I am trying to troubleshoot this 1.4 kW three-phase motor and I'm unsure how its internal windings are interconnected or whether they are shorted.
On the plate it says "Delta/YY 400 V", and I'm not sure what YY means. Most articles online describe delta and star (Y) configurations. But what is YY? Star-star?
The motor has 6 wires coming out of it, color coded in pairs of red, green, and white.
I assumed the pairs with wires of the same color are the two ends of a winding, but then this wiring diagram on the motor got me confused.
"niedrige Drehzahl" means "low speed", and "hohe Drehzahl" means "high speed". But how is the Delta configuration the "low speed"? I thought Delta was the high speed, with more power.
And how is that even a Delta configuration with 2U, 2V, and 2W left disconnected? Either the diagram is incomplete, or the motor already has some connections done internally, or something else.
Measuring resistance with a multimeter I get these values:
Between 1U and 2U -> 11.8 Ω, 1V and 2V 21.4 Ω, 1W and 2W 11.8 Ω. If these were to be the ends of each winding, the resistance should have been the same and close to zero, right?
What is also weird to me is the resistance value between wires of different colors, which I assumed correspond to different windings, and should have an "infinite" resistance between them, i.e not be shorted.
But I get between U1 and V1 19 Ω, U1 W1 19 Ω, V1 W1 19 Ω, and the same respectively for U2, V2, and W2.
The motor spins fine in both configurations, but without any load attached. I didn't test it under load, and I'm not sure if I should.
How can I find if the windings are damaged? Is it working just because somehow a magnetic field is still rotating even with damaged windings? Does this motor have more than 3 windings? Is this wiring scheme common? What is YY?