The type of winding used for low voltage, high current generator is

 

501. In a DC generator, commutation can be improved by
A) Using interpoles
B) Reducing armature current
C) Reducing speed
D) Weakening field
Ans: A

502. The function of equalizer rings in DC compound machine is
A) Avoid unequal current sharing
B) Increase voltage
C) Decrease armature reaction
D) None
Ans: A

503. The brushes in DC machine are shifted for
A) Sparkless commutation
B) Increasing torque
C) Decreasing flux
D) Speed control
Ans: A

504. The commutation process involves reversal of current in
A) Coil undergoing commutation
B) Field winding
C) Entire armature
D) Brushes
Ans: A

505. The reactance voltage in DC machine is due to
A) Self-induction of coil
B) Mutual induction
C) Armature reaction
D) Hysteresis
Ans: A

506. The voltage build-up in DC shunt generator stops when
A) Field resistance equals critical resistance
B) Load increases
C) Speed decreases
D) Armature current is high
Ans: A

507. The speed regulation of a DC shunt motor is
A) Good
B) Poor
C) Variable
D) Infinite
Ans: A

508. In DC generator, the emf is directly proportional to
A) Flux × Speed
B) Flux / Speed
C) Flux²
D) 1/Flux
Ans: A

509. The field coils of DC machine are wound with
A) Few turns, large wire
B) Many turns, thin wire
C) Aluminum wire
D) Copper bars
Ans: B

510. The field of DC series motor is excited by
A) Armature current
B) Field current
C) Supply voltage
D) Battery
Ans: A

511. A DC shunt generator fails to build up if
A) Residual magnetism is lost
B) Field resistance is more than critical
C) Wrong field connection
D) All of these
Ans: D

512. The function of pole shoe is
A) Spread flux uniformly
B) Provide mechanical support
C) Reduce reluctance
D) All of these
Ans: D

513. The type of winding used for low voltage, high current generator is
A) Lap winding
B) Wave winding
C) Progressive winding
D) Retrogressive winding
Ans: A

514. The type of winding used for high voltage, low current generator is
A) Wave winding
B) Lap winding
C) Duplex winding
D) Differential winding
Ans: A

515. The open-circuit characteristic (OCC) is also known as
A) Magnetization curve
B) Speed curve
C) Torque curve
D) Regulation curve
Ans: A

516. The critical speed of DC shunt generator is the speed at which
A) Voltage just builds up
B) Maximum current flows
C) Torque is maximum
D) Armature reaction is zero
Ans: A

517. In DC compound generator, voltage regulation is better than
A) Shunt generator
B) Series generator
C) Both A and B
D) None
Ans: C

518. The load current of DC generator is
A) Sum of armature and field current
B) Equal to armature current
C) Difference of armature and field current
D) Equal to field current
Ans: C

519. The purpose of diverter in DC compound generator is
A) Control series field current
B) Increase shunt current
C) Control speed
D) None
Ans: A

520. In cumulative compound generator, the flux due to series field
A) Aids the shunt field
B) Opposes shunt field
C) Is zero
D) Alternates
Ans: A

521. Differential compound generator is rarely used because
A) Poor voltage regulation
B) Poor efficiency
C) High cost
D) Complex design
Ans: A

522. If the armature of a DC machine rotates in the same direction but field polarity is reversed, the direction of emf
A) Reverses
B) Remains same
C) Becomes zero
D) Alternates
Ans: A

523. For DC machines, the Fleming’s right-hand rule is used to find
A) Direction of induced emf
B) Direction of torque
C) Direction of field
D) None
Ans: A

524. The main reason for brush sparking is
A) Poor commutation
B) High brush pressure
C) Weak field
D) High resistance
Ans: A

525. The commutation process takes place when
A) Coil is short-circuited by brush
B) Coil moves under pole
C) Field current is constant
D) None
Ans: A

526. The unit of reluctance is
A) Ampere-turns per weber
B) Weber per ampere-turn
C) Henry
D) Ohm
Ans: A

527. The efficiency of DC generator is maximum when
A) Variable losses = constant losses
B) Copper losses = iron losses
C) Armature current = max
D) Flux = constant
Ans: A

528. The no-load current of DC shunt generator is mainly used for
A) Exciting field winding
B) Overcoming losses
C) Developing voltage
D) All of these
Ans: D

529. The effect of armature reaction is neutralized by
A) Interpoles and compensating winding
B) Field coils
C) Yoke
D) None
Ans: A

530. The total power developed in DC generator is
A) Eg × Ia
B) V × Ia
C) Eg × If
D) Eg × IL
Ans: A

531. The shaft torque in DC machine is
A) (Eb × Ia) / ω
B) (Eg × Ia) / ω
C) V × Ia
D) Eg / Ia
Ans: B

532. The mechanical power developed by a motor is
A) Eb × Ia
B) V × Ia
C) Eb × If
D) V × If
Ans: A

533. The armature torque and shaft torque differ due to
A) Iron and mechanical losses
B) Armature losses
C) Copper losses
D) Flux leakage
Ans: A

534. In DC generator, brushes are advanced to
A) Reduce sparking
B) Increase current
C) Increase emf
D) None
Ans: A

535. The speed control by armature resistance gives
A) Below normal speed
B) Above normal speed
C) Constant speed
D) None
Ans: A

536. The speed control by field weakening gives
A) Above normal speed
B) Below normal speed
C) Both
D) None
Ans: A

537. In a DC shunt motor, when field current decreases, speed
A) Increases
B) Decreases
C) Remains constant
D) Stops
Ans: A

538. The braking of DC motor is possible by
A) Regenerative
B) Dynamic
C) Plugging
D) All of these
Ans: D

539. In regenerative braking,
A) Motor works as generator
B) Energy is dissipated as heat
C) Speed increases
D) Torque reverses
Ans: A

540. In dynamic braking,
A) Energy is dissipated in resistance
B) Fed back to supply
C) Converted to mechanical
D) None
Ans: A

541. Plugging is also known as
A) Reverse current braking
B) Dynamic braking
C) Regenerative braking
D) None
Ans: A

542. During plugging, the supply polarity is
A) Reversed
B) Same
C) Reduced
D) Increased
Ans: A

543. The speed–torque curve of DC compound motor lies between
A) Series and shunt motors
B) Induction and synchronous motors
C) AC and DC motors
D) None
Ans: A

544. The series field winding of a compound machine carries
A) Armature current
B) Field current
C) Load current
D) Both A and C
Ans: D

545. The shunt field winding of a compound machine carries
A) Constant current
B) Load current
C) Armature current
D) None
Ans: A

546. The compound generator used for DC distribution is
A) Cumulative compound generator
B) Differential compound generator
C) Shunt generator
D) Series generator
Ans: A

547. If load current increases, voltage of cumulative compound generator
A) Remains nearly constant
B) Increases sharply
C) Decreases rapidly
D) Becomes zero
Ans: A

548. The DC machine used for battery charging is
A) Shunt generator
B) Compound generator
C) Series generator
D) Differential generator
Ans: A

549. The DC motor used for traction work is
A) Series motor
B) Shunt motor
C) Compound motor
D) Cumulative compound motor
Ans: A

550. The DC machine used in elevators and rolling mills is
A) Cumulative compound motor
B) Differential motor
C) Shunt motor
D) Synchronous motor
Ans: A