Electrical
engineering jobs are lucrative, competitive positions for some of the brightest
minds out there. Companies that hire electrical engineers are hiring for the
future of their company. Without electrical engineers, their products are
services are not going to be completed successfully. They are a crucial part of
the businesses that hire them.
Electrical
engineering, like any job in technology, contains a lot of technical questions.
Your safest bet to succeed at an electrical engineering interview is to brush
up on your technical knowledge and review any of the latest updates in the
field. You are going to be tested on what you can do, because your job is too
important to be given to someone without the right technical knowledge.
Q1:- Why star delta starter is preferred with induction motor?
Star
delta starter is preferred with induction motor due to following reasons:
• Starting current is reduced 3-4 times of the direct current due to which
voltage drops and hence it causes less losses.
• Star delta starter circuit comes in circuit first during starting of motor,
which reduces voltage 3 times, that is why current also reduces up to 3 times
and hence less motor burning is caused.
• In addition, starting torque is increased and it prevents the damage of motor
winding.
Q2:- State the difference
between generator and alternator?
Generator
and alternator are two devices, which converts mechanical energy into
electrical energy. Both have the same principle of electromagnetic induction,
the only difference is that their construction. Generator persists stationary
magnetic field and rotating conductor which rolls on the armature with slip
rings and brushes riding against each other, hence it converts the induced EMF
into dc current for external load whereas an alternator has a stationary
armature and rotating magnetic field for high voltages but for low voltage
output rotating armature and stationary magnetic field is used.
Q3:- Why AC systems are
preferred over DC systems?
Due
to following reasons, AC systems are preferred over DC systems:
a. It is easy to maintain and change the voltage of AC electricity for
transmission and distribution.
b. Plant cost for AC transmission (circuit breakers, transformers etc) is much
lower than the equivalent DC transmission
c. From power stations, AC is produced so it is better to use AC then DC
instead of converting it.
d. When a large fault occurs in a network, it is easier to interrupt in an AC
system, as the sine wave current will naturally tend to zero at some point
making the current easier to interrupt.
Q4:- How can you relate
power engineering with electrical engineering?
Power
engineering is a sub division of electrical engineering. It deals with
generation, transmission and distribution of energy in electrical form. Design
of all power equipment's also comes under power engineering. Power engineers may
work on the design and maintenance of the power grid i.e. called on grid
systems and they might work on off grid systems that are not connected to the
system.
Q5:- What are the various
kind of cables used for transmission?
Cables,
which are used for transmitting power, can be categorized in three forms:
• Low-tension cables, which can transmit voltage upto 1000 volts.
• High-tension cables can transmit voltage upto 23000 volts.
• Super tension cables can transmit voltage 66 kV to 132 kV.
Q6:- Why back EMF used for
a dc motor? Highlight its significance?
The
induced EMF developed when the rotating conductors of the
armature between the poles of magnet, in a DC motor, cut the magnetic flux,
opposes the current flowing through the conductor, when the armature rotates,
is called back EMF. Its value depends upon the speed of rotation
of the armature conductors. In starting, the value of back EMF is zero.
Q7;- What is slip in an
induction motor?
Slip
can be defined as the difference between the flux speed (Ns) and the rotor
speed (N). Speed of the rotor of an induction motor is always less than its
synchronous speed. It is usually expressed as a percentage of synchronous speed
(Ns) and represented by the symbol ‘S’.
Q8:- Explain the
application of storage batteries?
Storage
batteries are used for various purposes, some of the applications are mentioned
below:
•
For the operation of protective devices and for emergency lighting at
generating stations and substations.
• For starting, ignition and lighting of automobiles, aircrafts etc.
• For lighting on steam and diesel railways trains.
• As a supply power source in telephone exchange, laboratories and broad
casting stations.
• For emergency lighting at hospitals, banks, rural areas where electricity
supplies are not possible.
Q9:- Explain
advantages of storage batteries?
Few advantages of storage
batteries are mentioned below:
• Most efficient form of storing energy portably.
• Stored energy is available immediately because there is no lag of time for
delivering the stored energy.
• Reliable source for supply of energy.
• The energy can be drawn at a fairly constant rate.
Q10:- What are
the different methods for the starting of a synchronous motor?
Starting methods: Synchronous
motor can be started by the following two methods:
• By means of an auxiliary motor: The rotor of a synchronous motor is rotated
by auxiliary motor. Then rotor poles are excited due to which the rotor field
is locked with the stator-revolving field and continuous rotation is obtained.
• By providing damper winding: Here, bar conductors are embedded in the outer
periphery of the rotor poles and are short-circuited with the short-circuiting
rings at both sides. The machine is started as a squirrel cage induction motor
first. When it picks up speed, excitation is given to the rotor and the rotor
starts rotating continuously as the rotor field is locked with stator revolving
field.
Content source By-