Basics of Power Systems: 2 Marks Important Questions with Answers

Basic Electronics and Electrical Engineering

CHAPTER 7: BASICS OF POWER SYSTEMS

 

2 Marks Important Questions with Answers

 

1. Mention the location of the HVDC transmission.

The locations of the HVDC transmission are Chandigarh, Delhi, Patiala and Faridabad.

 

2. What is primary transmission?

The electric power at generating station is stepped up to 132kV (to reduce the transmission loss) and transmitted by three phase, three wire overhead system to the outskirts of the city. This forms the primary transmission.

 

3. What is secondary transmission?

The primary transmission line continues via transmission towers till the receiving stations. At the receiving stations, the voltage level is reduced to 22kV or 33kV using the step down transformer. There can be more than one receiving stations. Then at reduced voltage level of 22kV or 33kV, the power is transmitted to various substations using overhead three phase three wire system. This is secondary transmission. The conductors used for the secondary transmission are called feeders.

 

4. Write the advantages of A.C transmission.

The advantages of A.C transmission are:

(i) It can be generate power at very high voltages,

(ii) The maintenance of A.C. substation is easy and cheaper.

(iii) A.C. voltage can be stepped up or stepped down with the help of Transformer.
(iv) Construction is simple.

(v) Fault can be detected very easily.

(vi) There is no converter device required.

 

5. Write the disadvantages of A.C transmission.

The disadvantages of A.C transmission are:

(i) More copper is required than D.C.

(ii) Construction is complicated than D.C.

(iii) Presence of skin effect to increase the effective resistance of the line.

(iv). In A.C system due to the presence of capacitance there is continuous loss of power due to charging current even when the line is open.

 

6. Mention the limitations of high transmission voltage.

The limitations of high transmission voltage are:

• The cost of insulating the conductor is very high.

• Cost of transformer, switch gear and other terminal apparatus are very high.

 

7. List the various systems of power transmission in D.C. system.

The various systems of power transmission in D.C. system are:

(i) D.C. two wire system

(ii) D.C. two wire with midpoint earthed.

(iii) D.C. three wire.

Single phase A.C. system

(i) Single phase two wire

(ii) Single phase two wire with midpoint earthed

(iii) Single phase three wire.

Two phase A.C. system

(i) Two phase four

(ii) Two phase three wire

Three phase A.C. system

(i) Three phase three wire (Transmission system)

(ii) Three phase four wire (Distribution system)

 

8. What is a feeder?

Feeder is defined as lines, which connect the distribution station and distributor.

 

9. What is a distributor?

Distributor is defined as a common bus bar, which connect the service main and feeder.

 

10. Distinguish between over head system and underground system.

Over head system

1. Construction cost is less.

2. To occupy the more spaces in metropolitan area.

3. It is operated above 66KV.

4. Fault can be easily detected and rectified.

5. Maintenance cost is high.

Underground system

1. Construction cost is high.

2. To enhance the city beauty

3. It is limits upto 66KV.

4. Fault cannot be easily detected.

5. Maintenance cost is very less.

 

11. List the components of a power system.

The components of a power system are:

• Generating station

• Step up transformer

• Step down transformer

• Transmission line

• Switching station

• Primary distribution line

• Secondary distribution line

• Feeder

• Distributor and

• Consumer

 

12. How distribution systems are classified?

Distribution systems are classified by,

• Nature of current

• Type of construction

• Scheme of connection

• D.C distribution.

 

13. What is a service main?

Service main is defined as a small cable or conductor which connects the distributor to the domestic terminal.

 

14. What is a distribution substation?

Distribution substation is a primary distribution system that delivers power to various substations.

 

15. Give the types of loading in distribution system.

The types of loading in distribution system are:

• Uniform loading

• Concentrated loading

• Combination of uniform loading and

• Concentrated loading.

 

16. What is meant by Electrical power system?

The flow of electrical power from the generating station to the consumer is called as an electrical power system

 

17. Define one line diagram.

One line diagram is defined as the way in which all electrical apparatus represented by single line in symbolic form.

 

18. Which system is adopted for transmission of electric power?

A.C system is suitable for transmission of electric power due to the technical difficulties of D.C system. There is possibility of saving the copper conductor.

 

19. What is neutral grounding?

Connecting the neutral or star point of any electrical equipment (generator, transformer etc) to earth.

 

20. Define coefficient of earthing.

(highest rms voltage of healthy line to earth)/(line to line rms voltage) * 100 to the power frequency

 

21. Mention 2 disadvantages of ungrounded neutral

(i) Occurance of insulation breakdown leading to the heavy phase to phase fault condition.

(ii) System cannot be protected from earth fault.

(iii) Voltages due to lightning surges do not find path to earth.

 

22. Name the various types of grounding.

(i) solid grounding

(ii) resistance grounding

(iii) reactance grounding

(iv) resonant grounding

 

23. Define screening coefficient.

Screening coefficient for 'n' electrodes in parallel is = (resistance of one electrode) / (resistance of n electrodes in parallel * n)

 

24. What is a substation?

The assembly of apparatus used to change some characteristic (eg: voltage, A.C to D.C frequency power factor etc) of electric supply is called a substation. ‒ frequency changer substation‒converting substations‒industrial substation.

 

25. Give the conditions of laying out a substation.

The conditions for laying out a substation are:

• It should be located at a proper site.

• It should provide safe and reliable arrangement.

• It should be easily operated and maintained.

• It should involve minimum capital cost.

 

26. Mention the classification of substation according to service.

According to service, substations are classified as,

(i) Transformer substations

(ii) Switching substations

(iii) Power factor correction substations

(iv) Frequency changer substations

(v) Converting substations

(vi) Industrial substations

 

27. List the classification of transformer substations.

Transformer substations are classified as,

(i) Step‒up substation

(ii) Primary grid substation

(iii) Secondary substation

(iv) Distribution substation

 

28. Define busbar

Busbar is defined as a conductor to which a number of circuits are connected.

 

29. What is neutral grounding (or) neutral earthing?

The neutral point of star connected three phase winding of power transformers, generators, motors, earthing transformers are connected to low resistance ground. Such a connection is called neutral grounding (or) neutral earthing.

 

30. State the advantages of neutral grounding.

The advantages of neutral grounding are:

(i) Arcing grounds are reduced or eliminated

(ii) The life of insulation is long

(iii) Reduced maintenance, repairs and breakdowns

(iv) Stable neutral point

(v) Improved service reliability

(vi) Greater safety

 

31. Define earth resistance.

Earth resistance is defined as the resistance of the earthing electrode to the real earth and is expressed in ohms.

Where,

Earth resistance ER = V/I

V ‒ Voltage between the electrode and the voltage spike

I ‒ Injected current

 

32. What are the devices that are used for transferring D.C. power at the substation by using converting machinery?

The devices that are used for transferring D.C. power at the substation by using converting machinery are:

(i) Mercury arc rectifier

(ii) Rotary converters and

(iii) Motor generator set

 

33. What is an interconnector?

The interconnector or inter connected network is a common development of simple ring system to reduce the power loss and voltage drop.

 

34. What is an interconnected system?

Interconnected system is a system in which the feeder ring is energized by two or more than two generating stations or substations.

 

35. Write the methods of earthing.

The methods of earthing are:

• Pipe earthing

• Plate earthing

 

36. Classify the connection schemes.

Classification of connection schemes are:

• Radial system

• Ring main system

• Interconnected system

 

37. Give the materials mainly used in busbar?

The materials that are mainly used in busbar are:

(i) Copper

(ii) Aluminium