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ENEE 352Bachelor in Electrical Engineering · Semester 62 Papers Available

Switchgear and Protection

Past examination question papers and complete curriculum syllabus for Switchgear and Protection (ENEE 352), Bachelor in Electrical Engineering Semester 6 under Institute of Engineering (IOE), Tribhuvan University.

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6th-sem_Switchgear and Protection.pdf

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Most Frequently Asked Questions

Top recurring IOE board exam questions for Switchgear and Protection with verified mark schemes, formula notation, and recurrence frequency.

Showing 30 of 30 top repeated questions

Fundamentals of Power System Protection

4 Questions
#1Repeated 4 Times[6 Marks]Fundamentals of Power System Protection
Explain the physics of electric arc phenomenon in circuit breakers. Explain High Resistance and Zero Current Interruption principles of arc extinction in AC circuits.
Appeared in:2083 Baishakh2081 Bhadra2079 Chaitra2076 Chaitra
#2Repeated 4 Times[8 Marks]Fundamentals of Power System Protection
Define Restriking Voltage, Recovery Voltage, and Rate of Rise of Restriking Voltage (RRRV). Derive the expression for restriking voltage: $v_r(t) = V_m (1 - \cos \omega_n t)$ and maximum RRRV ($RRRV_{\max} = \omega_n V_m = \frac{V_m}{\sqrt{LC}}$).
Appeared in:2082 Bhadra2080 Chaitra2077 Magh2075 Bhadra
#3Repeated 3 Times[6 Marks]Fundamentals of Power System Protection
Explain resistance switching in circuit breakers. Derive the expression for critical damping resistance: $R_{cr} = 0.5\sqrt{L/C}$ to prevent transient oscillation across circuit breaker contacts.
Appeared in:2082 Chaitra2080 Baishakh2078 Bhadra
#4Repeated 3 Times[6 Marks]Fundamentals of Power System Protection
Explain current chopping phenomenon in circuit breakers when interrupting low inductive currents (such as transformer on no-load). Derive the prospective overvoltage across contacts ($e = i \sqrt{L/C}$).
Appeared in:2083 Baishakh2081 Chaitra2079 Baishakh

Circuit Interruption Theory and Circuit Breakers

5 Questions
#1Repeated 3 Times[8 Marks]Circuit Interruption Theory and Circuit Breakers
Describe the construction, working principle, and arc extinction mechanism of an Air Blast Circuit Breaker (ABCB) with axial blast, cross blast, and radial blast designs.
Appeared in:2082 Bhadra2081 Baishakh2078 Chaitra
#2Repeated 3 Times[8 Marks]Circuit Interruption Theory and Circuit Breakers
Explain the physical and dielectric properties of Sulphur Hexafluoride ($SF_6$) gas. Describe the construction and operation of a puffer-type $SF_6$ circuit breaker.
Appeared in:2082 Chaitra2080 Chaitra2076 Chaitra
#3Repeated 3 Times[8 Marks]Circuit Interruption Theory and Circuit Breakers
Explain the arc extinction mechanism in Vacuum Circuit Breakers (VCB). Describe contact materials, butt and spiral contact geometries, and explain why VCBs are preferred in medium-voltage ($11\text{ kV} - 33\text{ kV}$) switchgear.
Appeared in:2083 Baishakh2081 Bhadra2077 Chaitra
#4Repeated 3 Times[6 Marks]Circuit Interruption Theory and Circuit Breakers
Compare Bulk Oil Circuit Breakers (BOCB), Minimum Oil Circuit Breakers (MOCB), Air Blast Circuit Breakers, $SF_6$ Circuit Breakers, and Vacuum Circuit Breakers with respect to dielectric medium, maintenance, fire hazard, and voltage limits.
Appeared in:2081 Chaitra2079 Chaitra2075 Bhadra
#5Repeated 3 Times[6 Marks]Circuit Interruption Theory and Circuit Breakers
Define circuit breaker ratings: Rated voltage, Rated normal current, Rated breaking capacity (symmetrical and asymmetrical), Rated making capacity ($2.55 \times I_b$), and Short-time withstand current rating.
Appeared in:2082 Bhadra2080 Baishakh2078 Chaitra

Protective Relays (Electromechanical and Microprocessor-Based)

5 Questions
#1Repeated 3 Times[6 Marks]Protective Relays (Electromechanical and Microprocessor-Based)
Explain the fundamental requirements of protective relaying: Selectivity (discrimination), Sensitivity, Speed, Reliability, Simplicity, and Economy.
Appeared in:2083 Baishakh2082 Chaitra2080 Chaitra
#2Repeated 3 Times[8 Marks]Protective Relays (Electromechanical and Microprocessor-Based)
Describe the construction and operating principle of an induction disc overcurrent relay. Derive the electromagnetic torque equation ($T = k \Phi_1 \Phi_2 \sin \alpha$). Define Plug Setting Multiplier (PSM) and Time Multiplier Setting (TMS).
Appeared in:2081 Bhadra2079 Baishakh2077 Magh
#3Repeated 3 Times[8 Marks]Protective Relays (Electromechanical and Microprocessor-Based)
Explain Inverse Definite Minimum Time (IDMT) characteristic according to IEC 60255 ($t = \frac{0.14 \times TMS}{(PSM)^{0.02} - 1}$). Calculate the operating time of an IDMT relay with $CT = 400/5\text{ A}$, plug setting $125\%$, $TMS = 0.5$, and fault current $4000\text{ A}$.
Appeared in:2082 Bhadra2080 Baishakh2076 Bhadra
#4Repeated 3 Times[8 Marks]Protective Relays (Electromechanical and Microprocessor-Based)
Explain the architecture of Numerical Protective Relays: signal conditioning, anti-aliasing filter, sample-and-hold, ADC, digital signal processor (DSP), and trip logic. Compare numerical relays with static and electromechanical relays.
Appeared in:2083 Baishakh2081 Chaitra2078 Bhadra
#5Repeated 3 Times[6 Marks]Protective Relays (Electromechanical and Microprocessor-Based)
Explain Current Transformer (CT) saturation and error characteristics: Ratio error and Phase angle error. What is CT Burden, Accuracy Class (5P10, 5P20), and Knee-Point Voltage ($V_k$) in protection CTs?
Appeared in:2082 Chaitra2080 Chaitra2079 Chaitra

Apparatus Protection (Generators and Transformers)

6 Questions
#1Repeated 3 Times[8 Marks]Apparatus Protection (Generators and Transformers)
Explain the percentage biased (restrained) differential protection principle (Merz-Price scheme) for power transformers. Derive the operating condition ($I_1 - I_2 > k \frac{I_1 + I_2}{2}$). Why is a percentage bias necessary?
Appeared in:2083 Baishakh2081 Chaitra2078 Bhadra
#2Repeated 3 Times[8 Marks]Apparatus Protection (Generators and Transformers)
Explain CT connection rules for differential protection of a Star-Delta power transformer. Why must CTs on the star side be connected in delta and CTs on the delta side in star?
Appeared in:2082 Chaitra2080 Chaitra2079 Chaitra
#3Repeated 3 Times[8 Marks]Apparatus Protection (Generators and Transformers)
Explain magnetizing inrush current in power transformers. What harmonic components dominate inrush current? How does Harmonic Restraint differential protection prevent false tripping during transformer energization?
Appeared in:2083 Baishakh2081 Bhadra2078 Chaitra
#4Repeated 3 Times[6 Marks]Apparatus Protection (Generators and Transformers)
Describe the construction and working of a Buchholz Relay for transformer internal fault detection. What types of faults trigger alarm and trip contacts?
Appeared in:2082 Bhadra2080 Baishakh2077 Chaitra
#5Repeated 3 Times[8 Marks]Apparatus Protection (Generators and Transformers)
Explain stator inter-turn fault protection and stator earth fault protection of large synchronous generators. Why can standard differential protection not detect $100\%$ of stator windings for ground faults near the neutral?
Appeared in:2081 Chaitra2079 Chaitra2076 Chaitra
#6Repeated 3 Times[8 Marks]Apparatus Protection (Generators and Transformers)
Explain rotor protection of synchronous generators: (a) Rotor earth fault protection, (b) Loss of excitation (loss of field) protection using offset Mho relays, and (c) Rotor overheating due to negative sequence currents.
Appeared in:2083 Baishakh2082 Chaitra2080 Chaitra

Transmission Line Protection and Distance Relaying

6 Questions
#1Repeated 3 Times[8 Marks]Transmission Line Protection and Distance Relaying
Explain time-graded and current-graded overcurrent protection for radial feeders. Explain the coordination of IDMT overcurrent relays in a series radial system.
Appeared in:2083 Baishakh2081 Bhadra2078 Chaitra
#2Repeated 3 Times[8 Marks]Transmission Line Protection and Distance Relaying
Explain directional overcurrent relays. Draw the schematic diagram of ring main feeder protection showing non-directional and directional relay placement and grading.
Appeared in:2082 Bhadra2080 Baishakh2077 Chaitra
#3Repeated 3 Times[8 Marks]Transmission Line Protection and Distance Relaying
Explain distance protection of transmission lines. Describe the operating characteristics on the R-X diagram for: (a) Impedance relay, (b) Reactance relay, (c) Mho (admittance) relay, and (d) Offset Mho relay.
Appeared in:2081 Chaitra2079 Chaitra2076 Chaitra
#4Repeated 3 Times[8 Marks]Transmission Line Protection and Distance Relaying
Explain three-zone distance protection of transmission lines. Why is Zone 1 set to $80-85\%$ of line length? What are the time delays and reach settings of Zone 2 ($120-150\%$) and Zone 3 ($100\% \text{ line} + 120\% \text{ next line}$)?
Appeared in:2083 Baishakh2082 Chaitra2080 Chaitra
#5Repeated 3 Times[6 Marks]Transmission Line Protection and Distance Relaying
Explain the effect of power swings and arc resistance on distance relays. Why is the reactance relay preferred for short lines and the Mho relay for long lines?
Appeared in:2081 Bhadra2079 Baishakh2077 Magh
#6Repeated 3 Times[8 Marks]Transmission Line Protection and Distance Relaying
Explain carrier-aided distance protection: Carrier Blocking, Permissive Underreach Transfer Trip (PUTT), and Permissive Overreach Transfer Trip (POTT) schemes.
Appeared in:2082 Bhadra2080 Baishakh2076 Bhadra

Busbar, Motor Protection and Surge Protection

4 Questions
#1Repeated 3 Times[8 Marks]Busbar, Motor Protection and Surge Protection
Explain high-impedance differential protection of substation busbars. How does high impedance in the relay circuit prevent false operation under severe external through-fault CT saturation?
Appeared in:2081 Bhadra2079 Baishakh2077 Magh
#2Repeated 3 Times[8 Marks]Busbar, Motor Protection and Surge Protection
Explain the causes and mechanisms of lightning overvoltages and switching surges in power systems. Describe the travelling wave phenomenon and reflection/refraction coefficients at line terminations.
Appeared in:2082 Bhadra2080 Baishakh2076 Bhadra
#3Repeated 3 Times[6 Marks]Busbar, Motor Protection and Surge Protection
Explain the working principle, volt-ampere characteristic, and advantages of Gapless Zinc Oxide (ZnO) Metal Oxide Surge Arresters (MOSA) over traditional silicon carbide surge arresters with spark gaps.
Appeared in:2083 Baishakh2081 Chaitra2078 Bhadra
#4Repeated 3 Times[6 Marks]Busbar, Motor Protection and Surge Protection
Define insulation coordination and Basic Impulse Insulation Level (BIL). Explain how protective margin is established between lightning arrester discharge voltage and equipment withstand voltage level.
Appeared in:2082 Chaitra2080 Chaitra2079 Chaitra

Curriculum Syllabus & Course Topics

Sourced from TU curriculum portal
Full Syllabus (PDF)
Chapter-wise Units & Micro-Syllabus Topics (6 Units)

  1. 1. Fundamentals of Power System Protection

    4

  2. 2. Circuit Interruption Theory and Circuit Breakers

    8

  3. 3. Protective Relays (Electromechanical and Microprocessor-Based)

    8

  4. 4. Apparatus Protection (Generators and Transformers)

    9

  5. 5. Transmission Line Protection and Distance Relaying

    8

  6. 6. Busbar, Motor Protection and Surge Protection

    8

Examination Scheme & Marks Distribution

Evaluation Structure

  • Final Board Theory Exam: 60 Marks (Pass mark: 24)
  • Internal Assessment: 40 Marks (Pass mark: 16)
  • Practical / Lab Exam: 25 or 50 Marks (Continuous lab evaluation + viva, where applicable)

* This is the general current IOE 60/40 scheme; verify course-specific details in the syllabus above.

Exam Preparation Guidelines

  • Review the 2 available past examination papers to identify recurring patterns, core problem types, and chapter weightage.
  • Cross-reference key answers with official syllabus units, standard textbooks, and lecture notes.
  • Structure answers with labeled diagrams, concise bullet points, and highlight final answers in numerical solutions.

Frequently Asked Questions (Switchgear and Protection)

Q: How can I download Switchgear and Protection past question papers?

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Q: What is the pass mark for Switchgear and Protection?

The general current scheme is a 60-mark final theory exam and a 40-mark internal assessment, with pass marks of 24 and 16. Verify the course-specific syllabus above.

Q: Where can I find the complete syllabus for this subject?

The available chapter-wise syllabus and topic breakdown is indexed in the Syllabus section above, with links to the curriculum PDF source.

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Curriculum Syllabus & Marking Scheme