POWER SYSTEM – II (KEE-601)
B.Tech Semester VI – Theory Examination (2022–23)
POWER-SYSTEM-II-KEE-601
Power System-II is a core subject that deals with analysis, operation, stability, protection, and fault behavior of electrical power systems. The paper mainly focuses on per-unit system, load flow studies, travelling waves, fault analysis using symmetrical components, power system stability, circuit breakers, and protective relays. This subject demands strong conceptual clarity along with mathematical derivations, and answers must be written in a clear, logically connected manner to score well.
SECTION A – FUNDAMENTAL CONCEPTS AND SHORT THEORETICAL APPLICATIONS
Section A tests the student’s understanding of basic mathematical tools, power system terminology, and numerical fundamentals. Even though the questions are short, they cover extremely important concepts that form the base for advanced topics.
For example, the proof of the expression 1+α+α2=01 + \alpha + \alpha^2 = 01+α+α2=0, where α\alphaα is a complex operator, is directly related to symmetrical components, which is a very important concept in fault analysis. This result is frequently used in deriving sequence networks.
Questions related to the per-unit system test understanding of base conversion. Students must clearly explain how impedance changes when base voltage and base MVA are changed, highlighting the importance of the per-unit system in simplifying power system calculations.
The slack bus, also known as the reference bus, is a key concept in load flow analysis. Students should explain that it supplies the real and reactive power losses in the system and maintains the reference voltage magnitude and angle.
Travelling wave questions in this section introduce concepts of reflection and refraction of voltage and current waves at impedance discontinuities. Students should clearly explain how surge impedance mismatch affects voltage transmission when a wave moves from a transmission line to a cable.
Other questions related to transient stability improvement, accelerating power, relay pickup value, and circuit breaker breaking current test knowledge of system protection and stability. These answers should explain physical meaning, not just formulas.
SECTION B – LOAD FLOW, TRAVELLING WAVES, AND SWITCHING PHENOMENA
Section B requires detailed explanations, derivations, and systematic problem solving. Answers in this section should be written step-by-step in paragraph form.
The reactance diagram problem tests the ability to convert a practical power system into a simplified reactance model using per-unit values. Students must explain base selection, per-unit conversion, and representation of generators, transformers, and transmission lines.
The Gauss-Seidel load flow method is one of the most important numerical techniques in power system analysis. Students must explain how PV and PQ buses are handled differently, how power mismatch is calculated, and how voltages are updated iteratively until convergence.
The travelling wave equation derivation requires explanation of voltage and current wave propagation along a uniform transmission line and the concept of surge impedance.
The equal area criterion is a major topic in transient stability analysis. Students should explain how it is used to determine whether a synchronous machine remains stable following a disturbance.
The explanation of low resistance and high resistance arc extinction methods in circuit breakers should include physical explanation of arc behavior, cooling, and dielectric strength recovery.
SECTION C – FAULT ANALYSIS, STABILITY, AND PROTECTION
Section C is the most important section and tests deep conceptual understanding and derivation skills. Answers here must be written like a mini-theory note with proper derivations and explanations.
The single line-to-ground fault and double line-to-ground fault analysis questions require application of symmetrical components. Students must derive fault current expressions using positive, negative, and zero sequence networks and explain how these networks are interconnected for different fault types.
Questions related to bus classification and load flow calculations test understanding of how power flows are calculated and how system losses are evaluated.
The Y-bus formation problem tests matrix formulation skills. Students must explain self-admittance and mutual admittance before assembling the Y-bus matrix.
The reflection and refraction coefficient derivation is an extension of travelling wave theory and should be explained using impedance matching concepts.
The swing equation derivation is a core topic in power system stability. Students must explain the physical meaning of inertia constant, accelerating power, and rotor angle dynamics. Numerical calculation of angular momentum must be linked with theoretical explanation.
The differential relay question tests protection fundamentals. Students should explain operating and restraining forces and why restraining coils are used to prevent false tripping.
Finally, arcing phenomena in circuit breakers, along with restriking and recovery voltage, must be explained with emphasis on switching transients and system protection.
HOW TO WRITE POWER SYSTEM-II ANSWERS IN THE EXAM
In Power System-II, never write answers in short bullet points. Always begin with a short introduction of the concept, then derive equations step-by-step, and finally explain the physical significance of the result. Diagrams, sequence networks, and waveforms should always be supported with written explanation. Examiners focus heavily on clarity, derivation flow, and conceptual correctness.
