About this previous year paper
KEE074 – POWER QUALITY AND FACTS
Complete Solved Question Paper
SECTION A
(Attempt all questions – 2 × 10 = 20 marks)
Q1(a) Long-duration voltage variations
Long-duration voltage variations are sustained deviations of RMS voltage from the nominal value lasting more than 1 minute, such as overvoltage and undervoltage.
Q1(b) Voltage fluctuation
Voltage fluctuation is a series of rapid voltage changes that cause visible light flicker in lamps.
Q1(c) Common sources of voltage sag
Motor starting Short-circuit faults
Transformer energization Arc furnaces
Q1(d) Voltage sag mitigation (end-user level)
Uninterruptible Power Supply (UPS) Dynamic Voltage Restorer (DVR)
Q1(e) Atmospheric transients
Atmospheric transients are high-magnitude, short-duration overvoltages caused mainly by lightning strokes.
Q1(f) Overvoltage protection device
Surge arrester
Q1(g) FACT full form
FACTS stands for Flexible AC Transmission Systems.
Q1(h) Types of FACT devices
Static VAR Compensator (SVC) Thyristor Controlled Series Capacitor (TCSC)
Q1(i) Effects of harmonics on transformers
Increased losses Overheating
Reduced efficiency Noise and vibration
Q1(j) Harmonic mitigation technique
Passive filter
SECTION B
(Attempt any three – 10 × 3 = 30 marks)
Q2(a) Power quality terms
Transients: Sudden, short-duration voltage changes
Long-duration variations: Overvoltage/undervoltage
Short-duration variations: Voltage sag, swell, interruption
Waveform distortion: Harmonics, notching, noise
These affect system reliability and equipment performance.
Q2(b) Sources of voltage sag
Motor starting: High inrush current Arc furnaces: Irregular current draw
Fault clearing: Temporary voltage drop Impact: Malfunction of sensitive loads like PLCs and drives.
Q2(c) Sources of transient overvoltages
Atmospheric transients: Lightning
Switching transients: Circuit breaker operation, capacitor switching
Cause insulation stress and equipment damage.
Q2(d) FACTS definition & controllers
FACTS are power electronic-based controllers that improve power flow control and stability.
Controllers: SVC
STATCOM TCSC
SSC
Q2(e) Harmonics causes & measurement
Causes:
Power electronic devices Non-linear loads
Current harmonics: Generated by load Voltage harmonics: Caused by system impedance
Measurement: Harmonic analyzers, FFT-based meters
SECTION C
Q3(a) Impact of voltage fluctuations & waveform distortion
Flicker in lighting Overheating of motors
Malfunction of electronic equipment Reduced system stability
Q3(b) Power frequency variations
Causes: Load-generation imbalance
System disturbances
Effects: Speed variation in motors
Malfunction of sensitive equipment Industrial process instability
Q4(a) Voltage sag performance & protection
Estimation methods: Sag magnitude-duration analysis
Event monitoring
Protection principles: Voltage compensation
Ride-through capability Tools: Power quality analyzers, sag indices
Q4(b) Voltage sag mitigation solutions
Isolation transformers Voltage regulators
Static & rotary UPS Active series compensators (DVR)
Q5(a) Neutral voltage swings & UPS transients
Effects: Equipment malfunction
Data loss Reduced system stability
Mitigation: Proper grounding
Isolation transformers Improved UPS design
Q5(b) Overvoltage protection devices
Surge arresters Metal oxide varistors (MOV)
Spark gaps Used to divert excess voltage safely to ground.
Q6(a) FACT devices & applications
SSC: Voltage control SVC: Reactive power compensation
TCSC: Power flow control and stability improvement
Q6(b) Power flow control using FACTS
Power flow in a transmission line: P=V1V2XsinδP = \frac{V_1 V_2}{X} \sin \deltaP=XV1V2sinδ
FACTS devices control X, V, and δ, thereby controlling power flow.
Q7(a) Effects of harmonics
Transformers: Heating, losses Motors: Torque pulsations
Capacitors: Resonance Cables: Overheating
Communication lines: Interference
Q7(b) Harmonic mitigation techniques
Passive: LC filters Tuned filters
Active: Active power filters Hybrid filters
Used in modern industrial power systems.