Abstract
The traditional generating set is usually comprised of a classical, wound-field, salient-pole, or cylindrical rotor synchronous generator, excited by a separate smaller machine, via a rotating, uncontrolled diode rectifier. The effects of the commutation processes of the diode bridge are often overlooked and neglected. However, due to the uncontrolled nature of this process, the rectified voltage available at the main generator's rotor terminals can be significantly lower than the expected value. This is especially true for low-to-medium power rated systems. In this paper, a detailed investigation of these aspects is done and an accurate voltage drop prediction model is then proposed. The model is validated with finite-element analysis and with experimental results for a particular low–medium rated generating system in the 400 kVA power range. The validated tool is then integrated into an innovative design tool, which first performs an analytical presizing procedure and then utilizes a genetic algorithm approach to identify an optimal excitation system design, aimed at minimizing the voltage drop ensuing from the diode commutations, with minimum impact on the overall efficiency.
Highlights
T HE excitation system of classical, wound-field, Synchronous Generators (SGs) is a subpart of a relatively complex feedback control system, whose primary function is maintaining the output voltage constant at the main machine’s stator terminals
A more robust and modern solution is that of providing the excitation current by employing a brushless excitation system, consisting of a small “inside-out” electrical machine whose three phase output voltages are rectified by a rotating bridge and fed to the main generator’s field winding
The field current is regulated by an Automatic Voltage Regulator (AVR), which is powered either by a permanent magnet generator in separately-excited systems or by the SG residual voltage in self-excited systems
Summary
T HE excitation system of classical, wound-field, Synchronous Generators (SGs) is a subpart of a relatively complex feedback control system, whose primary function is maintaining the output voltage constant at the main machine’s stator terminals. The main alternator is a three-phase machine featuring 4 rotor poles, 48 stator slots with skewing and 6 damping bars per pole, designed to provide a rated voltage of 400V (50Hz) with a Y-connection of the armature phases This is achieved with field voltages and currents of 20.5V and 14.4A at no-load and 101.5V and 50A at full-load. Rated Power Rated Voltage Rated Frequency Stator Pole Number Rotor Slot Number Magnetic Material
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