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1)
What is the difference between
synchronization and synchronous motor?
Synchronization is a
process or method in which an Alternator is connected to the Grid. Generator
produces Electrical Power at a particular Voltage say 21 kV and frequency,
normally 50 Hz or 60 Hz. The generated Voltage is stepped up to the Grid
Voltage. Therefore when we want to connect the Generator to the Grid by Circuit
Breaker, the Voltage, Phase and frequency of generator should match to Voltage,
Phase and frequency. This is called Synchronization.
Whereas Synchronous
Motor is an equipment which rotates at Synchronous speed. Synchronous speed
means the speed at which field flux rotates in space. Suppose Synchronous motor
having 2 pole is connected with 50 Hz supply, the synchronous speed will be
3000 r.p.m.
2)
Can we use 3 phase motor in
single phase power source?
No we cannot use
three phase motor from single phase supply. As in three phase motor, all R, Y
and B phase is to be connected to get motor start. In case of single phase
motor, Capacitor is used for phase splitting for motor to start. So we can't
use.
3)
What type of motor is used in a
ceiling fan? How does a ceiling fan work?
Ceiling Fans are
direct driven mostly using single-phase Inductionmotor. Motors have
windings wound for 18, 20 or 22 poles, resulting in to lower operating speeds
(Most common: 18 pole). The rotor resistance is very high for wide speed
control range using the stator voltage control.
There's nothing better
than getting home from work on a sweltering afternoon, switching on the ceiling
fan, and relaxing in comfort with that fan passing over your head, cooling down
your hot, stressful day. Ceiling fans can make life a great deal more
comfortable, and they can save money on cooling bills as well. In fact, if
you've got good ceiling fans in a few rooms of your house, you probably don't
even need an expensive, bulky air conditioning unit. More than likely, you've
thought about how great ceiling fans can be. Not only do they cool down rooms,
but a beautiful ceiling fan in the right style and color can change the entire
ambience of a room. A ceiling fan is defined as a mechanical fan, usually
electrically powered, that is suspended from the ceiling of a room that uses
rotating paddles to circulate air.
Working:
This type of fan is
wired through the ceiling and connected to the wire that controls either a
remote box or a switch on the wall for operating. The ceiling fan capacitor
torques up the electric motor, allowing it to start and run. An electrical
current reaches the motor and then enters coils of wire that are wrapped around
a metal base. As this current passes through the wire, a magnetic field is
caused that expends force in a clockwise motion that actually changes the
electric energy into mechanical energy. This action causes the motor coils to
spin. As the coils are spinning, the fan captures this spinning motion, transferring
it to the fan blades. The slicing of the air caused by the fan blades is what
pushes the air downward, causing the breeze created by the ceiling fan. This
whole process circulates the air through the room, as air moves in to replace
the air that has been pushed down from the ceiling. Ceiling fans work are so
effective because of the fact that hot air rises. As the hot air reaches the
ceiling, it builds up the heat in the entire room. A fan mounted on the ceiling
forces this hot air away from the top of the room, and this action leaves room
for more hot air to rise, thus circulating the air in the room causing the
breeze.
4)
What should be the resistance
of rotor?
In Electrical Engineering, Rotor
means that of a Electrical Machine which rotates in space. In case of DC
Machine, armature winding is wound on the Rotor and it is made of laminated
sheet of Silicon Steel. Whereas in Alternator,field winding is wound on the
Rotor. So Rotor is only meant to carry magnetic flux and it is so designed that
eddy current loss is minimum, that is why it is made of lamination. Therefore,
Rotor has very small resistance.
5)
Does a resistor have polarity?
Why or why not?
There are two
types of circuit component, one is Unilateral and another one is Bilateral
device.Bilateral device is one which can carry current in both direction and
Unilateral is one which can carry current in single direction. An example of
Unilateral is Diode so when a Diode is forward biased only then it will allow
current to flow so unilateral. But if we take Resistance it may carry current
in either direction depending on the polarity of applied voltage across the
terminals of Resistance. So Resistance do not have any polarity.
6)
In 3 phase connections, if
there is voltage present in single phase, can there be a possibility that load
is present in all 3 phases?
As the voltage
is only in one phase, therefore you cannot connect a three phase load. Suppose
you are taking a three phase 4 wire supply and because of any reason the
MCB of two phase is switched off, then voltage will not be there in OFF phases
but will remain in single phase only, so you can connect single phase load
across phase and neutral wire but you can't connect 3 phase load. Hope it might
help you.
7)
Why Tan Delta test conducted at
Low Frequency Voltage?
It is important to note
that Low Frequency Voltage is applied in tanδ
test by Test Kit. There are two benefits of this:
a) Low frequency
means more 1/wC, as w = 2πf, which means that the Reactance offered by the
Capacitor will be High. Due to High Impedance the Capacitor will draw less
current from the Test Kit at a particular given voltage. Therefore the KVA
requirement of the Test Kit will be reduced.
8)
Does Eddy current occur on the
body of DC motor?
DC current do
not produce eddy current and hence no eddy current loss. But we know that in DC
Machine AC current flows in the armature winding and a constant airgap flux is
produced because of field wind but due to armature reaction the air gap flux gets
distorted and it links with the motor body which causes to Stary losses.
Because of eddy current loss the armature core is designed of laminated Silicon
Steel Sheet. Thus eddy current loss is there in armature and as the air gap
flux is constant with space, no eddy current loss on body of motor.
9)
What is "creepage
distance" and what factors affect this?
In Electrical
Terminology, Creepage Distance is the shortest distance separating
two conductors as measured along the surface touching both conductors.
Along the surface of most materials, flashover can occur at distances much
shorter than the flashover distance in air. Therefore, it is extremely
important in high voltage designs to look for places where creepage can occur.
10)
What is corona?
In Electrical
Terminology, a luminous discharge due to the ionization of the gas
surrounding a conductor caused by a voltage gradient exceeding a certain
critical value. It does not greatly heat the conductor, and it is limited
to the region surrounding the conductor. While corona is a low energy
process, over long periods of time, it can degrade insulators, causing a system
to fail due to dielectric breakdown.
11)
What is dissipation factor?
If the Capacitor had
been pure then it would have taken current Ic leading by angle 90 degree but
because of resistive component of dielectric, net current drawn is deviating
from 90 degree by some angle δ. This angle δ is hence called Loss Angle.
From the phasor diagram, it is clear that
tanδ = Ir / Ic =
Capacitive leakage current / Resistive leakage current.
This tanδ is also
called Dissipation Factor.
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