Power System-I
QUESTION 2014
(Multiple Choice Type Questions)
1) A string insultor has 4 units. The voltage across the bottom most unit is 30% of the total voltage Its string efficiency is
(a) 30 (b) 60% (c) 75% (d) 83.33%
Ans:-(d)
2) The capacitance between any two conductors of a 3-core cable with sheath earthed is 3 μF. The capacitance per phase will be
(a) 1.5 μF (b) 6 μF (c) 1 μF (d) none of these
Ans-(d)
3) Grading ring is used to equalize the potential distribution across the units of the suspension insulator because it
(a) forms capacitances which will help to cancel the charging current from link pins
(b) forms capacitances with link pins to cancel the charging current from link pins
(c) increases the capacitances of lower insulator units
(d) decreases the capacitances of upper insulator units
Ans-(b)
4) The presence of ground causes the line capacitance to
(a) increase by about 12% (b) decrease by about 12%
(c) increase by about 0.2% (d) none of these
Ans-(c)
5) The current drawn by the line owing to corona loss is
(a) non-sinusoidal (b) sinusoidal (c) dc (d) square
Ans-(a)
6) In terms of constants A,B,C and D for short transmission lines, which of the following relation (s) is/are valid?
(a) A= D = 1 (b) C = 0 (c) B = Z (d) all of these
Ans-(a)
7) Constant power locus of a transmission line at a particular sending end and receiving end voltage is
(a) a straight line (b) a circle (c) a parabola (d) an ellipse
Ans-(a)
8) Bundle conductors are used to
(a) reduce inductance of the line (b) reduce both inductance and capacitance
(c) reduce corona loss (d) reduce corona loss and line inductance
Ans-(d)
9) The diameter of each strand is 'd'. then the diameter of n-1ayer stranded conductor will be
(a) (2n + 1 )d (b) 3(n + 1 )d (c) (2n - 1 )d d)3(n-1)d
Ans-(a)
Power System-I
QUESTION-2015
(Multiple Choice Type Questions)
1)The size of conductor of modern EHV lines is obtained based on
(a)Voltage drop (b) Current density (c) Corona (d) Skin effect
Ans-(a)
2)As the load factor of a generating plant increases, the generation cost per KW generated
(a) decreases (b) increases (c) remains same (d) none of these
Ans-(a)
3)A synchronous compensator absorbs inductive reactive power. it is
(a) over excited (b) normally excited (c) under excited (d) none of these
Ans-(a)
4)Stringing chart is used in transmission lines for
(a) designing the tower
(b) calculating the sag in the conductor
(c) determining the distance between the conductor
(d) design of insulator string
Ans-(b)
5)The surge impedance of a100 Km long underground cable is 500 ohm. The surge impedance of a 40 Km long cable of similar type is
(a)20 ohm (b) 50 ohm (c)80 ohm (d) 125 ohm
Ans-(b)
6) The ratio or average demand or energy and energy required according to installed capacity for power system is termed as
a) diversity factor b) load factor
c) plant capacity factor d) plant use factor
Ans-(c)
7) The quantity of raw materials used for generating a given quantity of power is the least in the case of
a) thermal power plant b) hydral power plant
c) nuclcer power plant d) MHD
Ans-(c)
8) Th A,B,C,D constants of transmission line are expressed as follows
a) AD+ BC= 1 b) AD - BC=1 c) AD- BC= 0 d) AB + DC= 1
Ans-(b)
9) When the effective resistance of a conductor increases due to the presence of current carrying conductor nearby, then the effect is called
a) skin effect b) proxrm1ty effect c) Ferranti effect d) corona effect
Ans-(b)
10)At the time of transposition of three-phase line equivalent equilateral spacing between the conductors is
a)∛d1d2d3 b)√d1d2d3 c)d1d2d3 d)1/3 (d1d2d3)
Ans-(a)
11) A string of insulators has 4 insulators The voltage across the bottom unit is 30% of total voltage.The string efficiency of insulator is
a) 30% b) 60% c) 75% d) 83.33%
Ans-(d)
xii) What 1s the approximate efficiency of a normal thermal power plant?
a) 30 -40% b) 20 - 25% c) 40 -50% d) 60- 70%
Ans-(a)
Power System-I
QUESTION 2016
1) The presence of earth in case of overhead lines
a) increases the capacitance b) increases the inductance
c) decreases the capacitance d) decreases the inductance
Ans-(a)
2) Use of bundle conductors in EHV transm1ss1on system provides
a) increased one reactance b) decreased capacitance
c) reduced voltage grad ent d) increased corona loss
Ans-(c)
3) Transposition of transmission line is done to
a) reduce line loss b) reduce skin effect
c) balance line voltage drop d) reduce corona
Ans-(C)
4) The transmission efficiency of a line is
a) directly proportional to the load power factor
b) inversely proportional to the load power factor
c) does not depend on load power factor
d) proportional to the square of load power factor
Ans-(B)
5) For a stranded conductor, the ratio of GMR to actual radius is
a) equal to 1 b) greater than 1 c) equal to 0. 7788 d) less than 0. 7788
Ans-(d)
6) The electric stress in a cable is maximum at
a) centre of conductors b) interface of sheath and conductors c) lead sheath d) armour
Ans-(c)
7) The A, B, C, D parameters for short transmission line with a series impedance z are
a) z, 0, 1, 1 b) 0, Z, 1, 1 c) 1, Z, 0, 1 d) 1, 1, Z, 0
Ans-(C)
8) Load factor is defined as the ratio of
a) average demand to plant capacity
b) average load to maximum demand
c) maximum demand to connected load
d) average load to connected load
Ans-(c)
9) Nuclear power plant is invariably used as a/an
a) peak load point b) base load point
c) stand by plant d) emergency plant
Ans-(a)
10) The a.c. resistance of a conductor is greater than its d.c. value due to
a) skin effect b) proximity effect c) Ferranti effect d) both (a) & ( b)
Ans-(d)
11) 25% of the line of neutral voltage appears across the bottom-most unit in a string insulators with 5 identical discs The string efficiency is
a) 80% b) 75% c) 50% d) 25 %
Ans-(a)
12)By increasing the sag on the transmission line, the tension
a) increases b) decrease c) not affected d) may increase or decrease
Ans-(b)
Power System-I
Question-2017
1) The function of earth wire in a transmission line is to
a) prevent earth fault
b) provide a safety measure for any high flying objects
c) provide a shield to the phase conductors from direct lightning stroke
d) provide mechanical strength to the tower
Ans-(c)
2) The thickness of the layer of insulation on the conductor, in cables, depends upon
a) reactive power b) power factor
c) voltage d) current carrying capacity
Ans-(c)
3) Which of the following insulators is used in transmission lines at a river and road crossings
a) Pen type b) Suspension type c) Strain type d) Shackle type
Ans-(c)
4) Diversity factor is always
a) 1 b) 0 c) greater than 1 d)λ
Ans-(c)
5) A 3-phase, 4-wire system is commonly used for
a) primary distribution b) secondary distribution
c) primary transmission d) secondary transmission
Ans-(b)
6) Shunt compensation in a transmission line is resorted to
a) improve the stability
b) improve the voltage profile
c) reduce the fault level
d) as a substitute for synchronous phase modifier
Ans-(b)
7) Daily energy consumption of a plant 1s 30 units. Maximum demand is 2kW.Then the load
Will be
a) 60% b) 50% c) 75% d) 62.5%
Ans-(d)
8) In a 3-core cable, th capacitane between two conductor is 3mF. will be the
capacitance per phase?
a)1.5μF b)3μF c) 6μF d)12μF
Ans-(C)
9) String chart is useful for
a) f1nd1ng the sag in the conductor b) the design of insulation string
c) the design of tower d) finding the distance between towers
Ans-(a)
10) The leakage resistance of a 5Okm long cable is 1megaohm For a 100 km long cable, it will be
a) 1 Mohm b) 0.66Mohm c) 2Mohm d) 0.5Mohm
Ans-(a)
11) The economic size of a conductor is determine by
a) Kelvin's law b) Kirchhofs law c) Faraday's law
Ans-(a)
12) The AC resistance of a conductor is greater than its DC value due to
a) Skin effect only b) Proximity effect only c) Ferranti effect only
Ans-(a)
QUESTION 2018
Group-A
(Multiple Choice Type Questions)
1. Choose the correct alternative for any ten of the following·
i) The function of steel wire in an ACSR conductor is to
a) compensate for skin effect b) take care of surges
c) reduce inductance d) provide additional mechanical strength
Ans-(d)
2) When 1s the Ferranti effect on long over head line
a) The line is lightly loaded (b) The line is heavily loaded
c) The line is fully loaded (d) The power factor is unity
Ans-(a)
3) The sag of a transmission line is least effected owing to?
a) weight of the conductor b) Current through the conductor
c) atmospheric temperature d) ice deposition on the conductor
Ans-(b)
4) Transposition of transmission lirie is done to
a) reduce hne loss b) reduce skin effect
c) balance hne voltage drop d) reduce corona
Ans-(c)
5) The surge impedance of a 400kV surge impedance will be 100km transmission line is 3000 For a 200km length the line
a)3000 b)1500 c) 6000 d) 4000
Ans-(a)
6) Bundle conductor are used to
a) reduce inductance of the line
b) reduce corona loss
c) reduce both inductance and capacitance
d) reduce corona loss and line inductance
Ans-(d)
7) Corona occurs between two transm1ss1on conductors when they
a) have high potential difference b) are closely spaced
c) carry de power d) both (a) and (b)
Ans-(d)
8) If the frequency of a transmission system 1s changed from 50Hz to 1 OOHz, the string efficiency
a) will increase b) will decrease c) remain unchanged
d) may increase or decrease depending on the parameter
Ans-(c)
9) In a cable the sheath radius is R and conductor radius is r. As r changes from O.SR to 0.25 R to
maximum voltage gradient in the dielectric.
a) decrease by about 6% b) increase by about 6%
c) decrease by about 15% d) increase by about 15%
Ans-(b)
10) In thermal power plants. the pressure in the working fluid cycle is developed by
a) condenser b) superheater c) feed water pump d) turbine
Ans-(a)
11) In a stream power plant heat from the flue gases is recovered in
a) condenser b) chimney
c) economizer and air preheater d) desupeheater
Ans-(c)
12) Flat rate tariff can be charged on the basis of
a) connected load b) units consumed
c) maximum demand d) both (a) and (b)
Ans-(b)
13) Nuclear power plant is invariably used as a/an
a) Peak load plant b) Base load plant
c) Stand by plant d) Emergency plant
No comments:
Post a Comment