Power System Protection (EX-701) - Important Questions

Explain the process and significance of using symmetrical components to simplify fault analysis in power systems, especially unsymmetrical faults.

Explain the different types of faults in a power system, their causes and effects on system stability.

Derive an expression for the fault current of a double line to ground fault.

A $25$ MVA, $13.2$ kV alternator with a solidly grounded neutral has a sub-transient reactance of $0.25$ p.u. The negative and zero sequence reactance are $0.35$ and $0.1$ p.u. respectively. A single line to ground fault occurs at the terminals of an unloaded alternator, determine the fault current and the line-to-line voltage. Neglect resistance.

How does fault impedance affect the overall performance of a power system?

Discuss the role and types of current limiting reactors in managing short circuits.

Describe the types, construction and applications of current-limiting reactors.

Explain why fault currents are more than load currents? What is meant by fault level or fault MVA? Explain.

Distinguish between symmetrical and unsymmetrical faults occurring on a power system and draw the sequence-network diagrams for the following types of faults at the terminals of an unloaded generator

Three Generator are rated as follows: Generator 1 : 100MVA, 33 kV, reactance = 10% Generator 2 : 150MVA, 32 kV, reactance = 8% Generator 3 : 110MVA, 30 kV, reactance = 12% Choosing 200 MVA and 35 kV as base quantities, compute per unit reactance diagram of the three generates referred to these base quantities. Draw reactance diagram and mark per unit reactances. The three generators are connected to common bus-bars

Calculate the per-unit positive, negative, and zero sequence reactances from given three-phase, line-to-line, and line-to-ground fault currents.

Determine the time of operation of an IDMT over-current relay given plug setting, time multiplier setting, CT ratio and fault current using the relay characteristic curve.

Explain the operating principle of impedance / distance / directional relays and show their characteristics on the R-X plane.

Explain the construction, principle of operation, applications / recommended uses of induction disc type and induction cup type relays, including reset to pick-up ratio and measures to minimize disc overrun.

Describe the working principles of electromagnetic attraction type and induction type relays.

Describe the working principle of static directional and static distance relays.

Explain the advantages of static relays over electromechanical / electromagnetic relays.

Explain the key considerations when designing fault-sensing relays.

Explain Reverse power relay with neat sketch add all minute constructional detail.

Explain the effect of arc resistance and power swings on the performance of a distance relay.

Explain the meaning of PILOT in power line protection and how power line carrier protection is implemented.

Explain busbar protection schemes, including differential protection and frame-leakage protection, and their importance

Determine the required CT ratio on the high-voltage side for Merz-Price differential protection of a star-delta three-phase transformer given the CT ratio on the low-voltage side.

Explain pilot relaying schemes in transmission line protection, including the meaning of 'pilot', types of pilots, their role and fields of application.

Explain the basis on which protection zones in a transmission line are categorized in terms of current, time grading and distance.

Describe stator percentage differential protection of an alternator with neat sketch.

List and explain the different types of protection schemes for alternators.

Explain the methods used for protection of power transformers against internal and external faults.

Determine whether the percentage differential relay trips for given CT currents and slope setting.

How does the generator-transformer unit protection scheme function?

Describe common faults in alternators and the protection schemes used to safeguard them.

Explain carrier current protection including voltage range, merits and demerits, and the phase comparison scheme with sketches.

Types of air blast circuit breakers, their operating principles and areas of application, including which type is less affected by current chopping.

Explain arc quenching in circuit breakers and any two methods by which arc is quenched

Explain the rating of circuit breakers and the factors/criteria considered in their selection.

Construction, operating principle, applications and recommended voltage range of vacuum circuit breaker.

Define recovery voltage and restriking voltage and explain their significance in circuit breaker operation.

Explain the significance of breaking and making capacity and the phenomenon of arc formation in circuit breakers.

Comparison of SF6 and vacuum circuit breakers with their ratings and selection criteria.

What is the theory of current interruption and how is energy balance involved?

Compare the characteristics of bulk oil, minimum oil and SF6 circuit breakers.

How do HRC fuses function and what are their applications in low- tension switchgear?

Explain the criteria for selecting circuit breakers and the importance of testing them.

What is the function of an explosion pot in an oil circuit breaker? What are the different types of explosion pot? Describe their construction, working principle and application.

Explain comparators and level detectors and their functions in electronic / static relays.

What is the role of level detectors in static relays? Explain with a neat functional diagram.

Discuss the importance of security and reliability in modern protection systems. How are they ensured?

Explain the importance of software development for protection, security and reliability in power systems.

Describe the role of microprocessor-based protection schemes.

How do logic circuits improve relay functions in protection systems?

Derive how an amplitude comparator can be converted to a phase comparator and vice versa.

Draw the schematic diagram of a numerical relay and describe functions of its components.

Write a short note on any two:

Write a short notes on (any two):

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