Personal Interview Questions for Electrical Engineers
Personal Interview Questions for Electrical Engineers
1. Where CSA sheath is used in
cables?
#
Corrugated seamless aluminums
sheath is used in high voltage oil filled cables and telephone lines.
2. Why it is used?
#
It is used because it is very
flexible and easily by repeated bending the sheath is not distorted and it is
not damaged. It has lesser weight and reduced thickness.
3. Why protective covering is
done in cables?
#
To protect the cables from
mechanical damage, corrosion and electrolytic action when laid direct in the
ground the protective covering is made.
4. By what material protective
covering is made?
#
Bitumen &Bituminized
materials, PVC and layers of fibrous materials.
5. What is meant by serving of a
cable?
#
Layers of fibrous material
permitted with waterproof compound applied to the exterior of the cable is
called serving of a cable.
6. Why armoring is done in the
cables?
#
To protect the sheath from
mechanical damage.
7. Why armoring is not done in
single core cables?
#
The presence of magnetic material
within the alternating magnetic field of a single core cable produces excessive
losses. Hence single core cables are left unarmored with non-magnetic materials
like tin-bronze or silicon-bronze tapes or wires.
8. Why Al is used as an armour
material?
#
It has non-magnetic properties,
high conductivity and mechanical strength.
9. What is meant by grading of
cables?
#
The method of equalizing the
stress in the dielectric of the cable is called the grading of cables.
10.Mention
the methods of cables.
#
Capacitance grading and intersheath grading.
Capacitance grading and intersheath grading.
11.Why the capacitance of the cable is very high than the capacitance of the overhead lines?
The distance between the conductors are small. The distance
between the cores and the earthed sheath is also small. The permittivity of the
cable insulation is 3 to 5 times greater than that of air insulation.
12.Write the expression of the capacitance of a single core cable.
(
(2πε)
----------- = C=q/v
----------- = C=q/v
(
ln(R/r)
13.What
is meant by charging current of a cable?
#
The capacitance of a cable determines the charging current. The charging current restricts the use of cables on EHV lines. The current carrying capacity of an a.c cable is also reduced by the charging current.
The capacitance of a cable determines the charging current. The charging current restricts the use of cables on EHV lines. The current carrying capacity of an a.c cable is also reduced by the charging current.
14.Why
power loss occurs in the dielectric of a cable?
#
-due to conductivity of insulation
-Dielectric hysteresis or dielectric absorption.
-Ionization or corona
-due to conductivity of insulation
-Dielectric hysteresis or dielectric absorption.
-Ionization or corona
15. Why all transmission
and distribution systems are 3 phase systems?
# A 3 phase a.c circuit using the same size conductors as the single phase circuit can carry three times the power which can be carried by a 1 phase circuit and uses 3 conductors for the 2 phases and one conductor for the neutral. Thus a 3 phase circuit is more economical than a 1 phase circuit in terms of initial cost as well as the losses. Therefore all transmission and distribution systems are 3 phase systems.
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