Average thyristor current in a 3-phase full converter A 3-phase fully controlled bridge converter supplies an average (DC) load current of 150 A. What is the average current through each thyristor?

Introduction / Context:
In a 3-phase 6-pulse full converter, each thyristor conducts for 120 electrical degrees in each cycle. The relationship between average DC load current and average device current follows from the conduction pattern of the six devices.

Given Data / Assumptions:

• Six SCRs conduct in sequence; at any time two devices conduct (one from the top group, one from the bottom group).
• Average DC load current, Idc = 150 A (continuous current assumed).

Concept / Approach:
Because each individual SCR carries the load current for 120° out of every 360°, the average current in one device over a full cycle equals Idc multiplied by the duty fraction (120/360 = 1/3). Therefore, Iavg_thyristor = Idc/3.

Step-by-Step Solution:
Conduction interval per device = 120°.Duty fraction = 120/360 = 1/3.Iavg_thyristor = Idc * (1/3) = 150 * (1/3) = 50 A.

Verification / Alternative check:
Instantaneous current through a conducting device equals line current ≈ load current (ideal case). Averaging over one period with 1/3 duty confirms 50 A.

Why Other Options Are Wrong:
150 A (A): Would imply continuous conduction through a single device, which is not the case.
75 A (B): Corresponds to 1/2 duty, not applicable.
25 A (D): Would imply 1/6 duty, incorrect for 120° conduction.

Common Pitfalls:
Confusing RMS with average; here the question explicitly asks for average current per thyristor.

Final Answer:
50 A