Development of a variable-shaft-speed alternator
The development of a variable speed alternator with output voltage and current synchronized and phase-locked to the power grid is reported. The variable shaft speed alternator (VSSA) consists of an ordinary unmodified 1-1/2 Hp wound-rotor motor, with polyphase excitation controlled by solid state switching and a hybrid of analog and digital circuitry. This circuitry senses both shaft speed and line phase resulting in logic levels which control the current flow in each rotor coil. In various bench tests the VSSA was observed under no load, nearly-resistive passive load, and power grid load conditions. Under no load, and at various shaft speeds measurements were made of output voltage harmonic content and spectral quality using the Fourier transform method, output amplitude vs excitation, and the lock-in range of the VSSA phase-lock property. Typically 95% of the output power is phase-locked in a +- 0.2 Hz band width centered at 60 Hz. Under three-phase passive-load conditions at a constant rms terminal voltage (110V), output power was observed to depend linearly on excitation current only. A first order polynomial was also found using the least-squares regression method which accurately expressed the relationship among shaft speed, excitation power, and output power. VSSA torque was inferred from observations to be proportional to output power. Efficiency for converting mechanical power to electrical was inferred over a range of shaft speeds. A break-even speed below which no net power is produced was observed to be 0.375 of the synchronous speed for all output power levels. Similar behavior was observed with power fed to the power network (grid). Additional measurements involved VSSA performance at various power factors. Conclusions are drawn, and suggestions for future development are offered.
- Research Organization:
- Science Applications, Inc., Palo Alto, CA (USA)
- DOE Contract Number:
- FC07-80ID12203
- OSTI ID:
- 5252584
- Report Number(s):
- DOE/ID/12203-T1; ON: DE82012334
- Country of Publication:
- United States
- Language:
- English
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