| The shipboard power cables play a significant role in transporting energy in power system, their insulating state has a direct impact on the safe operation of the whole electrical equipment. Due to the complex laying environment, the insulating material can be easily damaged under the influence of multi-factors. Thermal aging which was influenced by temperature is the key to result in the decline and even failure of cable insulation. The thermal aging life evaluation of cables in service should be carried out to guarantee their stable and safe operation. Up to now, most researchers take the accelerated thermal aging testing in laboratory as a means of cables thermal life evaluation, by establishing thermal life model to extrapolate the service life under cables rated temperature. But most works offer no reliability demonstration of the test data and model. In addition, cables normal aging temperature is lower than their rated temperature, life assessment at the rated temperature is conservative to some extend. It is necessary to deduce the aging temperature of cable in service to improve the assessment accuracy.In view of the mentioned problems, the accelerated thermal aging testing in laboratory combined with the parameters measured in service were applied by using Ethylene Propylene Rubber (EPR) insulated marine cable as the research object. Firstly, accelerated thermal aging testing for EPR insulated cables were performed, relational function between elongation at-break and thermal aging time were established, and changes of elongation at-break affected by thermal aging time and temperature. Meanwhile, thermal aging model of EPR cable based on Arrhenius equation was calculated by using variance analysis to the test data. Statistic test was applied, the result shown that the thermal aging model built before was appropriate and can provide reference for the life assessment of EPR cable. Secondly, an on-line monitoring system for cable in service was designed based on the C8051F340microcontroller, PT100temperature sensor and hall current sensor were adopted for signal acquisition. The temperature and current preprocessing circuits were designed and monitor data can real-time display on LCD12864interface after signal processing and AD converting. Moreover, the key circuit and alarm circuit were also designed, and then detailed introduced data storage in the USB flash disk by means of reading and writing program of CH375chip. This system can achieve the function of current and skin temperature monitoring for marine cables in service according to the detailed design of hardware and software. Finally, the equivalent thermal circuit model of EPR cable was built based on the thermal resistance itself. Current and skin temperature data of EPR cable were continuously measured in lab by imitating on-site operating condition, the operating core temperature was deduced and using it as its normal aging temperature by analyzing temperature rise between skin and conductor calculation combined with the monitoring data. The experimental result showed that the aging life of EPR cable was close to the practical service life of low-voltage marine rubber cables, and also meet the design requirement of power cable industry for30-50years.This combination method of accelerated thermal aging testing and operating parameter monitoring can give a credible assessment for EPR cable, and provides preventive replacement references for rubber insulated marine cables in service. |
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