(SEM V) THEORY EXAMINATION 2017-18 ELEMENTS OF POWER SYSTEM

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