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Torque input of synchronous machine 
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#1
Feb114, 10:02 PM

PF Gold
P: 372

I am reading from grainger about transient stability.
I know this will be a amateur question, but... It says that when a prime mover is turning a synchronous machine, there is a equal and opposite counter torque (electrical counter torque) when the machine rotates at synchronous speed. This is odd to me, as I would expect an equal and opposite counter torque to stall the machine. 


#2
Feb114, 11:10 PM

HW Helper
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P: 5,155

If the driving torque changes to a new level, then a new equilibrium point must be established such that the new electrical torque exactly counters the new driving torque. (If this new equilibrium can't be established within certain parameters, then, yes, it will fall out of sync.) It should be clearer if you think of the generator as being "directly" connected into the power network, alongside many others, so that the prime mover torque alone determines whether this machine is generating or motoring. 


#3
Feb214, 02:32 PM

Sci Advisor
PF Gold
P: 3,518

So ω stays constant , presumably at ω_{synchronous} 


#4
Feb214, 03:27 PM

PF Gold
P: 372

Torque input of synchronous machine
got it thanks guys.
This was what I assumed of course, a torque difference tends to change accln to a new steady state speed, but I was having trouble trying to understand that for some reason. 


#5
Feb314, 12:25 AM

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#6
Feb314, 09:46 AM

PF Gold
P: 372

Yeah I was referring to torque difference in general. What you are saying makes sense, the reason I asked the question is because im writing a program that simulates synch. generator swing angles for large disturbances. We are finding critical breaker trip times to limit loss of synch. I have written and tested the program vs IEEE standard buses (14,30) and AEP standards (57,118) and it's working. There was just some issues with the torque that I was wanting to understand better.
Thanks 


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