Generator Life and Power Electronics
The deleterious effect of full bridge rectifiers on the output of an ac generator deserves attention by the naval community. The harmonics witnessed at the stator of the generator not only introduce hysteresis and eddy current losses, but voltage spikes which impact the life of the generator. The two primary factors compromising life are localized heating due to harmonics, and voltage spikes which cause insulation failure through partial discharge. Induced eddy currents are proportional to frequency squared.
There are two ways that rectification presents problems to a generator. First, turning off current quickly induces L di/dt voltages earmarked by spikes. This kind of voltage degrades the insulation, contributing both to partial discharge and localized field stress. Second, the currents are no longer sinusoidal. Fourier decomposition shows that the current and voltage traces are composed of multiple frequencies, dominated by the first few odd harmonics. These harmonic frequencies add to the electrical loss in both the rotor and stator by eddy current induction and hysteresis.
The discussions in the paper, “Generator life and power electronics,” by Kent Davey, Howard Jordan, Rigoberto Rodriguez, and Robert Hebner assume a typical diode-based 6-pulse rectification. This paper will be published in Naval Engineering Journal, vol. 121, no. 2, 2009.
For more information, contact Robert Hebner add link to r.hebner@cem.utexas.edu
High-Speed Flywheel and Motor Drive Operation for Energy Recovery in a Mobile Gantry Crane.
Rubber-Tired Gantry (RTG) cranes are commonly used in shipping ports around the world to move containers massing up to 40 metric tons. These cranes are mobile and derive their electrical power requirements for the hoist motor from a diesel engine and generator set rather than from the utility system. Because these cranes are independent of the utility system, energy regenerated via the hoist motor as a container is lowered to the ground is typically wasted as heat in dissipator resistors.
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The operation of a novel long-life flywheel motor and its drive system which can capture the regenerated energy and provide it for subsequent container lifts was tested. Such a flywheel system has proven to significantly reduce fuel usage and diesel engine emissions. The results of the experimental testing using a high-speed permanent magnet synchronous machine and its motor drive designed to recover potential energy in mobile gantry crane applications was detailed in “High-Speed Flywheel and Motor Drive Operation for Energy Recovery in a Mobile Gantry Crane,” by Mark Flynn, Patrick McMullen, and Octavio Solis, and presented at the Applied Power Electronics Conference (APEC 2007) in February 2007. The paper was edited into “Saving Energy Using Flywheels” and published in the November/December 2008 edition of the IEEE Industry Applications Magazine. For more information, please contact Mark Flynn.
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