Steady State Short Circuit Characteristics of Turbine-Generators from Design Data Using Field Calculations

The steady state short circuit characteristics of a turbine-generator is obtained from design parameters using magnetic field calculations. The stator windings are represented by an equivalent current sheet lumped into the stator slots, and the two axis theory is used to calculate the short circuit current in the stator windings. A two- dimensional analysis of the field is made using the nodal method to give relationships between current and magnetic field for each node. In the stator windings the currents depend on the rotational voltage calculated in the field analysis and the drop in the overhang leakage reactance. This leads to a matrix of conductivities which is defined to allow for the evaluation of the short circuit currents and the field distribution simultaneously. The problem being nonlinear, the iron permeabilities being dependent on the resultant field pattern, the problem is solved iteratively using Newton-Raphson and sparsity techniques. Calculated values compare well with the experimental results for a 333 MVA turbine-generator.