Electrical Engineering · Question Bank

Alternators

109 of 157 questions match · page 2 of 6. Answer in your head first, then check the solution.

#21📜 EE Pre-Board August 2017📘 PowerhouseEasy

A three-phase, wye-connected, 6.25 kVA, 220-volt synchronous generator has a reactance of 8.4 ohms per phase. Using the rated kVA and voltage as base values, determine the per unit reactance.

A0.627 pu

B0.362 pu

C1.085 pu

D1.879 pu

#22📜 EE Pre-Board August 2017📘 PowerhouseEasy

A two-pole alternator is running at 1,500 rpm. What is the angular velocity?

A314.2 rad/s

B78.5 rad/s

C157.1 rad/s

D25 rad/s

#23📜 EE Pre-Board August 2017📘 PowerhouseEasy

At leading p.f., the armature flux in an alternator ________ the rotor flux.

Aopposes

Bis in quadrature with

Caids

Dhas no effect on

#24📜 EE Pre-Board March 2018📘 PowerhouseEasy

Calculate the effective voltage in one phase of an alternator, given the following particulars: f = 60 cps; turns per phase N = 240; flux per pole = \(2.08 \times 10^{6}\) maxwells.

A1,330v

B2,304v

C1,225v

D2,122v

#25📜 EE Pre-Board March 2018📘 PowerhouseEasy

The power factor of an alternator is determined by its

Aspeed

Bload

Cexcitation

Dprime mover

#26📜 EE Pre-Board March 2018📘 PowerhouseEasy

For coil having a span of 2/3 of pole pitch, the coil span factor is

A0.8

B0.866

C0.786

D0.966

#27📜 EE Pre-Board August 2018📘 PowerhouseEasy

In a 6-pole alternator how many mechanical degrees is the equivalent of 180 electrical degrees?

A60

B30

C120

D90

#28📜 EE Pre-Board August 2018📘 PowerhouseEasy

For two alternators operating in parallel, if the load shared by one of them is to be increased, its field excitation is

Ato be strengthened keeping input torque the same

Bto be weakened keeping input torque the same

Cto be kept constant but input torque should be increased

Dto be kept constant but input torque should be decreased

#29📜 EE Pre-Board August 2018📘 PowerhouseEasy

The field system of a 50 Hz alternator has a sinusoidal flux per pole of 0.1 Wb. Calculate the emf generated in one turn which spans two-thirds of a pole pitch.

A17.4 v

B19.2 v

C12.2 v

D9.6 v

#30📘 EE Pocket Reviewer RojasEasy

What is the function of the damper windings in a large alternator?

AIt will reduce voltage fluctuations

BIt will reduce frequency fluctuations

CIt will increase stability

DNone of these

#31📘 EE Pocket Reviewer RojasEasy

The distribution of load between two alternators in parallel operation is changed using one of the following methods?

AChange the driving torque of the prime movers

BChange the frequency of the alternators

CChange the phase sequence of the alternators

DChange the excitation of the alternators

#32📘 EE Pocket Reviewer RojasEasy

The drop in the terminal voltage of an alternator due to armature reaction is countered by which of the following?

AEffect of saliency

BDamper windings

CAutomatic voltage regulator

DIncreased prime mover output

#33📘 EE Pocket Reviewer RojasEasy

After wiring two alternators, you checked their frequency and voltage and found them to be equal. Before connecting them in parallel, which of the following should be checked next?

APrime mover speed

BPhase rotation

CSteam pressure

DLubrication of rotor

#34📘 EE Pocket Reviewer RojasEasy

The load sharing between two steam driven alternators operating in parallel are adjusted using which of the following methods?

AAdjust steam supply to their prime movers

BAdjust the power factors of the alternators

CAdjust the speed of the alternators

DAdjust the field strength of the alternators

#35📘 EE Pocket Reviewer RojasEasy

When an alternator is supplying a zero leading pf load, the armature reaction will produce which of the following conditions?

ADemagnetization of the main field flux

BMagnetization of the main field flux

CCross magnetization of the main field flux

DAll of these

#36📘 EE Pocket Reviewer RojasEasy

What is the purpose of hydrogen in a large alternator?

ATo strengthen the magnetic field

BTo cool the alternator

CTo reduce the eddy current loss

DTo reduce distortion of the waveform

#37📘 EE Pocket Reviewer RojasEasy

Which of the following is not required in the parallel operation of alternators?

AThey must have the same terminal voltage

BThey must have the same phase rotation

CThey must have the same frequency

DThey must have equal ratings

#38📘 EE Pocket Reviewer RojasEasy

Which of the following coils is the generated emf be more, for a given flux and number of turns?

AFull pitch coil

BShort pitch coil

COver pitch coil

DAll of these will generate equal emf

#39📘 EE Pocket Reviewer RojasEasy

What is the reason why hydrogen is used for cooling of large size generators?

AIt is light

BIt offers reduced fire risk

CIt has high thermal conductivity

DAll of these

#40📘 EE Pocket Reviewer RojasEasy

Which of the following describes the rotor used in turbo alternators?

ASmall diameter and long axial length

BLarge diameter and short axial length

CLarge diameter and long axial length

DSmall diameter and short axial length

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