BS 7970:2005 pdf free.Electric cables — Metallic wire and foil sheath constructions of power cables having XLPE insulation forrated voltages from66 kV (Um= 72.5 kV) to132 kV (Um= 145 kV)
BS 7970 This British Standard specifies requirements for construction and performance, and gives methods of test,for metallic wire and foil sheath constructions of power cables having XLPE insulation for rated voltagesfrom 66 kV(Um =72.5 kV) to 132kV(Um = 145 kV).The tests and requirements in this British Standardare additional to the tests and requirements for cables and their accessories specified in BS 7912.
This British Standard is applicable to single-core cables for usual conditions of installation and operation,but not to special cables,such as those designed for submarine applications.
NOTE Guidance on selection of cables is given in Annex A.
The following referenced documents are indispensable for the application of this document. For datedreferences, only the edition cited applies. For undated references,the latest edition of the referenceddocument (including any amendments) applies.
BS 6360,Specification for conductors in insulated cables and cords.
BS 7870-2:1999,LV and MV polymeric insulated cables for use by distribution and generation utilities—Part 2: Methods of test.
A layer of metallic wires shall be applied over the semi-conducting insulation screen in a single helicallayer.The wires shall be spaced with an average gap not greater than 4 mm and no gap shall exceed 8 mm.An equalizing metallic tape shall be applied.
Semi-conducting water blocking/cushioning tape(s) shall be applied above and below the metallic wires.
A continuous metallic foil sheath shall be longitudinally applied over the water blocking tapes with aminimum overlap of 7 mm. Joins in the foil shall have the same electrical performance as a continuouspiece of foil. The metallic foil overlap shall be sealed to prevent ingress of moisture.
The metallic foil sheath shall be either plain or corrugated foil bonded to the oversheath.
The thickness and the material of the metallic foil sheath shall be as agreed between the manufacturer andthe purchaser.
NOTE1 An energy absorbing bedding layer may be applied under the metallic foil sheath by agreement between the manufacturerand the purchaser.
NOTE2 Other designs, e.g.using a longitudinally-welded,thick metallic foil sheath, may be used and tested in accordance with thisBritish Standard by agreement between the manufacturer and the purchaser. Additional or alternative testing might be necessary.
The earth fault capability in current (kA) and duration (seconds) shall be as specified by the purchaser.The cross-sectional area,approximate number and approximate diameter of the metallic wires shall be asspecified by the manufacturer.BS 7970 pdf download.