ANALYSIS OF VOLTAGES GENERATED IN AUXILIARY WINDINGS OF LARGE STEAM TURBINE-GENERATORS.

摘要

The factors which determine the fundamental frequency voltage induced in the potential windings of the excitation system of a large synchronous generator during a steady state armature short circuit have been investigated by a magnetostatic finite element analysis.; The windings, which consist of conductors (P-bars) placed at the top of the slots containing the armature winding, are subject to the following six voltages: (1) A voltage proportional to the armature slot leakage reactance which arises because the P-bar is linked by flux from the field winding that is equal to the armature slot leakage flux. (2) A voltage proportional to the armature and leakage reactance that is generated by magnetic flux in the stator yoke equivalent to the voltage behind that reactance. (3) A voltage increase for a P-bar located at the top of a slot where the armature bars beneath it are not in phase. This voltage is caused by a reduction in the net current in the slot available to cancel flux from the field. (4) A voltage reduction induced in the P-bar end arms by leakage flux in the ends of the machine. (5) A voltage reduction because the P-bar may be located within rather than at the top of the stator slot. (6) A voltage induced in the end connection ring by the armature currents flowing in adjacent connection rings.; A 2-D magnetostatic finite element method was employed to investigate the voltages induced in the P-bar. Such an approach is useful in analyzing the P-bar voltage, especially for voltages induced in the end region of the machine. However, even though steps were taken to achieve a balance of the field and armature MMF's under the short circuit condition, it was found that even errors of less than one percent in this balance introduced serious errors in the P-bar voltage.; Previous methods based upon selected components of the armature leakage reactance have not included all of the components identified in this work. Their accuracy for any given machine rests on the cancellation of the voltage components each has neglected to include.; The algorithm developed in this investigation uses the same constituents of the armature leakage reactance, but includes the voltage components listed above. The results are compared to test data and the previous methods and show that the overall accuracy has been improved and the variations from machine to machine are much less.