Single-phase converter with center-tapped transformer and highly inductive load For a single-phase full converter using a center-tapped secondary and a highly inductive (continuous current) load, with firing angle α, each thyristor conducts for what electrical angle?
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Aπ
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Bα
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Cπ − α
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Dπ/2
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E2π − α
Answer
Correct Answer: π
Explanation
Introduction / Context:Full-controlled single-phase converters commonly use either a bridge or a center-tapped secondary with two thyristors. With a highly inductive load, current is continuous and each device conducts for a fixed span independent of the firing angle, apart from overlap. The question targets recognition of conduction intervals under continuous current.
Given Data / Assumptions:
- Single-phase full control with center-tapped transformer secondary.
- Load inductance is large enough to maintain continuous current.
- Overlap and source impedance are neglected for simplicity.
Concept / Approach:
In continuous conduction, once fired, a thyristor continues to conduct until current is naturally transferred to the other device. In the ideal case, each device conducts for 180 degrees (π radians). Firing angle α shifts the current transfer instant but does not reduce the total conduction angle per device for a continuous current scenario.
Step-by-Step Solution:
Assume continuous current: current never falls to zero within a half-cycle.At each half-cycle, the newly fired SCR takes over and conducts until the opposite half-cycle ends.Conduction interval per device → 180° = π radians.Verification / Alternative check:
Waveforms in standard texts show rectangular device current pulses of width π when load inductance is high.
Why Other Options Are Wrong:
α or π − α would apply if current were discontinuous; π/2 is for special commutation intervals; 2π − α is not meaningful for single device conduction in one cycle.
Common Pitfalls:
Assuming conduction width shrinks with larger α even under continuous current; forgetting that inductance sustains current.
Final Answer:
π