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?
Answer & step-by-step solution
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.
HVDC कन्वर्टर के फायरिंग कोण नियंत्रण के संबंध में निम्नलिखित कथनों पर विचार कीजिए:
1. फायरिंग कोण बढ़ाने से DC आउटपुट वोल्टेज घटता है।
2. 90° पर कन्वर्टर शून्य DC वोल्टेज पर कार्य करता है।
3. 90° से अधिक फायरिंग कोण इन्वर्टर मोड से संगत है।
ऊपर बताए गए कौन-से विकल्प सही हैं?
उत्तर और चरणबद्ध हल
C — 1, 2 और 3। Vd = Vd0 cosα, इसलिए α बढ़ाने पर DC वोल्टेज घटता है, α = 90° पर शून्य होता है और α > 90° पर Vd ऋणात्मक हो जाता है — धारा की दिशा वही रहते हुए शक्ति उलटती है, यानी कन्वर्टर इन्वर्टर मोड में चलता है।
विस्तृत हल (मूल भाषा में)
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.
HVDC કન્વર્ટરના ફાયરિંગ કોણ નિયંત્રણ અંગે નીચેનાં વિધાનો ધ્યાનમાં લો:
1. ફાયરિંગ કોણ વધારવાથી DC આઉટપુટ વોલ્ટેજ ઘટે છે.
2. 90° પર કન્વર્ટર શૂન્ય DC વોલ્ટેજે કાર્ય કરે છે.
3. 90° થી વધુ ફાયરિંગ કોણ ઇન્વર્ટર મોડને અનુરૂપ છે.
ઉપર જણાવેલા કયા વિકલ્પો સાચા છે?
જવાબ અને પગલાવાર ઉકેલ
C — 1, 2 અને 3. Vd = Vd0 cosα, તેથી α વધારતાં DC વોલ્ટેજ ઘટે છે, α = 90° પર શૂન્ય થાય છે અને α > 90° પર Vd ઋણ બને છે — પ્રવાહની દિશા એ જ રહેતાં પાવર ઉલટાય છે, એટલે કન્વર્ટર ઇન્વર્ટર મોડમાં ચાલે છે.
વિગતવાર ઉકેલ (મૂળ ભાષામાં)
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.
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