Divided-winding-rotor synchronous generator. A comparison of simulated 30 MW conventional- and divided-winding-rotor turbogenerators

Experiment with a 5kVA machine showed the feasibility of a new form of turbogenerator using a rotor winding of two sections, in X formation, controlling the torque and reactive requirements separately. The performance of a conventionally wound rotor turbogenerator (c.w.r.) of 30MW size, described by Shackshaft, is compared with that of a divided-winding-rotor (d.w.r.) arrangement (CEGB patent application 2240/65) of the same machine. The analogue simulation shows that the d.w.r. can control power and reactive output satisfactorily, without altering the rotor position in relation to the generator air-gap flux. Fully rated stator current at leading power factor can be obtained continuously from no load to full load. The speed of response of the d.w.r.-generator reactive power to a step change of infinite-busbar voltage is, on average, twice that of the c.w.r. Turbogenerator stability is improved, and is shown to be independent of reactive generation or absorption, being affected only by active-power generation. Transient-stability comparisons are made by simulating 3-phase short-circuit faults close up to the high-voltage busbar, with low- and high-impedance connections to the infinite busbar. The c.w.r. simulation at full load with full excitation withstands a fault duration of 0.45s, which comes down, with reducing excitation, to 0.32s when Q u = - 0.225 p.u. and rotor angle = 70°; 0.2s when Q u = - 0.6 p.u. and rotor angle = 100°; and less than 0.1 s when Q u = - 0.9 p.u. and rotor angle = 120°. Comparable d.w.r. simulation of load and excitation conditions all require a fault duration exceeding 0.4s to cause instability. Even the Q u = - 2.3 p.u. condition is simulated without deterioration of control, and requires 0.4s fault duration to cause instability. The high-impedance connection to the infinite-busbar simulation shows, in general, that the maximum fault duration for each type of generator is reduced by 0.1s.