EX-701 Power System Protection - Dec 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aWhat are the different types of faults in power systems and how do they affect system stability?
   How to answer

   • Define symmetrical and unsymmetrical faults with types
   • List L-G, L-L, L-L-G, L-L-L, L-L-L-G with frequency/severity
   • Explain effect on voltage, current, power transfer and synchronism
   • Explain transient stability impact and fault clearing
2. 7 Marks
   bDescribe the types, construction and applications of current-limiting reactors.
   How to answer

   • Define current-limiting reactor purpose
   • Types: generator, feeder, bus-bar reactors
   • Construction: air-cored, oil-immersed, concrete structure
   • Applications and location advantages
3. 7 Marks
   aWhat are the key considerations when designing fault-sensing relays?
   How to answer

   • Define fault-sensing relay function
   • Sensitivity, selectivity, speed, reliability considerations
   • CT/VT errors, burden and setting range
   • Stability against transients and inrush
4. 7 Marks
   bHow are directional and distance relays represented on an R-X diagram?
   How to answer

   • Define R-X plane impedance representation
   • Directional relay characteristic as straight line through origin
   • Distance relay: impedance, reactance, mho circles
   • Sketch relative positions on R-X diagram
5. 7 Marks
   aOn what basis, the protection zones in a transmission line are categorized?
   How to answer

   • Define protection zones concept
   • Basis: location, reach, time grading and overlap
   • Primary, backup, Zone-1, Zone-2, Zone-3 for lines
   • Need for overlapping to avoid blind spots
6. 7 Marks
   bAn Alternator stator winding protected by a differential relay have a 15% slope of characteristics a fault is occur on winding and the current is 400A through CT1 and 320A through CT2, assuming that the CT ratio of 500/5A, will the relay trip?
   How to answer

   • Convert primary currents to CT secondary using 500/5A
   • Calculate differential current Id and bias/through current
   • Compare operating ratio with 15% slope setting
   • Decide trip/no-trip
7. 7 Marks
   aExplain the role of pilot relaying schemes in transmission line protection.
   How to answer

   • Define pilot relaying and channel types
   • Role in high-speed simultaneous tripping at both ends
   • Types: wire pilot, carrier, microwave, fibre
   • Advantages for long EHV line protection
8. 7 Marks
   bHow does the generator-transformer unit protection scheme function?
   How to answer

   • Define generator-transformer as single unit zone
   • Overall differential covering both equipments
   • Restricted earth fault, overfluxing, backup features
   • Tripping and interlocking sequence
9. 7 Marks
   aWhat is the theory of current interruption and how is energy balance involved?
   How to answer

   • Define arc interruption and contact separation
   • Energy balance: heat generation vs dissipation
   • Cassie and Mayr theories for high/low current
   • Role of deionization and recovery voltage
10. 7 Marks
    bCompare the characteristics of bulk oil, minimum oil and SF6 circuit breakers.
    How to answer

    • List construction and medium for each breaker
    • Compare interrupting capacity, speed, maintenance
    • Compare fire risk, cost and voltage application
    • Tabulate merits/demerits
11. 7 Marks
    aDescribe the common faults in alternators and the protection schemes used to safeguard them.
    How to answer

    • List stator earth fault, phase fault, inter-turn, rotor faults
    • Differential, restricted earth fault protection
    • Overcurrent, overvoltage, loss of excitation, overheating
    • Diagram of alternator protection zones
12. 7 Marks
    bHow is power line carrier protection implemented in transmission systems?
    How to answer

    • Define power line carrier principle using transmission line
    • Coupling capacitor, line trap and transceiver equipment
    • Transmission of blocking/intertripping signals
    • Application to distance and pilot protection
13. 7 Marks
    aHow do HRC fuses function and what are their applications in low- tension switchgear?
    How to answer

    • Define HRC fuse construction with silica filler
    • Current-limiting action and arc extinction process
    • Time-current characteristics
    • Applications in LT switchgear and motor circuits
14. 7 Marks
    bExplain the criteria for selecting circuit breakers and the importance of testing them.
    How to answer

    • List rated voltage, current, breaking capacity criteria
    • Operating duty, speed and environmental factors
    • Types of tests: type, routine, short-circuit tests
    • Importance for reliability and safety
15. 7 Marks
    aDescribe the role of microprocessor-based protection schemes.
    How to answer

    • Define microprocessor relay architecture
    • Sampling, filtering, phasor estimation functions
    • Adaptive, self-checking and communication features
    • Advantages over electromechanical/static relays
16. 7 Marks
    bHow do logic circuits improve relay functions in protection systems?
    How to answer

    • Define logic circuits: AND, OR, NOT in relaying
    • Implementation of composite characteristics and interlocking
    • Improvement in speed, flexibility and accuracy
    • Example of distance and bus-bar schemes