Starting Current Star/Delta Starter

I'll have to recheck. I think it may be 1/√3 for starting current (~52A), and 1/3 starting torque.

I also agree with Mr Tornado i-e Starting current will be approximately 52 A. It is either 10 KW or 7.5 KW motor

Rewriting the Question

1.A motor 10 KW, 400 V, 50 Hz, D, 19 A, P.F 0.86, 1450 rpm, when connected in Delta configration takes starting current of 90 A.

How much starting current would it take if it is connected in Star Configuration and 400 V are applied to it

a).When Motor is Connected in Delta Configuration and 400 V are applied:

Starting Current in case of Delta Configuration : 90 A

During Starting Motor takes 473 % of its rated current : 90/19 = 4.736

Motor other Parameters

Mechanical Power : 10 KW

Full Load Current : 19 A

Motor Full Load Torque = 65.9 N.m

b).When Motor is Connected in Star Configuration and 400 V are applied:

Mechanical Power : 3.33 KW (Approximately 1/3 * 10 KW)

Full Load Current : 10.97 A (Approximately / 1.732)

Motor Full Load Torque = 21.966 N.m (Approximately 1/3 * 65.9)

c).From 400 V Delta configuration to 400 V Star Configuration:

Mechanical Power : Reduces from 10 KW to approximately 3.33 KW

Full Load Current : Reduces from 19 A to approximately 10.97 A

Motor Full Load Torque = Reduces from 65.9 N.m to approximately 21.966 N.m

d). Starting Current for 400 V Star Configuration :

When the motor in Delta Configration starting current was approximately 4.736 times the rated current (4.736 * 19 = 90 A)

Starting current for motor in Star configration for 400 V will be approximately 4.736 * 10.97 = 51.95 A

2. For 7.5 KW, 400 V, 50 Hz, D, 14.6 A, P.F 0.85, 1450 RPM

Starting Current in case of Delta Configuration : 90 A

During Starting Motor takes 616 % of its rated current : 90/14.6 = 6.16

When Motor is connected in Star Configration Current will be : 8.429 A

So starting current for 7.5 KW in Case of Star Configuration: 8.429 * 6.16 = 51.92 A

http://cr4.globalspec.com/thread/54100#comment562035