3 Phase Motor Troubleshooting?

Randy,

From your description, it sounds like you don't have 3-phase power going to the motor. The clue is that you are measuring 120V across some of the wires. You should be seeing 240V between all of the wires coming from the wall. What you are describing is what you would get from standard 240V single phase with a neutral.

I don't know if you are in an industrial setting, but 3-phase power in a residence would be very unusual.

Best of luck.
Glen Zoerner
Spicewood, TX
 
A few things seem odd
The motor was 3 A @ 220v from the plate. Normally this would be 220vac between each leg and neutral. This is 660 va per leg. Normally the name plate specs the output power including efficiency and power factor. Each leg contributes to the output power 3x660 = 1980 w. 1 hp = 735 W. So for the input power one should have a 2.7 hp motor.

With 60 HZ power 2 poles would produce 3600 rpm. This would be the right number for a synchronous motor but it is specified as an induction where the stator usually slips From the rotating field under load. Typically this is 2-5% or something like 3500 rpm

You should be measuring 220 vac between each leg and neutral. Between any 2 legs 380 vac as each leg is at 120 degrees from each other using a leg to netural reference.


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In a Delta (3 wire) 3 phase system, there is no neutral. All 3 wires are "hot". I'm guessing that Randy will need to get either a rotary phase converter or a VFD to generate the 3 phase his motor needs. He'll get the benefit of variable speed and soft start with a VFD.

Glen
 
A few things seem odd
The motor was 3 A @ 220v from the plate. Normally this would be 220vac between each leg and neutral.

I must be misunderstanding something. I guess that happens during retirement! :)

If I was checking voltages on a 220vac 3-phase system, I would expect to see 110v to neutral/ground on each individual leg and 220vac across any two of the 3 legs.

Oh well,
Ted
 
Randy, I assumed you had 3-phase power... is that not the case?

I guess I know how we spell assume! :)

Ted
 
Phase to ground you'll have 120 v. Phase to phase 240v.
 
Assuming this is a delta four wire.
 
So does the OP have a 3 phase service or is he using a phase converter?

I reread and he has three phase service.
 
Randy: with power off you can disconnect and measure those 3 wires from the motor with an ohmmeter on the lowest range (hopefully RX1) and measuring between any 2 wires you should get the same very low reading (1 or 2 ohms or so) plus or minus 5 percent. If not equal then the motor has one or more bad windings. Check also that the windings are not shorted to the case.
Mark S.
 
If you have true Delta-Wye 3-phase coming into your shop, the high leg or "wild leg" should be giving you a erratic reading of about 177-190 volts to ground. If this is the case, get the power company out to check the pole fuses on their side of the meter. One of them may have gone bad. I had that to happen at the family homestead up in Conroe several years ago. Couldn't get any motor to fully start in the shop. Started checking line voltages and that's what I found. A call to the utility company and discussing with the service guy that came out, he traced it to the high leg fuse on the pole.

Last thing could be a clogged up motor from years of saw dust collecting. Seen motors on machine tools clogged up from years of crud build up not wanting to run right.

Edit: I meant to say, if you are not getting this erratic reading of 177-190 volts to ground, and it is closer to 100-120volts, get a hold of your power company. Sorry.
 
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