480 volt transformer problem

[M. Moore]

I have 120/208 3ph to my shop. I use a 208 to 480 volt transformer to run my Webb pyramid rolls. Today the roll motor started acting funny, thought it was the motor brake but that checked out ok. Temporarily removed the brake and the roll motor worked fine. Re-installed the brake and hit forward switch, rolls moved fine. Hit reverse and the brake chattered, motor didn’t move.
So I started checking voltages at the main disconnect and at the roll contactors. Was getting a crazy high voltage at the contactor? Like 600, 800, 575, sometimes 0, very strange.
The 208 to the transformer is fine. After the transformer it is very strange and this after the rolls worked for one test and then stopped again. . Transformer has always had a buzz sound when on and that sound has not changed nor is there any bad smell of burnt insulation.

I have not pulled the cover off the transformer yet. Having lunch now and wanted to ask about this weird high voltage. I think it is a 15 kva size but will check. All the wiring is sized correctly and it has been running for at least six years. I don’t use it often but it also runs my heat treat furnace and my plasma cutter. Those three I don’t use often but I do use it to run my drill press and I use that all the time.

Any ideas on what this could be? I will try my other meter just to make sure it is not the meter. However something is not right given the motor problem on the rolls.

 

[M. Moore]

Ignore all that, second meter tests voltages as fine.
Problem is with reverse contactor on Webb rolls. Sometimes forward contactor has a similar problem. When I manually engage the solenoid the motor and brake work perfectly. These contactors are quite old so I am not sure I can even get parts and may have to replace.

 

[Dan from Oakland]

take it motor starter apart and clean the contacts? PITA, but better than a rewire job.

 

[M. Moore]

Dan,
On my list of things to do. I cycled it a few more times manually. Then tried the remote push button control and it worked fine, well enough to finish the job I was doing. It has been very cold and damp here lately and the machine is outside under cover, not the best arrangement for electrics.
Very happy it was not the transformer.

 

[BT Fabrication]

Ignore all that, second meter tests voltages as fine.
Problem is with reverse contactor on Webb rolls. Sometimes forward contactor has a similar problem. When I manually engage the solenoid the motor and brake work perfectly. These contactors are quite old so I am not sure I can even get parts and may have to replace.

most contactors are legos, just need coil control voltage and contactor voltages to replace one, or retrofit one from any other manufactuer. common as dirt

 

[M. Moore]

Bt, thanks for the reply. First need to determine exactly what the problem was and then replace or repair. I suspect it is worn main contacts on the reverse switch.
I also should have realized the meter was faulty despite it giving good readings for the lower voltage (208). It also happened a long time ago and after calling hydro about the problem their truck showed up within a half hour! My radial arm saw had strangely blown a fuse and after replacing it I checked the voltage and it was quite high. I was a bit embarrassed to tell them it was the meter but they were happy it wasn’t their equipment.
Don’t trust a cheap digital meter, my fluke is reliable.

 

[huleo]

Don’t trust a cheap digital meter, my fluke is reliable.

I hear that! Check 480 with a Harbor Freight meter No thanks!

If you don't have overloads on that motor, be careful as you can burn a motor if a leg is missing. Bad contacts are common, especially with 480.

 

[M. Moore]

Huleo,
I will check the contacts. With a roller there are lots of starts and stops so it does get a lot of cycles. Plus I don’t use it that much so it sits a lot.
It is properly wired from the factory with overloads.