The reason for using compensating winding is

 81. The voltage regulation of a DC generator is defined as—

A) $\frac{V_{no-load} - V_{full-load}}{V_{full-load}} \times 100\%$
B) $\frac{V_{full-load} - V_{no-load}}{V_{full-load}} \times 100\%$
C) $\frac{V_{full-load}}{V_{no-load}} \times 100\%$
D) None
✅ Answer: A
Explanation: Regulation = (No-load voltage – Full-load voltage)/Full-load voltage × 100%.

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82. A cumulatively compounded generator has voltage–current characteristics that—
A) Rise with load
B) Fall with load
C) Remain constant
D) First rise then fall
✅ Answer: D
Explanation: Initially rises due to series field strengthening, then slightly falls due to armature reaction.

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83. Differentially compounded generators are rarely used because—
A) Their voltage decreases rapidly with load
B) Efficiency is too high
C) Field control is difficult
D) They are expensive
✅ Answer: A
Explanation: Differential compounding opposes main field, causing unstable output.

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84. When two DC shunt generators operate in parallel, the load sharing depends on—
A) Their speed
B) Their voltage characteristics and droop
C) The brush material
D) Field resistance only
✅ Answer: B
Explanation: Load sharing depends on voltage–current characteristics and droop (voltage drop with load).

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85. In parallel operation, if one generator has slightly higher voltage—
A) It will take more load
B) It will take less load
C) It will share equally
D) It will run in reverse
✅ Answer: A
Explanation: Higher terminal voltage generator supplies more current.

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86. Two DC series generators cannot be operated in parallel because—
A) Voltage increases with load
B) Load sharing is unstable
C) They have different field resistances
D) Speed is too high
✅ Answer: B
Explanation: In series generators, an increase in load current increases emf → cumulative effect → instability.

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87. The compounding level in a DC generator can be adjusted by—
A) Diverter across series field
B) Speed variation
C) Changing pole number
D) Brush shift
✅ Answer: A
Explanation: A diverter (shunt resistance) across series field controls compounding degree.

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88. For lighting loads, the preferred generator is—
A) Cumulatively compounded
B) Differentially compounded
C) Series
D) Shunt
✅ Answer: A
Explanation: Cumulative compound generator maintains nearly constant voltage with varying load.

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89. The brush shift in the direction of rotation results in—
A) Advanced commutation
B) Retarded commutation
C) No effect
D) Flux increase
✅ Answer: B
Explanation: Brush shift in direction of rotation delays current reversal → sparking.

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90. The efficiency of a DC generator can be determined by—
A) Swinburne’s test
B) Hopkinson’s test
C) Brake test
D) All of the above
✅ Answer: D
Explanation: All methods can be used: Swinburne (no-load), Hopkinson (back-to-back), brake (direct).

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91. Swinburne’s test is a—
A) No-load test
B) Full-load test
C) Half-load test
D) Short-circuit test
✅ Answer: A
Explanation: Swinburne’s test is a constant loss, no-load test.

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92. Hopkinson’s test on DC machines requires—
A) Two identical machines
B) One machine only
C) Three-phase supply
D) Alternator coupling
✅ Answer: A
Explanation: Two identical DC machines are mechanically coupled and electrically connected for back-to-back test.

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93. Stray load losses in a DC generator are—
A) Losses due to nonuniform current distribution and flux distortion
B) Copper losses
C) Hysteresis losses
D) Mechanical losses
✅ Answer: A
Explanation: Stray load losses arise due to irregular current and flux, typically 1% of output.

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94. If a DC generator runs at half the rated speed, its generated emf will be—
A) Half
B) Double
C) Same
D) Zero
✅ Answer: A
Explanation: $E ∝ N$, so emf halves when speed halves.

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95. A separately excited generator can build up voltage only if—
A) External DC supply is given to field winding
B) Residual magnetism is high
C) Load is connected
D) Armature reaction is strong
✅ Answer: A
Explanation: It requires external excitation for field current.

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96. In a shunt generator, as load increases, field current—
A) Decreases
B) Increases
C) Constant
D) Zero
✅ Answer: A
Explanation: Voltage drop reduces field current, weakening the field.

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97. The percentage efficiency of a DC generator at full load is 88%. At half load, it will be approximately—
A) 90%
B) 86%
C) 80%
D) 70%
✅ Answer: B
Explanation: Efficiency slightly decreases at lower load due to constant losses.

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98. The brush contact drop per brush in small generators is around—
A) 0.5–1.0 V
B) 2–3 V
C) 5 V
D) 10 V
✅ Answer: A
Explanation: Typical brush drop ≈ 0.5 to 1.0 V per brush for small machines.

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99. For same armature current, wave winding produces—
A) More emf
B) Less emf
C) Same emf
D) Higher torque
✅ Answer: A
Explanation: Wave winding has fewer parallel paths → higher emf for same current.

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100. The induced emf in a generator depends on—
A) Flux per pole and speed
B) Field current only
C) Armature resistance
D) Brush drop
✅ Answer: A
Explanation: $E ∝ ΦN$, directly proportional to flux and speed.

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101. The residual magnetism in DC generator is generally—
A) 1–4% of full rated flux
B) 10%
C) 25%
D) Zero
✅ Answer: A
Explanation: A small portion of flux (1–4%) remains even without excitation.

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102. When a DC generator is loaded, its speed—
A) Remains same
B) Slightly decreases
C) Increases sharply
D) Doubles
✅ Answer: B
Explanation: Load increases torque demand, slightly reducing speed.

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103. The output equation of a DC generator is—
A) $E = \frac{PΦZN}{60A}$
B) $P_{out} = VI$
C) $P_{out} = T × ω$
D) All of the above
✅ Answer: D
Explanation: All equations represent emf and power relationships in generator operation.

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104. Which loss does not occur at no-load?
A) Armature copper loss
B) Iron loss
C) Mechanical loss
D) Field copper loss
✅ Answer: A
Explanation: No armature current at no-load → no I²R loss in armature.

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105. Armature reaction effect is directly proportional to—
A) Armature current
B) Field current
C) Speed
D) Voltage
✅ Answer: A
Explanation: Armature reaction ∝ armature current.

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106. Neutral plane is defined as—
A) Plane where no emf is induced in armature coil
B) Plane of maximum emf
C) Plane perpendicular to flux
D) None
✅ Answer: A
Explanation: In neutral plane, emf = 0; brushes are placed here for sparkless commutation.

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107. The load curve of a DC generator shows—
A) Relation between terminal voltage and load current
B) Field current and emf
C) Speed and torque
D) Power factor vs current
✅ Answer: A
Explanation: Load characteristic: terminal voltage vs load current.

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108. When the generator load increases, armature reaction—
A) Increases
B) Decreases
C) Constant
D) None
✅ Answer: A
Explanation: Higher load → higher armature current → more armature reaction.

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109. The reason for using compensating winding is—
A) To neutralize armature mmf under pole faces
B) To increase torque
C) To reduce iron losses
D) To improve efficiency
✅ Answer: A
Explanation: Compensating winding counters armature mmf to maintain flux distribution.

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110. The function of the commutator is to—
A) Convert AC to DC
B) Transfer current to brushes
C) Reverse current direction in armature coil
D) All of the above
✅ Answer: D
Explanation: Commutator acts as mechanical rectifier, maintains unidirectional output, and transfers current via brushes.