A simplified approach to determination of saturated synchronous reactances of large turbogenerators under load

This paper details the use of computerized magnetic field solutions, based on magnetic vector potential, to develop a simplified approach to the calculation of saturated values of steady state reactances of turbogenerators under various load conditions. When magnetic nonlinearity of the stator and rotor materials is taken into account, the turbogenerator reactances become dependent on the saturation conditions in the machine, which are a function of the operating conditions (terminal voltage, current and power factor). Quadrature axis synchronous reactances are reduced by as much as 40% from their classical unsaturated values under rated load. Torque angles deduced from the model at rated load are lower by as much as 20% than values obtained by standard methods. The method is applied to two typical 4-pole, 659 MVA and 2-pole, 733 MVA turbogenerators of the gas inner-coaled type. Supportive shop floor test results are provided.