Tamim said:
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!
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.
