EE 452, Power Systems Laboratory, Lab #1



Lab 3

Power Factor of Nonlinear Loads

Objectives

• Understand how to measure current harmonics with the Power Analyzer

• Understand how to compute non-active volt-ampere components

• Understand the effects of a filter capacitor in a full-wave rectifier circuit.

Background Theory

A nonlinear load supplied by a sinusoidal source draws nonsinusoidal current. The distortive current, ID, (current harmonics above the fundamental component) increase the RMS value of the load current but contribute nothing to the average power absorbed by the load. The volt-ampere product due to current harmonics is called the distortive power:

[pic]

Once the distortive power is known, the reactive power is computed from

[pic]

Total harmonic distortion is the ratio of distortive current to the fundamental current

[pic]

The distortion factor is computed from the RMS values of the source current and the first harmonic:

[pic] [pic]

From the measured power factor and computed distortion factor, the displacement factor is determined by

[pic] [pic]

Average and RMS Voltage Measurements with Digital Multimeters

Voltmeters are designed to measure average values when a DC voltage measurement is selected. When an AC voltage measurement is selected, the instrument is designed to measure only the RMS value of the voltage harmonics, that is, the average value (DC component) is excluded from this measurement.

Procedure

Connect the AC input of the unregulated supply to the variable AC power supply as shown in Figure 3.1. Connect the heat lamp to the DC output of the supply.

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Figure 3.1 Unregulated DC power supply with resistive load.

Apply 50 Vrms to the circuit and measure:

• RMS source current (Irms)

• RMS fundamental component of source current (I1,rms). Select Arms, HARM, 1, Arms.

• Measure harmonic currents of order 2,3,5,7,9,11,13. Select Arms, HARM, 2,3,5, .., Arms.

• Apparent volt-amperes (S)

• Average power (P)

• Power factor (pf)

• Average load voltage (Vdc) and RMS ripple voltage (Vac) with the digital multimeter.

Calculate D, Q, DF, THD, and DPF. Calculate ID two ways.

THE LAB WRITE UP SHOULD CONFORM TO DEPARTMENTAL STANDARDS AS DESCRIBED IN THE GUIDELINES FOR LABORATORY REPORTS. INCLUDE THE FOLLOWING :

• Diagrams

• Measurements

• Calculations

• Conclusions

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A

0 - 135 VAC

Hampdon

Power Supply

BLK

DC Output

AC Input

Power Analyzer

V

BLK

YEL

Heat

Lamp

Unregulated

Supply

YEL

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