- #1
tim9000
- 867
- 17
Hi,
I'm trying to ascertain when you're driving an asynchronous motor with VVVF or whatever else a VSD uses, when do you draw the most current?
For instance, say you're talking about a train/tram: I would have thought intuitively that since power = torque / angular speed, that starting up, to move the big mass the motor and system would draw the most power (torque very high, speed very low). But I heard a rumour that the vehicles actually draw the most power when motoring at full speed.
Now, obviously when you're starting up you lower the voltage and the frequency, so is there some sort of algorithm that VSDs use as a standard to draw the most power/current when operating at full speed...some industry profiles I should know about?
Thanks very much!
P.S. I'm not sure what conservation of energy says about keeping a mass moving (overcoming friction etc) at full speed, vs starting a mass to move from stationary.
I'm trying to ascertain when you're driving an asynchronous motor with VVVF or whatever else a VSD uses, when do you draw the most current?
For instance, say you're talking about a train/tram: I would have thought intuitively that since power = torque / angular speed, that starting up, to move the big mass the motor and system would draw the most power (torque very high, speed very low). But I heard a rumour that the vehicles actually draw the most power when motoring at full speed.
Now, obviously when you're starting up you lower the voltage and the frequency, so is there some sort of algorithm that VSDs use as a standard to draw the most power/current when operating at full speed...some industry profiles I should know about?
Thanks very much!
P.S. I'm not sure what conservation of energy says about keeping a mass moving (overcoming friction etc) at full speed, vs starting a mass to move from stationary.