# Homework Help: Real transformer question! help me solve it please!

1. Jun 17, 2012

### cheewei0913

1. The problem statement, all variables and given/known data
the circuit values of a 60Hz,20kVA 2400/240V real transformer:
R1=3.0Ω
X1=j6.5Ω
R2=0.03Ω
X2=0.07Ω
Xm,magnetizing reactance=j15kΩ
Rc,core loss resistance=100kΩ

the transformer with rated load is said to be having a lagging power factor of 0.8

compute
1. primary and secondary current
2.primary and secondary voltage
3.source voltage
4.power loss in the transformer
6.input power
7.power effiency

2. Relevant equations

3. The attempt at a solution
1.I1=20k/2400=8.33A
I2=20k/240=83.33A

2.V1=2400V
V2=240V

3.Is=(2400/100k)+(2400/j15k)+8.33
=8.36 L -1.10°A

Vs=V1+Is(3+j6.5)
=2426.11 L 1.27° V

4. power loss=Pcore+Presistance
=[(2400^2)/100k]+[(8.33^2)3]+[(83.33^2)0.03]
=474.08W

5. Vout=V2-I2(R2+jX2)
=240-(83.33)(0.03+j0.07)
=237.5V
Pout=237.5(83.33)(0.8)
=15832.7W

6.input power=VsxIs
=2426.11x8.36
=20282.28W

7.effiency= 15832.7/(15832.7+474.08)x100%
=97.09%

this is my solution
i think all is wrong