DC motor - Speed torque curve

[SuryaGG]

I beleive the speed torque curve of a DC motor is different from a AC motor. Why is this so?

Do any one have typical Speed torque curve of both DC motor and pump?

 

[ScottyUK]

Have a read of any decent electrical machines text and you will find your answers.


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If we learn from our mistakes I'm getting a great education!

 

[Skogsgurra]

The normal operating part of the speed/torque curve is very similar if you compare a DC and an AC machine. Speed drops a few percent when load increases from zero to 100 %.

There are different DC motor characteristics and different AC motor characteristics. But, in practical use, they can be regarded as almost identical.

It is only when you get above the break-down torque that they differ and have very different characteristics. As Scotty says, find a text-book and do some studying.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[7anoter4]

There are many DC motor types. But, usually, at least in our time, 4 types are most employed [for power actuation]:
Separate [independent] excitation, shunt excitation, series excitation and combined excitation.
For information only, the Torque-speed relations may be considered as follows:
Separate [independent] excitation or shunt excitation:
n[rpm] =Ua/(Ke*Phi)-Ra*Torque/(KT*Phi) –linear function
Ua=rotor voltage
Phi=magnetic flux
Ra=rotor resistance
Series excitation:
n=Ua/(K1*sqrt(Torque)-(Ra+Re)*K2- it is a hyperbole [aproximate]
The combined excitation characteristic is an intermediate curve.
For AC Induction Motor one may use this formula:
Torque=2*MaximumTorque/(s/sk+sk/s)
s [slip]=(nsynchron-n)/nsynchron
sk is the slip corresponding to maximum Torque.
See the attachment for illustration