MadSci Network: Engineering

Subject: Can electric motors be used as emergency electric generators?tors

Date: Wed Feb 4 22:39:49 1998
Posted by Arnim K. Zimmer
Grade level: nonaligned
School: No school entered.
City: St, Albert State/Province: Alberta
Country: Canada
Area of science: Engineering
ID: 886653589.Eg

As a young man working on a farm in Europe just after WWII I observed 
locals using electric motors to generate electricity, whenever 
unreliable power utility supplies failed. 

A farm tractor with a belt drive pulley on its side was used to drive 
a 3 to 5 HP motor using a 5" wide leather belt. The utility power grid 
was disconnected at the main switch to the farm's electric panel, the 
motor's plug was inserted into an outlet, and the output generated 
from the driven motor could be used to drive another motor located 
elsewhere and connected to the farm's wiring.  Thus a feed chopping 
machine on the second floor of a building could be used, when driven 
by a tractor standing in the yard, etc. The motors used were AC, and 
some of them were 3 phase 360V connected to 3-phase plug-ins. 

If there was a prolonged power failure, such as recently occurred in 
Quebec, why could farmers there not have resorted to a similar method 
to produce electricity for necessary farm operations such as milking 
and running furnaces? Most had plenty of electric motors and  gasoline 
or Diesel engines, but no generators.  Authorities failed to advice 
people that emergency electric power could thus be created.

Are all electric motors capable to generate electricity if driven?

Does an AC motor generally produce the same phase and voltage that it 
is rated for when driven at its RPM design speed?

Does a DC motor similarly produce DC current at its rated voltage  
when driven at its RPM design speed? 

What would happen if the driving speed is increased/decreased?

What kind of current would be generated when a 110V single phase motor 
is driven at its design speed, Would it be 110V single phase? 

Can we assume that if the voltage output is measured as accurate for 
the 220V motor design, that the motor is driven at its design speed, 
and that AC cycles are alternating at proper cycle frequency? 

I am looking forward for your answers.

A. K. Zimmer 

Re: Can electric motors be used as emergency electric generators?tors

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