Power cable residual life prediction
1, the service life of the cable
cable manufacturers qualified cable products leaving the factory, after laying installation, inspection and acceptance by the operation of the up in load, running under normal conditions, however, the life should be in more than 15 years, including polyvinyl chloride (PVC) and polyethylene cable should be in more than 20 years, nylon sheathed cable service life is longer.
2, polyethylene insulated cable residual life prediction of
polyethylene and crosslinking polyethylene cable application increased year by year, in the process of running by environmental conditions, often appear 'water tree' and 'sulfide tree' of the so-called 'branches' phenomenon, and prolong the life of it under serious threat, use fixed number of year, this has caused cable factory and use the unit and the attention of relevant departments. Especially large factories and mines and regional users increasingly pay attention to this kind of cable exactly how long it can run normally without the correct estimation method, in order to estimate how much is left has been put into operation of cable life, accomplish know fairly well, prepare for change. Will now, internal and external research analysis and estimation method is introduced as follows.
( 1) 'Branches' phenomena affect the qualitative analysis of polyethylene cable
because of polyethylene and other plastic cable will appear the phenomenon of 'branches' in the running, some professionals at home and abroad through multiple research, draw the conclusion: polyethylene insulation and cross-linked polyethylene insulated cable in running failure rate increases with the increase of using years increased, the higher failure rate is according to the relationship between logarithmic ratio change. Because this type of cable, ' 'the growth of branches 'will cause the change of the dielectric loss tangent of the cable. It can be 'branches' of production and the dielectric loss Angle tangent relationship with cable expected residual life each other. Cable at the same time in the running process of be affected with damp be affected with damp and water invasion is also common, water invasion will not only reduce the cable insulation resistance, and can make the dielectric strength of the cable serious decline, especially at the beginning of the cable into the water and half months, moisture affects the dielectric strength is significantly, after this will further reduce the breakdown voltage of the cable, but slowly from the previous stage. But these studies only for determining the cable dielectric strength will decrease due to the phenomenon of 'branches', dielectric loss Angle tangent value will be the formation of 'branches' phenomenon and aging and increase the qualitative relationship, and there is no enough data to illustrate the quantitative relationship between them.
( 2) By measuring the value of the estimated cable residual life
in qualitative research, concluded some professional cable breakdown failure associated with the phenomenon of 'branches' of big, but just weak link between them relation; The dielectric loss Angle tangent value and the operation condition of the cable and the average water content are related. Research and analysis prove that the cable failure rate is roughly proportional to the value of the cable, when its value increases to a critical value, the failure rate of the cable increases to difficult to guarantee the normal operation, that the cable has reached its service life.
( 3) Estimates that
with the above formula estimating method is a non-destructive evaluation practices, it need not run cable line power first, then remove a specimen is calculated, this is the more approximate a method to estimate the residual life of the cable. With the development of the cable testing technology and the accumulation of practical experience, a more accurate cable directly or indirectly the determination method of residual life calculation or will study, and get the popularization and application.