Exercise 3: Varying Firing Angle

In the panel, choose under Pre-Selected: Three Phase: Varying Inductive Load, and set the AC-source voltage to 140 V.
Set the load to R=25 ohms, L=40 mH.

Figure 23: Three-Phase Thyristor Bridge Rectifier Panel with R = 25 ohms, L = 40 mH

Vary the firing angle from zero to 120 degrees and complete table 22 below.

Table 22: Effect of Varying Firing Angle (indutive load scenario)

Plot on the same graph:

1. the firing angle versus the average load voltage based on Table 20
2. the firing angle versus the average load voltage based on equation (18)

Do the two plots match one another?
Explain your observation.

What is the firing angle for which the load power vanishes to zero?

How does inductive load impact the operation limit of the rectifier?
     Hint: compare to operation limit with purely resistive load.

How does the increasing firing angle impact the THD of the AC-source current?

Exercise 4: Varying Inductive Load

Set the AC-source amplitude to 140 V, and the firing angle to zero.

Change the inductance as shown in table 23 below and fill out the table.

Table 23: Effect of Varying Inductance

What are the effects of increasing the inductance on:

• THD of AC-source current
• Average load voltage and current
• Load power?

Explain your observations.