165 / 2018-08-25 19:41:24

The Application of System Identification Method in Calculating the Transient Temperature Rise of Power Cables

transient temperature; system identification;power cables

To study the discipline of temperature rise of power cables in their actual operation and solve the problem of the real time rapid calculation of cables’ transient temperature rise in order to provide effective decision-making supporting information for power dispatchers in emergency situations such as load transfer caused by other cables’ fault, the mathematical expressions of transient temperature rise of cables caused by the heat from their own conduct and other adjacent cables’ conduct were studied in this paper. The mathematical relationship of the cables’ running load, the running time and the temperature of the cables’ core was established which can be used to build the foundation of fast and real time calculation of power transmission capacity of cables in the future.
In order to find this mathematical representation, the heat transfer process of three three-core cables directly buried in the soil in urban power grid was studied in this paper. Firstly, based on the basic heat transfer principle, the equivalent two-dimensional heat transfer model was established with the help of the finite element analysis software. And the corresponding boundary situations such as the air temperature and the deep soil temperature were determined according to the actual situation.The basic data that would be used in system identification method was obtained by numerical simulation method. For any one of the cables, the temperature rise value and the time of temperature rise caused by the cable’s self-loss and the loss of adjacent cables were obtained by calculating the transient heat transfer process between the cables and the heat transfer process of the self-heating. Based on the temperature rise data and the time spent on the heat transfer process, the linear autoregressive model was used to identify the temperature rise caused by the cable self-heating and the temperature rise caused by the mutual thermal influence of adjacent cables. The coefficients in the mathematical model was found to form the identification results. The stability of the identified model was verified by observing the pole distribution of the system equations. The results showed that the system was stable. One cable’s heating model was composed with the self-heating model and the heat transfer model of the adjacent cable heating transferred to its conduct. Finally, in order to test the actual effect of the model, based on the new input loss of the three three-core cables, based on the principle of temperature rise superposition, the total output of the model was compared with the calculation result of the finite element model.