Question
No. 01: What are the advantages of VSCF wind electrical system?
Answer: Advantages of VSCF wind electrical
system are:
- No complex pitch changing mechanism is needed.
- Aero turbine always keeps going at maximum efficiency point.
- Extra energy in the high wind speed region of the speed - duration curve can be extracted
- Significant reduction in aerodynamic stresses, which are associated with constant - speed operation.
Question
No. 02: What are the various
kind of cables used for transmission?
Answer: 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.
Question
No. 03: Why in a three pin plug
the earth pin is thicker and longer than the other pins?
Answer: It depends upon R = rho l/a
where area (a) is inversely proportional to resistance (R), so if (a) increases,
R decreases & if R is less the leakage current will take low resistance
path so the earth pin should be thicker. It is longer because the First to make
the connection and last to disconnect should be earth Pin. This assures Safety
for the person who uses the electrical instrument.
Question
No. 04: What are the transformer
losses?
Answer:
TRANSFORMER LOSSES - Transformer losses have two sources-copper loss and
magnetic loss. Copper losses are caused by the resistance of the wire (I2R).
Magnetic losses are caused by eddy currents and hysteresis in the core. Copper
loss is a constant after the coil has been wound and therefore a measurable
loss. Hysteresis loss is constant for a particular voltage and current.
Eddy-current loss, however, is different for each frequency passed through the transformer
Question
No. 05: What is an exciter and
how does it work?
Answer:
There are two types of exciters, static exciter and rotary exciter. Purpose of
exciter is to supply the excitation dc voltage to the fixed poles of generator.
Rotary exciter is an additional small generator mounted on the shaft of main
generator. if it is dc generator, it will supply dc to the rotor poles through
slip-ring and brushes( conventional alternator). if it is an ac exciter, output
of ac exciter is rectified by rotating diodes and supply dc to main fixed
poles.ac exciter is the ac generator whose field winding are stationary and
armature rotates. Initial voltage is built up by residual magnetism. It gives
the starting torque to the generator.
Question
No. 06: Why synchronous
generators are used for the production of electricity?
Answer:
Synchronous machines have capability to work on different power factor (or say
different imaginary power varying the field emf. Hence synchronous generators r
used for the production of electricity.
Question
No. 07: Why, when birds sit on
transmission lines or current wires doesn't get shock?
Answer:
It’s true that if birds touch the single one line (phase or neutral) they don't
get electrical shock. If birds touch 2 lines than the circuit is closed and
they get electrical shock. So if a human touch single one line (phase) then he
doesn't get shock if he is in the air (not touching - standing on the ground if
he is standing on the ground then touching the line (phase) he will get a shock
because the ground on what we standing is like
line (ground bed - like neutral) and in the most of
electric lines the neutral is grounded, so that means that human who touch the
line closes the circuit between phase and neutral.
Question
No. 08: Operation carried out in
Thermal power station?
Answer:
The water is obtained in the boiler and the coal is burnt so that steam is
obtained this steam is allowed to hit the turbine; the turbine which is coupled
with the generator generates the electricity
Question
No. 09: Why most of analog o/p devices having o/p range 4 to 20 mA and not
0 to 20 mA?
Answer: 4-20 mA is a standard range used to
indicate measured values for any process. The reason that 4 mA is chosen instead
of 0 mA is for fail safe operation .For example- a pressure instrument gives
output 4 mA to indicate 0 psi, up to 20 mA to indicate 100 psi, or full scale.
Due to any problem in instrument i.e. broken wire, its output reduces to 0 mA.
So if range is 0-20 mA then we can differentiate whether it is due to broken
wire or due to 0 psi.
Question
No. 10: What is the full form of KVAR?
Answer: We know there are three types of
power in Electrical as Active, apparent & reactive. So KVAR is stand for Kilo
Volt Amps with Reactive component.
Question No. 11: What is
the difference between delta-delta, delta-star transformer?
Answer: Delta-delta transformer is used at generating station or a receiving station for Change of Voltage (i.e.) generally it is used where the Voltage is high & Current is low. Delta-star is a distribution kind of transformer where from secondary star neutral is taken as a return path and this configuration is used for Step down voltage phenomena.
Answer: Delta-delta transformer is used at generating station or a receiving station for Change of Voltage (i.e.) generally it is used where the Voltage is high & Current is low. Delta-star is a distribution kind of transformer where from secondary star neutral is taken as a return path and this configuration is used for Step down voltage phenomena.
Question No. 12: Explain the application of storage batteries.
Answer: 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.
Question
No. 13: Explain thin film
resistors and wire-wound resistors
Answer:
- Thin film resistors: It is constructed as a thin film of resistive material is deposited on an insulating substrate. Desired results are obtained by either trimming the layer thickness or by cutting helical grooves of suitable pitch along its length. During this process, the value of the resistance is monitored closely and cutting of grooves is stopped as soon as the desired value of resistance is obtained.
- Wire wound resistors: Length of wire wound around an insulating cylindrical core are known as wire wound resistors. These wires are made of materials such as Constantan and Manganin because of their high resistivity, and low temperature coefficients. The complete wire wound resistor is coated with an insulating material such as baked enamel
Question
No. 14: Where should the
lighting arrestor be placed in distribution lines?
Answer:
Near distribution transformers and outgoing feeders of 11 kV and incoming feeder
of 33 kV and near power transformers in sub-stations.
Question
No. 15: Why series motor cannot
be started on no-load?
Answer: Series motor cannot be started
without load because of high starting torque. Series motors are used in Trains,
Crane etc.
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