Distribution System - Power System Part - 2

1. Which of the following is used to maintain constant voltage in the feeder circuit?

A. Induction regulator
B. Booster
C. Tap changer
D. Phase advancers

Answer
A. Induction regulator

Explanation:

• Feeder voltage regulators are extensively used to regulate or control the voltage in the feeder circuit
• The voltage regulator is used to maintain the voltage of each feeder separately to maintain a reasonably constant voltage at the point of utilization

Induction regulator:

• The induction voltage regulator is the simplest and most commonly used electrical machine to regulate the voltage in the feeder circuit
• It is a type of electrical machine in which the output voltage may be varied from zero to a certain maximum value
• In an induction type voltage regulator, the primary winding is a high voltage winding which is connected across the circuit to be regulated and low-voltage winding is connected in series with the circuit

Phase advancers:

• Phase advancers a source of reactive power connected either to certain junction points in an electrical network or directly to the load terminals;
• It is used to compensate for the phase shift between voltage and current
• Phase advancers improve the power factor of the electrical network
• Phase advancers also adjust or maintain the voltage in the network, lower the power loss, and increase the carrying capacity of electrical systems
• Phase advancers may be adjustable or nonadjustable
• Adjustable phase advancers make it possible to change the capacitive or inductive characteristics of the reactive power in a network, ensuring that the specified performance is maintained even under changing conditions.

2. The 400 V distribution lines are commonly known as

A. Feeder
B. Service mains
C. Substation
D. Distributors

Answer

D. Distributors

Explanation:

The 400 V distribution lines are commonly known as Distributors.

Feeders are the power lines through which electricity is transmitted in power systems. Feeder transmits power from generating station or substation to the distribution points.

Service mains: The overhead line or U.G cable connecting the supplier's distributing line to the consumer's premises is called service mains or service connection or service line. The service line terminates at the point where the supply conductor enters the consumer meter.

Sub-station: A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions between the generating station and consumer, electric power may flow through several substations at different voltage levels.

Distributors: The distributor is a conductor that distributes electrical power in a particular area. The output from a distribution transformer is carried by a distributor conductor. Tappings are taken from a distributor conductor for power supply to the end consumers. The current through a distributor is not constant as tappings are taken at various places throughout its length.

3. The feeder is designed mainly from the point of view of
A. Its current carrying capacity

B. Voltage drop in it
C. Operating voltage
D. Operating frequency

Answer
A. Its current carrying capacity

Explanation:

• Feeders are the conductors which have a large current carrying capacity
• The feeders connect the substation to the area where power is to be finally distributed to the consumers.
• It feeds to power end distributor
• No tapings are taken from the feeders
• The feeder current always remains constant
• The voltage drop along the feeder is compensated by compounding the generator

Feeder:

• A line or conductor which connects the major substations to the distributor is known as a feeder.
• It feeds the electrical power to the distributor.
• Since no tapping is taken from the feeder, generally it carries the same current through its length.
• The current carrying capacity is the main consideration taken into account while designing a feeder.

4. Factor of safety is the ratio of

A. Permissible stress/Ultimate stress
B. Ultimate stress/Permissible stress
C. Permissible strain/Ultimate strain
D. Ultimate strain/permissible strain

Answer
B. Ultimate stress/Permissible stress

Explanation:

• The factor of safety is defined as the ratio of ultimate to working stress (in case of brittle material).
• The factor of safety may also be defined as the ratio of the resisting force to failure causing force.
• The higher factor of safety means the design is more conservative but at the cost of the economy, a lower factor of safety on other hand increases the risk factor.

5. A DC two-wire distributor system supplies a constant load. What is the saving in copper, if the voltage is doubled with power transmitted remaining the same?

A. 25%
B. 50%
C. 75%
D. 25% increased

Answer

B. 50%

Explanation:

Let L = length of each conductor in metre
σ = current density in A/m2
P = power supplied in watts
A = Area of Conductor

The volume of Cu required for both conductors is
V = 2 × A × L

6. The percentage ratio of copper for 3-wire DC system to 2-wire DC distribution system for same cross-section of neutral wire as outer wire is:

A. 40.5%
B. 40.6%
C. 31.25%
D. 37.5%

Answer
C. 31.25%

Explanation:

The percentage ratio of copper for 3-wire DC system to 2-wire DC distribution system for same cross-section of neutral wire as outer wire is 31.25%.

7. In a radial distribution system, the distributor is

A. From both end
B. From the center
C. From one end
D. At different point

Answer
C. From one end

Explanation:

• This system is used only when the substation is located at the center of the consumers. In this system, different feeders radiate from a substation and feed the distributors at one end.
• Thus, the main characteristic of a radial distribution system is that the power flow is in only one direction.
• The major advantage of a radial distribution system is that it is the simplest system and has the lowest initial cost.

Major drawbacks of a radial distribution system are,

• It is not highly reliable.
• A fault in the feeder will result in supply failure to associated consumers as there won't be any alternative feeder to feed distributors.
• Voltage is affected much at far away from load from the substation.

8. A radial power system is represented by-

A. Closed paths
B. Closed and open paths
C. Only open paths
D. None of the other options

Answer
C. Only open paths

Explanation:

• In radial power distribution system, different feeders radially came out from the substation and connected to the primary of distribution transformer. 
• It is represented by only open paths.
• But radial electrical power distribution system has one major drawback that in case of any feeder failure, the associated consumers would not get any power as there is no alternative path to feed the transformer. In case of transformer failure also, the power supply is interrupted.

9. The main criterion for the design of the distributor is:

A. The voltage drop
B. Corona loss
C. Temperature rise
D. Radio interference

Answer

A. The voltage drop

Explanation:

• The main criteria for the design of a feeder are its current carrying capacity which accounts for thermal limits rather than voltage drops.
• A distributor has variable loading along its length due to the service conditions of tapping by the individual consumers.
• The voltage variation at the consumer end must be kept under ±5%.
• So, the main criterion for the design of a distribution feeder is voltage regulation or voltage drop.
• For alternators and transformers, voltage regulation is not the main criteria of design.

10. Which of the following systems of distribution offers the best economy at high voltages?

A. Direct current system
B. AC single-phase system
C. AC 3 phase 3 wire system
D. AC 3 phase 4 wire system

Answer
A. Direct current system

Explanation:

• The wire required for DC system is lesser than AC distribution systems. So, we can save more copper through DC distribution system at higher voltage distribution.
• Hence direct current distribution system offers the best economy at high voltages.
• High voltage direct current (HVDC) power systems use D.C. for transmission of bulk power over long distances.
• For long-distance power transmission, HVDC lines are less expensive, and losses are less as compared to AC transmission.
• It interconnects the networks that have different frequencies and characteristics.
• HVDC transmission is economical only for long-distance transmission lines having a length of more than 600kms and for underground cables of length more than 50kms.

11. In a transmission system, feeder feeds power to-

A. Distributors
B. Distributors and Generating Stations
C. Generating Station
D. Service Mains

Answer
A. Distributors

Explanation:

• Feeders are the conductors which have a large current carrying capacity
• The feeders connect the substation to the area where power is to be finally distributed to the consumers.
• It feeds to power end distributor
• No tapings are taken from the feeders
• The feeder current always remains constant
• The voltage drop along the feeder is compensated by compounding the generator.

12. Which of the following is connected in series with the feeder?

A. Conductors
B. Distribution Transformer
C. Booster
D. Earth Connection

Answer
C. Booster

Explanation:

• Boosters are basically transformers.
• 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 are connected in Series with the Feeders.

13. Radial system is used when:
A. energy is to be produced on high potential

B. energy is to be produced on low potential
C. substation is far away from load station
D. number of consumers are more

Answer

B. energy is to be produced on the low potential

Explanation:

• This system is used only when the substation is located at the center of the consumers. In this system, different feeders radiate from a substation and feed the distributors at one end.
• Thus, the main characteristic of a radial distribution system is that the power flow is in only one direction.
• The major advantage of a radial distribution system is that it is simplest system and has the lowest initial cost.

Major drawbacks of a radial distribution system are,

• It is not highly reliable.
• A fault in the feeder will result in supply failure to associated consumers as there won't be any alternative feeder to feed distributors.
• Voltage is affected much at far away load from the substation.

14. When a feeder ring distributes energy from two or more than two production plants, then this distribution system is known as:

A. Radial system
B. Ring main system
C. Interconnected system
D. Underground system

Answer
C. Interconnected system

Explanation:

• When a ring main feeder is energized by two or more substations, it is called as an interconnected distribution system. 
• This system ensures reliability in an event of transmission failure. Also, any area fed from one generating station during peak load hours can be fed from the other generating station or substation for meeting power requirements from the increased load.

15. For the stable operation of an interconnected system, which passive element can be used as an interconnecting element?

A. Resistor
B. Relay
C. Capacitor
D. Reactor

Answer

D. Reactor

Explanation:

• For the stable operation of an interconnected system, the passive element that can be used as an interconnecting element is Reactor.
• Under no-load conditions or light load conditions, medium and long transmission lines may operate at the leading power factor due to the capacitance effect.
• So that receiving end voltage becomes greater than sending end voltage.
• In this case, shunt reactors are needed to bring down receiving end voltage at light loads.
• The leading power factor can be changed to a lagging power factor by using a shunt reactor.
• By using a shunt reactor, it will compensate for the effect of capacitance and changes the power factor, and hence maintain the voltage within the limit.

Important Points

• The shunt capacitor bank is used to improve the power factor.
•  A series reactor smoothens the wave shape.
• A Series capacitor reduces the net reactance in a line.
• The shunt inductor reduces the Ferranti effect by limiting overvoltages at the load side under lightly loaded conditions.
• A synchronous condenser is used to improve the power factor.
• Static Var compensator (SVC) is a type of FACTS device, used for shunt compensation to maintain bus voltage magnitude. SVC regulates bus voltage to compensate continuously the change of reactive power loading.