The Research Of The Estimation Method Of Power Cables Temperature

Power cable will be aging under the effect of electrical, thermal, mechanical, chemical and other factors during operation, the cable core temperature is one of the important parameters which determine the cable aging rate. If make the power cables operate efficiently and safely, the temperature of the wire core must be sure less than the long-term maximum allowed operating temperature, otherwise, when the cable operating temperature was too high, the aging of insulation materials would be accelerated and the life of the cable would be shorten. In some special application place, for example a ship, where cabin temperature was relatively high, and the air humidity was relatively large. When the cable ampacity was too large, the wire core loss would be very huge, which would make the temperature of cable rise sharply, and the insulation property would be reduced or even failure. So high temperature of cable may lead to fire or other accidents finally, that seriously threat the safety of crew. So it is very necessary to master the temperature of cable accurately. In the actually using process of the cable, it was very difficult to measure the temperature of cable core accurately, because of the complex laying environment. Monitoring cable epidermal temperature was the widely used method currently, and then estimate the temperature of cable core through the calculation method.Steady state and transient state were the temperature states of cable in the process of being used. When the load current was relatively stable, the heat generation and exotherm of cable maintained balance, the temperature of cable would reach relatively stable state, which was called steady state of cable temperature. When the cable load current fluctuated fiercely, the temperature of cable followed fluctuate, which was called the transient state of the cable temperature. In order to master cable temperature state accurately and ensure the safe operation of the cable, the cable estimating methods of the cable steady state and transient state were researched respectively in this paper as following:The structure of the marine ethylene-propylene rubber insulated cable was researched in this paper, the heat transfer path and heat transfer equation of cable steady state were detail introduced, which were commonly used IEC methods. The calculating method and parameter determination method of cable dielectric loss, dielectric loss and body thermal resistance were also given out. The calculating method of the cable’s steady state core temperature was deduced, according to the cable body steady state heat transferring model built by approximate principle of thermal circuit and circuit; The defects of the cable’s steady state core temperature calculating method in the IEC standard were analyzed and researched in this paper, and these defects were improved through proposing the cable’s steady state core temperature calculating method whose calculating accuracy was higher; In order to verify the superiority of improved method, a strict experimental system was designed. The accuracy of the experiment was guaranteed by selecting suitable experimental device. The experiments were did in the condition of single loop cable and large circulation, the experimental data were collected, analyzed and calculated. The comparison between two results through two calculating methods, and the superiority of IEC improved method was verified; According to the principle of heat conduction, the cable structure and the surrounding environment were analyzed, the finite element model of cable temperature field was built, the cable transient temperature field calculation formula was also deduced in this paper. The finite element model of the cable was simulated and calculated by ANSYS software, that verify the fact, if cable Transient conductor temperature could be calculated accurately by the cable temperature field finite element model or not. The core temperature calculated by finite element method was compared with the core temperature calculated by thermal circuit method, then which method was more accurate would be judged. This paper simulated the actual load, and the variation of cable core temperature was researched.