EX-702-B Hvdc & Facts - Dec 2025 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aWhat are FACT controllers and explain different categories of FACT controllers?
   How to answer

   • Define FACTS controllers as power-electronic based controllers
   • List four categories: series, shunt, combined series-series, combined series-shunt
   • Give examples: TCSC, SVC/STATCOM, IPFC, UPFC
   • State functional role of each category in power flow / voltage control
2. 7 Marks
   bExplain the principle of reactive power control in electrical power transmission?
   How to answer

   • Relate reactive power to voltage magnitude and power transfer
   • Explain need for reactive power balance for voltage regulation
   • Describe shunt/series compensation principle
   • State effect on stability and losses
3. 7 Marks
   aExplain the flow of power in AC parallel paths and meshed systems with suitable diagrams.
   How to answer

   • Show two parallel AC paths with impedances and power division
   • Extend to meshed system with loop flows
   • Give power flow expressions based on angle/impedance
   • Sketch single-line diagrams of parallel and meshed cases
4. 7 Marks
   bExplain with a neat block diagram general control scheme of Static VAR Compensator (SVC).
   How to answer

   • Define SVC components: TCR, TSC, control system
   • Draw general control block diagram with voltage measurement and firing control
   • Explain voltage regulator, susceptance control logic
   • State steady-state V-I control objective
5. 7 Marks
   aWhat is a STATCOM? Discuss its construction and working?
   How to answer

   • Define STATCOM as shunt VSC-based compensator
   • Describe main parts: VSC, DC capacitor, coupling transformer
   • Explain reactive power exchange by voltage magnitude control
   • State operating modes: capacitive/inductive
6. 7 Marks
   bExplain the power angle characteristics of a series-compensated line and show how compensation affects the power transfer limit?
   How to answer

   • Write power-angle formula $P = V^2 \sin\delta / (X_L - X_C)$
   • Plot $P-\delta$ curves for uncompensated and compensated cases
   • Show increase in peak power and power transfer limit
   • Explain degree of series compensation effect
7. 7 Marks
   aExplain the basic operating principles and characteristics of Interline Power Flow controller (IPFC).
   How to answer

   • Define IPFC with multiple series converters on different lines
   • Explain common DC link for real power exchange
   • Describe independent reactive and real power control
   • State P-Q capability characteristics
8. 7 Marks
   bWith a neat diagram, explain the construction, operating principle, and control of the Unified Power Flow Controller (UPFC).
   How to answer

   • Draw UPFC schematic with shunt and series VSCs and common DC link
   • Explain construction: converters, transformers, DC capacitor
   • Describe series voltage injection and shunt current control
   • Explain P, Q and voltage control modes
9. 7 Marks
   aDiscuss how Active Power Filters help in reactive power and harmonic compensation.
   How to answer

   • Define active power filter concept with VSC injection
   • Explain sensing and generation of compensating harmonic/reactive current
   • Describe shunt APF control for harmonics and power factor
   • State advantages for power quality
10. 7 Marks
    bWith a neat schematic diagram, state the various apparatus required for HVDC station and explain the purpose of each.
    How to answer

    • Draw HVDC station schematic with converters, transformers, filters, smoothing reactor
    • List apparatus: valves, converter transformer, filters, electrodes, protection
    • Explain purpose of each apparatus
    • Relate to AC/DC conversion and harmonic control
11. 7 Marks
    aDerive the expression for input power, output power and power factor of 12-pulse bridge converter with delay angle $\alpha$. Assume there is no overlap?
    How to answer

    • Assume ideal 12-pulse bridge with delay angle $\alpha$ and no overlap
    • Derive DC voltage/current then $P_{in}$, $P_{out}$ expressions
    • Derive displacement power factor $\cos\alpha$ relation
    • State assumptions and final formulas
12. 7 Marks
    bDraw and explain the equivalent circuit representation of a rectifier and inverter configuration in HVDC systems.
    How to answer

    • Draw equivalent circuit with rectifier and inverter voltage sources and line resistance
    • Explain rectifier and inverter modes with firing/extinction angles
    • Write voltage-current relation $V_d$, $I_d$
    • State power flow direction control
13. 7 Marks
    aCompare series MTDC and parallel MTDC system in terms of operation, control, and reliability.
    How to answer

    • Define series vs parallel MTDC topologies
    • Compare on operation, control complexity and current/voltage ratings
    • Compare reliability and fault behaviour
    • Summarize in tabular form
14. 7 Marks
    bExplain the Voltage Source Converter (VSC)-based HVDC system?
    How to answer

    • Define VSC-HVDC with IGBT-based VSC stations
    • Explain independent active/reactive power control and PWM
    • Describe components: converters, DC capacitors, AC filters
    • State advantages: weak AC, black start, compact
15. 14 Marks
    Write short notes on any **two**:

    1. a)Current control and extinction angle control used in HVDC systems.
    2. b)Power angel control using series compensation.
    3. c)Basic principle and control of SSSC.
    4. d)Ignition angle control in a converter station.
    How to answer

    • Select any two topics from (a)-(d)
    • Define key terms: current/extinction/ignition angle, series compensation, SSSC
    • Explain principle with control characteristics/diagram
    • State applications in HVDC/FACTS