ABOUT THE AUTHOR—JOHN COWDREY
John Cowdrey is an electrical engineer and hydro-power consultant. He taught electrical machinery lab at the Colorado School of Mines, and developed and taught a Hydro Plant Operator’s school for employees from Denver Water, Northern Water, and the City of Boulder. He has twelve years experience operating, troubleshooting, modifying, and maintaining six City of Boulder hydroelectric power plants ranging from 70kW to 3100kW, and has been a docent at the historic Fall River Hydroelectric Plant in Estes Park, Colorado. He has presented various lectures to the Osher Lifelong Learning Institute (OLLI) at CSU, and the Loveland Historical Society.
This paper discusses the use of the induction machine as a motor or generator. Historically there was a need for a simple and reliable motor to replace the DC motor. Both Nikola Tesla and Galileo Ferris invented a method to produce a rotating magnetic field, using polyphase power. Single phase power and the double revolving field theory.
PART ONE Motor key concepts: Squirrel-cage and wound-rotor field construction for motors and generators – armature and field. Slip (difference in speed) between the rotating magnetic field and the field itself induces a voltage in the field and its current produces a magnetic field which eliminates the need for the DC machine’s commutator. Induction motor construction and its advantages and disadvantages. Single- two- and three-phase power. Phase rotation. Balanced and unbalanced systems. Power factor and its effect on power transfer. Eddy currents and the use of laminated steel for both the field and armature. Motor starting methods and NEMA torque-speed characteristics. The induction motor equivalent circuit. Motor inrush current and ways to limit it. NEMA standard machine designs. Effect of unbalanced voltages and loss of a phase. Insulation classes. Insulation temperature and operation at altitude. Amortisseur windings for synchronous generator starting. Motor losses, efficiency, and motor power flow diagram. Cost of electricity over the life of the motor. Variable speed drives.
PART TWO Generator Key concepts: The three Phase induction Machine as a Generator: Use of turbines and grid-connected induction generators on the City of Boulder’s water system for pressure reduction. Pumps as turbines (PAT). Induction generator power factor correction, construction and its advantages and disadvantages. Synchronization to the grid. Utility protective relay requirements for grid connection. Self-excited induction generators (SEIG) for off-grid applications. The C-2C method of operating an induction generator single-phase with balanced generator currents. Converting single phase to three phase using the C-2C method.Zero crossover switching and high inrush current. Double fed induction generator using a wound rotor (DFIG).
Please direct any correspondence to hydroman303@msn.com ©2024 JMCPublications. All Rights Reserved.