Consider the following statements regarding firing angle control of HVDC Converter:1.Increasing firing angle reduces DC output voltage.2.At 90°, converter operates at zero DC voltage.3.Firing angle greater than 90° corresponds to inverter mode.Which options stated above is/are correct?

Correct Answer: C - 1, 2 and 3 only

Quick Concept Explanation

Line-commutated HVDC uses thyristors and depends on the AC system voltage for commutation, so adequate short-circuit strength and reactive-power support are important. AC voltage disturbances can produce commutation failure, particularly at the inverter. Key relation: LCC reactive demand is a significant fraction of transmitted power and is compensated locally.

Exam focus: Strong AC system and commutation margin matter for LCC. Common trap: LCC cannot normally operate a passive AC network without a voltage source.

Statement-wise Verification

• Statement 1 - Correct.
  Increasing firing angle reduces DC output voltage.
  AC voltage disturbances can produce commutation failure, particularly at the inverter.
• Statement 2 - Correct.
  At 90°, converter operates at zero DC voltage.
  AC voltage disturbances can produce commutation failure, particularly at the inverter.
• Statement 3 - Correct.
  Firing angle greater than 90° corresponds to inverter mode.
  AC voltage disturbances can produce commutation failure, particularly at the inverter.

Core Concept

Line-commutated HVDC uses thyristors and depends on the AC system voltage for commutation, so adequate short-circuit strength and reactive-power support are important. AC voltage disturbances can produce commutation failure, particularly at the inverter.

Formula / Key Relationship

LCC reactive demand is a significant fraction of transmitted power and is compensated locally.

Why the Other Options Are Wrong

Option A is incorrect because it omits correct statement(s) 3. Option B is incorrect because it omits correct statement(s) 1. Option D is incorrect because it omits correct statement(s) 2.

Exam Shortcut / Approach

Strong AC system and commutation margin matter for LCC.

Common Mistake

LCC cannot normally operate a passive AC network without a voltage source.

Quick Revision

Firing Angle and Rectifier-Inverter Operation is linked with Converter Control, HVDC Transmission and Power Systems. Strong AC system and commutation margin matter for LCC.