# Generators and the associated force?

## Main Question or Discussion Point

Question, does the force required to turn a generator change with changing current loads?
Basically I’m wondering if it would take more force to turn a generator when there is a load, apposed to if there were zero load?
Thanks
Philip

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chroot
Staff Emeritus
Gold Member
Originally posted by philipc
Basically I’m wondering if it would take more force to turn a generator when there is a load, apposed to if there were zero load?
Yup, it does. The conservation of energy applies everywhere.

- Warren

chroot,
Thanks for the quick response,
So could it also be said the only forces on the generator with out load(not including friction ect) would be from losses in the generator it self?
In other words an "Ideal" generator would spin indefinitely until there was a current load put on it?
Wow this Physics II stuff is making me go crazy!!
Thanks again
Philip

chroot
Staff Emeritus
Gold Member
Originally posted by philipc
chroot,
Thanks for the quick response,
So could it also be said the only forces on the generator with out load(not including friction ect) would be from losses in the generator it self?
In other words an "Ideal" generator would spin indefinitely until there was a current load put on it?
Wow this Physics II stuff is making me go crazy!!
Thanks again
Philip
Also correct.

- Warren

Another question, since load effects force, what keeps the generators at 60hz when the load is constantly changing on the power grid.
Philip

turin
Homework Helper
There are usually hundreds of generator that can be turned on and off. If the load reduces for a given number of generators, the frequency goes up. If the load increases frequency goes down. The frequency is used as an indicator to signal generators to turn on and off. Turning on more generators will increase the frequency. Turning off generators will decrease the frequency.

russ_watters
Mentor
Originally posted by turin
There are usually hundreds of generator that can be turned on and off. If the load reduces for a given number of generators, the frequency goes up. If the load increases frequency goes down. The frequency is used as an indicator to signal generators to turn on and off. Turning on more generators will increase the frequency. Turning off generators will decrease the frequency.
I think you have it but its a little unclear. Frequency in ac motors/generators is a function of the physical design and rpms. So on the supply side, the rpms are controlled (very precisely as a matter of fact) to regulate the frequency. Its done electronically but I don't know exacly how. On the demand side, the motor always runs at its design rpm (unless it has a variable frequency drive). If you add load to the motor, the amperage will go up and the rpm will stay the same. Obviously, if you overload it, it will fail to maintain the rpm and the power output will drop radically (or you'll just burn out the motor). The supply side is a similar delicate balance as seen recently with cascade power failures in NY and Italy. One little blip can destabilize the whole grid and knock it off line if they are riding the edge of their capacity.

turin
Homework Helper
I don't think phillip was asking about the demand side. The generators output a power which depends on the load (because they have an output impedance and there are also other factors). As, I believe, phillip has realized, a higher load means more current, which means a different impedance mismatch. There are two ways to solve the problem: 1) have an adjustable impedance matching network that couples the imput shaft to the electrical output at a constant mechanical impedance, 2) reduce or increase the current requirement for any given generator by simply engaging or disengaging other generators in parallel. There are complications, but, it can be done. The feedback is derived from the same principle as FM.