engrkira
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- Philippines
Given a generator rated 50 Hz at 1500 rpm with a 3.9 kw. How can I compute the power if the generator was run into 60 hz, 1800 rpm?
Equivalent power
- Thread starter engrkira
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Basically, your generator capacity is limited by the current carryign capacity of the generator windings. Your current rating will be the same (as this is dependent on the size of wire used in the windings). Once you have changed the required jumpers at the generator AVR's UFRO to 60Hz, the voltage regulation will be taken cared of --> meaning, if the terminal voltage of your genny was 120V at 50 Hz, it will still be around 120 volts even if the generator is running at 1800 rpm. The same with other machines, higher speeds means higher windage losses, hence you will expect your drive engine to labor more at 60Hz than if it were running at 50Hz.
All you need to worry is try to know if your engine drive is fit to run at that elevated speed (wear and tear). Usually, engines run at higher speeds will deliver a higher output, though not linearly as the change in speed.
Depends on the prime mover. That's what delivers the power.
junkhound
Senior Member
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- Renton, WA
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- EE, power electronics specialty
no simple answer
Need to know the type of generator. A capacitor controlled brushless gen will give you about 140 Vac at 60 Hz, but as others already stated, you engine may stall out, but maybe not as HP increases with speed for most gas engines up past 3600 RPM.
Say you hook up a 50 HP engine, then you CAN get up to 9 or 10 kW or so IF you cool the generator sufficiently (as put a BIG separate fan blowing air thru it to keep it cool) and adjust the regulaton.
No simple answer, no harm done in trying it out if you pay attention to generator temperature so you don't burn it up.
To keep voltage down to 120, you may have to adjust your voltage regulation circuit (brush current for brushed generator, control capacitance for that type brushless gen).
mbrooke
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- United States
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- Technician
On average, doesn't a 50Hz motor or transformer deliver 17% more power on 60Hz? The higher frequency means more speed for the same torque, and 60Hz has a smaller magnetic circuit so a high voltage can be applied. Id imagine generators are similar in some respect at least to speed. I've seen Generator manuals where the same generator configured for 60Hz does put out something like 10% more power.
Here is one example where the same alternator is rated higher on 60Hz:
http://www.kohlerpower.com/onlinecatalog/pdf/g5365.pdf
http://www.kohlerpower.com/onlinecatalog/pdf/g5388.pdf
Here is one example where the same alternator is rated higher on 60Hz:
http://www.kohlerpower.com/onlinecatalog/pdf/g5365.pdf
http://www.kohlerpower.com/onlinecatalog/pdf/g5388.pdf
makes sense
Power = Torque x w (w = 2 Pi n, n = speed in rev/sec)
for a constant torque, increase speed, increase power
but many times for most engines increase speed and torque decreases if > peak torque rpm, hence instead of 6/5 or 20% more you only get 10% or so, speed increased but torque decreased
but in this case it is limited by the alternator rating
- Location
- San Francisco Bay Area, CA, USA
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- Electrical Engineer
So if I connect a 30kW generator to a 5,000HP engine, I can get 3,000 kW from it?
I know what you meant, I just couldn't resist ribbing you for the way you worded it...
mbrooke
Batteries Included
- Location
- United States
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- Technician
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
So if I connect a 30kW generator to a 5,000HP engine, I can get 3,000 kW from it?
I know what you meant, I just couldn't resist ribbing you for the way you worded it...
In theory yes, if you could cool the windings
Julius Right
Senior Member
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- Electrical Engineer Power Station Physical Design Retired
In my opinion, theoretically speaking, a 50 Hz engine could work-even better-on 60 Hz-as already was said. However, it could be a limit for critical speed [usually it is not such a problem, agreed].
The forces acting on a shaft are very complex, but some of the more obvious ones are:
Unbalanced magnetic pull due to finite number of stator and rotor slots[induction machine mainly].
Centrifugal force due to rotation of shaft.
Force due to the torque transmitted from the driving motor.
Accelerating force due to stator’s rotating flux.
These forces do not all act at the running frequency[50 Hz].
So, in my opinion, the manufacturer has to state if the generator is able to run at 20% more speed.
The forces acting on a shaft are very complex, but some of the more obvious ones are:
Unbalanced magnetic pull due to finite number of stator and rotor slots[induction machine mainly].
Centrifugal force due to rotation of shaft.
Force due to the torque transmitted from the driving motor.
Accelerating force due to stator’s rotating flux.
These forces do not all act at the running frequency[50 Hz].
So, in my opinion, the manufacturer has to state if the generator is able to run at 20% more speed.
Please remember also that the windage and cooling fan loss will increase to the cube of the speed change. In this case (1800/1500)^3 = 1.728 times the cooling fan power at 50 Hz.
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