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Star Delta troubleshooting

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Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
A customer has a table saw that suddenly won't run. When you press start, the main (K1M) and star contactors (K3M) pull in, but the motor doesn't turn. When the timing relay switches to delta, the delta contactor (K2M) tries to pull in, but then the whole thing shuts down. I had to replace the main contactor about a year ago, so I was suspecting the delta contactor failing, but with the motor not turning in star, I have second thoughts. One other important thing is that this is at a residence and is using a rotary phase converter to get 3-phase.
Thoughts on things to check or try?
 

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J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Is the phase converter working correctly?
Is there a problem with the driven load?
Does the motor turn when started across the line?
 
R

retirede

Senior Member
Location
Illinois
1. Check incoming voltage.
2. Measure voltage load size of main contactor when starting.
3. Measure phase-to-phase on star contactor during start. Should zero.

Next steps depend on these results.
 
Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
It's a very fancy German Kolle. They're long out of business, so no support. I had to troubleshoot the servo motor for the blade tilt a while back, and it came down to a control board for which there's no chance of finding a replacement.

I thought I had strange voltage readings coming into the machine. Even a high impedance meter should read 240V between all phases off a rotary converter, right? The customer didn't mention any of the other 3-phase machines not working, so I dismissed it.
 
T

Teaser2

Member
Location
MDDENJ
Occupation
Electrician/EE
Electromatic said:
It's a very fancy German Kolle. They're long out of business, so no support. I had to troubleshoot the servo motor for the blade tilt a while back, and it came down to a control board for which there's no chance of finding a replacement.

I thought I had strange voltage readings coming into the machine. Even a high impedance meter should read 240V between all phases off a rotary converter, right? The customer didn't mention any of the other 3-phase machines not working, so I dismissed it.
Click to expand...
The voltage readings may not be equal between the phases and phases to the ground. Attached, please find a sample document that illustrates the voltage readings, I am not sure what kind of rotary converter you have, you should try to find the manual for it.

Obviously, verifying that the required 3 -phase line side power present is a good start. I assume you hear no humming or noise from the motor as its being "single" phased?

I would do a quick inspection of the wiring on the motor terminal box as well.
 

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Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
I understand the principles of phase converters and star-delta starting, but I can't say I run into either very often. The customer says the other 3-phase machines are operating properly. I'm going back tomorrow to take another look at things.
I believe it's safe to say that if the motor doesn't begin to get to speed during the star cycle, the switch to delta would cause an overload and the control drop-out that I observed, correct?

I recall years ago this same customer had a problem with a lathe running off the same converter. It had a brake circuit that was too much load for the generated phase. That was an interesting but easy fix of swapping a couple of line-side wires.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Is this the motor for the blade?
Is it time to look at a VFD instead of the star-delta controller?
 
T

Teaser2

Member
Location
MDDENJ
Occupation
Electrician/EE
Assumptions:
-3 phase line voltage is good
-Nobody changed the wiring or replaced any contactors and time delay relays etc. to cause issues (Auxiliary contacts switched, wires switched etc.)
-Assuming that the O.L. is functioning
-Non of the 3 phase contactors are "stuck on" or sticking
The main 3 phase contactor K1M kicks in at the same time as the K3M Wye contactor. At this point motor should run in wye and the on -delay timer K1T is timing; the time is up and K3M should drop and K2M for Delta should kick in....

The common connection points are terminal 4 5 6 to motors connections W2 U2 V2. The fact that you are not able to run neither in wye or delta. Assuming that the 3 phase power is present via the K1M main contactor,
 
Little Bill

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Electromatic said:
I understand the principles of phase converters and star-delta starting, but I can't say I run into either very often. The customer says the other 3-phase machines are operating properly. I'm going back tomorrow to take another look at things.
I believe it's safe to say that if the motor doesn't begin to get to speed during the star cycle, the switch to delta would cause an overload and the control drop-out that I observed, correct?

I recall years ago this same customer had a problem with a lathe running off the same converter. It had a brake circuit that was too much load for the generated phase. That was an interesting but easy fix of swapping a couple of line-side wires.
Click to expand...
Can you manually push in the contactor and make the motor run?
 
Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
I just got back from the customer's house...with major egg on my face: The twist-lock receptacle for the saw was partially dislodged! I re-secured it, and everything is dandy. A real KISS moment!
I'm going to have to think about why the controls only dropped out on the switch to delta.
 
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