| Among various types of electrical equipment in the ship,the marine power cable has a special status,it is responsible for the task of transferring energy and signal to all other electrical equipments on board,once a fault occurs,it will cause incalculable losses.Unlike the land cable,marine cable has its unique working environments,it often work in a complex environment which mixed with high temperature,high salt,high humidity,oil contamination,radiation and so on.The ship cables affected by multi-factors including physical and chemical aspects,these external factors will result in the decline of cable insulation performance and eventually lead to insulate failure,make the cable unable work up to its expected value of lifetime.Maintenance the cable had been damaged or replace the invalid cable during the overhaul period when the ship in port are main methods used to deal with these problems currently,however blind replacement is bound to cause a waste of resources because the cable is expensive and the actual lives of cables operating in different environments are also different.Substitute the ineffective cable is also a complicated project which need to cost massive time and money,the economic loss caused by tardy task is more difficult to accept.So how to effectively assess the working states of the cable' insulate and draw a conclusion of the residual life for the cables to make the maintenance or replacement more scientific become the research purpose in practical work.The methods for cable insulation states assessment are mainly qualitative analysis in now days,which only able to make a rough analysis for the cable's insulation state,still hardly to get accurate conclusions about the residual lifetime through a quantitative analysis.Furthermore,the current detection means are mostly destructive which will cause secondary damage to itself make the cables' follow-up service lifetime decreased,and this testing process need a long time to complete,so it's still a difficult problem to evaluation the cables service lifetime.In order to better study the aging state of the cable insulation material and predict its life,a accelerated aging test for the samples of cable at four aging temperatures of120?,135?,150? and 165? which were chosen based relevant standards was carried out,each group set the corresponding sampling time in this experiment?First of all,measuring tan?(Dielectric loss tangent)for the cable segment specimens after accelerated thermal aging,choose the dielectric loss tangent value of selected 0.01Hz-1Hz interval doing integral operation.In order to avoid the influence of the measured temperature,the time temperature shift algorithm is applied to translate the integrated curve at high temperature to the reference temperature,fitting these curves at reference temperature and then extrapolated it to the actual operating temperature.Secondly,testing EAB(Elongation at break)of the same cable dumbbell samples at the same accelerated thermal aging condition,The EAB at high temperature were shifted from the high temperatures to the reference temperature by the time temperature shift algorithm and curve fitting was performed.Based on the obtained mathematical models,establishing the relationship between the integral value of the tan? and the EAB,then using Arrhenius equation to analyze the lifetime value when the EAB decreases to 50% of the initial value as the end point,the calculated results of the EAB were set as standard conclusion to verify the results come from tan?.The results show that the errors between the tan? analysis method and the calculation of the EAB are relatively small,which provides a non-destructive and rapid detection method for the assessment of the insulation state and the residual life of the cable. |
PDF Full Text Request