could someone tell me what the different effects would be of wiring a soft start unit to a 3ph induction motor in star formation or in delta.

 

Istart is line current of start connected motor.
Idelta is line current of delta connected motor.

Istart = Idelta /sqr3

You can use start connection for giving power.
this reduce the start current. After the motor
arrive nominal speed you can change delta connection.

But very important!!! your mechanical load can not be connect the shaft while starting. !!!

 

Star connection reduce the current for factor
sqr (3).

Idelta = Istar * sqr(3)

Line current reduce if motor start with star connection.

Motor arrive the max speed you can change the delta connection.

This is classic soft start technics.

But !!!!

You can use this methode for only if your load
not connected to motor while starting. !!!

For example. Drill, turn machine, lathe machine ok
but you can not use direct coupled load for example pump.

Best regards

Bunalmis

www.geocities.com/cnc_designer

 

You should connect the motor in delta. If you connect in star, you cannot use the rated torque of the motor.

 

Mr Unalmýs,

First of all it has been asked about soft starters, not a conventional star/delta starting.

Secondly, in general it is not true that the load should not be connected to the motor at starting phase. If soft starter lets enough starting load, then connecting the load is permissable. Otherwise soft starters would be impractical.

 

I'm not sure of your query:

Is it your intent is to replace the Y-D starter? If so, use the soft-start with the delta connection.. Then, there is no reason to reuse
the existing starter. Also, uncoupling the load duing start is unnecessary.

One precauion. Make sure that the resultant feeder cables, whether new (3 leads) or existing (6 leads) are properly sized and (re)arranged for
the delta connection.

Regards,
Phil Corso, PE
(Boca Raton, FL) [[email protected]] {[email protected]}