Enrolment No.
/Seat No_____________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER–VI (NEW) EXAMINATION – SUMMER 2024
Subject Code:3160921 Date:24-05-2024
Subject Name:HVDC Transmission Systems
Time:10:30 AM TO 01:00 PM Total Marks:70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Simple and non-programmable scientific calculators are allowed.
MARKS
Q.1 (a) State the relative merits of HVDC transmission and HVAC 03
transmission by taking in to consideration
(i) Economics of power transmission (ii) Technical Performance (iii)
Reliability
(b) Explain with neat sketch different types of HVDC links (i) Monopolar 04
HVDC link (ii) Bipolar Homopolar HVDC link and (iii) Homopolar
HVDC link.
(c) With a neat schematic diagram, state the various apparatus required for 07
HVDC station and explain the purpose of each.
Q.2 (a) Sketch the waveforms of output voltage and the transformer secondary 03
current in the case of 3 – phase, 6 pulse bridge circuit (Graetz’s circuit)
(b) Identify the various sources for generation of harmonics in HVDC 04
systems and mention the various adverse effects caused due to the
presence of harmonics.
(c) Distinguish between delay in firing angle α and extinction angle Ƴ of 07
an HVDC converter. Explain the operation of a converter when working
as an inverter, and state the necessary conditions required for inverter
operation.
OR
(c) Explain 12 pulse converter with schematic diagram. 07
Q.3 (a) State difference in power control in HVDC and HVAC systems and 03
explain the necessity of power control in an HVDC link.
(b) Explain the operation of pulse frequency control and state why it is 04
preferred in modern HVDC systems?
(c) What do you understand by constant extinction angle control? What are 07
the parameters that should be taken in to account while designing
constant extinction angle controller?
OR
Q.3 (a) Explain starting and stopping of an HVDC link. 03
(b) Explain the relative merits and demerits of constant current and 04
constant voltage operation of an HVDC link.
(c) Explain real and reactive power control using VSC. 07
Q.4 (a) Explain principles of DC Link control in a LCC HVDC system. 03
1
(b) Describe selective harmonic elimination techniques. 04
(c) Explain basic principles of synchronous and asynchronous links. 07
OR
Q.4 (a) Mention the essential requirements of ground electrodes in HVDC 03
systems and explain the necessity of each item briefly.
(b) How are insulators for DC different from that for AC? What are their 04
requirements?
(c) Write notes on voltage stability problems in HVAC/DC systems. 07
Q.5 (a) Why are multiterminal DC systems needed? What are the different 03
types of MTDC systems used?
(b) How is power sharing and power control achieved in an MTDC 04
systems.
(c) Give the principle of different types of DC circuit breaker schemes. 07
Why is a surge diverter needed across the DC circuit breaker.
OR
Q.5 (a) Classify PWM techniques. 03
(b) What is modular multilevel converter? 04
(c) Explain different aspects to be considered for a parallel operation in 07
MTDC systems.
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