Suppose we have a new Induction motor without any marking of the leads, then we need to identify its polarity before using it.
Here is the process explained.
Step 1:
Continuity test to identify each of the winding terminals [AA BB CC]:
We can do this test with the help of Multimeter by checking continuity between any two terminals. If the two terminals belong to same winding a beep will come.
Do this procedure for all and identify terminals, then mark the terminals as AA, BB and CC.
Step 2:
Test to identify polarities [A1A2 B1B2 C1C2]:
Take any two windings randomly and mark the terminals as A1 A2, B1 B2 (this is the assumption) as shown in figure.
Now connect A2 with B1 so that the two windings are in series.
Now apply 230V A.C between A1 and A2 and measure the voltage across A1 and B2.
If we notice the measured voltage is less than the applied voltage then our assumption is correct. Otherwise interchange the terminals A1 and A2 and repeat the process so that we can find the terminals A1, A2, B1 and B2.
Now take the third winding mark it as C1, C2 (this is the assumption) and take second winding B1B2 (already known) connect B2 with C1 so that the two windings are in series as shown in fig.
Now apply 230V A.C between B1 and B2 and measure the voltage across B1 and C2.
If we notice that the measured voltage is less than the applied voltage then our assumption is correct. Otherwise interchange the terminals C1 and C2 and repeat the process so that we can find the terminals B1, B2, C1 and C2.
Once we can identify all the terminals they are connected for Star or Delta fashion, for star connection join A2B2C2 or A1B1C1, for delta connection connect A2B1, B2C1 and A1C2.