EX-802-A Power Quality Problems and Mitigation Techniques - Jun 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 is traditional power quality? What are the reasons of traditional power quality? Why should you be concerned the power quality?
   How to answer

   • Define traditional power quality as steady sinusoidal voltage/current at rated magnitude and frequency.
   • List reasons/causes: nonlinear loads, switching, faults, grounding, EMI etc.
   • Explain concerns: equipment malfunction, losses, heating, downtime, economic impact.
2. 7 Marks
   bWhat are the solutions for power quality problems? How can you check good quality of electrical power?
   How to answer

   • List mitigation solutions: filters, PFC, UPS, DVR, STATCOM, grounding, surge protection.
   • Explain checking good quality: monitoring voltage, frequency, harmonics, PF, THD.
   • Mention standards and measuring instruments/power quality analyzers.
3. 7 Marks
   aWhat is voltage fluctuation? Why is electricity fluctuating throughout the house lights dim when appliances AC turn on power to microwave and refrigerator fluctuate?
   How to answer

   • Define voltage fluctuation/flicker as rapid variation in RMS voltage.
   • Explain causes: high inrush loads like AC, microwave, refrigerator, loose wiring.
   • Explain dimming due to voltage drop on shared impedance when large load starts.
4. 7 Marks
   bWhat are the benefits of power factor correction services? Explain, where can you install power factor correction capacitors banks?
   How to answer

   • Define power factor correction and capacitor banks.
   • List benefits: reduced losses, penalty avoidance, increased capacity, voltage improvement.
   • Explain installation locations: at load, motor terminals, MCC, substation, utility feeder.
5. 7 Marks
   aWhat do you mean by flexible in flexible AC transmission system? Why capacitance is taken as shunt in Transmission lines?
   How to answer

   • Define flexible in FACTS/flexible AC transmission system.
   • Explain controllability of power flow, voltage, impedance.
   • Explain shunt capacitance for charging, reactive support and line modelling.
6. 7 Marks
   bWhat is the basic principle of shunt active filter? Why do we pay a reactive power compensation penalty?
   How to answer

   • State principle: inject compensating harmonic/reactive current in parallel.
   • Explain sensing load current and generating anti-phase compensation.
   • Explain reactive power penalty due to low PF burden on utility.
7. 7 Marks
   aWhat is better, SVC or STATCOM? What is the difference between an active power filter and a STATCOM?
   How to answer

   • Define SVC (thyristor-based) and STATCOM (VSC-based).
   • Compare speed, footprint, harmonic performance, low-voltage capability.
   • Compare active power filter vs STATCOM in function and application.
8. 7 Marks
   bWhat is the principle of UPQC? Explain the working and operation of UPQC.
   How to answer

   • Define UPQC as combined series-shunt active filter.
   • Explain series APF for voltage and shunt APF for current compensation.
   • Explain working/operation with DC-link and control.
9. 7 Marks
   aWhat is sag and swell in a power system? Write the difference between voltage surge and swell.
   How to answer

   • Define sag (dip) and swell (rise) with magnitude-duration.
   • Differentiate surge vs swell in cause, duration, magnitude.
   • Give examples: faults for sag, capacitor switching/lightning for surge/swell.
10. 7 Marks
    bWhat is a power spike, and how do surge protectors protect electrical equipment? Why do power surges happen, and how do you prevent them?
    How to answer

    • Define power spike/surge as short high-voltage transient.
    • Explain surge protector operation: clamping/diverting excess energy.
    • List causes of surges and prevention methods.
11. 7 Marks
    aWhat is a voltage sag protector? Why is the protection scheme needed for a power system?
    How to answer

    • Define voltage sag protector/DVR/UPS for ride-through.
    • Explain need for protection scheme: continuity, equipment safety.
    • Mention coordination, detection and mitigation.
12. 7 Marks
    bWhat commonly causes transient voltages? Explain the factors affecting transient recovery voltage.
    How to answer

    • List causes of transient voltages: switching, lightning, faults, capacitor switching.
    • Define transient recovery voltage (TRV).
    • Explain factors affecting TRV: system inductance, capacitance, fault current, power factor.
13. 7 Marks
    aWhat are the best methods to protect or with-stand impulse voltages for high voltage equipment? How can you safely work with high voltage equipment?
    How to answer

    • List methods: shielding, surge arresters, insulation coordination, BIL, grounding.
    • Explain withstand design for impulse voltages.
    • List safety practices for high-voltage work: PPE, clearance, interlocks.
14. 7 Marks
    bWhy is the zero-voltage crossing optimal for harmful transient mitigation, e.g., overvoltage when switching capacitor banks at a substation?
    How to answer

    • Explain capacitor switching transient and overvoltage mechanism.
    • Explain zero-crossing switching minimizes dV/dt and inrush.
    • Relate to synchronous switching/point-on-wave control at substation.
15. 7 Marks
    aWhat is the best method to eliminate Harmonics in a Power System? How can filters reduce harmonics?
    How to answer

    • State best methods: passive, active, hybrid filters, design practices.
    • Explain filter action: provide low-impedance path or inject cancelling harmonics.
    • Mention THD reduction and resonance considerations.
16. 7 Marks
    bWhat is a shunt active filter? What are the advantages and disadvantages of an active harmonic filter?
    How to answer

    • Define shunt active filter as parallel compensator.
    • List advantages: dynamic, multi-harmonic, PF correction.
    • List disadvantages: cost, complexity, rating limits.