KUMARAN
POLYTECHNIC
COLLEGE
DIPLOMA IN
ELECTRICAL AND ELECTRONICS ENGINEERING
23051-POWER
SYSTEM - I
ONE
MARK QUESTIONS AND ANSWERS
PREPARED
BY : N.SURESH KUMAR B.E.,
UNIT-I
GENERATION OF ELEEECTRICAL POWER AND ENERGY
CONSERVATION
1. State the
conventional source of power generation.
Ø Fuels
Ø Water power
Ø Nuclear power
2. State the
non-conventional sources of power generation.
Ø Solar power
Ø Wind power
Ø Tidal power
3. State the
classifications of hydrel power plants according to natural of load.
Ø Base load plants
Ø Peak load plants
Ø Pumped storage
plant
4. State the
merits of hydro electric power stations.
Ø The plant is
simple in construction, and requires low maintenance.
Ø It can be put in
the service instantly.
5. State the
demerits of thermal power station.
Ø It pollutes the
atmosphere due to the production of large amount of smoke
Ø and fumes.
Ø It is costlier
in running cost as compare to hydro electric plant.
6. State the
working principle of diesel power station.
A generating station in which
diesel engine is used as the prime mover for the generation of electric energy
is known as diesel power station.
7. State the
Advantages of diesel power station.
Ø The design and
layout of the plant are quite simple.
Ø It occupies less
space as the number and size of the auxiliaries is small.
8. What is the
function of heat exchanger?
The coolant gives heat to the
heat exchanger which is utilized in raising the steam.
9. What is the
function of alternator?
The steam turbine drives the
alternator which converts mechanical energy into electrical energy.
10. What is load
curve?
The curve showing the variation
of load on the power station with reference to time is known as a load curve.
11. What is the
load duration curve?
When the loads curve are arranged
in the order of descending magnitude, the curve thus obtained is called load
duration curve.
12. What is
demand factor?
It is the ratio of maximum demand on the power
station to its connected load.
Demand factor = (Maximum demand/
connected load).
13. What is
Average load?
The average of loads occurring on
the power station in a given (day or month or year) is known as average load or
average demand.
Daily average load = No. of units
(KWh)generated in a day/24 hours
14. What is load
factor?
The ratio of average load to the
maximum demand during a given period
is known as load factor.
Load factor = Average
load/Maximum demand
15. What is
diversity factor?
The ratio of the sum of
individual maximum demands to the maximum demand on power station is known as
diversity factor
16. What is
capacity factor?
It is the ratio of actual energy
produced to the maximum possible energy that could have been produced during a
given period.
Capacity factor = Actual energy
produced/Maximum energy that could have been produced.
17. What is
plant use factor?
It is the ratio of Kwh generated
to the product of plant capacity and the number of hours for which the plant
was in operation.
Plant use factor = Station output
in Kwh/plant capacity * hours of use
18. What is
grid?
The connection of several
generation stations in parallel is known as interconnected grid system.
19. What is the
necessity of grid system?
Ø When a load is
supplied power from two generating stations,
Ø It is always
necessary to interconnect the generating stations,
Ø So that there is
no over loading and the loads are shared almost equally.
20. State the
advantages of inter connected system.
Ø Exchange of peak
load.
Ø Ensure
Economical operation
Ø Increase
Diversity factor
21. What is base
load?
The unvarying load which occurs
almost the whole day on the station is known as base load.
22. What is peak
load?
The various peak demand of load
over and above the base load of the station is known as peak load.
23. What are the
applications of solar energy?
Ø Solar water
heating
Ø Solar cooker
Ø Solar driers
24. What are the
applications of wind energy?
Ø For Pumping
operations
Ø Food processing
Ø Electric power
generation
25. What are the
applications of geo-thermal power plant?
Ø
Generation
of electric power
Ø
Industrial
process heating
Ø
Salt
recovery from sea water.
26. What is
co-generation?
Whenever both generation of
electrical power and process steam are needed, it is thermodynamically and
economically better to produce both the products in a single plant is called
cogeneration.
UNIT-2
AC TRANSMISSION & HVDC TRANSMISSION
1. State the types of various
system of power transmission.
o
DC
system
o
Single
phase AC system
o
Two
phase AC system
o
Three
phase system
2. What are the
elements used in transmission line?
o
Conductors
Step-up and step down transformers
o
Line
insulators supports
o
Protective
devices Voltage regulating devices
3. State Kelvin’s law.
The most economical area of the
conductor is that which makes the annual cost of transmission line is equal to
the annual cost of energy wasted.
4. State the
limitations of kelvin’s law.
o
Since
the conductor area is small.
o
The
conductor may be too weak or too strong from the mechanical point of view.
5. What are the
components of over head lines?
o
Conductors
o
Supports
o
Insulators
o
Cross
arms
6. What are the
types of conductors?
o
Copper
Aluminium
o
Steel
Aluminium conductor with steel reinforced
o
Cadmium
copper
7. What are the
types of line supports?
o
Wooden
poles
o
Tubular
steel poles
o
Reinforced
concrete poles
8. What are the
factors deciding the spacing between the conductors?
o
Working
voltage
o
Sag
under worst condition
9. What is sag?
The difference in level between
points of supports and the lowest point on conductor is calles sag.
10. What are the
conditions to the calculations of sag?
o
Supports
are at equal levels
o
Supports
are at unequal levels
11. State the
transmission line constant.
o
Resistance
o
Inductance
o
Capacitance
12. State the
advantages of reduction in resultant current.
o
Reduces
the line losses
o
Reduces
the voltage drop
13. What is skin
effect?
The tendency of AC current to
concentrate near the surface of a conductor is known as skin effect.
14. What is
Ferranti effect?
The phenomenon of rise in voltage
at the receiving end is called Ferranti effect.
15. What is
voltage regulation?
It is the difference between the
sending end voltage and the receiving end voltage and is expressed as a
percentage of receiving and voltage.
% voltage regulation = (Vs-Vr)/Vr
* 100
16. What are the
equipments used to improve the power factor?
o
Static
capacitor
o
Synchronous
condenser
17. What are the
causes of over voltages?
o
Internal
causes
o
External
causes
18. What is
lightning?
An electric discharge between
cloud and earth, between clouds or between the charge centres of the same cloud
is known as lightning
19. What are the
productive devices used for protection against lightning?
o
Earthing
screen
o
Overhead
ground wires
o
Lightning
arresters or surge diverters
20. State the
types of DC link.
o
Mono
polar link
o
Bipolar
link
o
Homo
polar link
21. What are the
advantages of HVDC transmission?
o
No
skin effect
o
Line
losses is lesser
22. What is
voltage surge?
A sudden rise in voltage for a
very short duration on the power system is known as a voltage surge or
transient voltage.
23. State the
properties of line supports.
o
They
must be cheap
o
They
must be light in weight
24. State as the
electric supply system.
The conveyance of electric power
from a power station to consumers premises is known as electric supply system.
UNIT-3
LINE INSULATORS AND UNDERGROUND CABLES
1. What is the
purpose of insulators?
o
The
line conductors must be properly insulated from supports in order to avoid any
leakage current from conductor to earth.
o
This
is achieved with the help of insulators.
2. What are the
requirements of insulators?
o
They
must be mechanically strong.
o
Their
dielectric strength must be very high.
o
They
must provide high insulation resistance.
3. What are the
types of insulators?
o
Pin
insulators
o
Suspension
insulators
o
Strain
insulators
4. What are the
causes of failure of insulators?
o
Cracking
of insulator
o
Defective
insulator material
o
Porosity
of the material
o
Improper
glaze
5. What are the
tests adopted in insulators?
o
Flash-over
test
o
Performance
test
o
Routine
test
6. What are the
advantages of suspension type insulators?
o
The
mechanical stress on the string is less
o
The
line conductors are less affected by lightning
7. What is
string efficiency?
o
The
voltage ratio across the whole string to the product of number of discs and the
voltage across the disc nearest to the conductor is known as “string
efficiency”
o
String
efficiency=(𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑎𝑐𝑟𝑜𝑠𝑠 𝑡ℎ𝑒 𝑠𝑡𝑟𝑖𝑛𝑔)/(𝑛 ∗𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑎𝑐𝑟𝑜𝑠𝑠 𝑑𝑖𝑠𝑐 𝑛𝑒𝑎𝑟𝑒𝑠𝑡 𝑡𝑜 𝑡ℎ𝑒 𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑜𝑟)
8. What are the
methods of improving the string efficiency?
o
By
using longer cross arms
o
By
grading the insulators
9. What is
corona?
o
When
the voltage is increased gradually, a point is reached at which a faint
luminous bluish glow appears along the length of the conductors with a hissing
sound.
o
This
bluish discharge is known as corona.
10. State the
effects of corona.
o
A
bluish glow is observed around the conductor.
o
It
produces a hissing noise.
11. What are the
advantages of corona?
o
Corona
reduces the effects of transient produced by surges.
o
The
increased in diameter of the conductor will reduces the electrostatic stresses
between the conductors.
12. What are the
disadvantages of corona?
o
Ozone
is produced by corona.
o
The
corona is accompanied by a power loss. This affects the transmission efficiency
of the line.
13. State the classification
of cables based on voltage.
o
Low
tension cables
o
High
tension cables
o
Supartention
cables
14. State the
properties of insulating materials used in cables.
o
High
insulation resistance to avoid leakage current
o
Non-inflammable
o
Low
cost
15. State the
methods of laying of underground cables.
o
Direct
laying
o
Draw
in system
16. What is
grading cables?
The method of achieving uniform
electrostatic stress in the dielectric of cables is known as grading of cables.
17. What are the
faults occur in the cables?
o
Open-circuit
fault
o
Short
circuit fault
o
Earth
fault
18. What are the
advantages of direct laying?
o
It
is simple and cheap
o
It
is easy for dissipation of heat
o
It
is clean and safe method
19. State the
methods of grading of cables.
o
Capacitance
grading
o
Intersheath
grading
20. State the
types of pressure cables.
o
Oil
filled cables
o
Gas
pressure cables
21. State the
types of oil filled cables.
o
Single
core conductor channel
o
Single
core sheath channel
o
Three
core filler space channel
22. State the
advantages of underground cables.
o
Less
maintenance is required
o
There
is no interference to communication circuits
o
Its
use does not spoil the beauty of the cities
23. What are the
effects of corona?
o
A
bluish glow is observed around the conductor
o
It
produces a hissing noise
o
It
produces ozone which can be detected by its characteristic odour
24. State the
types of flash over test.
o
Dry
Flash-over test
o
Wet
flash-over test
25. What is
meant by Serving in underground cables?
In order to protect armouring
from atmospheric conditions, a layer of fibrous material similar to bedding is
provided over the armouring is known as Serving.
UNIT-4
CIRCUIT BREAKERS AND FUSES
1. What is meant
by switch gear?
An apparatus used for switching,
controlling and protecting the electrical circuit and equipment is known as
switchgear.
2. What are the
essential features of switch gear?
o
Complete
reliability
o
Absolute
certain discrimination
o
Quick
operation
3. What are the
faults in a power system?
o
Symmetrical
faults
o
Unsymmetrical
faults
4. State the
classifications of unsymmetrical fault.
o
Single
line to ground fault
o
Line
to line fault
o
Double
line to ground fault
5. What is the
function of circuit breaker?
o
A
circuit breaker is a switching and interrupting device in the switchgear.
o
It
makes or breaks a circuit either manually or by remote control under normal condition.
6. State the
methods of extinguishing the arc in circuit breakers.
o
High
resistance method
o
Low
resistance or current zero method
7. What is meant
by arc voltage?
o
When
the contacts of the circuit breaker are apart, an arc is formed.
o
The
voltage that appears across the contacts of the circuit breaker during arcing
period is called arc voltage.
8. What is meant
by restriking voltage ?
The transient voltage that
appears across the contacts at the instant of arc extinction is called the
“restriking voltage”
9. What is meant
by rate of rise of restriking voltage?
o
It
is the rate of increase of restriking voltage and is abbreviated by R.R.R.V .
o
R.R.R.V=(𝑃𝑒𝑎𝑘 𝑟𝑒𝑠𝑡𝑟𝑖𝑘𝑖𝑛𝑔 𝑣𝑜𝑙𝑡𝑎��𝑒)/(𝑇𝑖𝑚𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑧𝑒𝑟𝑜 𝑎𝑛𝑑 𝑝𝑒𝑎𝑘 𝑣𝑜𝑙𝑡𝑎𝑔𝑒)
o
The
R.R.R.V I sin KV/μ.sec
10. What is
meant by breaking current?
Breaking current of a circuit
breaker is the highest value of short circuit current which is capable of breaking
under specified conditions of transient recovery voltage and power frequency
recovery voltage.
11. State the
classification of circuit breakers.
o
Air
blast circuit breaker Oil circuit breaker
o
Sulphur
Hexa Fluoide circuit breaker Vacuum circuit breaker
12. State the
types of Air blast circuit breaker.
o
Axial-blast
air circuit breakers
o
Cross-blast
air circuit breakers
13. State the
merits of Air blast circuit breaker.
o
Can
be used for very high voltage
o
High
speed of operation
o
The
risk of fire is eliminated
14. State the
types of Oil circuit breakers.
o
Bulk
Oil circuit breaker
o
Minimum
Oil circuit breaker
15. State the
types of Bulk Oil Circuit breaker.
o
Plain
break oil circuit breaker
o
Arc
control oil circuit breaker
16. State the
advantages of SF6 circuit breaker.
o
Noiseless
Operation
o
Requires
less maintenance
17. State the
disadvantages of SF6 circuit breaker.
o
These
breakers are costly due to the high cost of SF6 gas.
o
Imperfect
joints will leak out the SF6 gas.
18. State the
types of circuit breaker contacts.
o
Tulip
type contacts
o
Finger
wedge contacts
o
Butt
contacts
19. What is
meant current chopping?
It is the phenomenon of current
interruption before the natural current zero is reached.
20. State the
types of breaking capacity of a circuit breaker.
o
Symmetrical
breaking capacity
o
Asymmetrical
breaking capacity
21. What is
meant by making capacity?
o
The
peak value of current during the first cycle of current wave after the closure
of circuit breaker is known as making capacity.
o
Making
capacity=2.55*Symmetrical breaking capacity
22. What is
meant by Short time rating?
It is the period for which the
circuit breaker is able to Carry fault current while remaining closed.
23. What is
Fuse?
A fuse is a short piece of metal
inserted in series with the circuit, which melts when excessive current flows
through it and thus breaks the circuit.
24. What are the
desirable characteristics of fuse element?
o
Low
melting point
o
Low
cost
o
High
conductivity
25. State the
classifications of fuses.
o
Low
voltage fuses
o
High
voltage fuses
26. State the
types of low voltage fuses.
o
Semi
enclosed rewirable fuse
o
High
Rupturing capacity cartridge fuse
o
HRC
fuse with tripping device
27. What is
meant by arcing time?
This is the time accounted from
the instant of arc initiation to the instant of Arc being extinguished.
28. State the
types of High voltage fuses.
o
Cartridge
type fuse
o
Liquid
type fuse
29. What it is
meant by total operating time?
It is the sum of pre arcing time
and arcing time
30. What is
meant by breaking capacity?
It is the RMS value of AC
component of maximum protective current that a fuse is capable of breaking at
rated service voltage.
UNIT-5
PROTECTIVE RELAYS AND EARTHING
1. What are the
functions of protective relay?
o
It
denotes which type of fault occurs in the power system
o
It
also denotes the area in which fault occurs in the power system
2. What are the
fundamental requirements of protective relay?
o
Selectivity
Reliability
o
Speed
Simplicity
o
Sensitivity
Economy
3. State the
types of protection.
o
Primary
protection
o
Backup
protection
4. State the
types of functional relay.
o
Induction
type over current relays
o
Induction
type reverse power relay
o
Distance
relays
o
Differential
relays
5. State the
application of Non directional relay.
o
It
is used to protect the system from the short and earth fault.
o
When
used for earth fault detection, it is called earth leakage relay.
6. State the
types of earth leakage relay.
This relay protects the system
from earth fault.
7. State the
application of distance relay.
This type of relays is used for
protection of feeders from fault conditions.
8. State the
types of differential relays
o
Current
differential relay
o
Voltage
differential relay
9. What is meant
by Static relay?
The relays which do not use
moving parts or armature and use the solid state electronic components such as
diodes, transistors etc., are called static relays.
10. State the
types of static relays.
o
Static
current relay
o
Static
differential relay
o
Static
distance relay
11. What are the
elements of a static relay?
o
Input
element Measuring element
o
Output
element Feed element
12. State the
uses of microprocessor based directional relay.
o
It
is used as directional relay in conjunction with the over current relays for protection
of parallel lines.
o
It
can be used to sense the reversal of power flow where it is required.
13. What is
meant by grounding?
The earthing or grounding is
nothing but the connection of neutral point of supply system to the general
mass of earth in such a way that immediate discharge of electricity can takes
place without danger.
14. State the
classifications of neutral grounding.
o
Solid
grounding Resistance grounding
o
Reactance
grounding Resonant grounding
15. State the
advantages of neutral grounding.
o
This
system provides a reliable service
o
Earth
fault relays can be installed to isolate the faulty portion.
16. State the
disadvantages of Solid grounding.
o
It
is very difficult to handle the circuit breaker
o
Heavy
earth fault current will cause greater interference to neighbouring communication
circuits.
17. State the
advantages of Peterson coil grounding.
o
In
this system the arcing is extinguished
o
Even
in fault condition, the other healthy phases continue to supply power.
18. State the advantages
of voltage transformer grounding.
o
Arcing
grounds are eliminated
o
The
transient over voltages due to switching and arcing grounds are reduced
Ø because voltage
transformer provides very high reactance to the earth path.
19. State the
classifications of relay circuit connections.
o
Primary
winding
o
Secondary
winding
o
Tripping
circuit
20. State the classifications
of static distance relay.
o
Static
impedance relay
o
Static
reactance relay
o
Static mho (admittance ) relay
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