Energia em redes AC

Luan Dutra

ELEC 236 SEC 001

Fall 2014

Lab 4 – Power in AC Networks

8th, October 2014

Partner in the experiment: Michael Gharzai

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Introduction

In this experiment, it is talked about the behavior of circuits using alternative current (AC). It is shown that the effective value of a voltage or a current is found by defining the RMS (root mean square) for the waveform.

The complex power S (VA) is known as apparent power. The real part of the complex power is P (W) or the active power. The imaginary part of this is Q (VAr) or reactive power.

The ratio of the average power to the apparent power is known as power factor and is given by

Pf=P/S=cos(θv-θi)

Procedure

Fig 1. Circuit built in the part 1 of the experiment

It was built the circuit shown in Fig. 1 with a sine wave of 10V peak-to-peak and frequency of 1 kHz. The oscilloscope was used to measure the phase angle between the load voltage and the current.

The multimeter was used to measure the voltage across the load, the generator and the 100Ω resistor. After all the measurements, the power factor, average power, reactive power and complex power were calculated.

The capacitor needed to be placed in parallel with the load to raise the power factor to unity. It was used the closest possible capacitor to this value, and all the calculation was made again.

Results and discussions

Components Theoric values Actual Values

Resistor 1 220Ω 219.2Ω

Resistor 2 1kΩ 971.7Ω

Resistor 3 100Ω 98.34Ω

Capacitor 1 0.1µF 96.4nF

Capacitor 2 1nF 1.6nF

Inductor 1 0.1H 0.097H

Table 1. Actual values of components

Fig 2. Oscilloscope image of part 1 of the experiment – 10V peak-to-peak sine wave

Data collected and equations used in part 1 and 2 of the experiment:

Δt=140µs f=1.027kHz

Ф=2πf

ф=50.4°

Pf=cos ф

Pf=0.63

Vload=3.22V

Vr=0.33V

I=Vr/R3 => I=3.3mA

Vsource=3.55V

S=VI*