A question on generators

There is a question on generators that I would like to ask.

I know that in shunt generators there is a particular upper limit to generator field resistance which should not be exceeded. This resistance is called CRITICAL RESISTANCE. If this resistance is exceeded then there won't be any build up of voltage in the generator.

I would like to know whether there is some particular lower limit to the field resistance also when the generator is operating on load. What will happen when the resistance is lowered below this limit.

Reply to
dhanu
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The lower limit on resistance is the resistance of the field winding itself. To decrease this requires a rewind. Nothing of particular interest occurs at this point.

In the first case the upper limit to resistance is determined by the magnetisation characteristic (open circuit voltage vs field current) of the machine and the "field line (V/Rf). The two must intersect to have self excitation. Now look at what happens to the field line and this intersection as the field resistance is decreased. -All that occurs is that the intersection shifts to a higher voltage until saturation limits any further change. The voltage at any speed and load will be higher with a higher field current (excluding saturation). Nothing more.

-- Don Kelly snipped-for-privacy@peeshaw.ca remove the urine to answer

Reply to
Don Kelly

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