# induction motor

Discussion in 'Homework Help' started by mary_owen, Apr 30, 2008.

1. ### mary_owen Thread Starter New Member

Apr 30, 2008
5
0
hi guys, ive just joined the froum so helpfully you dont mind helping me. im totally lost with this question

a 3.3kw single-phase induction motor. The power factor is 0.8 lagging

Determine:

A)Current drawn from the 230V supply.
B)The output power if the overall motor efficiency is 85%
C)The active and reactive components of the input current.
D) The apparent power and reactive power consumed.

2. ### mik3 Senior Member

Feb 4, 2008
4,846
70
A) current drawn =power/voltage=3300/230=14.35 amps

B) input power is Vrms*Irms*cosφ , where cosφ is the power factor=0.8
thus input power Pin=230*14.35*0.8=2640.4 watts
the efficiency is 85% thus the motor outputs 85% of its input power
so output power Pout=Pin*85%=2640.4*85/100=2244.34 watts

C) i am not sure what do you want

D) apparent power S=Vrms*Irms=230*14.35=3300 VA
reactive power Q=Vrms*Irms*sinφ

φ=arccos(0.8)=36.86 degrees

therefore Q=230*14.35*sin(36.86)=1979.84 VAR

3. ### mary_owen Thread Starter New Member

Apr 30, 2008
5
0
thats great mike. very much apreciated. just ne lastquestion. where abouts did the 36.86 degress come from?

4. ### mik3 Senior Member

Feb 4, 2008
4,846
70
power factor=cos(φ)=0.8

thus φ=arccos(0.8)=36.86