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Exercise 1: Varying Firing Angle
- In the panel, choose under Pre-Selected: Three Phase: Varying Resistive Load, and set the AC-source voltage to 140 V.
- Keep the resistance R to 16.7 ohms.
Figure 22: Three-Phase Thyristor Bridge Rectifier Panel with an AC-source amplitude of 140 V
Vary the firing angle from zero to 120 degrees and fill out table 20 below.
Firing angle (Deg) | 0 | 20 | 40 | 60 | 80 | 90 | 110 | 120 |
|---|---|---|---|---|---|---|---|---|
Mean of load voltage (V) | ||||||||
Mean of load current (A) | ||||||||
AC-source power (W) | ||||||||
Load power (W) | ||||||||
THD of AC-source Current (%) |
Table 20: Effect of Varying Firing Angle
Plot on the same graph:
- the firing angle versus the average load voltage based on table 20 above
- 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 the increasing firing angle impact the THD of the AC-source current?
Exercise 2: Changing Resistive Load
Set the AC-source amplitude to 140 V.
Change the resistance R to 25 ohms.
Fill out table 21 below for different values of the firing angle.
Firing angle (Deg) | 0 | 20 | 40 | 60 | 80 | 90 | 110 | 120 |
|---|---|---|---|---|---|---|---|---|
Mean of load voltage (V) | ||||||||
Mean of load current (A) | ||||||||
AC-source power (W) | ||||||||
Load power (W) | ||||||||
THD of AC-source Current (%) |
Table 21: Effect of Varying Firing Angle with R=25 ohms
How does the change of resistance value impact the results?
Hint: compare results of tables 20 and 21