Turbogenerator Electromagnetic Analysis with Changing Reactive Load

Abstract

Comparative numerical analysis of electromagnetic processes in the end zone of powerful turbogenerators has been carried out at changes in reactive load from rated duty to underexcitation, as well as performance parameters of static overload that determine the stability of synchronous operation of turbogenerators in the power system. It was demonstrated that the representation of magnetic field sources and calculation results in the form of rotating waves allows simplifying and speeding up the solution of threedimensional electromagnetic problems in the turbogenerator end zone. Using a previously developed calculation method, the electromagnetic fields and processes in over- and underexcitation modes, in particular, peculiarities of shielding in turbogenerators are studied. It was established that the added losses and electrodynamic forces in underexcitation modes acting on the outermost core packages, pressure plate, and stator shield increased by 1.5–3.0 times, resulting in accelerated aging of the turbogenerator end zone. An appropriate margin shall be provided in the cooling system and the structural design of the turbogenerator end zone. Static overload capacity in nominal conditions is determined by the ratio of maximum power to rated power. An analytical functional relationship between static overload capacity and load conditions was established. It was demonstrated that when switching to the underexcitation mode while maintaining the active load due to a decrease in the excitation current and maximum power, the static overload factor decreases to unity, that there is virtually no static stability margin of the turbogenerator in this mode. Calculations were made for turbogenerators with a capacity of 200–1111 MVA. It is recommended to limit the operation of turbogenerators in underexcitation modes and to use specialized compensators more extensively.