About this previous year paper
Elements of Power System (NEE-501)
Section-Wise Important Questions & Study Notes
SECTION–A
(Attempt all questions – short answer type)
This section checks basic understanding and definitions. Answers should be short, direct, and clear (2–3 lines each).
Important Topics to Prepare
1. Circuit Breaker
A circuit breaker is a protective device used to automatically interrupt current flow during fault conditions like short circuits or overloads, protecting equipment and people.
2. Single Line Diagram (SLD)
A single line diagram represents a three-phase power system using a single line, showing major components like generators, transformers, and transmission lines.
3. Components of Transmission Line
Transmission line mainly consists of conductors, insulators, supports (poles/towers), and ground wires.
4. Transposition of Transmission Line
Transposition is the process of periodically changing the positions of conductors to balance inductance and reduce interference.
5. Advantages of Bundled Conductors
Bundled conductors reduce corona loss, radio interference, and line reactance while increasing power transmission capability.
6. Corona
Corona is the ionization of air around high-voltage conductors, causing power loss, noise, and light emission.
7. Insulator Failure
Insulator failure occurs due to flashover, puncture, mechanical stress, or environmental pollution.
8. Sag in Transmission Line
Sag is the vertical distance between the lowest point of the conductor and the line joining two supports.
9. Neutral Grounding
Neutral grounding is the connection of the neutral point of a system to earth to control over-voltages and improve safety.
Tip: Write definitions neatly. Do not explain more than required.
SECTION–B
(Attempt any three questions – descriptive type)
This section tests conceptual clarity and explanation skills.
1. Parameters of Transmission Line (A, B, C, D Constants)
These constants represent the relationship between sending-end and receiving-end voltage and current.
They are used in modeling short, medium, and long transmission lines and help in performance analysis.
You should be able to:
Define A, B, C, D constants Write their equations
Explain their physical meaning Draw phasor diagrams (important)
2. Corona Phenomenon and Critical Voltage
Corona occurs when electric field intensity exceeds critical value.
Critical disruptive voltage depends on: Conductor size
Spacing Atmospheric conditions
Surface condition
Explain: Formation of corona
Effects (loss, noise, interference) Methods to reduce corona
3. Vibrations Due to Wind and Ice Loading
Wind causes aeolian vibrations in conductors, while ice loading increases weight, causing excessive sag and tension.
You should explain: Causes of vibration
Mechanical stress on conductors Methods of damping (dampers, spacers)
4. Advantages of HVDC Transmission
HVDC transmission is preferred for long distances and underwater cables.
Explain: Reduced losses
No reactive power Better voltage regulation
Economic advantages over EHV-AC
5. Kelvin’s Law for Economic Size of Conductor
Kelvin’s law states that the most economical conductor size is when annual cost of energy loss equals annual capital charges.
Explain: Statement
Assumptions Limitations
Practical significance
SECTION–C
(Attempt any two questions – long answer type)
This section requires derivations, diagrams, numerical problems, and detailed explanations.
1. Sag and Tension – Catenary Method
This is a very important numerical + theory question.
Prepare: Meaning of sag and tension
Catenary equation Assumptions used
Derivation of sag formula
Numerical problem based on given span, weight, and tension
Always write formula, substitute values clearly, and mention units.
2. Cable Grading and Capacitance Grading
Cable grading improves voltage distribution in underground cables.
Explain: Why grading is required
Types of grading Capacitance grading with circuit diagram
Advantages and limitations
3. Earthing and Neutral Grounding
Explain clearly: Difference between earthing and neutral grounding
Methods of neutral grounding Solid grounding
Resistance grounding Reactance grounding
Petersen coil grounding Advantages of grounding
Neat sketches (very important)
4. EHV Transmission Lines and HVDC Comparison
Prepare: Conductor configurations
Choice of voltage levels Number of circuits
Economic comparison between EHV-AC and HVDC
Situations where HVDC is preferred