# 3 Phase Induction Motor

• posted

I am designing a power electronic converter (converting a single phase ac power supply to a three phase ac supply). I have purchased a three phase induction motor (250 Watss,squirrel cage). In order to design my converter i need to know the following components of the motor.

1)Rotor Resistance 2)Stator Resistance 3)Stator leakage Inductance 4)Rotor leakage inductance 5)Magnetising inductance

If any1 has measured these values for their work in the past would they please let me know ASAP as i cant do any work unless i know these values. Thanks u very Much!

• posted

The first problem I see is the fact that your motor is Squirrel Cage - therefore the rotor resistance will be essentially zero as most motors of this low power will use aluminium bars and shorting rings. I am assuming that this is a constant speed convertor, with no frequency conversion (the calculations get a lot harder as you move away from the motor's design frequency) The stator resistance can be easily measured with an ohm meter (it will be in the order of 10's of ohms probably) ( I am assuming 220V phase to phase as you do not say) The inductances can most easily be found by asking the manufacturer of the motor. What percentage slip is the motor intended to run at? from this you can calculate the frequency of the rotor current (I would expect this to be around 3-5 Hz but may be more in such a small motor), and this, combined with the manufacturer's data on the rotor impedance will give you some indication of the rotor excitation. Having said all this, what are you intending to drive with this? The characteristics of the load will have to be taken into account in your design and I would recommend you consider the following parameters:

Start torque required and its relationship to speed (linear, fan law etc) Time to acelerate the load to full speed Number of starts per hour Requirements for reversal Is rapid stopping required?

From the electrical side, you also need to consider: Starting method (D.O.L, Star/Delta, Soft etc) Supply characteristics Power factor permissable Filtering Maximum current draw permissable Protecton etc.

I suggest that for such a small motor, you either exchance it for a suitable single phase motor, or buy a ready made convertor (the cost of letting the magic snoke out of power semiconductors as you try your design will quickly exceed the cost of a small convertor.

Dave.

• posted

Hi Dave, Thanx for ur reply. I forgot to tell u that im designing this converter for my third year university project.So i cant buy i ready made one! I contacted the manufacturers and they have given me all the values of the paramaters. Thanks alot for ur advice. Regards Tamim

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