remote switching between star and delta (both ways)

Gmag · Feb 10, 2013

The point was to allow the fan to run at a lower speed to save on running costs when full speed wasn't needed.
But going by the replies here I gather that the power consumption in star would not be any or much less over all.
This seems strange to me all the same.

Darkwood · Feb 10, 2013

Gmag said:
The point was to allow the fan to run at a lower speed to save on running costs when full speed wasn't needed.
But going by the replies here I gather that the power consumption in star would not be any or much less over all.
This seems strange to me all the same.

The winding arrangements are different hence in star you are injecting 400v into 690v windings and in delta 400v in 400v winding set up

In star you are effectively undervoltaging the motor which limits inrush but will also give you an understanding why full torque wont be achieved in star.

billyfender · Feb 10, 2013

motor speed is fixed whether running in star or delta by the formula, N=Fx60/p (N=speed, F= frequency, p= pairs of poles). The only way to vary speed is to alter the frequency as p is fixed. You need to fit a VSD

Knobhead · Feb 10, 2013

You forgot slip, which makes this idea so inefficient

AndyOz · Feb 11, 2013

Gmag said:
In this case there is quite a difference in running speed between star and delta. I tested this by adjusting the timer to say 10-15secs. The fan starts and holds a steady (lower) speed in star after around 2-3secs. The speed stays steady until the timer switches to delta where it significantly increases in speed. I would guess star gives around 60% of full speed.

I will need to test the current draw as mentioned but by the sound of things, this can be done?
I am thinking a second lower rated trip switch wired in line somewhere with the star contactor would solve the overload protection issue with the original overload left to handle delta running?

As others have already said this is an unconventional idea to control speed through a star/delta starter. Before you go any further please check your original theory on the actual speeds. Check the star and delta speeds with a tachometer. I very much doubt they is so much difference. The tone of a motor definitely changes when a motor goes into delta and this may be leading you astray.
Also think about how you will protect agains overload in star. If you just add another overload ti the star contractor the delta overload will still be in circuit, therefore it will trip as soon as more torque is required. As a 15kW fan has been installed I am assuming the process requires it.