News 5: What materials are better for insulation and sheath of aluminum alloy cable

 

The conductor of aluminum alloy cable “substituting aluminum for copper” can not only effectively reduce the material cost of the cable, but also reduce the cost of transportation and installation. Its performance has not dropped significantly. Everyone has reached a consensus. The market prospect of aluminum alloy cable is still quite good. Okay, we usually only pay attention to cost reduction, but rarely discuss the selection of aluminum alloy cables. This time we will first talk about the selection principles of insulation materials and sheath materials for aluminum alloy cables, and we will also organize them later. The selection of voltage grade, number of cores and cross-sectional area of aluminum alloy cable, and the selection standard of replacing copper with aluminum alloy.

Choice of cable insulation type

The selection of cable insulation type should meet the following requirements:

1) Under the operating voltage, operating current and its characteristics and environmental conditions, the cable insulation characteristics should not be less than the conventional expected service life.

2) The selection should be based on factors such as operational reliability, ease of construction and maintenance, and comprehensive economy of allowable maximum operating temperature and cost

3) It shall meet the requirements of fire prevention places and shall be beneficial to safety.

4) When it is clear that it is necessary to coordinate with environmental protection, an environmentally-friendly cable insulation type should be selected.

5) It is recommended to choose the cross-linked polyethylene insulation type. For the 6kV important circuit or the cross-linked polyethylene cable above 6kV, the form of the three-layer co-extrusion process characteristics of inner and outer semi-conducting and insulating layers should be selected.

Selection of cable sheath type

1. General principles for the selection of cable sheath

1) For AC system single-core cables, when it is necessary to increase the resistance of the cable to external forces, a non-magnetic metal armor layer should be used, and steel armor that has not been effectively treated with non-magnetic properties should not be used.

2) For cables laid in a humid, chemically corrosive environment or an environment prone to water immersion, the metal layer, reinforcement layer, and armor are recommended to adopt polyethylene outer sheath.

3) In crowded public facilities and places with low-toxicity, flame-retardant and fire-proof requirements, halogen-free outer protective layers such as polyolefins can be selected instead of polyvinyl chloride outer protective layers.

4) Except for low-temperature environments below -15℃ or places where medicinal chemical liquids are immersed, as well as cables with low toxicity and flame retardancy requirements, the outer sheath of the cable should be polyethylene, and the outer sheath of polyvinyl chloride can be selected.

5) The aluminum alloy cable adopts aluminum alloy belt interlocking armor to be installed in the building to replace the bridge frame, and it can improve the bending performance and compression performance of the cable. If it is used outdoors in a humid place, the outer sheath must be squeezed.

2. Relevant regulations for selecting cable sheath when laying directly

1) When the cable is under heavy pressure or is in danger of mechanical damage, it should have a reinforced layer or metal tape armor.

2) Cables should be armored with steel wires in soils where displacement may occur such as quicksand layers and backfilled soil belts.

3) For extruded cables used in areas where termites are severely endangered, a higher hardness outer sheath should be used, or a thin outer sheath with higher hardness can be extruded on the ordinary outer sheath. The material can be nylon or special polyolefin. Copolymers, etc., can also be armored with metal sleeves or steel tapes.

4) In areas with high groundwater level, polyethylene outer sheath should be used.

5) In addition to the above, an outer protective layer without armor can be selected.

3. Relevant regulations for selecting cable sheath when laying in the air

1) When the small cross-sectional area extruded insulated cable is directly laid on the arm support, it should be armored with steel tape.

2) In places with high safety requirements and severe rodent damage, such as underground passenger transportation and commercial facilities, plastic insulated cables should be armored with metal tape or steel tape.

3) When the cable is in a high drop stress condition, the multi-core cable should have steel wire armor, and the AC single-core cable should use non-magnetic metal wire armor.

4) Cables that are laid on bridges and other densely supported cables may not contain armor.

5) When it is clear that it is necessary to coordinate with environmental protection, the outer protective layer of polyvinyl chloride shall not be used.

6) For laying in buildings, aluminum alloy belt interlocking armor can be used instead of bridge laying.

Remarks: The cables laid in the protective tube should have an extruded outer sheath.