Simulation of heat transfer and air cooling in a power rectifier cabinet for generator excitation system

As an important part of the modern generator excitation system, the power rectifier cabinet accommodates the silicon-controlled rectifiers (SCRs) whose junction temperature should be kept within limit at all times. For excitation systems of 1000MW steam turbine generator and 700WM hydro generator, the required output DC current for each rectifier cabinet can be as high as 4,000A, which raises challenge for cooling design. Meanwhile, under normal operation conditions, excessive cooling wastes energy and causes frequent change of air filter due to high volume cooling air flow. In order to optimize the cooling design, the heat transfer and cooling processes are simulated for a power rectifier cabinet with 6 SCRs and using forced air cooling. First the heat generated by the SCR is calculated as a function of the rectifier cabinet output current. 3D implicit unsteady k-ε turbulent model is used to simulate the air flow. The energy is coupled between the solid and the fluid (air) to reflect the heat transfer from the SCR to the heat sink and then to the cooling air. For given output current and inlet air velocity, the temperature of the SCRs, heat sinks and the cooling air is simulated; the air velocity at each location in the cabinet is also calculated. The simulation results showed good agreement with the experiment data which laid the foundation for future application of the simulation tool.