Subject: Elements of Power System (EE403)
Exam Type: Theory
Semester: IV (4th Semester)
Session: 2016–17
Time: 3 Hours
Maximum Marks: 100
Section A – Short Answer Questions (10 × 2 = 20 Marks)
This section tests fundamental knowledge and conceptual understanding of power transmission and distribution systems.
Topics Covered:
Proximity Effect: Explanation and its impact on AC transmission efficiency.
Transposition of Transmission Lines: Need to balance inductance and capacitance among phases.
Neutral Grounding: Purpose and advantages of grounding in power systems.
Types of Conductors: Examples such as ACSR, AAC, and AAAC.
Critical Disruptive Voltage: Definition related to corona inception.
Kelvin’s Law Limitation: Discussing economic balance between capital and running cost.
Isolator vs. Circuit Breaker: Operational and safety differences.
Grounding Transformer Use: Role in neutral creation for ungrounded systems.
Problems in EHVAC Transmission: Voltage regulation, corona, and reactive power issues.
Bundled Conductors: Purpose and benefits in EHV lines (reducing corona loss and reactance).
Section B – Descriptive / Analytical Questions (5 × 10 = 50 Marks)
This section focuses on transmission line analysis, mechanical design, insulation, and advanced transmission systems.
Key Questions Include:
Skin Effect in AC Transmission:
Causes, effects on resistance and efficiency.
Methods to minimize skin effect (using stranded conductors, hollow conductors, etc.).
Nominal Π Model:
Derivation of A, B, C, D parameters for a medium transmission line.
Phasor diagram and significance of each parameter.
Sag Calculation Under Different Conditions:
Given data: conductor diameter, span length, sag, temperature, ice and wind loading.
Determine the temperature for equal sag in fair weather using mechanical equations.
Single Line Diagram of Power System:
Explanation of generation, transmission, and distribution network representation.
String Efficiency Calculation:
For six insulator units with mutual and shunt capacitance ratio 10:1.
Derive voltage distribution and string efficiency.
HVDC vs. EHVAC Transmission:
Need for HVDC systems, comparison, advantages (reduced losses, no reactive power issues).
Limitations of EHVAC systems (corona, insulation, charging current).
Corona Effect:
Explanation, causes, factors influencing corona discharge, and preventive measures.
Surge Impedance Loading (SIL):
Definition and significance in long transmission lines.
Also, discuss advantages and disadvantages of neutral grounding in power systems.
Section C – Long Analytical / Design Questions (2 × 15 = 30 Marks)
This section focuses on economic design, mechanical loading, and line construction.
Questions Include:
Economic Design of Transmission Line:
Derivation of formulas for economic voltage and economic conductor size using Kelvin’s Law.
Discussion on the trade-off between capital and operating cost.
Short Notes:
(i) Kelvin’s Law: Explanation and its application in determining economic conductor size.
(ii) Wind and Ice Loading Effects: Impact on mechanical stress and line design safety factors.
Transmission Line Design Factors:
Electrical (voltage, current, power capacity).
Mechanical (span length, conductor strength, wind/ice loads).
Ground wire selection criteria for lightning protection.
Major Topics Covered
Transmission line parameters and models
Sag, tension, and mechanical design of overhead lines
Insulators and string efficiency
Corona effect and EHVAC system limitations
HVDC transmission concepts
Grounding systems and surge impedance
Economic and mechanical design of power lines
Purpose of the Paper
This exam evaluates the student’s understanding of power transmission system design and operation, focusing on:
Balancing electrical and mechanical aspects.
Minimizing losses and maintaining system stability.
Understanding advanced transmission technologies (EHVAC & HVDC).
It combines theoretical analysis, mathematical derivation, and design-oriented problem-solving — essential for any electrical engineer specializing in power systems.
