Applications of thyristors – assertion and reason Assertion (A): Thyristors are used in controlled heating, alternator excitation systems, motor speed control, and HVDC transmission. Reason (R): Static VAR systems using thyristors are very commonly employed in high-voltage AC systems.

Introduction / Context:
Thyristors (SCRs and related devices) are ubiquitous in high-power conversion and control. Evaluating assertion–reason statements helps reinforce where and why thyristors are applied across industry sectors such as drives, power transmission, and reactive power control.

Given Data / Assumptions:

• Applications listed: controlled heating, alternator excitation, motor control, HVDC.
• Static VAR compensators (SVC) or STATCOMs include thyristor-switched capacitors/reactors.

Concept / Approach:

A is correct: All listed applications are standard for thyristor technology due to high current capability, robustness, and latching behavior. R is also correct: SVCs widely use thyristors to modulate reactive power in AC networks. However, R does not explain A; it merely cites one common application area rather than providing the causal justification for the broad versatility in A.

Step-by-Step Solution:

Verification / Alternative check:

Power electronics textbooks and utility practice confirm both statements; propulsive drives, HVDC links, and thermal processing all employ thyristors, and utilities deploy SVCs using thyristors for voltage stabilization and power factor correction.

Why Other Options Are Wrong:

• Stating R explains A misattributes causality.
• Declaring either A or R false conflicts with established practice.

Common Pitfalls:

Confusing SVCs (thyristor-switched) with STATCOMs (converter-based) and assuming one invalidates the other; both exist.

Final Answer:

Both A and R are correct but R is not correct explanation of A