Full-Length Mock Test 8 — RRB JE CBT 2 Technical Abilities Pattern (100 MCQs)

Section A: Circuit Fundamentals and AC/DC Basics (20 Questions)

1. Ohm's law states that current through a conductor is directly proportional to:
   (a) The voltage across it, at constant temperature (b) The square of the voltage regardless of resistance (c) The resistance alone, with voltage playing no role (d) The conductor's colour code
2. Kirchhoff's Current Law (KCL) states that at any node, the sum of currents entering equals:
   (a) The sum of currents leaving the node (b) Zero regardless of currents leaving (c) Twice the sum of currents leaving (d) The node's voltage
3. Kirchhoff's Voltage Law (KVL) states that around any closed loop, the algebraic sum of voltage drops and rises equals:
   (a) Zero (b) The supply current (c) The loop's total resistance (d) Infinity
4. The power dissipated in a resistor carrying current I with resistance R is given by:
   (a) I²R (b) I/R (c) IR² (d) R/I
5. Two resistors of 6 Ω and 3 Ω connected in parallel give an equivalent resistance of:
   (a) 2 Ω (b) 9 Ω (c) 4.5 Ω (d) 18 Ω
6. Two resistors of 6 Ω and 3 Ω connected in series give an equivalent resistance of:
   (a) 9 Ω (b) 2 Ω (c) 4.5 Ω (d) 18 Ω
7. The RMS value of a pure sinusoidal voltage with peak value Vm is:
   (a) Vm/√2 (b) Vm√2 (c) Vm/2 (d) 2Vm
8. The average value of a full sinusoidal wave over one complete cycle is:
   (a) Zero (b) Vm/√2 (c) 0.637 Vm (d) Vm
9. The average value of a half-wave rectified sinusoid (over the full cycle) is:
   (a) Vm/π (b) Vm/2 (c) Vm (d) Zero
10. The "form factor" of a sinusoidal waveform is the ratio of:
    (a) RMS value to average value (b) Average value to RMS value (c) Peak value to RMS value only (d) Peak value to average value only
11. The "peak factor" (crest factor) of a sinusoidal waveform is the ratio of:
    (a) Peak value to RMS value (b) RMS value to peak value (c) Average value to peak value (d) Peak value to average value alone with no RMS involvement
12. In an AC circuit, "power factor" is defined as the cosine of the angle between:
    (a) Voltage and current phasors (b) Two different voltage phasors only (c) Two different current phasors only (d) Frequency and time
13. A purely inductive AC circuit has a power factor of:
    (a) Zero, lagging (b) Unity (c) Zero, leading (d) 0.5 lagging
14. A purely capacitive AC circuit has a power factor of:
    (a) Zero, leading (b) Unity (c) Zero, lagging (d) 0.5 leading
15. A purely resistive AC circuit has a power factor of:
    (a) Unity (b) Zero (c) 0.5 (d) Undefined
16. In a series RLC circuit at resonance, the net reactance is:
    (a) Zero, so the circuit is purely resistive (b) Maximum, purely inductive (c) Maximum, purely capacitive (d) Infinite
17. At resonance in a series RLC circuit, the impedance is:
    (a) Minimum, equal to R (b) Maximum, equal to R (c) Zero (d) Infinite
18. The resonant frequency of a series RLC circuit is given by:
    (a) 1/(2π√(LC)) (b) 2π√(LC) (c) 1/(LC) (d) LC
19. "Active power" in an AC circuit is measured in:
    (a) Watts (b) VAR (c) VA (d) Ohms
20. "Reactive power" in an AC circuit is measured in:
    (a) VAR (b) Watts (c) VA (d) Henry

Section B: Electrical Machines (20 Questions)

21. A DC generator converts:
    (a) Mechanical energy into electrical energy (b) Electrical energy into mechanical energy (c) Chemical energy into electrical energy directly (d) Thermal energy into mechanical energy directly
22. A DC motor converts:
    (a) Electrical energy into mechanical energy (b) Mechanical energy into electrical energy (c) Chemical energy into mechanical energy directly (d) Thermal energy into electrical energy directly
23. The EMF equation of a DC generator includes which of the following variables?
    (a) Flux per pole, speed, number of poles, number of armature conductors, and parallel paths (b) Only the armature resistance (c) Only the field current (d) Only the brush contact resistance
24. In a DC shunt motor, the field winding is connected:
    (a) In parallel with the armature (b) In series with the armature (c) Independently with no relation to the armature circuit at all (d) Only across the brushes with no other connection
25. In a DC series motor, the field winding is connected:
    (a) In series with the armature, carrying full armature current (b) In parallel with the armature (c) Independently excited from a separate source only (d) Not connected at all
26. A DC series motor is particularly suited for applications requiring:
    (a) High starting torque, such as traction and cranes (b) Constant speed regardless of load, such as machine tools (c) Zero starting torque applications only (d) Applications with no load variation ever
27. A DC series motor should never be started on:
    (a) No load, as it may reach dangerously high speed (b) Full load, as it will not start at all (c) Any load, as series motors cannot start under any condition (d) Only under laboratory test conditions with a special power supply
28. The back EMF in a DC motor:
    (a) Opposes the applied voltage, limiting armature current (b) Aids the applied voltage, increasing armature current uncontrollably (c) Has no effect on armature current (d) Only exists in generators, never in motors
29. A synchronous motor runs at a speed:
    (a) Exactly equal to the synchronous speed, determined by supply frequency and poles (b) Always less than synchronous speed by a fixed slip amount (c) Independent of the supply frequency (d) That varies continuously with load
30. A synchronous motor, unlike an induction motor, is not inherently self-starting because:
    (a) At standstill, the rotor poles cannot lock into synchronism with the rapidly rotating stator field (b) It has no rotor at all (c) It requires no starting torque under any condition (d) It can only run on DC supply
31. An induction motor's slip is defined as the difference between synchronous speed and rotor speed, expressed as a:
    (a) Fraction (or percentage) of synchronous speed (b) Fraction of rotor speed only (c) Fixed constant regardless of load, motor design, or synchronous speed (d) Value always exactly zero
32. At standstill, an induction motor's slip is:
    (a) 1 (100%) (b) 0 (c) 0.5 (50%) always (d) Undefined
33. A three-phase induction motor's direction of rotation can be reversed by:
    (a) Interchanging any two of the three supply phase connections (b) Interchanging all three phase connections simultaneously, which has no effect (c) Reducing the supply voltage only (d) Increasing the supply frequency only
34. The "double squirrel cage" induction motor rotor design provides:
    (a) Improved starting torque with reasonable running efficiency, combining high and low resistance cages (b) Reduced starting torque compared to a single cage design (c) No change in starting characteristics compared to a single cage (d) Only cosmetic differences with no electrical significance
35. A transformer operates on the principle of:
    (a) Mutual electromagnetic induction between primary and secondary windings (b) Mechanical commutation (c) Chemical reaction between electrodes (d) Direct current conduction with no magnetic coupling
36. In an ideal transformer, the ratio of primary to secondary voltage equals the ratio of:
    (a) Primary to secondary turns (b) Secondary to primary current only, with no relation to turns (c) Primary to secondary core area only (d) Primary to secondary frequency
37. The "open-circuit test" on a transformer is used primarily to determine:
    (a) Core (iron) losses and no-load parameters (b) Copper losses at full load (c) The transformer's physical weight (d) The transformer's insulation colour
38. The "short-circuit test" on a transformer is used primarily to determine:
    (a) Copper losses and equivalent circuit impedance parameters (b) Core (iron) losses at no load (c) The transformer's physical weight (d) The transformer's insulation colour
39. Transformer core laminations are used primarily to reduce:
    (a) Eddy current losses (b) Copper losses in the windings (c) Mechanical vibration (d) The core's physical weight
40. An alternator (synchronous generator) is typically driven at a speed related to system frequency by the relation:
    (a) N = 120f/P (b) N = Pf/120 (c) N = f/P (d) N = 120P/f

Section C: Power Systems and Protection (20 Questions)

41. The primary reason for transmitting electrical power at high voltage over long distances is to:
    (a) Reduce line current and thus I²R transmission losses (b) Increase transmission losses deliberately for safety (c) Reduce the need for insulation entirely (d) Eliminate the need for towers and conductors
42. A step-up transformer at a generating station is used to:
    (a) Raise the generated voltage to a higher transmission-level voltage (b) Lower the voltage for local consumption directly at the plant (c) Convert AC to DC for transmission (d) Convert DC to AC for transmission
43. A step-down transformer at a distribution substation is used to:
    (a) Lower the transmission voltage to a level suitable for distribution/consumption (b) Raise the distribution voltage further for transmission (c) Convert AC to DC for consumers (d) Convert single-phase to three-phase supply
44. The "string efficiency" of a suspension insulator string refers to the:
    (a) Ratio of voltage across the whole string to the product of (units × voltage across the unit nearest the conductor) (b) Total number of insulator discs in the string (c) String's physical length only (d) String's manufacturing cost
45. A "grading ring" (or guard ring) fitted to a suspension insulator string is used to:
    (a) Equalize voltage distribution across the individual insulator units (b) Provide mechanical support only, with no electrical function (c) Increase the string's physical length (d) Serve only a decorative function
46. The "corona effect" on transmission lines refers to:
    (a) Ionization of air around the conductor surface at high voltage gradients, producing a visible glow and hissing sound (b) A mechanical vibration phenomenon unrelated to voltage (c) A phenomenon that occurs only on underground cables (d) A phenomenon that occurs only at very low voltages
47. Corona effect can be reduced by:
    (a) Increasing conductor diameter or using bundled conductors (b) Decreasing conductor diameter as much as possible (c) Reducing the number of conductors used per phase (d) Operating at even higher voltage without any conductor changes
48. "Ferranti effect" refers to the phenomenon where, on a lightly loaded or open-circuited long transmission line:
    (a) The receiving-end voltage exceeds the sending-end voltage (b) The sending-end voltage always exceeds the receiving-end voltage regardless of loading (c) Voltage remains exactly constant along the entire line at all times (d) Current flow reverses direction spontaneously
49. An overcurrent relay operates when the current through it:
    (a) Exceeds a preset pickup value (b) Falls below a preset value (c) Reaches exactly zero (d) Equals the rated voltage
50. A differential protection scheme operates based on comparing:
    (a) Currents entering and leaving the protected zone, operating on the difference (b) Only the voltage at one end of the protected zone (c) Only the frequency at both ends (d) Only the ambient temperature
51. A distance (impedance) relay is commonly used for the protection of:
    (a) Transmission lines, by measuring the impedance to the fault point (b) Only small distribution transformers (c) Only low-voltage domestic wiring (d) Only capacitor banks
52. The Buchholz relay is a protective device used with:
    (a) Oil-immersed transformers, to detect incipient faults via gas accumulation (b) Only dry-type transformers with no oil (c) Only overhead transmission lines (d) Only underground cables
53. A "reclosing relay" (auto-recloser) is commonly used on overhead lines because most faults on such lines are:
    (a) Transient in nature and can be cleared by a brief supply interruption (b) Always permanent and never clear on their own (c) Only ever caused by internal transformer failure (d) Impossible to clear by any means
54. The purpose of a lightning arrester (surge arrester) connected near equipment is to:
    (a) Divert high-voltage transient surges to earth, protecting the equipment (b) Attract lightning strikes toward the equipment deliberately (c) Increase the equipment's susceptibility to surges (d) Serve only a decorative/signalling function
55. A circuit breaker differs from a fuse primarily in that a circuit breaker:
    (a) Can be reset and reused after operation, without replacement (b) Must always be discarded and replaced after each operation (c) Cannot interrupt fault current at all (d) Only operates on DC circuits
56. An air circuit breaker (ACB) is typically used at:
    (a) Low voltage levels, such as in LT distribution panels (b) Extra-high-voltage transmission levels exclusively (c) Only underground mining applications (d) Only overhead line applications above 400 kV
57. SF6 gas is preferred as an arc-quenching medium in high-voltage circuit breakers primarily due to its:
    (a) Excellent dielectric strength and arc-quenching properties (b) Poor dielectric strength requiring frequent replacement (c) Flammability, which aids arc quenching (d) High cost with no performance benefit
58. The "unit protection" principle in power system protection means that a protection scheme:
    (a) Protects a clearly defined zone/unit of the system, independent of conditions outside that zone (b) Protects the entire national grid as a single unit with one relay (c) Has no defined protection zone at all (d) Only protects generators, never lines or transformers
59. Earthing (grounding) of electrical equipment is primarily done to:
    (a) Provide a low-resistance path for fault current, protecting personnel from shock (b) Increase the equipment's operating voltage (c) Reduce the equipment's efficiency deliberately (d) Serve only a cosmetic/labelling function
60. A "pilot wire" protection scheme for a transmission line uses:
    (a) A communication channel between the two line ends to compare currents for differential protection (b) No communication between line ends at all (c) Only local overcurrent relays with no inter-end comparison (d) Only a Buchholz relay

Section D: Measurements, Electronics, Control, and Power Electronics (20 Questions)

61. A moving-coil (PMMC) instrument can measure only:
    (a) DC quantities, unless used with a rectifier for AC (b) AC quantities exclusively, never DC (c) Both AC and DC natively with no additional circuitry (d) Only resistance, never current or voltage
62. A moving-iron instrument can measure:
    (a) Both AC and DC quantities (b) Only DC quantities (c) Only AC quantities, never DC (d) Only resistance
63. A Wheatstone bridge is used to measure:
    (a) Unknown medium resistance values with high accuracy (b) Only very high resistance values in the megohm range (c) Only very low (fractional-ohm) resistance values (d) Only inductance values
64. A Kelvin double bridge is specifically used to measure:
    (a) Very low resistance values, accounting for lead and contact resistance (b) Very high resistance values only (c) Capacitance values only (d) Frequency values only
65. A megger (insulation resistance tester) is used to measure:
    (a) Very high insulation resistance values, typically in megohms (b) Very low resistance values in milliohms (c) AC current magnitude only (d) Power factor only
66. In a diode, the "depletion region" is formed:
    (a) At the p-n junction, due to diffusion of charge carriers across the junction (b) Only in metallic conductors, never in semiconductors (c) Only when the diode is forward biased, never otherwise (d) Only in the external circuit wiring
67. A zener diode is normally operated in:
    (a) Reverse breakdown region, for voltage regulation (b) Forward bias region only, never in reverse (c) Cutoff region only, with no current flow ever (d) Saturation region only, as in a BJT
68. A bipolar junction transistor (BJT) has three terminals named:
    (a) Emitter, base, and collector (b) Anode, cathode, and gate (c) Source, drain, and gate (d) Grid, plate, and cathode
69. In a BJT operating in the active region, the base-emitter junction is:
    (a) Forward biased, while the base-collector junction is reverse biased (b) Reverse biased, while the base-collector junction is forward biased (c) Both junctions forward biased simultaneously (d) Both junctions reverse biased simultaneously
70. A silicon-controlled rectifier (SCR) is a __ terminal device.
    (a) Three (anode, cathode, gate) (b) Two (anode, cathode only) (c) Four (d) Five
71. An SCR, once triggered into conduction, continues to conduct until:
    (a) The anode current falls below its holding current value (b) The gate signal is removed, regardless of anode current (c) The supply is reversed in polarity only momentarily (d) Indefinitely, with no way to turn it off
72. A full-wave bridge rectifier uses:
    (a) Four diodes arranged to conduct in pairs on alternate half-cycles (b) Only a single diode for the entire waveform (c) Two diodes with no centre-tapped transformer and no bridge arrangement (d) No diodes at all, only capacitors
73. In a negative feedback control system, the feedback signal is:
    (a) Subtracted from the reference/input signal (b) Added directly to the output with no comparison (c) Always exactly equal to the input signal, making the system open-loop (d) Irrelevant to the system's stability
74. The primary benefit of negative feedback in a control system is improved:
    (a) Stability and reduced sensitivity to parameter variations (b) Instability, which is always desirable (c) Gain increase with no other effect (d) Cost, which always increases regardless of performance
75. A PID controller combines:
    (a) Proportional, integral, and derivative control actions (b) Only proportional action, with no other terms (c) Power, inductance, and distance terms (d) Voltage, current, and impedance terms
76. The "integral" term in a PID controller helps to:
    (a) Eliminate steady-state error (b) Increase steady-state error deliberately (c) Have no effect on steady-state error (d) Only affect the transient response, never the steady state
77. The "derivative" term in a PID controller helps to:
    (a) Improve transient response by anticipating future error trends (b) Eliminate steady-state error entirely on its own (c) Have no effect on system response of any kind (d) Only amplify noise with no other benefit
78. A variable frequency drive (VFD) controls an induction motor's speed primarily by varying the:
    (a) Supply frequency (and proportionally the voltage, to maintain flux) (b) Number of poles physically, in real time (c) Rotor resistance only, with no frequency variation (d) Motor's physical size dynamically
79. In a VFD, the "V/f" (volts-per-hertz) control principle aims to maintain:
    (a) A constant air-gap flux by keeping the voltage-to-frequency ratio constant (b) A constantly increasing flux with frequency (c) A constantly decreasing flux with frequency, unrelated to voltage (d) A random flux pattern
80. An uninterruptible power supply (UPS) commonly uses a battery bank together with an inverter to provide backup:
    (a) AC power during mains supply failure (b) Only DC power with no inversion at all (c) No power at all, only synchronisation signals (d) Only mechanical energy storage with no electrical output

Section E: General Awareness, Computer Applications, and Current Affairs (20 Questions)

81. The Central Electricity Authority (CEA) in India functions under which ministry?
    (a) Ministry of Power (b) Ministry of Railways (c) Ministry of Home Affairs (d) Ministry of Finance
82. The Bureau of Indian Standards (BIS) is responsible for:
    (a) Standardisation, marking, and quality certification of goods (b) Railway safety inspections exclusively (c) Currency printing (d) Postal service regulation
83. RAM in a computer is a form of memory that is:
    (a) Volatile, losing its contents when power is removed (b) Non-volatile, retaining contents without power (c) Used only for permanent long-term archival storage (d) Found only in printers, never in computers
84. ROM in a computer is a form of memory that is:
    (a) Non-volatile, retaining contents without power (b) Volatile, losing contents when power is removed (c) Used only for temporary calculations during a program's execution (d) Found only in external hard drives
85. An operating system's primary function is to:
    (a) Manage hardware resources and provide a platform for application software (b) Only display a decorative screen background (c) Only manage internet browsing (d) Only manage printer connections
86. A "firewall" in computer networking is used to:
    (a) Monitor and control incoming/outgoing network traffic based on security rules (b) Physically cool down the computer's processor (c) Increase internet speed with no security function (d) Store user files permanently
87. The full form of "URL" is:
    (a) Uniform Resource Locator (b) Universal Reference Link (c) Unified Router Location (d) Unique Resource Language
88. The full form of "HTTP" is:
    (a) HyperText Transfer Protocol (b) High Transmission Text Protocol (c) Home Terminal Transfer Program (d) Hyperlink Text Transmission Path
89. In MS Excel, the function used to sum a range of cells is:
    (a) SUM() (b) TOTAL() (c) ADDUP() (d) COUNT()
90. In MS Word, the keyboard shortcut for "Save" is typically:
    (a) Ctrl+S (b) Ctrl+P (c) Ctrl+O (d) Ctrl+N
91. The National Solar Mission is a part of India's:
    (a) National Action Plan on Climate Change (NAPCC) (b) Five Year Defence Plan (c) Railway Electrification Plan exclusively (d) National Digital Literacy Mission
92. The "One Nation One Grid" concept in India refers to:
    (a) Integration of all regional power grids into a single national grid (b) A single railway ticketing system (c) A single mobile phone network operator (d) A single national currency scheme
93. The Indian Railways' electrification programme predominantly uses which traction voltage/type?
    (a) 25 kV AC, 50 Hz single-phase (b) 1500 V DC exclusively across the network today (c) 11 kV three-phase AC (d) 440 V DC
94. The Ujjwal DISCOM Assurance Yojana (UDAY) scheme was aimed at:
    (a) Financial turnaround of debt-ridden power distribution companies (b) Rural road construction (c) Railway station modernisation (d) Digital banking expansion
95. The Saubhagya scheme launched by the Government of India aimed at:
    (a) Universal household electrification (b) Universal internet connectivity (c) Universal LPG connections exclusively (d) Universal railway connectivity
96. The "Smart Grid" concept in power systems refers to a grid that incorporates:
    (a) Digital communication and automation for efficient, reliable power delivery (b) Only manual meter reading with no automation (c) Only mechanical switching with no digital elements (d) Only diesel generation with no grid integration
97. The Central Electricity Regulatory Commission (CERC) primarily regulates:
    (a) Inter-state transmission and tariff matters (b) Only intra-state distribution tariffs (c) Only railway fares (d) Only telecom tariffs
98. A "smart meter" differs from a conventional electromechanical meter primarily by offering:
    (a) Two-way digital communication and remote data access (b) No measurement capability at all (c) Only mechanical dial displays with no digital features (d) Only manual reading with no remote capability
99. The acronym "RRB" in the context of this examination stands for:
    (a) Railway Recruitment Board (b) Regional Rural Bank (c) Reserve Reconciliation Bureau (d) Road Regulatory Body
100. Renewable Purchase Obligation (RPO) requires distribution licensees to purchase a certain percentage of power from:
     (a) Renewable energy sources (b) Only imported coal-based sources (c) Only nuclear sources exclusively (d) Only captive diesel generation

Answer Key with Explanations

1.(a) In a purely resistive circuit, voltage and current are in phase, crossing zero together.

2.(a) At DC steady state, a series RC has no current and full voltage across the capacitor.

3.(a) At DC steady state, an inductor is a short circuit, so current is limited only by resistance.

4.(a) Time-domain representation shows variation with time.

5.(a) Frequency-domain representation shows frequency component magnitudes/phases.

6.(a) Fourier series expresses a periodic waveform as fundamental plus harmonics.

7.(a) Capacitive reactance Xc = 1/(2πfC), inversely proportional to frequency.

8.(a) Inductive reactance XL = 2πfL, directly proportional to frequency.

9.(a) As f→0, XL→0 (inductor acts as short at DC).

10.(a) As f→0, Xc→∞ (capacitor acts as open at DC).

11.(a) A coupling capacitor blocks DC bias while passing AC signal between stages.

12.(a) A bypass capacitor provides a low-impedance AC path around a resistor.

13.(a) A voltage divider's output is a fraction of input based on resistor ratio.

14.(a) A current divider splits current inversely to resistor values.

15.(a) I1 = I_total × R2/(R1+R2), the standard current-divider formula.

16.(a) Equivalent circuit simplification reduces complexity for easier analysis.

17.(a) Load-line analysis plots device characteristic with circuit constraint line to find the Q-point.

18.(a) The Q-point represents the actual operating voltage/current in that circuit.

19.(a) Active power is measured in watts.

20.(a) Reactive power is measured in VAR.

21.(a) A generator converts mechanical energy into electrical energy.

22.(a) A motor converts electrical energy into mechanical energy.

23.(a) The EMF equation includes flux/pole, speed, poles, conductors, and parallel paths.

24.(a) In a shunt motor, field winding is in parallel with the armature.

25.(a) In a series motor, field winding is in series with the armature.

26.(a) Series motors give high starting torque, suited for traction/cranes.

27.(a) A series motor must never be started on no load (risk of overspeeding).

28.(a) Back EMF opposes applied voltage, limiting armature current.

29.(a) A synchronous motor runs at exactly synchronous speed.

30.(a) It is not self-starting since the rotor cannot lock into synchronism from standstill.

31.(a) Slip is the difference between synchronous and rotor speed, as a fraction of synchronous speed.

32.(a) At standstill, slip = 1 (100%).

33.(a) Reversing rotation requires interchanging any two of the three phase connections.

34.(a) Double squirrel cage gives improved starting torque with good running efficiency.

35.(a) A transformer works on mutual electromagnetic induction.

36.(a) V1/V2 = N1/N2 for an ideal transformer.

37.(a) OC test determines core losses and no-load parameters.

38.(a) SC test determines copper losses and equivalent impedance.

39.(a) Laminations reduce eddy current losses.

40.(a) N = 120f/P is the standard synchronous speed formula.

41.(a) High-voltage transmission reduces current and thus I²R losses.

42.(a) A step-up transformer raises generated voltage for transmission.

43.(a) A step-down transformer lowers transmission voltage for distribution.

44.(a) String efficiency is the ratio of string voltage to (units × voltage of unit nearest the conductor).

45.(a) A grading ring equalizes voltage distribution across insulator units.

46.(a) Corona is ionization of air around a conductor at high voltage gradient, with visible glow/hiss.

47.(a) Corona is reduced by increasing conductor diameter or using bundled conductors.

48.(a) Ferranti effect: receiving-end voltage exceeds sending-end voltage on a lightly loaded long line.

49.(a) An overcurrent relay operates when current exceeds a preset pickup value.

50.(a) Differential protection compares currents entering/leaving the protected zone.

51.(a) Distance relays measure impedance to the fault point, used for line protection.

52.(a) Buchholz relay detects incipient faults via gas accumulation in oil-immersed transformers.

53.(a) Auto-reclosers exploit the fact that most overhead-line faults are transient.

54.(a) A lightning arrester diverts transient surges to earth, protecting equipment.

55.(a) A circuit breaker can be reset/reused after operation, unlike a fuse.

56.(a) ACBs are typically used at low-voltage LT panels.

57.(a) SF6 has excellent dielectric strength and arc-quenching properties.

58.(a) Unit protection protects a defined zone independent of conditions outside it.

59.(a) Earthing provides a low-resistance fault path, protecting personnel.

60.(a) Pilot wire protection uses a communication channel between line ends for differential comparison.

61.(a) PMMC measures DC directly; AC needs a rectifier.

62.(a) Moving-iron instruments read both AC and DC.

63.(a) A Wheatstone bridge measures unknown medium resistance accurately.

64.(a) A Kelvin double bridge measures very low resistance, compensating lead/contact resistance.

65.(a) A megger measures very high insulation resistance in megohms.

66.(a) The depletion region forms at the p-n junction due to carrier diffusion.

67.(a) A zener diode is operated in reverse breakdown for voltage regulation.

68.(a) A BJT has emitter, base, and collector terminals.

69.(a) In active region, base-emitter is forward biased and base-collector reverse biased.

70.(a) An SCR is a three-terminal device: anode, cathode, gate.

71.(a) An SCR continues conducting until anode current falls below the holding current.

72.(a) A full-wave bridge rectifier uses four diodes conducting in pairs.

73.(a) Negative feedback subtracts the feedback signal from the reference input.

74.(a) Negative feedback improves stability and reduces sensitivity to parameter variation.

75.(a) PID combines proportional, integral, and derivative actions.

76.(a) The integral term eliminates steady-state error.

77.(a) The derivative term improves transient response by anticipating error trends.

78.(a) A VFD varies supply frequency (and voltage) to control motor speed.

79.(a) V/f control keeps voltage-to-frequency ratio constant to maintain flux.

80.(a) A UPS uses battery plus inverter to supply backup AC power.

81.(a) CEA functions under the Ministry of Power.

82.(a) BIS handles standardisation and quality certification.

83.(a) RAM is volatile memory.

84.(a) ROM is non-volatile memory.

85.(a) An OS manages hardware resources and provides an application platform.

86.(a) A firewall monitors/controls network traffic per security rules.

87.(a) URL stands for Uniform Resource Locator.

88.(a) HTTP stands for HyperText Transfer Protocol.

89.(a) SUM() sums a range of cells in Excel.

90.(a) Ctrl+S is the Save shortcut in MS Word.

91.(a) The National Solar Mission is part of the NAPCC.

92.(a) "One Nation One Grid" integrates regional grids into a single national grid.

93.(a) Indian Railways predominantly uses 25 kV AC, 50 Hz single-phase traction.

94.(a) UDAY aimed at financial turnaround of debt-ridden DISCOMs.

95.(a) Saubhagya aimed at universal household electrification.

96.(a) A smart grid incorporates digital communication/automation for efficient delivery.

97.(a) CERC regulates inter-state transmission and tariff matters.

98.(a) A smart meter offers two-way digital communication and remote access.

99.(a) RRB stands for Railway Recruitment Board.

100.(a) RPO requires a certain percentage of power purchase from renewable sources.