View Full Version : [ask] identifying 3 phase motor

05-28-2007, 03:12 AM
Hi, i'm a newbie here

Some one help me please, I have a 3 phase induction motor 45 kW, the problem is, i missed wire letter, which U,V or W and which X,Y, or Z,

How to identify the letter, anyone know? please tell me the trick, or is any method to identify that letters without pull out stator from body or open the winding connection?

help me please, thank you for advice

05-28-2007, 10:54 AM
im not sure what you mean there but...

just wire the 3 phases in and if the motor turns the wrong way - change any two around - easy...

05-28-2007, 11:23 AM
There are normaly 6 wires conected to an board with 6 conectors. they are marked u1,v1,w1 and u2,v2,w2. where u1,u2 is one winding and so on. Then you must know the voltage you will run it on. If the motor is marked 110/220Volts, meaning for 110 connect the windings in delta.for 220 in star. To locate the windings use an ohmmeter and you will find 3 simular walues repesenting the windings. For the 45Kw motor the resistans in the windings is very low.

05-29-2007, 05:27 AM
Oh sorry, fogot it, the motor should run at 3 phase 380 volts.


yes, you're correctly, the motor have 6 wires and each motor may different at wire mark, ok i done it what you mean about U1,V1, or W1 and U2,V2 or W2, also i has try your advice to check and search similar-winding use a Ohm-meter.

The result, now i already find 3 winding with similar resistance, but how to surely which U1 and U2 (may be i can do that if i use it at one winding) but how to check V1 and V2 or W1 and W2?

Is any problem if i miss-identification? for example: i already know it as V1 but the true this wire is V2 or vice-versa, do you know how to surely check it? may be that a problem?

hope your next advice, thank for attention

05-29-2007, 03:15 PM
Before you try to locate the windings with ohm-meter you must have all 6 wires unconected from the terminals, ore at least all the copper bridges remowed. If suppose youre motor is market 230/380V then you have to run it in a star configuration. then one end off the windings are simply connected together and the three remaining wires is given a live fase eatch.

05-30-2007, 04:50 AM

Now I already follow your advice, i got 3 winding, i also make a STAR configuration of course 3 remain wires are connected to 380 v/3 phase power source.

But, is any problem if i false to connect one wire? example: i connect V1 together with other wire, and of course the end of V1 is V2, are connected to live phase, is that cause a problem?

hope your next advice, thank you very much

05-30-2007, 05:36 AM
Find 3 coil by ohmmeter.

For example (A1 A2), (B1 B2), (C1 C2)

After, connect randomly.

For example (A1=U A2=U1), (B=V B2=V1), (C1=W C2=W1)

05-30-2007, 01:20 PM
Yes that will not work. For this a big engine you should use som motor protection like a motorinterupptor switsh. And you should know that the start current for this motor is wery high, in terms of choosing sercuiteswitshes. A common rule for asyncronemotors is that you can multiply the Nomminell current bye six times to find the start current that will accure for some millisecond.

05-30-2007, 01:34 PM
What is the max full line voltage of the motor?
As Magvat mentioned, for a ~60hp motor, the inrush current can be considerable, There are a couple of methods of soft starting, one is Star-Delta (start-Run) where the current in star is 1/3 current in Delta, The other way is with a 3phase auto transformer.

06-08-2007, 03:29 AM

Can i do identify one by one winding..? using a magnetic Compass? basicly the motor winding is 360 degree total, if they divide into 3 groups may be i'll find each at 120 degree, is like that..? and if i connect each wire at same direction, i'll get same magnetic pole..

Hope your advice for next step, and please make it sure..
what should i do for testing like that?

WA Toolman
06-10-2007, 02:16 AM
Reading this thread reminds me of a story my father used to tell about the Pacific islands and the war... Apparently they were on some island (Iwo Jima?) where they had to set up a base for aircraft...runway, runway lights, etc. Anyway they gave the job of wiring up electrical motors to GI's, many of whom came from farms that didn't even have electricity. Short story is they just made sure all the wires were hooked to something. There were three types of motors: those that ran backwards, those that ran forward, and those that just sat there and made a lot of smoke!
We now return to the regular thread in progress. :D