Bradenton, FL--A standard motor or generator configuration has the rotor surrounded by the stator. If the roles are reversed-stator inside, rotor outside-the inertia of the machine increases dramatically.
Written-Pole motors are synchronous motors that require low starting current (See Design News, 1-23-95, pg. 92). The written-pole feature also serves as a constant-frequency generator. In the inside-out configuration, the unit's written-pole and high inertia team up to create a generator with excellent ride-through characteristics. During an outage, the generator's high inertia keeps it spinning, and the written-pole keeps the output frequency constant.
Precise Power Corp. has been building motor-generator sets for use as power conditioners and uninterruptible power supplies (UPS) for several years. Both motor and generator stators mount on the same shaft and the common rotor shell serves both units. The sets provide isolation from line spikes and supply clean, constant-frequency power for sensitive loads. They also supply constant-frequency ride-through protection for outages that last as long as 15 seconds.
The latest twist is to add a clutched gasoline engine (converted to burn propane) to the package. In normal operation, the motor-generator set supplies clean power to a computer installation or other critical equipment. During brief power outages, its ride-through capability continues to supply clean power.
If the outage exceeds a predetermined period, say 5 to 8 seconds, the clutch actuates, starting the IC engine in about one second. Powered by the engine, the generator, with its Written-Pole rotor, continues to supply clean power to the critical equipment. The motor now can serve as a generator, supplying power to lighting circuits and other non-critical loads.
"We call this the PUPPY, that's Precise Uninterruptable Power Protecting You," says Precise's Richard Morash. A typical unit is a 15-hp motor driving a 10-kVA generator. When powered by the IC engine, the motor produces an additional 10 kVA. Single-phase units carry ratings to 20 kW, three-phase to 60 kW output.
Additional details...Contact Richard T. Morash, P.E., Precise Power Corp., Box 9547, Bradenton, FL 34206, (813) 746-3515.