Computational And Experimental Research On Conductor Temperature Of Single-core Cables

Conductor temperature of single-core cable is not allowed to exceed the long-term maximum permissible temperature of its insulation in operation, so as to ensure cables to operate safely, economically and reasonably. Conversely, if conductor temperature is too high, aging of insulation will be accelerated and life of cables will be shortened. Therefore realization of monitoring on conductor temperature is very necessary. However, limited by current technology, it is difficult to realize the direct accurate measurement of conductor temperature, so computation of conductor temperature is a feasible option. Accordingly, working condition could be monitored to ensure that the cable operates within a rated temperature range and the transmission capacity could be adjusted appropriately in emergent operation, which can improve the utilization efficiency of cable as well as ensure the safety and reliability of its operation. The following issues are researched in this dissertation:1) Structure of single-core XLPE cables is analyzed; the heat equation, equivalent thermal circuit and computational formulas of cable body resistance, dielectric loss, and metal sheath loss in IEC standard under steady-state condition are introduced, and the algorithm for steady-state conductor temperature of cables is deduced.2) According to defects of IEC conductor temperature algorithms of steady-state, improved method with better applicability and higher accuracy is proposed. And conductor temperature rising tests are carried out to verify the correctness of this method.3) The transient thermal circuit model of cable body and ambient medium is established, and concept of thermal time constant is adopted to research the algorithm of transient cable conductor temperature under emergent load. And conductor temperature rising tests are carried out to verify the calculation.4) Based on the online monitoring on load current and outer sheath temperature of the cable, transient thermal circuit model of cable body is established; and the calculating method of transient conductor temperature via historical data of load current and outer sheath temperature is studied; and conductor temperature rising tests are carried out to verify the calculation. Computational methods of cable conductor temperature under steady-state and transient-state condition are studied in this dissertation, and related theoretical computations are executed. The calculated results of conductor temperature which are contrasted with test data are verified to be correct and effective. Algorithms studied in this dissertation can be used for temperature control, condition monitoring and fault prediction in operation of single-core cables.