Test: Electrical Machines- 3 - Electrical Engineering (EE) MCQ

# Test: Electrical Machines- 3 - Electrical Engineering (EE) MCQ

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## 20 Questions MCQ Test SSC JE Electrical Mock Test Series 2025 - Test: Electrical Machines- 3

Test: Electrical Machines- 3 for Electrical Engineering (EE) 2024 is part of SSC JE Electrical Mock Test Series 2025 preparation. The Test: Electrical Machines- 3 questions and answers have been prepared according to the Electrical Engineering (EE) exam syllabus.The Test: Electrical Machines- 3 MCQs are made for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Electrical Machines- 3 below.
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Test: Electrical Machines- 3 - Question 1

### In a generator a dynamically induced emf is produced according to:

Detailed Solution for Test: Electrical Machines- 3 - Question 1

An electrical generator is a machine which converts mechanic energy into electrical energy. It is based on the principle of production of dynamically induced emf

According to Faraday's Laws of Electromagnetic Induction, whenever a conductor cuts magnetic flux, dynamically induced emf is produced in it. This emf causes a current to flow in the conductor if circuit is closed.

Test: Electrical Machines- 3 - Question 2

### The EMF induced in the armature of a shunt generator is 500 V. The armature resistance is 0.2 Ω if the armature current is 200 A, what is the terminal voltage?

Detailed Solution for Test: Electrical Machines- 3 - Question 2

Given that, Eg = 500 V, Ra = 0.2 Ω, Ia = 200 A

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Test: Electrical Machines- 3 - Question 3

### In case of four pole, lap wound machine if the air gap under each pole is the same, then what will be the result?

Detailed Solution for Test: Electrical Machines- 3 - Question 3

In case of lap wound, number of parallel paths (A) = number of poles (P)

The current in the each path will be same.

The terminal voltage will be higher in wave wound machine

In lap wound machine, the hysteresis losses will be reduced whereas eddy current losses will be reduced in wave wound machine

Test: Electrical Machines- 3 - Question 4

In d.c. generator armature reaction is produced by:

Detailed Solution for Test: Electrical Machines- 3 - Question 4

There are two kinds of magnetic fluxes acting in DC generator.

1. The flux produced because of the stator poles called main flux

2.  The flux produced because of the current flowing in the armature called armature flux

This armature flux weakens and distort the main flux. Thus the overall effective flux in DC generator gets decrease. This mutual action of armature flux on the main field flux is known as armature reaction.

Test: Electrical Machines- 3 - Question 5

Which of the following is not necessarily the advantage of D.C motor over A.C Motor?

Detailed Solution for Test: Electrical Machines- 3 - Question 5

DC motors have the advantage of

1. Higher starting torque

2. Quick starting and stopping, reversing

3. Variable speeds with voltage input and they are easier to control than AC

Test: Electrical Machines- 3 - Question 6

Which DC motor has got maximum self-loading property?

Detailed Solution for Test: Electrical Machines- 3 - Question 6

In a differentially compound DC motor at higher values of load, the flux reduces so sharply at small increase in load. It is advisable that motor should not be used beyond some load value, as it may damage itself by self-loading.

Test: Electrical Machines- 3 - Question 7

The no load primary input is approximately equal to the:

Detailed Solution for Test: Electrical Machines- 3 - Question 7

When transformer is operated at no load, its secondary winding is open circuited or no load is connected to the secondary winding and hence no current flows through it.

When we apply a primary input voltage, the current produced in the primary winding will supply the core losses (ohmic loss are almost negligible) and would magnetize the core producing mutual flux. This current would be very small in magnitude as it induces a back emf in the primary winding.

Test: Electrical Machines- 3 - Question 8

Booster transformer are used to:

Detailed Solution for Test: Electrical Machines- 3 - Question 8

Booster transformer is used towards the end of a power line to raise the voltage to the desired value. It is used for controlling the voltage of a feeder at a point far away from the main transformer.

The secondary of the booster transformer is connected in series with the line, and its primary is supplied from the secondary of the regulating transformer.

Booster transformer is used in railways for eliminating the flow of stray current. The stray current disturbs the communication system and also damage the electronic devices of the trains passing through them.

Test: Electrical Machines- 3 - Question 9

How the leakage flux is minimized in an actual transformer?

Detailed Solution for Test: Electrical Machines- 3 - Question 9

We can minimize the leakage flux in a transformer by following methods

1) By reducing the magnetizing current to the minimum

2) By reducing the reluctance of the iron core to the minimum

3) By reducing the number of primary and secondary turn to the minimum

4) By sectionalizing and interleaving the primary and secondary windings

Test: Electrical Machines- 3 - Question 10

Which test on transformer provides information about regulation efficiency and heating under load conditions?

Detailed Solution for Test: Electrical Machines- 3 - Question 10

Back to back test on transformer is a method for determining transformer efficiency, voltage regulation and heating under loaded conditions. In this method, two identical transformers are connected back to back such that their primaries are in parallel across the same voltage source and the secondaries in series so that one transformer is loaded on the other.

Short circuit and open circuit tests on transformer can give us parameters of equivalent circuit of transformer but they cannot help us in finding the heating information.

Test: Electrical Machines- 3 - Question 11

Synchronous generator can _________ reactive power:

Detailed Solution for Test: Electrical Machines- 3 - Question 11

The reactive power of a synchronous generator is given by,

1) When EfV = cosδ then generator works under unity power factor condition

2) When EfV > cosδ then reactive power will be positive, i.e. generator supplies reactive power

3) When EfV < cosδ then reactive power will be negative, i.e. generator absorbs reactive power

Test: Electrical Machines- 3 - Question 12

To reduce the peripheral speed of an alternator, diameter of the rotor is:

Detailed Solution for Test: Electrical Machines- 3 - Question 12

Peripheral speed refers to the speed on the periphery or the circumference of the rotor. The peripheral speed is given by the product of the circumference and the speed.

Ps = π × D × RPM

The peripheral speed is dependent on the speed as well as the diameter of the rotor.

Hence to reduce the peripheral speed of an alternator, we need to reduce the diameter of the rotor and increase the axial length.

Test: Electrical Machines- 3 - Question 13

The Statement “Generators are Coherent”, implies that:

Detailed Solution for Test: Electrical Machines- 3 - Question 13

‘’Generators are Coherent’’ implies that all the generators connected in parallel to a common bus are oscillating at same frequency.

When two alternators are connected in parallel, their frequency, terminal voltage and phase angle should be equal to busbar’s frequency, terminal voltage and phase angle.

Test: Electrical Machines- 3 - Question 14

A 3-phase induction motor when started picks up speed but runs stably at about half the normal speed. This is because of:

Detailed Solution for Test: Electrical Machines- 3 - Question 14

A 3-phase induction motor when started picks up speed but runs stably at about half the normal speed. This happens because of the non-sinusoidal nature of the supply voltage.

Test: Electrical Machines- 3 - Question 15

Slip rings and brushes are found in:

Detailed Solution for Test: Electrical Machines- 3 - Question 15

In squirrel cage type rotors, the rotor bar is permanently shorted at the end of the ring. Hence slip rings and brushes are not present in these type of rotors

Slip rings and brushes are present in wound type rotor

Test: Electrical Machines- 3 - Question 16

For an induction motor the torque is proportional to the product of:

Detailed Solution for Test: Electrical Machines- 3 - Question 16

The torque of an induction motor is,

T∝ϕI2cosϕ2

Where, ϕ is the flux

Iis rotor current at standstill condition

ϕis the angle between rotor emf and rotor current

Test: Electrical Machines- 3 - Question 17

What does happen if tripled harmonics given to induction motor?

Detailed Solution for Test: Electrical Machines- 3 - Question 17

When a sinusoidal input is applied to electronic circuit the output is distorted wave form. This distorted wave is because of nonlinear characteristics of electronic circuit. Those distorted wave is called harmonics. The component having triple times of the fundamental are known as third harmonics. Generally all third harmonics are equal in all phases.

When these harmonics is applied to induction motor, it will fail to start because rotating magnetic field won’t develop.

Test: Electrical Machines- 3 - Question 18

Which of the following is true for a synchronous condenser?

Detailed Solution for Test: Electrical Machines- 3 - Question 18

Synchronous condenser is an over-excited synchronous motor operating at no-load with leading power factor.

The efficiency of long power transmission lines may be increased by placing synchronous condensers along the line to compensate lagging currents caused by line inductance.

More real power may be transmitted through a fixed size line if the power factor is brought closer to unity by synchronous condensers absorbing reactive power.

The ability of synchronous condensers to absorb or produce reactive power on a transient basis stabilizes the power grid against short circuits and other transient fault conditions

Test: Electrical Machines- 3 - Question 19

Which of the following is an unexcited single phase synchronous motor?

Detailed Solution for Test: Electrical Machines- 3 - Question 19

Unexcited single phase synchronous motor runs at constant speed equal to synchronous speed of revolving flux. They do not need a dc excitation for their rotors.

Reluctance motor and Hysteresis motors are unexcited single phase synchronous motors.

Test: Electrical Machines- 3 - Question 20

The common type of servo motor is different from normal induction motor as it has:

Detailed Solution for Test: Electrical Machines- 3 - Question 20

The differences between servo motor and induction motor are:

1) Servo motor is closed loop system where as induction motor is an open loop system

2) An induction motor has high inertia and servo motor has a very low inertia. Hence servo motors are used in applications where instant and accurate positioning of load is required

3) Servo motor has high rotor resistance and low power rating compared to induction motor

## SSC JE Electrical Mock Test Series 2025

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## SSC JE Electrical Mock Test Series 2025

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