3 phase fan motor question

[# Robin]

Hi, before I rip into this and send the motor for rewinding, can I run this past you guys please?
As I see it, the fan motor isn't starting in star but when relays change to delta it ramps up.
So I press start and on 3 wires down to motor off the star relay I've got 240V available on 3 phases but with clampmeter I can see the motor is only drawing current on 2 phases (17Amp). Understandable then that the fan is just rocking slightly, not spinning and god awful hum.

But then the relays change to delta (I assume its a timer after about 5sec?) and the motor accelerates hard from standstill upto full speed.
Now the 3 windings above + 3 more off the delta relay are all drawing an equal 8 Amp.
So scratching my head why the winding isn't drawing current in star but is in delta. At limit of my knowledge here is it a knackered winding or magnet? Or am I missing something simple?
@Mursal , @anyone with bright ideas? Cheers

 

[Mursal]

You probably have three relays or contactors controlling the motor.
The main and Delta relays (working) and a Star relay may not be working as it should.
Here is a bit on the wiring which you probably have already, click
If you have pullout relays its easy enough to interchange them and see if the fault moves.
Also check all connections.

 

[simon-0116]

Contactor one terminal burned out on star side. Does it smell burnt.

 

[Pheasant Surprise]

As said, motor has lost a phase on start, but has all phases on run. So fault looks like it's either a loose terminal connection/broken wire or busted contactor/relay inside the star/delta unit.

Obvious warning, be very careful if your considering DIYing this; the connections etc are straightforward enough but the voltages are lethal.

 

[# Robin]

That's brilliant thanks guys. Thats a very good link thanks, I'll follow the wiring through again. I couldn't think once relay pulls in how I can have voltage on the motor winding side but it not draw any current.
2 relays are connected with a buzz bar but I will see if I can swap one with the suspect. Yes there is a faint burned aroma in the control box.
Any thoughts on where to get old fashioned relays?
Thanks for your help

 

[Pheasant Surprise]

Photo?

 

[simon-0116]

Put pic up have a few in stock

 

[# Robin]

Quick photo and how I remember it working. Need to go back and work through Mursal's link properly to figure it out.
Relay A on start-up. Draws current on 2 of 3 and motor in stall.
Relay B comes in after a time delay and then all 6 motor wires draw equal current.
Relay C looked to be linked into relay 1 on small dia wires.
The rest of the control box is for the heater bank (the yellow wires go down to heater relays)

Thanks again

 

[Tommy]

We lost continuity through an isolator once on one phase. There is a way of checking the windings with a multimeter but not sure of the procedure, our motor rewinder talked us through it

 

[Mursal]

Lovely bit of work with the layout and labeling.
Swap a good set of phase wires with the dud set on contactor A. See if the problem moves (hopefully not) or stays on the same set of contacts?
Swap both wires on each set of contacts