# Electrical Engineering Interview Question And Answer-Electrical Machine Part 1

[1]
Define the term synchronous speed [Dec-2003]
For
synchronous machines there exists a fixed relationship between number of poles
P, frequency (f) and the speed of the machine. The speed of the synchronous
machine for the given number of poles and the rated frequency is called the
synchronous speed mentioned as NS.

[2] Write an expression for synchronous speed
(Dec-2004)
An
expression for synchronous speed is Ns = 120f/P.
Where
f =
frequency
P = No of
poles of the machine.

[3] What does speed voltage mean? (Dec-2007)
When the
magnetic flux is constant as well as stationary and the coil rotates to cut the
flux then EMF gets induced due to relative speed between flux and coil. This
EMF is called speed EMF, rotational EMF or dynamically induced EMF.

[4] Mention the factors on which hysteresis loss
depends (Dec-2008)
The
hysteresis loss is directly proportional to the area under the hysteresis curve
ie area of the hysteresis loop.
It is
directly proportional to frequency ie number of cycles of magnetization per
second.
It is
directly proportional to volume of the material.

[5] Distinguish between statically induced and
dynamically induced EMF (Dec – 2010, 2011, 2009)
How
is EMF induced dynamically ( May-2010)
An induced
EMF which is due to physical movement of coil, conductor with respect to flux
or movement of magnet with respect to stationary coil, conductor is called
dynamically induced EMF or motional induced EMF.
The change
in flux lines with respect to coil can be achieved without physically moving
the coil or the magnet. Such induced emf in a coil which is without physical
movement of coil or a magnet is called statically induced EMF.

[6] Define torque (May-2010)
A turning or
a twisting force about an axis is called as torque.

[8] What are the three types of basic rotating electric
machines? (May-2011)
DC machines
Induction
Machines
Synchronous
Machines

[9] What are the causes of core loss? what are the
components of core loss?
When a core
is subjected to an alternating flux then it undergoes the cycles of
magnetisation and demagnetisation. This produces hysteresis effect which causes
hysteresis loss in the core.
Similarly
core is under the influence of the changing flux and under such condition
according to the Faraday’s law of electromagnetic induction, EMF gets induced
in the core. Such currents in the core which are due to induced emf in the core
are called as eddy current loss. Thus eddy current and hysteresis are the two
components of the core loss.