.5	4
    Thickness of protective covering	Nominal, mm	1.20	1.20
    	Minimum at any point, mm	0.96	0.96

    ELECTRICAL AND MECHANICAL CHARACTERISTICS

    The aerial bundled cables shall comply with the following table:

    Table 2: Electrical and Mechanical Characteristics

    Conductor size, mm²			70	95	185
    Diameter over conductor, nominal, mm			9.3-10.2	11.6	16.4
    Thickness of dielectric	Nominal, mm		3.4	3.4	3.4
    	Minimum at a point, mm		2.96	2.96	2.96
    Diameter over insulation Nominal, mm			16.1-17.0	21.3	25.9
    Diameter over semi-conducting core screen Nominal, mm			18.1-19	23.3	27.9
    Thickness of copper tape Nominal, mm			0.15	0.15	0.15
    Thickness of sheath		Nominal, mm	1.8	1.8	1.9
    		Minimum at a point, mm	1.43	1.43	1.51
    Catenary size, mm²			50	50	70
    Overall diameter of bundle, Nominal, mm			Bidder to state	67.8	79.2
    Nominal mass, kg/m			Bidder to state	3.25	4.65
    Resistance, Ω/km			0.443	0.32	0.164
    Strands, no.			12	15	30