I have a 3 phase 6 pole 415V induction motor which has 24 VAC applied between the R & Y phases 3 seconds after the main power is removed as a means of preventing condensation by heating the winding. Usually the applied 24 VAC does not cause motor rotation but after a rewind the unloaded motor will now continue to rotate if 24 VAC is applied before the motor has stopped turning after main power is turned off.
This ability to operate on "single phase" AC at low voltage seems contrary to what we would expect for a 3 phase 415 VAC motor, and not what we have experienced before the rewind.
Can anyone explain why the motor may now operate in this manner and why a rewind was able to change how it operated?
We have an 08 motor of rating 15KW, 6 Pole, 415V, CGL make installed. these induction motor has anti condensate winding heating provision given of 24V AC(Between R and Y phase) through its power cable lead when motor is in stop condition. there is a timer of 3 sec installed in control circuit between motor stop and winding heating start.
One motor was overhauled and when it restored without coupled to the load, it runs perfectly fine but when we stop it, within 3 Sec 24V AC between R and Y phase (4.5 Amp current in R & Y phase) gets starts and motor remain in continuous in running state with reduced speed, even its main supply 440V AC) gets isolated through contactor logic.
since the motor is decoupled and its inertia is high it dosent come to zero speed within 3 Sec of stoppage and 24V AC between R & Y phase gets starts and it remain continue in rotation with reduced speed (may be due to required rotating field gets fulfilled with 24V AC only in running condition, and due to the single phasing with 24V AC)
When we remove 24V AC winding heating space heater fuse, motor come down to zero speed.
This seems a unique finding in my career, please share any experience related to this and some theory part.