IEEE 635-2003 pdf download IEEE Guide for Selection and Design of Aluminum Sheaths for Power Cables
3. Definitions
3.1 aluminum sheath: An impervious aluminum or aluminum alloy tube, either smooth or corrugatedwhich is applied over a cable core to provide mechanical protection.
3.2 extra high-oltage aluminum-sheathed power cable: Cable used in an electric system having amaximum phase-to-phase rms ac voltage above 242 000 V, the cable having an aluminum sheath as a majorcomponent in its construction.
3.3 high-voltage aluminum-sheathed power cable: Cable used in an electric system having maximumphase-to-phase rms ac voltage above 72 500 V to 242 000 V, the cable having an aluminum sheath as amajor component in its construction.
3.4 low-voltage aluminum-sheathed power cable: Cable used in an electric system having a maximumphase-to-phase rms ac voltage of 1000 V or less, the cable having an aluminum sheath as a major componentin its construction.
3.5 medium-voltage aluminum-sheathed power cable: Cable used in an electric system having a maximum phase-to-phase rms ac voltage above 1000 V to 72 500 V, the cable having an aluminum sheath as amajor component in its construction
4. Advantages and limitations of aluminum sheaths
A cable designer or user should be aware of the merits and limitations of aluminum-sheathed cable andassign an order of importance to each property to satisfy the requirements of the specific application wherepower cables are inyolved
4.1 Advantages
4.1.1 Weight reduction
The use of an aluminum sheath reduces the weight of the cable compared with those having other metallicsheaths, thereby simplifying installation and lowering shipping costs. Furthermore, longer pulling lengthsare possible with reduced cable weight.
4.12 Electrical protection
As a sheath, aluminum is characterized by high electrical conductance and consequently by high short-circuit capability.In addition, high conductance offers excellent protection against lightning
4.1.3 Fatigue resistance
Aluminum has very good mechanical properties, for example, hardness and fatigue resistance. Thereforethe possibility of sheath fatigue failure due to vibrations and movement induced by thermal cycling isminimal.
4.1.4 Mechanical protection
Aluminum has a higher yield point, higher tensile strength, and less creep by comparison with other moreductile sheathing materials. These attributes permit fewer clamps for installations in tunnels or aboveground. The high hoop strength of aluminum sheath is particularly important in pressurized cables, since itmay permit a reduction in the number of stop joints and pressure tanks.
4.2 Limitations
4.2.1 Corrosion resistance
Aluminum is a relatively active metal chemically, and care must be taken to provide adequate protectionagainst corrosion.
4.2.2 Bend performance
Because of its rigidity, smooth-aluminum-sheathed cable is more difficult to bend than corrugated-aluminum-sheathed cable.
4.2.3 Jointing and terminating
For jointing and terminating, an aluminum sheath requires techniques different from those applicable toother commonly used metals, and retraining of splicing and terminating crews may be necessary.
4.2.4 Sheath losses
Because of its high electrical conductance, losses resulting from induced sheath currents and eddy currentsare substantial. These losses can be reduced by selecting thinner sheaths and by using special sheath bondingmethods for single-conductor cables.
IEEE 635-2003 pdf download
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