Power Systems MCQ Set 1
1. If a line is considered with negligible power losses, then the real power transmitted will be proportional to voltage drop and the reactive power drop is proportional to cosδ.
a) True
b) False
Answer
Answer: b [Reason:] Real power = |Vs||Vr|(sinδ)/X
2. If a line is considered with negligible power losses, then the real power transmitted will be proportional to ______ and the reactive power drop is proportional to ____
a) sinδ, voltage drop across line
b) cosδ, voltage drop across line
c) δ, voltage drop across line
d) voltage drop across line, sinδ
Answer
Answer: a [Reason:] Real power = |Vs||Vr|(sinδ)/X
3. Choose the most feasible method for raising the power to be delivered at the reactive end.
(i)Reducing the line reactance
(ii)Raising the voltage level
a) (i)
b) (ii)
c) (i), (ii)
d) None of the methods
Answer
Answer: a [Reason:] Increasing the voltage level is not always economical and reducing the voltages at stations is easier.
4. The lagging reactive power delivered by a line is proportional to the line _____ and independent of _____
a) voltage,δ
b) δ, voltage
c) voltage, sinδ
d) voltage drop, cos δ
Answer
Answer: a [Reason:] The lagging reactive power delivered by a line is proportional to the line voltage and independent of δ.
5. Assume a 275 kV transmission line having the following line constants:A = 0.8∠5° ; B = 200∠75°
For obtaining 275 kV voltage at the receiving end obtaining unity power factor, the power transmitted will be _______
a) 124 MW
b) 117.2 MW
c) 116 MW
d) 110 MW
Answer
Answer: a [Reason:] Qr = 0
0=(275*275)/200 sin(75-δ)-0.8/200 sin(75-5)
0=378sin(75-δ)-284.26
δ=26.23°
Pr = (275*275)/200 cos(75-δ)-0.8/200 cos(75-5)
= 124 MW.
6. Assume a 275 kV transmission line having the following line constants:A = 0.8∠5° ; B = 200∠75°
For obtaining 275 kV voltage at the receiving end obtaining unity power factor, the power angle required to be set as ____
a) 26.23°
b) 22°
c) 25°
d) 24°
Answer
Answer: a [Reason:] Qr = 0
0=(275*275)/200 sin(75-δ)-0.8/200 sin(75-5)
0=378sin(75-δ)-284.26
δ=26.23°.
7. Assume a 275 kV transmission line having the following line constants:A = 0.8∠5° ; B = 200∠75°
If a load is connected at receiving end at unity power factor but maintaining the same voltage profile. Will this system now need any type of compensation?
a) Yes
b) No
c) Cannot be said
d) Never
Answer
Answer: a [Reason:] Yes this system will require a compensation system to be employed as the net reactive power will not be zero due to the load mentioned.
8. Assume a 275 kV transmission line having the following line constants:A = 0.8∠5° ; B = 200∠75°
If a load is connected at receiving end at unity power factor but maintaining the same voltage profile. Will this system now need any type of compensation? If so, then which one?
a) Yes, capacitive
b) No
c) Yes, inductive
d) Yes, inductive and capacitive
Answer
Answer: a [Reason:] yes, it will need compensation. As ∆Q≠0 and it will be less than zero.
9. Assume a 275 kV transmission line having the following line constants:A = 0.8∠5° ; B = 200∠75°
If a load is connected at receiving end at unity power factor but maintaining the same voltage profile. Then ___ compensation will be needed at ______
a) capacitive, receiving end
b) inductive, sending end
c) capacitive, sending end
d) inductive, receiving end
Answer
Answer: a [Reason:] The positive VARs are to be fed to the line at the load end.
10. Assume a 275 kV transmission line having the following line constants:A = 0.85∠5° ; B = 200∠75°
If a load is connected at receiving end at unity power factor but maintaining the same voltage profile. The receiving end voltage if the compensation equipment is not installed will be ____
a) 245 kV
b) 280 kV
c) 255 kV
d) 272 kV
Answer
Answer: a [Reason:] Pr = 150 MW, Qr = 0
|Vs| = 275 kV, |Vr| = ?
150 = (275*|Vr|)/200 cos(75-δ)-0.8/200 cos(75-5)
0=(275*|Vr|)/200 sin(75-δ)-0.8/200 sin(75-5)
Solving the quadratic equations above and retaining the higher value for the voltage, |Vr| = 245 kV.
Power Systems MCQ Set 2
1. Which of below factor(s) contribute to the more receptibility to pollution of insulators?
a) Ionic current
b) Uniform voltage
c) Electrostatic voltage
d) Ionic current and Electrostatic voltage
Answer
Answer: a [Reason:] The ionic current and the electrostatic voltage that develops contributes towards the receptibility of pollution in insulators.
2. More number of insulators are needed in AC line as compared to DC line
a) True
b) False
Answer
Answer: b [Reason:] No, DC line need more because of thermal runaway, high unit flashover and contamination.
3. The factors which contribute more to the addition of insulator in HDVC line are ______
a) high unit flashover
b) contamination
c) thermal runaway
d) high unit flashover, contamination and thermal runaway
Answer
Answer: d [Reason:] All the factors add to the insulator addition.
4. What makes porcelein type insulator to be off market?
a) Weight
b) Greater failure rate
c) Self clearing
d) Weight and greater failure rate
Answer
Answer: d [Reason:] They have higher probability of fault occurrence and possess larger weight.
5. Most industrially accepted insulators used in HVDC is/are _____
a) high resistance toughened glass type
b) porcelein type
c) silicon rubber composite type
d) all of the mentioned
Answer
Answer: a [Reason:] HRTG is mostly accepted.
6. What is the major problem in current interruption in DC circuit?
a) No natural zero current
b) Extra energy stored in circuit
c) High flashover
d) All of the mentioned
Answer
Answer: a [Reason:] There is no natural zero current in DC circuit which poses problem.
7. A two conductor DC line is more reliable than a three conductor AC line.
a) True
b) False
Answer
Answer: a [Reason:] A two conductor DC can always find path through earth or sea than AC system.
8. Stunt capacitors are installed on ____ and smoothing reactor is installed in ____ in TL.
a) AC side, DC side
b) DC side, DC side
c) AC side, AC side
d) DC side, AC side
Answer
Answer: a [Reason:] Shunt capacitors are connected at dc side while inductor at ac.
9. There is no requirement of reactive power at the converter station of a HVDC link.
a) True
b) False
Answer
Answer: a [Reason:] There is requirement of reactive power due to phase shift between fundamental as current and voltage and commutation process.
10. _______ polarity is preferred on OH lines due to less radio interference.
a) Negative
b) Positive
c) Ground
d) Any of the mentioned
Answer
Answer: a [Reason:] Negative polarity is preferred on overhead lines.
Power Systems MCQ Set 3
1. Which of the following is not a reason of heating feed water?
a) It improves overall efficiency
b) It removes dissolved impurities
c) It prevents from thermal stress which may cause due to enter of cold water into boiler
d) It produces steam from feed water
Answer
Answer: d [Reason:] Steam production is work of boiler. Feed water is heated only for four reasons : to improve overall efficiency, to remove dissolved impurities, to avoid thermal stress going to entering of cold water to the boiler and to precipitate impurities carried by steam and condensate outside the boiler.
2. Feed water for boiler of thermal power plant is obtained from:
a) Natural sources like river and lake
b) Partly from condensed steam and natural sources
c) Condensed steam and small percentage from natural resources
d) Natural sources and small percentage from condensed steam
Answer
Answer: c [Reason:] The steam coming out of turbines is condensed and the condenset is fed back to the boiler. Some of water losses due to the blow-down, leakage etc.. and to make up these losses additional water called “makeup water” is taken from natural sources after treatment. This makeup water is obtained from natural sources like river and lake and about 1 – 4% of total feed water.
3. Mechanical method of water treatment is done to _______
a) Heat the feed water
b) To remove solid matter and impurities
c) To add some solid materials
d) To remove dissolved gases
Answer
Answer: b [Reason:] Mechanical method of water treatment involvs sedimentation and filtration. During sedimentation water kept at standstill or flow with a very low velocity which causes the solid matter to settle down and finally removed. During filtration the dirty water is allowed to flow downword through the beds of filtering materials to remove suspended matters.
4. Which method is used in large modern thermal power plants to heat feed water?
a) Open type heatre is used
b) Close type heater is used
c) Steam is directly taken from main turbine and used to heat it feed water
d) Surface type heater is used
Answer
Answer: c [Reason:] Open and contact type haters are in small power plants. Such heaters recives steam from back pressure turbine. In large modern power plants heaters bleed steam from the main turbine and use it for heating of feed water.
5. Thermal treatment methods used to remove impurities like:
a) Dissolved carbon dioxide and other gases
b) Solid materials
c) Carbonate
d) Bacterial impurities
Answer
Answer: a [Reason:] Thermal treatment method involves distillation and derative heating of feed water. During distillation water is evaporated then condensed and collected. During derating heating water is broken up into fine droplets and heated to produced vapour within the deaerator. During these process carbon dioxide and other days of devices separated from feet water.
6. Heat treatment arrangement used to separate or remove deserved gases and impurities from feed water is called the year later.
a) true
b) False
Answer
Answer: a [Reason:] A deaerator is a device that is widely used for the removal of oxygen and other dissolved gases from the feedwater to steam-generating boilers. These gases make house corrosion scale formation.
7. Chemical method of treatment is used for treatment of:
a) Diissolve gases
b) Carbonate and carbon dioxide
c) Bacterial impurities
d) Send and suspended materials
Answer
Answer: b [Reason:] Chemical treatment involvs line treatment, soda treatment, lime and soda treatment. Zeolite treatment and demineralisation. Iime treatment is done for treatment of carbonate hardness, carbon dioxide in water. soda treatment is done for treatment of water containing non carbonate hardness and line soda treatment is used when both carbonate and none carbonate hardness for feed water.
8. Scall formation in boiler tube causes ______
a) reduction of heat transfer and overheating of boiler tube
b) corrosion of boiler surface
c) feeling up of steam passage
d) cracks in the ages rivites
Answer
nswer: a [Reason:] Dissolved gases include oxygen and carbon dioxide which may lead to scale formation corrosion, carry over and imbrittlement in boiler and other apprature. Scale formation reduces the heat transmission through the heating surface.
Power Systems MCQ Set 4
1. Ferranti effect is not a problem for ________
a) Long Transmission lines
b) Medium Transmission lines
c) Short Transmission lines
d) Transmission line having high capacitance
Answer
Answer: c [Reason:] Ferranti effect is happens when line to earth capacitance becomes more than the inductance parameter. This effect is more predominant in medium and long transmission lines but is not a problem for short transmission lines. This is because line to earth capacitance for short transmission line is negligible.
2. What happens during the Ferranti effect?
a) Reciving end current becomes more than sending end current
b) Reciving end voltage becomes more than sending end voltage
c) Reciving end power becomes more than sending end power
d) Reciving end frequency becomes more than sending end frequency
Answer
Answer: b [Reason:] In a medium or long transmission line when open circuited or lightly loaded the receiving end voltage is found more than the standing in voltage. This phenomenon of rise in voltage at receiving end of open circuited or lightly loaded line is called Ferranti effect.
3. During Ferranti effect the voltage drop across line resistance _____
a) In phase with reciving end voltage
b) lags behind reciving end voltage
c) lead the reciving end voltage
d) lags behind sending end voltage
Answer
Answer: c [Reason:] During Ferranti effect the leading charging current is more than lagging component of current. Net line current leads the sending end and reciving end voltage. Hence the iR drop leads these voltages.
4. A transmission line of 200 Km is supplying at 50Hz frequency. What is the percentage rise in voltage at reciving end?
a) 20%
b) 1.2%
c) 2.19%
d) 20.8%
Answer
Answer: c [Reason:] Percentage rise in voltage = (ω2 l2 10-8 )/18
Solving this % Vrise = {(2 × Ω × 50) × 2002 × 10-8}/18
= 2.19%.
5. Which of the following equipment or element can reduce Ferranti effect?
a) Relay
b) Circuit Breaker
c) Resistors
d) Current limiting reactors
Answer
Answer: d [Reason:] For high voltage and extra high voltage lines shunt reactors are provided to absorb part of charging current. As leading charging current is reduced. Ferranti effect is also reduced.
6. Under no load condition inductance of line predominant the line to earth capacitances.
a) True
b) False
Answer
Answer: b [Reason:] Under no load condition capacitance between line and earth predominant the inductance of long and medium transmission lines.
7. What is the limit within which the consumer’s end terminal voltage should be maintained?
a) ± 9 %
b) ± 10 %
c) ± 5 %
d) ± 6 %
Answer
Answer: d [Reason:] The voltage fluctuations at consumers end may cause malfunction or event damage of consumer’s equipments. So, the voltage at the consumers end must be maintained within prescribed limit upto ± 6% of declared supply voltage so that the consumers apparatus may operate satisfactorily.
8. What is the main reason for maintaining consumer end voltage within prescribed limit?
a) Because it is declared by the supplier
b) For satisfactory operation of electrical equipments
c) For easy calculation of units supplied
d) To reduce the line losses
Answer
Answer: b [Reason:] All electrical equipments are designed to work at a certain voltage mentioned as voltage rating of that equipment. Change of supply voltage beyond a certain limit may cause malfunction or even damage to the equipment. So, the consumer end voltage must be maintained to a prescribed limit for satisfactory operation of consumer’s equipments.
9. Which of the following equipment is not used for voltage control?
a) Tap changing transformer
b) Induction generators
c) Series compensators
d) Synchronous phase modifiers
Answer
Answer: b [Reason:] Induction generators are not used for voltage control. Tap changing transformer is used to control distribution end voltage for upto limited voltage variations. Series compensators and Synchronous phase modifiers controls line voltage by supplying required leading or lagging VAR.
10. What is the full form of AVR? This term is related to voltage control?
a) Automatic Voltage Rectifier
b) Actuated Voltage Rectifier
c) Automatic Voltage Rectifier
d) Automatic Voltage Regulator
Answer
Answer: d [Reason:] AVR stands for Automatic Voltage Regulator. It operates on the principle of detection of error and is used to control the line voltage.
11. On which side of the transformer tap changer is provided?
a) On High Voltage side
b) On low voltage side
c) On high voltage and low voltage side
d) In core
Answer
Answer: a [Reason:] In tap changing transformer there is always a typing on the high voltage winding which when connected to the rated voltage gives rated voltage on the low voltage side. This tapping is called principal typing.
Power Systems MCQ Set 5
1. A 500 MW, 21 kV, 50 Hz three phase two pole alternator has 0.8 lagging p.f. with moment of inertia of 27.5×103 kgm-2. The inertia constant H will be _______ MJ/MVA.
a) 2.17
b) 4.2
c) 2.82
d) 2.62
Answer
Answer: a
2. If the power system network is at Vs∠δ and receiving end voltage is Vr∠0 consisting of the impedance of TL as (R+j5)Ω. For maximum power transfer to the load, the most appropriate value of resistance R should be ____
a) 1.732
b) 3
c) 1.2
d) 0.33
Answer
Answer: a [Reason:] For maximum power transfer, X=√3 R
3=√3 R
R=√3.
3. At a 33kV 50 Hz to a bus a load of 35 MW is connected. To improve the power factor to unity a synchronous phase modifier is connected taking 5 MW. If the SPM is represented as delta connected impedance, where in each phase we have capacitor connected parallel to resistance forming RC parallel network, then the value of this resistance is _____
a) 653.4 Ω
b) 753.6 Ω
c) 280.4 Ω
d) 682 Ω
Answer
Answer: a [Reason:] Reactive power fed by SPM = 35tan36.87 = 26.25 MVAR
Active power consumed by prime mover = 5 MW
5*106 = 3V2/R
R=3(33×1000)2/(5*106) = 653.4 Ω.
4. At a 33kV 50 Hz to a bus a load of 35 MW is connected. To improve the power factor to unity a synchronous phase modifier is connected taking 5 MW. If the SPM is represented as delta connected impedance, where in each phase we have capacitor connected parallel to resistance forming RC parallel network, then the value of this capacitance is ____
a) 25.57 μF
b) 76.2 μF
c) 32.2 μF
d) 24 μF
Answer
Answer: a [Reason:] Q=3V2Cω
C= 25.57 μF.
5.The transmission efficiency for a single phase line can be expressed as ______
Answer
Answer: a [Reason:] The efficiency of single phase is
6. The transmission efficiency for a three phase line can be expressed as ___
Answer
Answer: a [Reason:] The efficiency of three phase system is 
7. If the flux linkages are varied sinusoid with current, then what can be concluded about the inductance?
a) Constant
b) Varying with the current
c) Linearly varying
d) Exponential change
Answer
Answer: b [Reason:] Inductance = flux linkages/current.
8.The principle behind the influence of the power lines on the telephone lines is ____
a) Faraday’s laws
b) Mutual inductance
c) Self inductance
d) All of the mentioned
Answer
Answer: a [Reason:] The concept of mutual inductance is the main reason for the interference between telephone lines and the power lines.
9. The magnetic flux intensity due to the current flowing inside the conductor is ___
Answer
Answer: a [Reason:] Referring the ampere’s Law,
2πyH=Iy
Assuming uniform current density,
10. The flux density B, y meters from the centre of conductors in the following diagram, is _______
Answer
Answer: a [Reason:] Referring the ampere’s Law,
2πyH=Iy
Assuming uniform current density,
11.The internal flux linking the single infinite conductor causes the inductance of _____
a) 0.5 *10-7 H/m
b) 2 *10-7 H/m
c) 0.5 *10-7 ln(r) H/m
d) 2 *10-6 H/m
Answer
Answer: a [Reason:] λint = I/2 x 10-7 Wb-T/m
L= λint/I = 0.5 *10-7 H/m.
12. The inductance of the conductor contributed by the flux between the point D outside at the distance d from conductor is _______
a) 0.461 log(d/r) mH/km
b) 0.4 log(d/r) mH/km
c) 0.461 log(r/d) mH/km
d) 0.461 log(d/r) H/km
Answer
Answer: a [Reason:] L= 0.461 log(d/r) mH/km.
