1. What do you know about star and delta connection ?

8. Q1: 380-V, 60 Hz, 9kw three-phase induction motor is connected delta star at 0.8 PF calculate the current in and delta also calculate the starting current and power developed in star ?
1) IL∆=P/√3*cos
6*103/√3*380*0,9=10.12A
2) Ip∆= IL/√3
10.12A/√3=5.84A
3) Z=Vp/Ip
380V/5.84=65.06Ω
4)Vph=Vl/√3
380/√3=219.34V
5) IL=Ip=vp/Z
219.34/65.66=3.37A
6) Is=7*IL
7A*3.8=23.6A
7) p=√3*VL*Ic*cos
=√3*380*0.9*3.37=2KW

9. 1-How to connect the motor ?
Star – Delta
2-why we connect star-delta?
To avoid damage to the motor and an increase in energy consumption.
3-when we convert to delta?
After the speed up to about 75% of the speed of your connection is converted to Delta.
4-why we connect the delta?
Because Delta can bear loads in excess of the motor.

11. 1) what different between star and delta ?
Star has high voltage and low current and Delta has low voltage and high current.
2) why we start motor in the beginning in star?
Because the star has high voltage ,so we need high-torque to starting the motor.