DE LA SALLE UNIVERSITY – DASMARINAS

COLLEGE OF ENGINEERING, ARCHITECTURE AND TECHNOLOGY

EXPERIMENT NO. 6

“POWER IN AC CIRCUITS”

SCORE:

CANIEDO, JOHN CARLO T. SUBMITTED TO:

DATE PERFORMED: JANUARY 27, 2015 ENGR. JUANCHO O. NATIVIDAD

DATE SUBMITTED: FEBRUARY 3, 2015

I. DISCUSSIONS AND ANALYSIS OF RESULTS

In this experiment, we are about to determine the importance of power in

ac circuits. This power of a circuit in ac is the rate of flow of energy in a given point of

circuit. According to the basic information in DC circuits power only consumed by the

resistive components. There are several ways to compute for the power in ac circuits,

apparent power PA in an AC circuit is the product of the source voltage and the line

current PA = VS x IT, where V is the applied voltage and I is the current taken by the

circuit. The true power dissipated by the circuit is the product of V and I and the power

factor PF. The power factor is equal to the cosine of the angle between the voltage and

current in the circuit in the circuit, that is, PT = VS x IT x cosθ . Besides that, other

formulas for true power are PT = IT2 x R where IT is total current in the circuit in amperes,

R is total resistance of the circuit in ohms, and VR is voltage measure across the total

resistance of the circuit.

Electric power constitutes the most common form of electric power distribution; in

this section, the phasor notation will be employed to analyze the power absorbed by

both resistive and complex loads.

Theoretically, we can calculate the VR by ohm’s law with VR = IT x R. The current

flow in circuit can be determined by the reactant XC = 1/2π f C, IT = VS / XC. For the

phase angle between the applied circuit voltage Vs and the current IT, we can get it by

determine the power factor of an AC circuit. The power factor is PT / PA and also equal to

cosθ . So, we can also determine the phase angle from it by calculate cos-1 (PT / PA).

Reference:

1001 Solved Problems in Electrical Engineering by Romeo A. Rojas

Self-Sufficient Guide to ECE Electronics Engineering by Jason M. Ampoloquio,

PECE

II. CONCLUSION

After the experiment, As a conclusion, we can say that the different between true

power and apparent power in AC circuits is about a cosine of phase angle. Power in an

AC circuit may be determined by measuring the applied voltage V and the current I and

the phase angle and substituting the measured values in the formula PT = VS x IT x cosθ

. However the true power may be measured directly, using a wattmeter.

I also concluded that For a purely resistive circuit the power factor is 1. When

R=0, cos(f)=0 (energy is traded but not dissipated). Usually the power factor depends

on frequency.

Since Pav corresponds to the power absorbed by the load resistance, it is also

called the real power, measured in units of watts (W). On the other hand, Q takes the

name of reactive power, since it is associated with the load reactance. Table 7.1 shows

the general methods of calculating P and Q. The units of Q are volt-amperes reactive,

or VAR. Note that Q represents an exchange of energy between the source and the

reactive part of the load; thus, no net power is gained or lost in the process, since the

average reactive power is zero. In general, it is desirable to minimize the reactive power

in a load.

III. QUESTIONS AND PROBLEMS