Similarity And Application Of Cable Ventilation And Heat Dissipation Characteristics Of Power Cabin In Utility Tunnel Under Multi-Factor Constraints

The rapid development of the economy and society has led to a sharp increase in the demand for electricity in the city,and the cable laying method in the power cabin of the integrated utility tunnel with unique advantages has been gradually promoted.As an important parameter for cable operation and maintenance,cable temperature is extremely important for the selection of working conditions and expected design of power cabins.Only by correctly understanding the changing law of the cable temperature under various factors and the heat dissipation mechanism can improve the expected design efficiency of the power cabin and reduce the maintenance cost.The reduced-scale test conducted by the similarity theory is currently widely used in the physics analysis of various buildings.Therefore,based on the Ar number,a reduced-scale model was built with a 1:5 ratio based on a integrated utility tunnel.Through the Ar number,each physical quantity proportional relationship between the scale model and prototype building is obtained.Under various working conditions,the computational fluid dynamics?CFD?software Fluent is used to perform numerical simulation calculation on the prototype power cabin.The accuracy of the numerical simulation is proved by comparing the cable temperature and the wind speed of the numerical simulation and the reduced-scale test.The relative error of the cable surface temperature is within 10%,which is within the scope allowed by the project.Based on numerical simulation,reduced-scaled CFD models were established,and 32cases were calculated and analyzed using orthogonal experiments.The key parameters that affected the cable temperature were obtained:heat dissipation,ventilation,ventilation temperature,fire separation length,and thermal conductivity of the insulation layer.Using the Ipsen method to dimensionless the cable temperature control equation,three kinds of dimensionless numbers composed of key influencing factors are obtained:Ar number,?₁number and?₂number.The dimensionless number is changed to obtain the simulation calculation results of 125 cases to establish a data set,and the classification and regression tree decision tree?CART?is used to analyze the data set to obtain the prediction model of the maximum temperature of the power cabin cable.The R²of the current model is 0.97.Through the analysis the effect of the main influent factors and the dimensionless parameters on maximum temperature of the cable on the simulation data sets of 125 work conditions,a dimensionless control equation with a prediction error of less than 16%is obtained,and it is found that the wind speed will not effectively reduce the maximum temperature of the cable when the wind temperature increases to a certain degree,and an increase in thermal conductivity will not effectively reduce the maximum temperature of the cable.In addition,the results show that when there are too many constrained variables in the thermodynamic model,the dimensionless function fitted by experiment has great limitations.Therefore,compared with the dimensionless parameter equation,the CART decision tree has better temperature prediction ability?relative error is less than 8.3%?.In order to improve the readability of the CART decision tree,the temperature of the leaf nodes of the decision tree is divided into 4 temperature sets,thereby obtaining 7 main temperature judgment paths.The F test proves the contribution of each influencing factor in the path to the temperature change.In addition,dividing the dimensionless number into value ranges yields the probability that each value range falls into a different temperature set.It is proved by additional simulation cases that this judgment method can effectively screen the temperature set of 70%of the cases.Finally,it is found that the decision tree has a better predictive ability compared with the traditional empirical formula?OHL?,and the reduced-scale experiment proves the good extension of the decision tree.In the temperature rise analysis of the dynamic ampacity of the cable,the influencing factors such as the airflow temperature around the cable,the airflow velocity and the initial temperature of the cable were selected to perform dynamic simulation calculation on the prototype cable.The dynamic temperature rise curve corrected by the influence factors of airflow temperature and airflow velocity is obtained by nonlinear fitting.The goodness of fit of various formulas R²is greater than 0.95.Finally,additional dynamic simulation proves that the error of the fitting formula is less than 4%.Therefore,it can provide a certain reference for the construction standards and energy-saving optimization of the integrated utility tunnel power cabin.