Consider the following statements regarding Line Commutated Converters (LCC):1.They require a strong AC system for commutation.2.They can operate without reactive power support.3.Commutation failure can occur due to AC faults.Which options stated above is/are correct?

Correct Answer: A - 1 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.
  They require a strong AC system for commutation.
  Strong AC system and commutation margin matter for LCC.
• Statement 2 - Incorrect.
  They can operate without reactive power support.
  LCC converters consume reactive power and normally require compensation/support
• Statement 3 - Correct.
  Commutation failure can occur due to AC faults.
  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 B is incorrect because it includes incorrect statement(s) 2 and omits correct statement(s) 1, 3. Option C is incorrect because it omits correct statement(s) 3. Option D is incorrect because it includes incorrect 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

Commutation and AC System Strength is linked with LCC-HVDC, HVDC Transmission and Power Systems. Strong AC system and commutation margin matter for LCC.