Sticks Mega
Posted on Friday, October 29th, 2010 at 6:00 amhelp i'm mega stuck i can't work out my engineering question can any one help please?
A three phase induction motor is rated at 150kW at a power factor of 0.9 when operating from a 1100V supply. If direct-on-line starting is used calculate: a) the line current when the motor is on full load. b) the apparent or input power. how do you work it out??????
As a three phase motor is a balanced load, use the formula:
Power in Watts = SqRr3 * V line * I line * PF
a) Power = 150 KW = 150,000 Watts
V line = 1100V
PF = 0.9
So, solve for I line!
I line
= Power / ( SqRt3 * V line * PF) Amps
= 150,000 / ( SqRt3 * 1100 * 0.9)
= 87.477 Amps = Answer a).
b) From PF = True Power / Apparent Power
and ignoring the additional input current
due to motor losses;
Apparent Input Power
= True Power / PF
= 150KW / 0.9
= 166.66KW = Answer b)
Note that Apparent Input Power
and Input Power are different terms.
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