Power Systems MCQ Set 1
1. The instantaneous voltage wave in the long transmission line is a function of _______
a) time and distance
b) time
c) distance
d) time, distance and reactive inductance
Answer
Answer: a [Reason:] It will be a function of time and distance.
2. At any point along the line, the instantaneous voltage is _____
a) sum of incident and reflected voltage
b) incident voltage
c) sum of incident and refracted voltage
d) twice the incident voltage
Answer
Answer: a [Reason:] V(t) = Vincident+Vrefracted.
3. The equation given below is the voltage equation,
Then it is ____
a) reflected wave receiving to sending end
b) reflected wave sending to receiving end
c) incident wave from receiving end to sending end
d) refracted wave from receiving end to next end
Answer
Answer: a [Reason:] From the equation, cos(wt-βx+Ф2), it is clear that the wave is travelling in left to right and the amplitude is reduced, so it’s a reflected wave.
4. When can an incident wave not distinguish between the termination and an infinite continuation of line?
a) When line is terminated by its characteristic impedance
b) When line is terminated by its surge impedance
c) When line is open
d) When line is terminated by its characteristic and surge impedance
Answer
Answer: a [Reason:] The characteristic (surge) impedance at the receiving end will cause a confusion for the incident wave.
5. Ferranti effect is more prominent due to ______
a) line capacitance
b) surge capacitance
c) stray capacitance
d) all of the mentioned
Answer
Answer: a [Reason:] Line capacitance causes the no load receiving end voltage to be more than receiving end.
6. The voltage rise happening at the receiving end due to the line charging capacitance has a magnitude of ___
a) ω2CLl2
b) ω2CLl2/2
c) ω2l2/v2
d) ω2CLl2 and ω2l2/v2
Answer
Answer: d [Reason:] The circuit diagram for the LTL is
Is= jVswCl
Vr = Vs – Is(jwLl) = Vs + Vsw2CLl2
=Vs(1+ w2CLl2).
7. The receiving end voltage at the no load will be ______
a) Vs(1+ w2CLl2)
b) (1+ w2CLl2)
c) Vs/(1+ w2CLl2)
d) Vs
Answer
Answer: a [Reason:] The circuit diagram for the LTL is
Is= jVswCl
Vr = Vs – Is(jwLl) = Vs + Vsw2CLl2
=Vs(1+ w2CLl2).
8. If a line is considered with negligible power losses, then the real power transmitted will be proportional to sinδ.
a) True
b) False
Answer
Answer: a [Reason:] Pr = |Vs||Vr|(sinδ)/X.
9. If a line is considered with negligible power losses, then the real power transmitted will be proportional to _____
a) sinδ
b) cosδ
c) δ
d) sin2δ
Answer
Answer: a [Reason:] Pr = |Vs||Vr|(sinδ)/X.
10. If a line is considered with negligible power losses, then the reactive power transmitted is proportional to receiving end voltage.
a) True
b) False
Answer
Answer: b [Reason:] Its incorrect, Q depends on the voltage drop across the line.
Power Systems MCQ Set 2
1. Length of long transmission line is more than _____
a) 80 Km
b) 50 Km
c) 120 Km
d) 200 Km
Answer
Answer: d [Reason:] Transmission lines having length more than 200 kilometres are categorised as long transmission lines. Transmission lines having length less than 200 kilometres are medium transmission lines.
2. In long transmission lines Resistance and Capacitance parameters of lines are connected in ____
a) Series, shunt
b) Series, series
c) Shunt, shunt
d) Shunt, parallel
Answer
Answer: d [Reason:] The resistance and inductance parameters are series elements of long transmission line. Capacitive susceptance and conductance parameters are shunt elements of transmission lines.
3. Range of surge impedance for an overhead transmission line is ______
a) 12 Ω – 144 Ω
b) 40 Ω – 60 Ω
c) 400 Ω – 600 Ω
d) 300 Ω – 900 Ω
Answer
Answer: c [Reason:] Surge impedance is the characteristic impedance of a loss free transmission line. It is the square root of ratio of line impedance(Z) and shunt admittance (Y). Its value varies between 400 Ω and 600 Ω.
4. Range of surge impedance for an underground cables is _______
a) 12 Ω – 144 Ω
b) 40 Ω – 60 Ω
c) 400 Ω – 600 Ω
d) 300 Ω – 900 Ω
Answer
Answer: b [Reason:] Surge impedance is the characteristic impedance of a loss free transmission line. It is the square root of ratio of line impedance(Z) and shunt admittance (Y). Its value varies between 40 Ω and 60 Ω.
5. Synchronous phase modifiers are installed at which of the following position of the transmission line?
a) Reciving end
b) Sending end
c) Between reciving end and sending end
d) Near reciving end
Answer
Answer: b [Reason:] For constant voltage transmission, specially designed synchronous motors, called synchronous phase modifiers. Synchronous phase modifiers are installed at receiving end to maintain the voltage drop along the line constant.
6. The voltage rating of long transmission line is ___
a) 20 KV to 100 KV
b) Upto 20 KV
c) Above 100 KV
d) 60 KV to 80 KV
Answer
Answer: c [Reason:] The transmission line having length above time 200 kilometre and line voltage above 100 KV fall into the category of long transmission line.
7. The shunt capacitive susceptance in long transmission line is greater than that in medium and short transmission line.
a) True
b) False
Answer
Answer: a [Reason:] Due to long length and high voltage of line the charging current is very high for the long transmission line and therefore the capacitance in long transmission line is also very high and is more than that in short and medium transmission line.
8. What is the value of characteristics impedance for loss free transmission line?
a) √(L/C)
b) √(R/C)
c) √(LC)
d) √(C/L)
Answer
Answer: a [Reason:] Characteristic impedance of a long transmission line is given by
Zc = √[(R+jX) / ( G+jB)]
For loss less transmission line resiatance (R) and shunt conductance (G) are equal to zero. And hence, Z0 ( Characteristic impedance for loss-free transmission line) is given by
Z0 = √(L/C).
9. The leakage current through the shunt admittance is ____
a) Maximum at sending end
b) Maximum at receiving end
c) Uniform over length of line
d) Maximum at centre of line
Answer
Answer : a [Reason:] The leakage current through the shunt admittance is maximum at the sending end of the transmission line. This current decreases continuously as it move towards the receiving end of the line and becomes zero at the receiving end.
10. Value of leakage current at reciving end of transmission line is zero.
a) True
b) False
Answer
Answer : a [Reason:] Value of leakage current through the shunt admittance is maximum at the sending end of the transmission line. This current decreases continuously as we move towards the receiving end of the line and becomes zero at the receiving end.
Power Systems MCQ Set 3
1. How can we check upon the transient stability of a power system?
a) By checking variation in load angle
b) By checking variation of real power with load angle
c) Checking variation in load angle and real power
d) Checking variation in load angle or real power
Answer
Answer: c [Reason:] Checking the variation in load angle and real power flow helps in deciding the transient stability.
2.To maintain the transient stability for a power system _______
Answer
Answer: c [Reason:] The rate of change of load angle must be positive and so the change in real power variation in order to supply the demand.
3. How can we improve the steady state stability of the synchronous generator for a better performance?
a) Increasing the excitation
b) Increasing reactance
c) Decreasing moment of inertia
d) Increasing moment of inertia
Answer
Answer: a [Reason:] P(max) = EV/X.
4. There is 2-machine model having losses too, with their transfer impedance being resistive. The maximum value of sending power P1max and maximum receiving end power P2max will take place with power angle ‘δ’ such that
a) Both P1max and P2max will occur at δ<90
b) Both P1max and P2max will occur at δ>90
c) P1max occurs at δ > 90 and P2max will occur at δ<90
d) P1max occurs at δ < 90 and P2max will occur at δ>90
Answer
Answer: a [Reason:] Even after connecting parallel machines, their maximum power will occur at load angle lesser than 90 degrees.
5. As per the system given, machine B will receive the active and reactive power from machine A when ________
a) δ is positive and Va is more than Vb
b) δ is positive and Va is less than Vb
c) δ is positive and Va is same as Vb
d) δ is negative and Va is more than Vb
Answer
Answer: a [Reason:] Real power flows from higher to lower δ while the reactive power flows from higher voltage to lower.
6. If there are two machines having moment of inertia M1 and M2, where M1<M2; The possible number of equivalent moment of inertia will be ___
a) 1
b) 2
c) 3
d) 4
Answer
Answer: c [Reason:] M1+M2, M1||M2 and M1-M2.
7. If there are two machines having moment of inertia M1 and M2, where M1<M2; Then one is proposing to add more inertia to the system. Then it will be added to _______
a) Machine 1
b) Machine 2
c) Machine 1 and Machine 2
d) Either of Machine 1 and Machine 2
Answer
Answer: a [Reason:] Since the inertia is less for machine 1.
8. The measure to improve the transient stability of the power system during the unbalanced or unsymmetrical fault can be taken as ________
a) Single pole switching of CB
b) Excitation control
c) Phase shifting transformer
d) Increasing turbine valve opening
Answer
Answer: a [Reason:] Single pole switching of CB allows the immediate isolation of the fault frim the system and thus safeguarding the healthy part.
9. Use of high speed circuit breaker will actually increase the system stability.
a) True
b) False
Answer
Answer: a [Reason:] High speed CB immediately cuts off the fault and saves the system to undergo transient oscillations.
10. What does the steady state stability of a power system signify?
a) Maintaining the rated voltage
b) Maintaining rated frequency
c) Maintaining a synchronism between machines and tie-lines
d) All of the mentioned
Answer
Answer: c [Reason:] Steady state stability means to maintain the stable system inside and outside too with the external tie lines.
Power Systems MCQ Set 4
1. Which of the following transmission line can be considered as medium transmission line?
a) Transmission line of length upto 600 Km
b) Transmission line of length upto 500 Km
c) Transmission line of length upto 200 Km
d) Transmission line of length upto 80 Km
Answer
Answer: c [Reason:] The transmission lines having length more than 80 Km and less than 200 Km are considered as medium transmission lines.Their operating voltage is more than short transmission lines but less than long transmission lines.
2. Which of the following is correct operating voltage range for medium transmission lines.
a) More than 765 KV
b) More than 400 KV
c) More than 20 KV
d) More than 132 KV
Answer
Answer: c [Reason:] Transmission lines having length more than 80 Km and less than 200 Km, operating voltage between 20 KV and 100 KV fall in the category of medium transmission lines.
3. What is the value of the charging current flowing to earth in medium transmission line.
a) Very high
b) Medium
c) Negligible
d) No capacitance
Answer
Answer: b [Reason:] Owing to appreciable length and voltage of the line the charging current is appreciable in medium transmission lines. Also the capacitance effect cannot be ignored in medium transmission lines.
4. Performance of short transmission lines depends on which of the following?
a) Resistance and Capacitance
b) Resistance and Inductance
c) Inductance and Capacitance
d) Resistance, Inductance and Capacitance
Answer
Answer: d [Reason:] Medium transmission lines have enough value of resistance and inductance. Length and operating voltage of the medium transmission lines are sufficiently large to cause unavoidable charging current and therefore capacitance effect can not be ignored. Hence, performance of Medium transmission lines depends on R, L and C.
5. Performance analysis of medium transmission line is done ________
a) By reactance diagram
b) By symmetrical component analysis method
c) By neglecting line inductance
d) On per phase basis
Answer
Answer: d [Reason:] Performance analysis of balance transmission line is done only. And is done on per phase basis. No symmetrical component method or reactance diagram method is required for performance analysis.
6. What is the value of shunt capacitance of medium transmission line?
a) Very high
b) Medium
c) Zero
d) Negligable
Answer
Answer: b [Reason:] Length and operating voltage of the medium transmission lines are sufficiently large to cause unavoidable charging current and therefore capacitance effect can not be ignored. Capacitance effect in medium transmission line is less than that in long transmission line.
7. In medium transmission line the reciving end voltage may be greater than sending end voltage due to Ferranti effect.
a) True
b) False
Answer
Answer: a [Reason:] Ferranti effect happens when capacitance effect in medium or long transmission lines becomes greater than inductance effect. This happens during low or no load period.
8. Series inductance and series resistance of medium transmission lines are taken as:
a) Distributed and Lumped
b) Lumped and Distributed
c) Distributed
d) Lumped
Answer
Answer: d [Reason:] The series inductance and resistance of medium transmission lines are taken as lumped. This makes the performance analysis easier.
9. Which of the following is like equivalent circuit of medium transmission line?
a) Series RLC circuit
b) RLC circuit in pie form
c) Series RL circuit
d) Parallel RL circuit
Answer
Answer: b [Reason:] Medium transmission lines have considerable amount of inductance, resistance and shunt capacitance. Medium transmission lines are represented as either pie form or as T form.
10. In medium transmission lines shunt capacitances are considered as lumped.
a) true
b) false
Answer
Answer: a [Reason:] In case of medium transmission lines the charging current is unavoidable but less than that in long transmission lines. So it does not cause much error in calculations if shunt capacitances are taken as lumped.
Power Systems MCQ Set 5
1. Which of the following power plant are put on load for maximum time?
a) Plant with minimum operating cost
b) Plant with medium operating cost
c) Plant with maximum operating cost
d) Operating cost does not matter
Answer
Answer: a [Reason:] The power plants with minimum operating cost are put on load for maximum time. Plants with medium operating cost are only loaded when required by the load demand on the system. Plants with maximum operating cost are kept in reserve and would operate only in emergency.
2. Which of the following power plants can be profitably employed for supplying base loads as well as peak loads?
a) Thermal power plant
b) Nuclear power plant
c) Hydroelectric power plant
d) Diesel power plant
Answer
Answer: c [Reason:] Seam and Nuclear power plants are only used to supply base load. Diesel power plants are suitable for only peak load. Only hydroelectric power plant can supply both peak load as well as base load because of its flexibility in operation and low operating cost.
3. Plants with higher operating cost and greater flexibility are suitable for?
a) Only Base load
b) Only Peak load
c) Base and Peak loads
d) Plants with higher operating cost are not used
Answer
Answer: b [Reason:] Plants which can meet sudden variation of load demand are said to have higher flexibility. Plants with higher operating cost can’t be used as base load plants. Plants with such capabilities are most suitable for peak load plants as they can respond immediately.
4. Plants with maximum operating costs are put on load for :
a) Maximum time
b) During peak load
c) Emergency conditions
d) During Medium loads
Answer
Answer: c [Reason:] Power plants with minimum operating cost are put on load for maximum time. Plants with medium operating cost are only loaded when required by the load demand on the system. Plants with maximum operating cost are kept in reserve and would operate only in emergency.
5. Gas turbine power plants are most suitable for which of the following loads?
a) Only Base load
b) Only Peak load
c) Base and Peak loads
d) Gas turbine power plants are not practical
Answer
Answer: b [Reason:] Gas turbine power plants have advantage of low initial cost and low startup time. So, it is ideally suited for supplying peak loads.
6. A power system will have greater flexibility of operation if they have ____
a) Various types of power plants operating in combination
b) Only Base load plants operating in combination
c) Only Peak load plants operating in combination
d) Only thermal power plants operating in combination
Answer
Answer: a [Reason:] If various types of power plants are operated in combination, the system will become more flexible i.e Steam and Nuclear power plants will supply base loads, Hydroelectric power plants will supply base or peak loads depending upon the availability of water, Gas turbine power plant will meet peak load demand and existing Diesel power plant will operate in emergency only.
7. Which of the following system is more reliable?
a) Hydroelectric power plant
b) Steam power plant
c) Combined operating steam and hydroelectric power plant
d) Diesel power plant
Answer
Answer: c [Reason:] The reliability of steam power plant depends upon the coal supply, that of hydroelectric power plant on stream flow. Due to greater diversity a combine operation of various types of power plant would be more reliable than individual steam or hydro power plant.
8. In combined operation of several power plants the reserve capacity requirement is reduced.
a) True
b) False
Answer
Answer: a [Reason:] In any electric power system the system has to have a certain reserve capacity in order to meet any unforeseen excess power demand. In combined system the effect of all the diversity is may result in still larger benefit from the point of view of Reserve capacity.
9. Thermal power plants are not suitable for supplying base peak loads.
a) True
b) False
Answer
Answer: a [Reason:] To operate as peak load plant, a power plant must be able to meet sudden variation of load. The major drawback of a steam power plant is that it requires appreciable time to start up, synchronize and take up load. Hence thermal power plant is not suitable to work as peak load plant.
10. Read the following statements:
I. Diesel power plant is generally used as base load plant.
II. Gas turbine power plant is used as peak load plant.
a) Only I is correct
b) Only II is correct
c) I and II are correct
d) I and II are wrong
Answer
Answer: b [Reason:] To supply base load the operation cost should be minimum, but Diesel power plant has very high operating cost. Diesel power plants are best suitable to supply peak loads. Gas turbine can be started in less time and so it is suitable to supply peak loads.
