Specific Features of the Replacement of the Available Flow Path by the Optimal Flow Path when Upgrading the Steam Turbine High-Pressure Cylinder

This scientific paper gives the main research data obtained during the solution of the search problem to define optimal parameter values for the thermal circuit of the К-540-23.5 turbine unit that would provide the most efficient operation both for the optimal version of the high pressure cylinder (HPC) as part of the turbine unit and the turbine unit on the whole. The effect of the distribution of heat differences in the stages of the optimal flow part of the high pressure cylinder used by the К-540-23.5 turbine on the integral quality factors of the turbine unit has been assessed. The calculation studies of the thermal circuit of the turbine unit with the optimal flow section of the high-pressure cylinder showed that the temperature of the underheated feed water in the high pressure heater (HPH) arranged near the steam generator has the most critical effect on the power and economical efficiency of the high pressure cylinder and entire turbine unit. The two-criterion Pareto problem for the upgrading of the turbine unit was formulated and solved to define optimal underheating temperature values. Consideration was given to the two variants of the solution of the optimization problem for the feed water underheating temperature in the high pressure heater. Comparison and analysis of the two variants of solution for the two-criterion optimization problem showed the identity of the obtained data and it confirms the correctness of the problem formulation and the algorithms used for its solution.

Detection and Prediction of Internal-Caused Fire in Tunnel Cable by an Equivalent Transient Thermal Circuit Model

Internal-caused cable fires are one of the most common cable fires, and anomalous temperature increase of the cable core is one of the first signs. However, when a cable is operating with electricity, the temperature of the core conductor cannot be monitored directly; therefore, this characteristic cannot be used in detection and prediction of internal-caused fire in electric cable effectively. An analogous transient thermal circuit model is created, simplified, and optimized to properly compute the temperature of the cable core. Afterward, by using the cable internal-caused fire experimental platform and adjusting current carrying capacity of the tested cable, an experiment is conducted for stimulating the very early stage of three-core cable internal-caused fire. The maximum relative errors of the transient thermal circuit model and the trisection transient thermal circuit model are less than 10% when comparing the experimental data with the calculation results, and the average relative error of the calculated value of trisection transient thermal circuit model is 1.08% after layered optimization. The algorithm model can satisfy the requirement for early detection and prediction in the very early stage of cable internal-caused fire.

Effect of Loads on Temperature Distribution Characteristics of Oil-Immersed Transformer Winding

The temperature of the hot-spots on windings is a crucial factor that can limit the overload capacity of the transformer. Few studies consider the impact of the load on the hot-spot when studying the hot-spot temperature and its location. In this paper, a thermal circuit model based on the thermoelectric analogy method is built to simulate the transformer winding and transformer oil temperature distribution. The hot-spot temperature and its location under different loads are qualitatively analyzed, and the hot-spot location is analyzed and compared to the experimental results. The results show that the hot-spot position on the winding under the rated power appears at 85.88% of the winding height, and the hot-spot position of the winding moves down by 5% in turn at 1.3, 1.48, and 1.73 times the rated power respectively.

TWO APPROACHES TO THE COMPUTATION OF ELECTROTHERMAL PROCESSES AT INDUCTION HEATING OF MOVING INGOTS – BY FIELD THEORY AND THERMAL CIRCUIT THEORY

The model for the computation of thermal processes in induction heating installations with moving ingots is developed using equivalent thermal circuits. The controlled current sources as additional elements in the model are used to take into account the convective heat transfer along the moving ingot. The model is implemented in the program Matlab/Simulink and makes it possible to determine the temperature distribution along the ingot under steady-state heating conditions. The results are compared with data obtained by the alternative method which is based on the electromagnetic and thermal field theory and realized in the Comsol program. As shown the computational results by two methods concerning the temperature distribution along the ingot are in good agreement. The existing advantages and shortcomings of the used approaches are discussed. Ref. 8, fig. 3, table.

Time-Series Temperature-Dependent Power Flow Considering Unbalanced Thermoelectric Equivalent Circuits for Underground LV and MV Cables

<p>This manuscript proposes a time-series temperature-dependent power flow method for unbalanced distribution networks consisting of underground cables. A thermal circuit model for unbalanced three-phase multi-core cables is developed to estimate the conductor temperature and resistance of Medium and Low Voltage distribution networks. More specifically, a novel approach is proposed to model and estimate the parameters of the three-phase thermal circuit of 3/4-core cables, using the results of Finite Element Method and Particle Swarm Optimization. The proposed approach is generic and can be accurately applied to any kind of 3- or 4-core cables buried in homogeneous or non-homogeneous soil. Furthermore, it is applicable in cases where one or more adjacent cables exist. Using the proposed approach, the conductor temperature of each phase can be individually and precisely calculated even in networks with highly unbalanced loads. The proposed approach is expected to be an important tool for simulating the steady state of unbalanced distribution networks and estimating the conductor temperatures. The proposed thermal circuit is validated using two 4-core LV and one 3-core MV cables buried in different depths in homogeneous or non-homogeneous soil. Time-series power flow for a whole year is performed in a 25-bus unbalanced LV network consisting of multicore underground cables.</p>

Time-Series Temperature-Dependent Power Flow Considering Unbalanced Thermoelectric Equivalent Circuits for Underground LV and MV Cables

<p>This manuscript proposes a time-series temperature-dependent power flow method for unbalanced distribution networks consisting of underground cables. A thermal circuit model for unbalanced three-phase multi-core cables is developed to estimate the conductor temperature and resistance of Medium and Low Voltage distribution networks. More specifically, a novel approach is proposed to model and estimate the parameters of the three-phase thermal circuit of 3/4-core cables, using the results of Finite Element Method and Particle Swarm Optimization. The proposed approach is generic and can be accurately applied to any kind of 3- or 4-core cables buried in homogeneous or non-homogeneous soil. Furthermore, it is applicable in cases where one or more adjacent cables exist. Using the proposed approach, the conductor temperature of each phase can be individually and precisely calculated even in networks with highly unbalanced loads. The proposed approach is expected to be an important tool for simulating the steady state of unbalanced distribution networks and estimating the conductor temperatures. The proposed thermal circuit is validated using two 4-core LV and one 3-core MV cables buried in different depths in homogeneous or non-homogeneous soil. Time-series power flow for a whole year is performed in a 25-bus unbalanced LV network consisting of multicore underground cables.</p>

Transient Thermal Performance of Power Cable Ascertained Using Finite Element Analysis

This paper presents the computation of the cable ampacity and the temperature distribution through long duration based on the equivalent thermal circuit based on IEC 60287 standard and the Finite element method using COMSOL (Multiphysics environment, version 5.5). This study investigated the cable ampacity and the temperature rise of the cable core and sheath at steady state and emergency conditions. The cable ampacity was investigated at different conditions such as the variation of cable depth, soil properties, and soil temperature. The results confirmed the adaptation between the thermal circuit results and the COMSOL results as well as the effectiveness of using the numerical method to compute the cable ampacity. Using the COMSOL-based thermal properties evaluations, the transient performance of the cable is ascertained. The transient study is performed for different cable loading currents and dry zone sizes.

Effect of arc extinction on formation of interlayer faulty fusions during consumable electrode arc welding of pipelines

Virtual study is performed using deterministic mathematical model of the welding process to assess the effect of arc interruptions on the formation of the weld pool and seam. It is found that interruptions in arc burning lead to the appearance of craters, the depth of which can reach the thickness of the filling layer. It is shown that the effect of the duration of the interruptions in arc burning on the crater depth depends weakly on the welding speed, but noticeably depends on the spatial position of the weld pool. It is necessary to take into account the criteria for the formation of defects from disturbances in the thermal circuit of the arc when analyzing of the welding monitoring data.