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Thread: Making 25 cycle
11-17-2005, 10:41 PM #1
If you drive a 3600 rpm motor with a 1800 rpm motor, Will it produce 30Hz? Would the windings need to be energized momentarily with DC when up to speed before applying the load to assure they are excited?If the slip of a 1800 rpm motor makes it more like 1725, than the 30Hz generated might be closer to 25Hz?If 220v 25Hz is needed and the 3600 rpm motor is spinning at half speed, would it produce half the voltage, and possibly need to be wired for 440v to get the wanted 220v? Will the voltage generated vary with the current being drawn? I know a lot of questions. Buffalo NY will be soon loosing the 25 cycle power currently being supplied from Montrael Canada. It used to come from the Shelkof station by the Rainbow bride, but that station was demolished by a rock slide in the '60's. So there are still a few places in Buffalo that use 25 cycle. One is the grain elivators. ArcherDanielsMidland, ConAgra, and General Mills. Also some places still have 25 cycle freight elevators. I am new to this problem, and just investagating things at this point to provide some alternatives to either new motors or a VFD. I am assuming 3 phase 25 cycle, but there used to have 400V 2 phase 25 cycle. If ths is the case, my idea would not work, I assumed 3 phase motors. I don't know where you would find a scott-T trans set-up today. As to the questions, just a general would it work type of thing, that might stimulate thoughts. Thanks for any info, --Doozer
11-18-2005, 12:49 AM #2
"One is the grain elivators. ArcherDanielsMidland, ConAgra, and General Mills. Also some places still have 25 cycle freight elevators. I am new to this problem, and just investagating things at this point to provide some alternatives to either new motors or a VFD."
At my family's former company, a group of limestone quarries, we used to buy 25 Hz from a rural co-op.
When they abandoned 25 Hz, we elected to generate our own 25 Hz, and for this specific purpose we installed two "Superior" diesel engine-generator sets, one being a backup. Each diesel was at least 5,000 HP (about 3.7 MW).
When one diesel threw its crank, and there being no spare cranks available, we made the decision to abandon 25 Hz for 60 Hz, thereby requiring the replacement of hundreds if not a thousand electric motors all over the plants. And their controls, of course.
At that time, about 1970, solid state frequency converters were in their infancy.
It is possible that today our decision would be different, but my family no longer owns the company.
11-18-2005, 02:07 PM #3
"When one diesel threw its crank..."
That must have been exciting.
11-18-2005, 02:28 PM #4
"That must have been exciting."
Yes, and it left the company with no backup, whatsoever.
These two had been operated alternately, and each probably had almost equal hours of operation over their lifetimes.
The failure of one didn't necessarily mean imminent failure of the second, but the handwriting was obviously on the wall.
Operation of the company's plants on the remaining "Superior" diesel-generator was reliable enough so the several month conversion to 60 Hz could be made.
Thereafter, the entire 25 Hz infrastructure was removed.