here is the question.......A series AC cuicuit consist of a resistor AB, an inductor BC ,and a capacitor DC when a current of 5A flow through the circiut the voltage across varius parts is of the circuits are:VAB=60V,VBC=130V,VAC=160V and the supply voltage is 140V 50HZ. if overall p.f is lagging calculate
1.1 The value of capacitor,resistor and inductor
1.2 The overall p.f

plz help this question come in every test and exam....its 10 percent of the paper!!!!!!!!!!!

 

Can you be a little more specific on the supply voltage? is it a sinusoidal source? Can you represent it in phasor form for us?

 

Ok........The HINT of that question is "Draw phasor diagram first"....and the supply voltage is a AC and its frequency is 50Hz...

 

Hey. I'm a little confused about this question for two reasons. 1. Are you supposed to figure out the phase angle of the supply voltage, or do you assume it is 0, or what?. 2. Are those voltage drops across those circuit elements just the magnitude? Because you should be getting a phase shift across the inductor and capacitor... that is, they should have non-zero real AND imaginary parts.

 

It doesn't work out. Since the current through the resistor and inductor is shared, their voltages must be 90 degrees out of phase. And the magnitude of the sum of their voltages is through the pythagorean theorem. However, 60^2 + 130^2 does not equal 160^2.

 

Vxy=IZxy
for pure resistor Z=R
pure cap; Z= 1/(2pi*frequency*C)=Xc
pure Inductance; Z= frequency*2pi*L=Xl
where C is capacitance and L is inductance.

total impedance
Z= sqrt(R^2 + (Xl -Xc)^2)

Pf = R/Z.

 

Have you drawn the circuit yet?

 

v/i will give you the reactance, so say 130 v /5 amps will igve you the reactance of what ever the volatge is across,5 amps will be common as itsa series circuit. once you have done i times v on all the compnents,140 volts/5 amps gives you total circuit impeadance.to get capacitor value, transpose to get c , you have xc v/5 amps, then use 1/2 pie.xc=c inductance L = xl/2 pie f r=v/i p.f =r/z

Hope that helps

 

mis type sorry v/i gives you reactance lol, sorry