Exercise 1: Varying Resistive Load (without smoothing capacitor C=0)

Open Three-Phase Diode Bridge Rectifier panel, choose in menu Pre-Selected: Three Phase: Varying Resistive Load without smoothing capacitor.

Figure 16: Three-Phase Diode Bridge Rectifier Panel with a Resistive Load of 16.5 ohms

Default Parameters

• AC Source Voltage : Ve= 120 V
• Frequency: 60 Hz
• R= 16.5 Ω

• For R = 16.5 ohms and Ve=120, measure the following values:
  • the maximum peak value of the output voltage
  • the minimum peak value of the output voltage
  • the average output voltage
• Compare these values with the calculated ones
• Set Ve to 120V and the frequency to 60 Hz, and complete the following table for many values of R

Table 10: Impact of Varying Resistive Load

• Justify the shape of the output voltage and output current.
• What is the effect of increasing the resistance value on THD?
• Deduce the role of the three-phase diode bridge rectifier and compare it with the single-phase diode bridge rectifier.

Exercise 2 - Varying Resistive Load (with smoothing capacitor)

In the panel, choose under Pre-Selected: Three Phase: Varying Resistive Load with smoothing capacitor.

Figure 17: Three-Phase Diode Bridge Rectifier Panel with R=16.5 ohms and C= 470 µF

Default Parameters

• AC Source Voltage : Ve= 120 V
• Frequency: 60 Hz
• R= 16.5 Ω
• C= 470 µF

Complete Tables 11, 12 and 13 for different values of the smoothing capacitor.

Case 1: C= 470 µF

Table 11: Case 1- Effect of varying Resistive Load With Smoothing Capacitor

Case 2 : C= 1100 µF

Table 12: Case 2- Effect of varying Resistive Load With Smoothing Capacitor

Case 3 : C= 0.1 F

Table 13: Case 3- Effect of varying Resistive Load With Smoothing Capacitor

Now, set R to 25 Ω.

• Compare values of the peak-to-peak output voltages (without and with smoothing capacitor).
• How does the ripple factor change with and without the smoothing capacitor?
• What’s the relation between the peak-to-peak output voltage and the resistance (when C is constant)?
• For which capacitor value is the filtering considered more effective?
• What is the effect of increasing the capacitor filtering on the total harmonic distortion (THD) of the AC-source current?