Cable insulation aging cause analysis
online running of power cables and electrical equipment with cable due to mechanical force, electric power, heat and chemical corrosion and other factors, the insulation aging brittle harden, affect the use, the cable breakdown caused by aging and make the shorten service life.
in the mechanical force, electric power, thermal and chemical effects of four factors, thermal and chemical function mainly is caused by the installations and the surrounding environment. Since the 1980 s, with a polyethylene insulation and crosslinking polyethylene as the main body of the plastic cable insulation, because of its good performance, light weight, low price and construction is convenient wait for a characteristic, therefore, in the domestic electric power circuit and control circuit, the application of increasing. This kind of cable with plastic insulation, influenced by environmental conditions and aging is more serious than other species. Now with polyethylene insulated cable as an example, the cable is affected by environmental conditions and aging.
( 1) The influence of different laying method of cable aging
the main laying mode of power cable directly buried installation with underground and overhead ( Including wire) Laying, cable conduit installation, and the bottom of the sea. For laying installation way different role in different environmental conditions, the possible form and degree of aging is different also, cause the service life of the cable length difference is very big.
( 2) A wide variety of environmental aging
the cable laying sites and the surrounding gas, liquid and solid three types of medium, three kinds of medium to a different impact on cable, such as corrosion of harmful gas in air will cable insulation, the same is true of harmful liquid and solid.
cold cable accessories
cold cable accessories is the use of elastomer materials ( Commonly used with silicone rubber and ethylene propylene rubber) Injection of vulcanization molding in the factory, then through hole enlargement, lined with plastic screw support constitute parts of various kinds of cable accessories. On-site installation, the pre expansion woolly, in after processing, the end of the cable or tapping out internal support article plastic screw ( Support) , the pressure on the cable insulation and cable accessories. Because it is in the room temperature by elastic retraction force, rather than the heat shrinkable cable accessories to use heat shrink, commonly known as the cold shrink cable accessories. Early cold shrink cable terminal head just additional parts adopt silicon rubber insulation from the cold, electric field treatment still USES the stress cone type or stress belt around the package type. Generally adopt cold shrinkage stress control tube, from 10 kv to 35 kv voltage level. Cold shrink cable joint, 1 kv level using cold contraction insulation tube reinforced insulation, 10 kv level with joint semiconduction shielding layer inside and outside the cold contraction insulation parts. With cold contraction are three core cable terminal bifurcation branches.
cold shrinkage cable accessories has small volume, convenient operation, quickly, without special tools, less scope width, and the product specifications, etc. Compared with the heat shrinkable cable accessories, don't need a fire heating, and move or bend after installation will not appear like heat shrinkable cable accessories accessories internal interlayer release dangerous ( Because the cold shrink cable accessories by elastic compression force) 。 Compared with prefabricated cable accessories, although everything elastic clamping force to ensure that the internal interface features, but it's not like prefabricated cable accessories and cable is one to one correspondence, specifications.
it must be noted that, before installation on the cable, the prefabricated parts is no tension of cable accessories, cable accessories and cold contraction is under a state of high tension, so in the period of storage, must ensure that the cold contraction type should be no obvious permanent deformation of the parts or elastic stress relaxation, or installed on the cable after can't guarantee enough elastic clamping force, which can guarantee good interface characteristic.