Transmission & Distribution MCQS

1. The minimum clearance distance that equipment should be kept away from 50 kV power lines is:

A. 20 feet
B. 10 feet
C. 15 feet
D. 5 feet

Answer: B. 10 feet

Explanation:
The minimum clearance distance that equipment should be kept away from power lines of different voltage levels is shown in the below table.

Voltage VS Minimum clearance distance (feet)

• Up to 50 kV---10
• 50 to 200 kV---15
• 200 to 350 kV---20
• 350 to 500 kV---25
• 500 to 750 kV---35
• 750 to 1000 kV---45
• Over 1000 kV----50

Mcqs On Minimum clearance of Transmission Line 

1. The minimum clearance distance that equipment should be kept away from 50 kV to 200kV power lines is:

A. 20 feet
B. 10 feet
C. 15 feet
D. 5 feet

Answer: C. 15 feet

2. The minimum clearance distance that equipment should be kept away from 200 kV to 350kV power lines is:

A. 20 feet
B. 10 feet
C. 15 feet
D. 5 feet

Answer: A. 20 feet

3. The minimum clearance distance that equipment should be kept away from 350 kV to 500kV power lines is:

A. 20 feet
B. 25 feet
C. 15 feet
D. 35 feet

Answer: B. 25 feet

4. The minimum clearance distance that equipment should be kept away from 500 kV to 750kV power lines is:

A. 20 feet
B. 25 feet
C. 15 feet
D. 35 feet

Answer: D. 35 feet

5. The minimum clearance distance that equipment should be kept away from 750 kV to 1000kV power lines is:

A. 20 feet
B. 25 feet
C. 45 feet
D. 35 feet

Answer: C. 45 feet

6. The minimum clearance distance that equipment should be kept away from 1000kV or above power lines is:

A. 50 feet
B. 25 feet
C. 45 feet
D. 35 feet

Answer: A. 50 feet

2. The loads on 3 phase 4 wire distributors are usually:-

A. Balanced

B. Unbalanced

C. Either of the above

D. None of the above

Answer: B. Unbalanced

Explanation:

1-phase 2-wire: 

• In this, one of the two wires is earthed or the mid-point of phase winding is earthed.
• This system is used for very short distances

1-phase 3-wire: 

• This system is identical in principle to the 3-wire dc distribution system.
• The neutral wire is center-tapped from the secondary winding of the transformer and earthed.
• This system is also called a split-phase electricity distribution system

 

2-phase 3-wire: 

• In this system, the neutral wire is taken from the junction of two-phase windings whose voltages are in quadrature with each other.
• The voltage between the neutral wire and either of the outer phase wires is V whereas, the voltage between outer phase wires is √2V. 
• As compared to a two-phase 4-wire system, this system suffers from voltage imbalance due to unsymmetrical voltage in the neutral

3-phase 4-wire: 

• This system uses star-connected phase windings and the fourth wire or neutral wire is taken from the star point.
• If the voltage of each winding is V, then the line-to-line voltage (line voltage) is √3V and the line-to-neutral voltage (phase voltage) is V. 
• This type of distribution system is widely used in India for secondary distribution.
• Loads on 3 phase 4 wire distributors are usually unbalanced.

3. As per the Indian Electricity rule in overhead systems, the recommended span in the case of wooden poles is ______.

A. 100-300 meters

B. 40-50 meters

C. 50-80 meters

D. 80-100 meters

Answer: B. 40-50 meters

Explanation:

Indian electricity rules:

• All-electric supply lines and apparatus shall be sufficient in power and size of sufficient mechanical strength for the work they may be required to do, and, so far as is shall be constructed, installed, protected, worked, and maintained under the standards of the Indian Standards Institution to prevent danger.
• For carrying the overhead line, wooden poles, concrete poles, steel poles, and rail electric poles are used.
• Which poles are to be used, depends on the importance of load, location, and place, the cost-effectiveness of such construction, including maintenance cost, keeping its profit element in mind.

Wooden poles:

• In the earlier period, wooden poles are used for 400 volts and 230 volts L.T. line and 11.K.V.H.T. line in a massive way.
• In some cases wooden poles are used for33 kV line.
• The cost-effectiveness of a wooden pole is much less in comparison to other electric poles and the expenditure incurred for its foundation is also comparatively very less.
• If proper maintenance and treatment are done on the wood, the wooden pole is lost for a long period.
• The recommended span in the case of wooden poles is 40 – 50 meters.
• The breakdown force is between 450 kg / cm2 and / above 850 kg / cm2.

Note:

Span: Span means the horizontal distance between two adjacent supporting points of an overhead conductor.

As per the Indian Electricity rule in overhead systems, the recommended span of various support poles is given below

Line-support VS  Recommended span

Wooden pole----40-50 meters

RCC pole-----80 - 100 meters

Steel pole-----50 to 80 meters

Steel tower-----300 meters or above

Mcqs On Line Supports 

1. As per the Indian Electricity rule in overhead systems, the recommended span in the case of RCC poles is

A. 100-300 meters

B. 40-50 meters

C. 50-80 meters

D. 80-100 meters

Answer: D. 80-100 meters

2. As per the Indian Electricity rule in overhead systems, the recommended span in the case of Steel Pole poles is

A. 100-300 meters

B. 40-50 meters

C. 50-80 meters

D. 80-100 meters

Answer: C. 50-80 meters

3. As per the Indian Electricity rule in overhead systems, the recommended span in the case of Steel Tower poles is

A. 300 meters or Above 

B. 40-50 meters

C. 50-80 meters

D. 80-100 meters

Answer: A. 300 meters or Above 

4. Neautral Earthing has the advantage(s) of 

A. Elimination of arcing Grounds 

B. Low maintenance and operating costs over isolated neautral systems.

C. Simplified Design of earth fault protection 

D. Dichrging Of Overvoltages Due to lighting to earth 

E. All of the Above 

Answer: E. All of the Above 

Explanation:

What is Neutral Grounding or Earthing?

The process of connecting neutral point of 3-phase system to earth (i.e. soil) either directly or through some circuit element (e.g. resistance, reactance etc.) is called neutral grounding. 

Neutral grounding provides protection to personal and equipment. It is because during earth fault, the current path is completed through the earthed neutral and the protective devices (e.g. a fuse etc.) operate to isolate the faulty conductor from the rest of the system.

ADVANTAGES OF NEUTRAL GROUNDING

• Voltages of the healthy phases do not exceed line to ground voltages i.e. they remain nearly constant.
• The high voltages due to arcing grounds are eliminated.
• The protective relays can be used to provide protection against earth faults. In case earth fault occurs on any line, the protective relay will operate to isolate the faulty line.
• The over-voltages due to lightning are discharged to earth.
• It provides greater safety to personnel and equipment.
• It provides improved service reliability.
• Operating and maintenance expenditures are reduced.

Note: It is interesting to mention here that ungrounded neutral has the following advantages:

• In case of earth fault on one line, the two healthy phases will continue to supply load for a short period.
• Interference with communication lines is reduced because of the absence of zero sequence currents.

5. Resistance Earthing is employed for voltages between 

A. 3.3 to 11kv 

B. 2.2 to 33 kv

C. 33 to 66kv 

D. 66 to 132 kv 

Answer: A. B. 2.2 to 33 kv

Explanation:

What is Resistance Earthing?

• The resistance offered by the earth electrode to the flow of current into the ground is known as the earth resistance or resistance to earth. 
• The earth resistance mainly implies the resistance between the electrode and the point of zero potential. Numerically, it is equal to the ratio of the potential of the earth electrode to the current dissipated by it. 
• The resistance between the earthing plate and the ground is measured by the potential fall method.
• In order to limit the magnitude of earth fault current, it is a common practice to connect the neutral point of a 3-phase system to earth through a resistor. This is called resistance grounding.

Advantages:

The following are the advantages of resistance earthing:

• The earth fault current is small due to the presence of earthing resistance. Therefore, interference with communication circuits is reduced.
• It improves the stability of the system.

Disadvantages:

• The following are the disadvantages of resistance grounding :
• Since the system neutral is displaced during earth faults, the equipment has to be insulated for higher voltages.
• This system is costlier than the solidly grounded system.
• A large amount of energy is produced in the earthing resistance during earth faults. Sometimes it becomes difficult to dissipate this energy to the atmosphere.

Applications:

It is used on a system operating at voltages between 2.2 kV and 33 kV with power source capacity of more than 5000 kVA.

6. Solid Earthing is employed for voltages 

A. Upto 11kv 

B. Upto 33 kv

C. Upto 66kv 

D. Upto 132 kv 

Answer: B. Upto 33 kv

Explanation:

What is Solid Earthing?

When the neutral point of a 3-phase system (e.g. 3- phase generator, 3-phase transformer etc.) is directly connected to earth (i.e. soil) through a wire of negligible resistance and reactance, it is called solid grounding or effective grounding.

Advantages

• The solid grounding of neutral point has the following advantages:
• The neutral is effectively held at earth potential.
• no arcing ground phenomenon or over-voltage conditions can occur.
• there is a saving in the cost of equipment.
• It becomes easier to protect the system from earth faults which frequently occur on the system. When there is an earth fault on any phase of the system, large fault current flows between the fault point and the grounded neutral. This permits the easy operation of earth fault relay.

Disadvantages

• The following are the disadvantages of solid grounding :
• Since most of the faults on an overhead system are phase to earth faults, the system has to bear a large number of severe shocks. This causes the system to become unstable.
• The solid grounding results in heavy earth fault currents. Since the fault has to be cleared by the circuit breakers, the heavy earth fault currents may cause the burning of circuit breaker contacts.
• The increased earth fault current results in greater interference in the neighboring communication lines.

Applications

• Solid grounding is usually employed where the circuit impedance is sufficiently high so as to keep the earth fault current within safe limits. 
• This system of grounding is used for voltages up to 33 kV with total power capacity not exceeding 5000 kVA.

7. Series capacitors are used to

A. compensate for line inductive reactance and improve the stability of the power system

B. improve the voltage

C. reduce the fault level

D. improve the power factor

Answer: A. compensate for line inductive reactance and improve the stability of the power system

Explanation:

Series capacitors: 

• Series capacitors are used to compensate the inductance of the transmission line. 
• They will increase the transmission capacity and the stability of the line. 
• These are also used to share the load between parallel lines.
• Series capacitor is used in a transmission line to compensate the voltage Drop.
• In series compensation, the FACTS is connected in series with the power system. 
• It works as a controllable voltage source. 
• Series inductance occurs in long transmission lines, and when a large current flows this causes a large voltage drop. 
• To compensate, series capacitors are connected, decreasing the effect of the inductance.

Shunt capacitors: 

• Whenever an inductive load is connected to the transmission line, power factor lags because of lagging load current. 
• To compensate this, a shunt capacitor is connected which draws current leading the source voltage. 
• The power factor can be improved.
• Shunt capacitors in an EHV line is used to improve fault level and voltage profile. 
• This method is used to improve the power factor. 
• Whenever an inductive load is connected to the transmission line, power factor lags because of lagging load current. 
• To compensate, a shunt capacitor is connected which draws current leading the source voltage. 
• The net result is an improvement in the power factor.

Shunt inductive compensation:

• This method is used either when charging the transmission line, or, when there is very low load at the receiving end. 
• Due to very low, or no load – very low current flows through the transmission line. 
• Shunt capacitance in the transmission line causes voltage amplification (Ferranti Effect). 
• The receiving end voltage may become double the sending end voltage (generally in case of very long transmission lines). 
• To compensate, shunt inductors are connected across the transmission line.

Mcqs on Shunt and Series Capacitors

1. Capacitors are used in the power systems to 

A. improve supply power factor 

B. improve voltage regulations 

C. change the load characteristics

D. all of the above 

Answer: B. improve voltage regulations 

2. No-load compensation in a line requires

A. Shunt capacitors 

B. Shunt reactors 

C. Series capacitors

D. None of these

Answer: B. Shunt reactors 

3. Full load compensation in a line requires

A. Shunt capacitors

B. Series capacitors 

C. Transformers

D. Shunt reactors

Answer: A. Shunt capacitors

4. Use of additional shunt capacitor can be made for increasing the capability of line as it 

A. Reduces surge impedance 

B. increase phase shift

C. Increase in Alpha

D. all of above 

Ans: A. Reduces surge impedance 

5. To increase the transmission capability of a high voltage long line 

A. The resistance can be increased 

B. The resistance can be decreased 

C. The Series Reactance can be reduced

D. Shunt admittance can be reduced 

Answer: C. The Series Reactance can be reduced

6. Power dispatch through a line can be increased by 

A. Installing series capacitors 

B. Installing shunt capacitors 

C. Installing series reactor 

D. Installing Shunt reactor 

Answer: A. Installing series capacitors 

8. Series capacitors on transmission lines are of little use when 

A. the load VAR requirement is small

B. the load VAR requirement is large 

C. the load VAR requirement is fluctuating

D. series capacitors are never used in the transmission lines

Answer: A. the load VAR requirement is small

Series reactors: 

• Series reactors are used as current limiting reactors to increase the impedance of a system. 
• They are also used to limit the starting currents of synchronous electric motors and to compensate reactive power in order to improve the transmission capacity of power lines.
• Fault current is inversely proportional to the reactance of the network. 
• Therefore with the series reactor, the fault current magnitude is reduced. 
• It is preferred in the generating stations in some special applications for limiting the current flowing through the low MVA rating circuit breakers.
• series reactor limits the high current.
• the series reactor uses a current limiter and increases the impedance of the circuit.
• It is used to filter high-frequency signals. 
• It is also used as fault current limiter just like NGR.

Shunt reactors

• A shunt reactor is an absorber of reactive power, thus increasing the energy efficiency of the system.
• Shunt reactor limits the overvoltage.
• Shunt reactor uses as reactive power absorber.
• it is used to compensate the undesirable voltage due to line capacitance (Ferranti effect). 
• The sending end voltage is higher than the receiving end voltage. The shunt reactor reduces the voltage when the receiving end voltage is higher than the sending end voltage. 
• Therefore, it increases the energy efficiency of the power system. 
• It is the most compact device commonly used for reactive power compensation in long high-voltage transmission lines and in cable systems.
• They are very costlier than series reactors.

Mcqs On Shunt and Series Reactor

1. For good Voltage profile under no-load condition, a long line needs

A. shunt capacitors at receiving End 

B. Shunt reactors at the receiving End 

C. Shunt resistance at the receiving End

D. None of these 

Answer:B. Shunt reactors at the receiving End 

8. In an ac Distribution System the Voltage can be controlled by using 

A. tap changing transformer 

B. Booster transformer 

C. Induction Regulator 

D. Any of the above 

Answer:D. Any of the above 

Explanation: 

Tap Changing Transformer 

• The purpose of a tap changer is to regulate the output voltage of a transformer by altering the number of turns in one winding and thereby changing the turns ratio of the transformer. 
• Tap changing Transformers are employed for both stepping up and stepping down the voltage.

Mcqs On Tap Changing Transformer 

1. Tap changing Transformer are Employed For 

A. Stepping Down the Voltage 

B. Stepping Up the Voltage 

C. Supplying low voltage current to instrument 

D. Both Stepping Up and Stepping down the voltage 

Answer: D. Both Stepping Up and Stepping down the voltage 

Booster Transformer

• Booster transformer is one which is often used towards the end of a power line to raise the voltage to the desired value. 
• It is used for controlling the voltage of a feeder at a point far away from the main transformer.
• Booster transformers are used to eliminate the stray currents and the disturbances, obliging the return current to flow to the return conductor.
• Booster transformer is used in railways for eliminating the flow of stray current. The stray current disturbs the communication system and also damage the electronic devices of the trains passing through them.
• They are used to maintain uniform voltage along the line that have distributed load, the voltage drops due to serial resistance is compensated periodically with a booster transformer, otherwise the voltage given to first users will go too high and last users too low.
• Booster is low voltage high current series wound DC generator inserted into a DC circuits to add or inject a certain voltage proportional to the circuit current. The main purpose of providing booster in power system is to compensate the voltage drop of feeder.
• Booster add voltage to the feeder and compensate the voltage drop. Hence it increase the efficiency and reliability of the system. 
• That is why it is one of the important device of power system.
• A booster transformer is used towards the end of a power line to raise the voltage to the desired value. It is used for controlling the voltage of a feeder at a point far away from the main transformer.
• The secondary of the booster transformer is connected in series with the line, and its primary is supplied from the secondary of the regulating transformer.
• Booster transformer is used in railways for eliminating the flow of stray current. The stray current disturbs the communication system and also damage the electronic devices of the trains passing through them.

Mcqs On Booster Transformer 

1. The best location for use of a booster transformer in a transmission line is 

A. at the sending End 

B. At the Receiving End 

C. At the intermediate point 

D. anywhere in the line 

Answer: C. At the intermediate point 

2. Booster transformers is used to:

A. To change the voltage magnitude and phase angle

B. Reduce the voltage magnitude

C. Increase the voltage magnitude

D. To change the voltage phase angle

Answer: C. Increase the voltage magnitude

Induction Regulator:

• An induction regulator is an alternating current electrical machine, somewhat similar to an induction motor, which can provide a continuously variable output voltage. 
• The induction regulator was an early device used to control the voltage of power system networks, mainly used in primary distribution.

9. A synchronous compensator absorbs inductive reactive power. It is

A. overexcited

B. normally excited

C. under excited

D. none of these

Answer: C. under excited

Explanation: 

synchronous compensator:

• If it is under the excited condition, it draws the lagging current and, therefore, supplies capacitive or absorbs inductive volt-ampere reactive. 
• Thus, a current drawn by a synchronous capacitor or condenser can be varied from lagging to leading smoothly by varying its excitation.
• Synchronous Condensor is also known as Synchronous Compensator or Synchronous Phase Modifier. 
• A synchronous condenser or a synchronous compensator is a synchronous motor running without a mechanical load.
• It can generate or absorb reactive volt-ampere (VAr) by varying the excitation of its field winding. 
• It can be made to take a leading current with over-excitation of its field winding.
• In such a case it delivers inductive or absorbs capacitive volt-ampere reactive. 
• If it is under the excited condition, it draws the lagging current and, therefore, supplies capacitive or absorbs inductive volt-ampere reactive. 
• Thus, a current drawn by a synchronous capacitor or condenser can be varied from lagging to leading smoothly by varying its excitation.
• Synchronous phase modifiers are installed at load end.
• Synchronous phase modifiers do not carry Load.
• Synchronous phase modifiers are nothing but synchronous motors.

Mcqs on Synchronous condenser or Synchronous Phase Modifier

1. A Synchronous condenser is a 

A. Synchronous Generator 

B. Synchronous Motor 

C. Paper Condenser 

D. None of these 

Answer: B. Synchronous Motor 

2. A Synchronous Phase Modifier supplies 

A. both active and reactive power

B. both leading and lagging reactive power

C. inductive reactive power only 

D. none of these 

Answer: B. both leading and lagging reactive power

3. A synchronous phase modifier as compared to the synchronous motor has same rating has 

A. larger shaft diameter and higher speed

B. Smaller shaft diameter and higher speed

C. larger shaft diameter and smaller speed 

D. smaller shaft diameter and smaller speed 

Answer: B. Smaller shaft diameter and higher speed

4. Phase modifier is normally installed in case of

A. short transmission lines 

B. medium length lines 

C. long lines 

D. for any length of lines 

Answer: C. long lines 

5. Which of the following statement is not true ?

A. Synchronous phase modifiers are installed at sending end.

B. Synchronous phase modifiers are installed at load end.

C. Synchronous phase modifiers are nothing but synchronous motor.

D. Synchronous phase modifiers do not carry Load.

Answer: A. Synchronous phase modifiers are installed at sending end.

6. For constant Voltage transmission, the voltage drop along the line is maintained constant by installing 

A. Capacitors 

B. Inductors 

C. Resistors 

D. Synchronous phase modifiers at the receiving End.

Answer: D. Synchronous phase modifiers at the receiving End.