Users Also Read

MCQ's Search Engine

Electrical Engineering

Mechanical Engineering

Civil Engineering

Automobile Engineering

Chemical Engineering

Computer Engineering

Electronics Engineering

Medical Science Engg

Q1. | The unit of flux density is |

A. | Tesla. [Correct Answer] |

B. | A/mm^{2} [Wrong Answer] |

C. | N/m^{2} [Wrong Answer] |

D. | Wb/m [Wrong Answer] |

View Answer
Explanation:-
Answer : ADiscuss it below :!! OOPS Login [Click here] is required to post your answer/resultHelp other students, write article, leave your comments |

**Also Read Similar Questions Below :**

⇒ For speeds higher than say 3000 rpm, the machine used is

induction motor.

synchronous motor.

universal motor.

none of the above.

⇒ A hysteresis motor

is a self starting motor.

is a constant speed motor

does not need dc excitation

all of the above

⇒ The core flux of a practical transformer with a resistance load

is strictly constant with load changes.

increases linearly with load.

increases as the square root of the load.

decreases with increase of load.

⇒ Dynamic braking is very effective if the dc motor

is series excited.

is shunt excited.

is separately excited.

has cumulative compound excitation. I.\.J.

⇒ When a synchronous motor is started, the field winding is energized

in the very beginning.

when the motor attains a speed slightly less than the synchronous speed.

after the motor has attained the synchronous speed and synchronized.

any time.

⇒ A brake test is usually restricted to ____ dc motors.

small kW output rating

variable speed

high speed

constant speed

⇒ What is the core loss in a high frequency ferrite core transformer used in SMPS power supply?

10% of rated power.

5% of rated power.

2% of rated power.

1% of rated power.

⇒ In an ac series motor, power factor is improved by

increasing the inductance of armature and field windings.

reducing the inductance of armature and field windings.

increasing the supply voltage.

both (a) and (c).

⇒ The factor that is not responsible for drop in terminal voltage of a dc shunt generator on load is

commutation.

armature reaction.

armature resistance drop.

field weakening due to (b) and (c).

⇒ Which of the following statements regarding ratios of line voltages and line currents on the ac side to that on the dc side of a synchronous convertor is true?

Both line voltage ratio as well as line current ratio decrease with the increase in number of phases.

Both line voltage ratio as well as line current ratio increase with the increase in number of phases.

Line voltage ratio increases but current ratio decreases with the increase in number of phases.

Line voltage ratio decreases but current ratio increases with the increase in number of phases.

⇒ A rotary convertor combines the functions of

an induction motor and a dc shunt generator.

an induction motor and a dc series generator

a synchronous motor and ade series generator.

a synchronous motor and a dc shunt or compound generator

⇒ The winding used in a 3-phase shell type transformer is ____ type.

circular

cylindrical

sandwich

rectangular

⇒ The power measurement in balanced three-phase circuit can be done by

one wattmeter method only.

two wattmeters method only.

three wattmeters method only

any one of the above

⇒ Which of the following dc motors has got maximum self relieving property?

Shunt.

Series.

Cumulative compound.

Differential compound.

⇒ For starting 3-phase squirrel cage induction motors reactors are preferred over resistors as the reactors

incur less power loss and effectively reduce the applied voltage to the motor

increase the starting torque

improve the power factor at start

all of the above

⇒ While operating on variable frequency supplies, the ac motor requires variable voltage as well in order to

protect the insulation

avoid the effect of saturation

improve the capabilities of the inverter.

protect the thyristor from dv/dt

⇒ The armature shaft must be able to withstand

any unbalanced magnetic pull on the armature core.

twisting strains due to transmission of torque.

bending moment due to weight of the armature and commutator.

all of the above.

⇒ The damper windings also called the squirrel cage windings or damper grids

are provided in a synchronous motor to make it selfstarting and to prevent hunting.

consists of short-circuited copper bars embedded in the field pole faces of a synchronous motor.

are provided on the stator of a synchronous motor for improving the power factor.

both (a) and (b).

⇒ Two alternators are operating in parallel. For taking one of the alternators out from the system

load shared by this alternator is transferred to the other by adjusting thepowerfedtotheprime moverbefore opening OCB.

power fed to the prime-mover is stopped.

OCB is switched off.

load connected to the bus-bar is reduced.

⇒ Equipotential surfaces about a pair of equal and opposite linear charges exist in what form?

Concentric spheres.

Concentric cylinders.

Non-concentric cylinders.

Planes.

⇒ An even waveform when expressed in exponential fourier series will contain

only imaginary coefficient

only real coefficient

both of (a) and (b).

none of these.

⇒ The operation of a 3-phase synchronous motor operating on constant excitation across infinite bus will not be stable if power angle δ

exceeds internal angle e.

is less than θ.

exceeds θ/2.

is less than θ/2.

⇒ In comparison to self excited generator, a separately excited generator

is more reliable.

is amenable to better voltage regulation.

has exciting current independent ofload characterisitc.

has all of the above features.

⇒ If all the stator coils of an induction motor are connected for the same magnetic polarity, there will be formed an equal number of

rotor poles with same polarity.

rotor poles with opposite polarity.

consequent poles with opposite polarity.

consequent poles with same polarity.

⇒ In rotor resistance control of induction motor, the hardness of speed torque characteristic

increases.

decreases.

remains same.

⇒ When the firing angle of a single phase, fully controlled rectifier feeding constant dc current into a load is 30°, the displacement power factor of the rectifier is

1

0.5

1/√3

√3/2

⇒ In a synchronous generator delivering lagging power factor load

the excitation emf leads terminal voltage by the power angle.

the excitation emf lags the terminal voltage by the power angle.

excitation emf leads the terminal voltage by the power factor angle.

none of the above.

⇒ A dc shunt motor, running lightly at 1,000rpm, is operated under plugging. With plugging connections left as it is the final speed of the motor will be

zero.

1,000 rpm.

-1,000 rpm

-2,000 rpm.

⇒ Armature torque of a dc motor is a function of which of the following factors?

1. Speed.

2. Field flux.

3. Armature current.

4. Residual magnetism.

Select the correct answer using the codes given below: Codes:

2 and 3.

1 and 4.

3 and 4.

1 and 2.

⇒ Stray losses are sum of:

Iron and mechanical losses.

Copper and iron losses.

Copper and mechanical losses.

None of these.