Sawmill engine buzzing but don't start

[darjiaus7]

Hello. My father has a sawmill but after not using it for a while now there is a problem. When turned on it humming/buzzing but engine does not rotate. Engine uses 3 phases and all of it coming to the main fuses. Saw is rotating easily with hand so it's not jammed.
I am not an expert in motors but I have a little bit experience in electronics. In electric box I saw that there is a autotransformer? (with SSRS tag ) and it looks rusted/corroded so I guess there is a problem with it. Could it cause such a problem that engine is buzzing and not start? Maybe someone could help and say what should I check to find a problem? (I have multimeter so I can check continuity/measure voltages etc.)

 

[BrianE22]

I'd check for one or more phases not present. Use your volt meter and measure each hot line relative to neutral (ground probably ok) All 3 phases should read about the same voltage. But first check the fuses.

 

[darjiaus7]

I checked voltage between 1-2 1-3 2-3 phases and all showed ~400V. Didn't check to neutral but as I know 3 phase motor don't use it. Main 3 fuses are ok, same voltage before/after fuses. Sawmill is 30km from where I live, so I want to get there knowing what to check. I found a video in youtube and as I remember schematic looks the same Link . My guess is 1 phase disappear somewhere after fuse box.

 

[waross]

Has anyone sharpened the saw lately?
I had a similar problem with the grinder motor on an automatic band saw sharpening machine.
All three phases present.
Motor hummed and turned very slowly.
Motor turned easily by hand.
Trying the old test for single phasing. Spun the motor and applied current when the motor was spinning. The motor immediately slowed to a slow crawl and hummed loudly.
The cause?
The saw filer had cleaned the machine with compressed air and had blown some iron filings into the motor.
The magnetic field magnetized the filings between the rotor and the stator and braked the motor.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[IRstuff]

Has anyone checked any motor start capacitors? That's a pretty common failure point. Newer capacitors have scored tops that "pop" after one particular failure mode.

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[waross]

Capacitors are not needed to start a three phase motor.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[darjiaus7]

Thanks for answers!
@WAROSS No, its stopped working after not being used for a long time. I guess there might be a problem with contactors/overload relay. Faulty contactors produces buzzing so sound I hear may not be from the motor.

 

[BrianE22]

Checking amps on each phase would tell you which line was bad.

 

[darjiaus7]

Went to sawmill today, checked contactors and looks like 2 of them missing 1 connection when testing continuity. Pulled them off and after inspection found that 1 contact inside is broken (looks like melted and broken). Didn't inspect the other 2 but will do that soon