In a certain inverter, each thyristor conducts 26.67 A for 60°, 13.33 A for 120°, and 0 A for 180° during each 360° cycle. Compute the rms current of one thyristor from these segment values and durations.

Introduction / Context:
RMS (root mean square) current of a switching device must be calculated from the actual current waveform segments over a full cycle. This is essential for thermal design and device selection in inverters.

Given Data / Assumptions:

• Segment 1: I = 26.67 A for 60°.
• Segment 2: I = 13.33 A for 120°.
• Segment 3: I = 0 A for 180°.
• Period = 360°.

Concept / Approach:
RMS is the square root of the mean of the squared current over the period. For piecewise-constant segments: Irms^2 = (Σ(I_i^2 * angle_i/360°)).

Step-by-Step Solution:
1) Compute squared contributions: 26.67^2 * 60 and 13.33^2 * 120.2) Divide total by 360 to find mean of squares: Irms^2 = [(26.67^2 * 60) + (13.33^2 * 120)] / 360.3) Take square root: Irms ≈ 13.33 A.
Verification / Alternative check:
Because the device conducts at a lower level for double the angle, the arithmetic works out to a balanced RMS near the smaller current value; exact computation confirms ≈ 13.33 A.

Why Other Options Are Wrong:

• 20 A: Too high; ignores the long interval at zero and the lower-current segment.
• 6.67 A or 3.33 A: Too low; underestimates higher-current contribution.
• 15.00 A: Not supported by squared-mean calculation.

Common Pitfalls:

• Using average instead of RMS for heating calculations.
• Forgetting to square currents before averaging.

Final Answer:
13.33 A (Option B).