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S, P, and pf for AC circuit " Help me please"

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Answers:

Shree_vani

Oracle

Karma Points: 9,336

Date Posted: 7/20/2008 11:14:37 PM Status: Live

Asker's Rating: Helpful

Response:

Given

V = 120Vrms , f=60Hz, C=200μF, R=15Ω and L=25mH

ω = 2πf = (2)(3.14)(60) = 377Ω

X_L= ωL = (377)(0.025) = 9.425Ω

X_C = 1/ωC = 1/ (377)(200μ) = 13.26Ω

The impedance of the circuit is given by

Z = -jX_C || (R+jX_L)

The current from the source will be

I = V/Z

With

|V| = 120 V

|I |= 7.9 A

φ = 44^o

P = |V| |I| cosφ = (120)(7.9)(cos44) = (948)(0.719)=682W

S = |V| |I| = (120)(7.9) =948 VA

pf = cosφ = cos44 = 0.719

The power factor is leading

b) With C removed

Z = R+jX_L

Z = 15+j9.425

Z = 17.7/_32^o Ω

I = 120 / (17.7/_32^o )

I= 6.78 /_32^o A

Now the pf is lagging.

aash's Comment:

Thanks man

prince_s

Expert

Karma Points: 1,030

Date Posted: 7/20/2008 11:15:14 PM Status: Live

Asker's Rating: Lifesaver

Response:

so here current leads the voltage.

So p.f is leading.

∴P=687.63W

if the capacitance is removed then the circuit is

So here current lags the voltage .

So p.f is lagging.

∴P=688.47W

So from above two case we can conclude that if capacitance is not there then the pf is lagging. because of capacitor p.f becomes leading.

and p.f is leading it delivers the reactive power i.e Q. if p.f is lagging then it absorbs the reactive power.

I hope this helps u................

aash's Comment:

Thank you so much

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S, P, and pf for AC circuit " Help me please"

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