UNIT I

INTRODUCTION

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, switchgear 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 wire

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.

S.No Over head system Underground system

1 Construction cost is less. Construction cost is high.

2 To occupy the more spaces in metropolitan area. To enhance the city beauty

3 It is operated above 66KV. It is limits upto 66KV.

4 Fault can be easily detected and rectified. Fault cannot be easily detected.

5 Maintenance cost is high. 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.

UNIT-II

TRANSMISSION LINE PARAMETERS

1. What are the line parameters in transmission line?

(i) Resistance

(ii) Inductance

(iii) Capacitance

2. What are the factors to be considered while designing the transmission line? (i) Type and size of a conductors

(ii) Line regulation and control of voltage

(iii) Efficiency of transmission

(iv) Corona loss

(v) Power flow capability

3. What are the types of aluminium conductor? (i) AAC- All Aluminium Conductor

(ii) AAAC - All Aluminium Alloy Conductor

(iii) ACSR - Aluminium Conductor with Steel Reinforcement

(iv) ACAR - Aluminium Conductor with Alloy Reinforcement

4. What are the advantages of ACSR conductor? (i) They have low corona loss

(ii) Skin effect is to reduced extent

(iii) Due to high mechanical strength the line span can be increased. This is

minimize cost of erection and maintenance.

5. Define inductance? The flux linkage per ampere is called the inductance.

L = / I

6. What is mean by skin effect? When a conductor is carrying steady direct current this current is uniformly distributed

over the whole cross section of the conductor. An alternating current flowing through does

not distribute uniformly rather it has the tendency to concentrate near the surface of the

conductor. This is known as skin effect.

7. What are the advantages of aluminium conductor? (i) They have low cost

(ii) Less resistance and corona loss

(iii) Less weight

8. What are the steps for reducing telephone interference? (i) The harmonics at the source can be reduced with the use of AC harmonic

filters, DC harmonic filters and smoothening reactors.

(ii) Use greater spacing between power and telephone lines.

(iii) The parallel run between telephone line and power line is avoided.

(iv) If the telephone circuit is ground return then replace it with metallic return.

9. What are factors influencing the telephone interference? (i) Because of harmonics in power circuit their frequency range and magnitudes.

(ii) Electromagnetic coupling between power and telephone conductor.

(iii) Due to unbalance in power circuits and in telephone circuits.

(iv) Type of return telephone circuit i.e. either metallic or ground return.

(v) Screening effect.

10. What is mean by telephone interference? The distortion effect and potential rise effect are disturbance which is produced in the

telephone communication because of power lines is called telephone interference.

11. Write down the comparison between single circuit and double circuit.

Sl.No Single circuit Double circuit

1. This type of arrangement is less

dangerous during repair work.

This type of arrangement is

comparatively dangerous.

2. From continuity of supply point of

view, the circuit is less reliable

With reference to continuity of

supply, the circuit is much reliable

3. It requires lesser foundation and less

weight of steel tower member

It requires more foundation as the

structure is of heavier. The height of

tower is more

4. The spacing of conductors required is

greater

The spacing of conductors required is

lesser.

12. Write down the depending factors of electrostatic effects. The electrostatic effect mainly depends on what is the distance between power and

communication circuits and length of the route over which they are parallel.

13. What is mean by proximity effect? The current distribution may be non uniform because of another effect known as

proximity effect. Consider two wire line as shown in fig, let each of the conductor is assumed

to be divided into three sections having equal cross sectional area. Three parallel loops are

formed by the pairs xx , yy and zz . The flux linking loop xx is least and it increases for the

remaining loops. Thus the inductance of inner loop is less. Thus the current density is highest

at inner edges of conductor.

14. Write down the depending factors for skin effect. (i) Nature of the material

(ii) Diameter of the wire

(iii) Frequency of supply

(iv) Shape of wire

15. What are the advantages of bundled conductor? (i) low radio interference and corona loss

(ii) reduced voltage gradient at conductor surface

(iii) increase in capacitance

(iv) low reactance due to increase in self GMD

(v) increase in surge impedance loading

16. What is mean by standard conductor? The standard conductor usually has a central wire which is surrounded by the layers of

wires. These layers consists of 6, 12, 18, .wires successively. Thus the total strands are 7,

13, 19,. This type of conductor is called stranded conductor.

17. What is mean by bundled conductor? The conductors of any one bundle are in parallel and charge per bundle is assumed to

divide equally between the conductors of bundle. The composite or stranded conductors

touch each other while the bundled conductors are away from each other. This type of

conductor is called bundled conductor.

18. What is mean by resistance? It is defined as the opposition offered by the transmission line conductors to the flow of

current.

19. What is mean by symmetrical spacing? Consider three conductors A, B and C. if the three conductors are placed symmetrically at

the corners of an equilateral triangle of sides. Then it is called symmetrical spacing.

20. What is mean by unsymmetrical spacing? When three phase line conductors are not equidistance from each other the conductor

spacing is said to be unsymmetrical spacing.

21. What is transposition of conductors?

The transposition is defined as interchanging of position of the line conductors at regular

intervals along the line so that each conductor occupies the original position of every other

conductor over at equal distance. Such an exchange of positions is known as transposition

UNIT III

MODELLING AND PERFORMANCE OF TRANSMISSION LINES

1. Write down the classification of overhead transmission line Short transmission line

Medium transmission line

Long transmission line

2.What is mean by Short transmission line?

If the transmission line length is about 50 km and the line voltage is low i.e. is 20kv or

less than that the line is treated as short transmission line.

3. What is mean by medium transmission line?

When the transmission line length is about 50 to 150 km and the line voltage is 20kv to

100kv than that the line is treated as short transmission line.

4. What is mean by long transmission line? When the transmission line length is about 150 km and the line voltage is Above 100kv than

that the line is treated as short transmission line.

5. What are the types of medium transmission line? End condenser method

Nominal T method

Nominal method 6. Define voltage regulation.

The difference in voltage at the receiving end of the transmission line at the no load and

full load is termed as voltage regulation expressed in terms of percentage of receiving end

voltage

% voltage regulation = (Vnoload Vfull load / Vfull load ) X100

7. Define transmission efficiency. The ratio of power obtained at the receiving end to the power at sending end is called

transmission efficiency of the line.

8. What is mean by Surge impedance? In the power system network the characteristic impedance is sometimes referred as surge

impedance. It is defined as square root of Z/Y.

Where,

Z = series impedance of line

Y = Shunt admittance of line.

9. What is mean by Surge impedance loading? The surge impedance loading of a line is the power delivered by a line to a purely

resistive load equal to its surge impedance. The line is assumed to have no resistance.

10. What is mean by Ferranti effect? At no load condition in transmission line the voltage at receiving and is more than that

sending end because of the effect of the line capacitance. This is called Ferranti effect.

11. Write down the line compensation using in transmission line. Series compensation

Shunt compensation

12. What are the advantages of series compensation?

Increase in power transmission capacity of line

Improvements in system stability

Improved voltage regulation

Load division between parallel circuits

Damping effect

12. What are the disadvantages of series compensation? Reduce the reactance of line and increase the fault currant level

It gives high torsional stresses

It will increasing the hunting

The series capacitor may cause faculty operation of distance relays of the line

protection if the degree of compensation and location of capacitor is not

proper.

13. Write down the various factors on which transmission line capability. Thermal limits of conductor

Transient and steady state stability

Transmission line capability depends on over voltage at the capacitor terminals of

series compensated line.

14. Write down the effect of shunt compensation. It reduces the line current losses owing to generation of reactive power.

It reduces the transmission line current to a value less than the current in the load

It improves the power factor of the transmitted power

It reduces the voltage drop uniformly along the length of the line

15. Write down the advantages of shunt compensation. The kw of alternators, transformers and lines are increased.

The line current is reduced

The losses in power transformer and cables are reduced which saves the energy

It prevents overloading of transformers and switchgears

Improved voltage is obtained at the receiving end

16. Write down the disadvantages of shunt compensation. The only disadvantage with shunt capacitor is that the response to voltage dips is not as

rapid as with series capacitor since the switching of the bank is initiated by change in voltage.

17. Write down the comparison between series and shunt capacitors. The rise in voltage due to a shunt capacitor is uniformly distributed along the length of

the transmission whereas in case of series capacitors the rise in voltage in sudden where

the capacitor is installed.

For the same rise in voltage the reactive power capacity of a shunt capacitor is greater

than that of a series capacitor

The power factor is improved because of a shunt capacitor while the power factor is

little effected by series capacitor

The series capacitors are found to be more effective for improving the system stability

18. What is mean by corona effect? It can be noticed that near the overhead lines there exists a hissing noise and sometimes a

faint violet glow. The effect due to which such phenomenon exists surrounding the overhead

lines is called corona effect.

19. What is mean by corona power loss? The ions produced in the air due to corona are moving. The energy required to keep them

moving is derived from the supply system. This additional power required which is dissipated in

the form of heat, sound and light in case of corona, is called corona loss.

20. What are the factors affecting corona and corona loss? Electrical factors

Line voltages

Size of the conductor

Surface conditions

Spacing between conductors

21. What are the advantages of corona? Due to corona the air surrounding the conductor is ionized and becomes conducting.

This increasing the virtual diameter of the corona

Corona reduces the effect produced by the surges and conductor is saved from

possibilities of lightning

22. What are the advantages of corona loss? The corona power loss is the biggest disadvantage which reduce the transmission

efficiency

The third harmonic components produced due to corona makes the current

nonsinusoidal. This increases the corona loss

The ozone gas formed due to corona chemically reacts with the conductor and can cause

corrosion

23. Write down the methods to reducing corona effect Increasing the conductor size

Increasing the conductor spacing

Using hollow and bundled conductors

24. Define radio interference. The corona discharge produces the radiations which may introduce noise signals in the

communication lines, carrier signal, radio and television receivers, navigation signals etc.. such

noise signals which adversely affect the wireless signals, produced by corona is called radio

interference.

25. How is corona loss related with the diameter of the conductor?

Corona loss related with the diameter of the conductor by the following Way,

Corona loss=r/d

Where,

d - Diameter of the conductor.

Hence lower the diameter of the conductor, higher is the loss.

26. What is local corona?

The corona does not start simultaneously on the whole surface, but it takes place at

different points of the conductor which are pointed is known as local corona.

UNIT IV

INSULATORS AND CABLES

1. What are the properties of insulators? (i) High mechanical strength.

(ii) High electrical resistance

(iii) High relative permittivity

(iv) High ratio of puncture strength

(v) The insulator material should be non porous

2. What are the types of insulators? (i) Pin type insulators

(ii) Suspension insulators

(iii) Strain insulators

(iv) Shackle insulators

(v) Stay insulators

3. What are the advantages of suspension type insulator? (i) Suspension type insulators are cheaper than pin type insulators

(ii) Each unit or disc of suspension type insulator is designed for low voltage

(iii) If any one disc is damaged the hole string does not affected

(iv) Greater flexibility the line

4. Define string efficiency? The ratio of voltage across the whole string to the product of number of discs and the

voltage across the disc nearest to the conductor is known as string efficiency.

5. What are the methods of improving string efficiency? (i) By using longer cross arms

(ii) By grading the insulators

(iii) By using a guard ring

6. What is mean by insulators? The insulators provide necessary insulation between line conductors and supports and

thus prevent any leakage current from conductors to earth.

7. What are the materials using in insulators? (i) Porcelain

(ii) Glass

(iii) Synthetic resin

8. What is mean by annealing? The glass also can be used instead of porcelain. The glass is made tough by heat

treatment which is called annealing.

9. What are the advantages of glass insulators (i) As transparent cracks bubbles and defects in the insulator can be easily

detected by inspection

(ii) The dielectric strength is very high

(iii) Cheaper than the porcelain

(iv) The resistivity is very high

10. What are the disadvantages of glass insulators? (i) Chances of moisture condensation on the surface are higher so leakage current

is high

(ii) Less stronger than the porcelain

(iii) High tension system

(iv) Cannot be moulded in irregular shape.

11. What are the advantages of synthetic resin? (i) High tensile strength

(ii) The weight is low

(iii) Cost is low

12. What is mean by self or mutual capacitance? The porcelain portion which is an insulator is in between the two metal fittings. Thus it

forms a capacitor. This is called self or mutual capacitance.

13. What is mean by shunt capacitance? In transmission line towers in addition to the self capacitance there will be capacitance

between each metal fittings and the earth. i.e. tower the air act as a insulating medium such a

capacitance is called shunt capacitance.

14. What are the advantages of suspension insulators? (i) The voltage distribution is not uniform

(ii) The charging currents through various mutual capacitors are varied

(iii) Voltage across bottom insulator is high

(iv) Electrical stress is high

15. What is mean by guard ring? The transmission line tower a large metal ring surrounding the line unit and connected to

the metal part of the bottom of the line unit is used. Such a ring is called guard ring.

16. What are the requirements of the cables?

(i) The size of the conductor used must be such that it should carry the specified

load without overheating and keeping the voltage drop well within the

permissible limits

(ii) At the voltage level for which cables are designed the insulation thickness

must be proper so as to provide high degree of safety and the reliability

(iii) The materials used in the manufacturing of the cables must be such that there

is complete chemical and physical stability throughout.

17. Write down the various parts of cables. (i) Core

(ii) Insulation

(iii) Metallic sheath

(iv) Bedding

(v) Armouring

(vi) Serving

18. What are the types of cables? (i) Low tension cable

(ii) High tension cable

(i) belted cable

(ii) super tension cable

(iii) extra tension cable

19. What are the advantages of separate lead sheath cables? (i) Due to individual lead sheath core to core fault possibility gets minimized

(ii) The electrical stress are radial in nature

(iii) Bedding of cable is easy

(iv) Increases the current carrying capacity

20. What are the types of super tension cable? (i) Oil filled cables

(ii) Gas pressure cables

21. What are the advantages of oil filled cables? (i) Thickness of insulation is less

(ii) The thermal resistance is less

(iii) The possibility of voids is completely eliminated

(iv) Reduced earth fault

22. What are the disadvantages of oil filled cables? (i) The initial cost is very high

(ii) The long length is not possible

(iii) The laying of cable is difficult

(iv) Maintenance of cable is difficult

23. What are the advantages of gas pressure cables? (i) Maintenance cost is small

(ii) The nitrogen in the steel tube helps in quenching any fire or flame

(iii) No reservoirs or tanks required

(iv) The power factor is improved

24. What is mean by grading of cables? The process of obtaining uniform distribution of stress in the insulation of cables is called

grading of cables.

25. What is mean by capacitance grading? The grading done by using the layers of dielectrics having different permittivity between

the core and the sheath is called capacitance grading

26. What are the types of suspension type insulator? (i) Cemented cap type

(ii) Hewlett or inter linking type

27. What are the methods used to secure insulator to the bolt? (i) The porcelain insulator has cement threads which are lined with a soft

material like lead. The pin is screwed into such cement screw

(ii) Solid lead screw is casted on the head of the pin and is screwed directly into

the porcelain

28. What are the properties of insulating materials? (i) It should be flexible

(ii) To avoid electrical breakdown

(iii) It should be non-inflammable

(iv) It should have high temperature

(v) To prevent leakage current

29. What are the main insulating materials used? (i) Poly vinyl chloride (PVC)

(ii) Paper

(iii) Cross linked polythene

(iv) Vulcanized India rubber

30. What are disadvantages of gas pressure cable? The only disadvantage of this cable is very high initial cost

UNIT-5

SUBSTATION, GROUNDING SYSTEM AND DISTRIBUTION SYSTEM

1. What is substation?

Substation is the assembly of apparatus used to change some characteristics of electric

supply.

2. 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.

3. Mention the classification of substation according to service.

According to service, substations are classified as,

Transformer substations

Switching substations

Power factor correction substations

Frequency changer substations

Converting substations

Industrial substations

4. List the classification of transformer substations.

Transformer substations are classified as,

Step-up substation

Primary grid substation

Secondary substation

Distribution substation

5. Define busbar.

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

6. Give the materials mainly used in busbar?

The materials that are mainly used in busbar are:

Copper

Aluminium

7. What are the factors to be considered for busbar design?

The factors to be considered for busbar design are:

Material

Cross section of conductors

Temperature rise

Distance between phase conductors

Enclosure design

8. Which tests are necessary on station busbars?

The tests conducted on station busbars are:

Temperature rise test

Rated short time current test

Rated momentary current test

High voltage test

9. 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.

10. State the advantages of neutral grounding.

The advantages of neutral grounding are:

Arcing grounds are reduced or eliminated

The life of insulation is long

Reduced maintenance, repairs and breakdowns

Stable neutral point

Improved service reliability

Greater safety

11. Define earth resistance.

Earth resistance is defined as the resistance of the earthing electrode to the real earth and

is expressed in ohms.

Earth resistance ER = V/I

Where,

V Voltage between the electrode and the voltage spike

I Injected current

12. 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:

Mercury arc rectifier

Rotary converters and

Motor generator set

13. 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.

14. 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.

14. Write the methods of earthing.

The methods of earthing are:

Pipe earthing

Plate earthing

16. Classify the connection schemes.

Classification of connection schemes are:

Radial system

Ring main system

Interconnected system

17. List the disadvantages of D.C. three wire distribution system.

Disadvantages of D.C. three wire distribution system are:

i. Three wires are required

ii. A balancer is required and as such the cost is increased

iii. The safety is partially reduced

18. Write the advantages of radial system.

The advantages of radial system are

i. The initial cost is low

ii. Useful when the generation is at low voltage.

iii. Preferred when the station is located at the centre of the load.

Subject : EE2303 -Transmission & Distribution

UNIT-I INTRODUCTION

PART-A

1. What is meant by power supply system?

2. What is meant by Transmission and Distribution system?

3. What are the different types of Power supply system?

4. What are the various components of power supply system?

5. What are the different types of power plants?

6. What are the different operating voltages used for generation, primary and secondary

transmission in AC power supply systems in India?

7. Define feeder, distributor and service mains.

8. List the advantages of high voltage transmission.

9. Define Break-even distance.

10. List the disadvantages of DC transmission.

11. List the different types of DC links.

12. What is meant by STATCOM

13. What are the advantages & limitations of high voltage transmission?

14. List the various types of distribution systems.

15. List the different types of distribution systems based on connection

16. What are the different components of a distribution system?

17. What is meant by stringing chart

18. What are the limitations of HVDC system?

19. List the two merits of HVDC system

20. List the HVDC systems present and which are in operation in India.

21. List the applications of HVDC system.

22. List the advantages of EHVAC transmission system.

23. What is the need of load dispatch centres? Where are the LDC's available inTamil Nadu?

24. List out objectives of FACTS.

25.What factors affect sag in transmission line.

26. Name any two FACTS controller devices.

27. What is the highest AC transmission voltage we have in India?

PART-B

1. (i) Discuss various types of HVDC links. Mention any one HVDC link available in India with

rating.

(ii) List out the main components of a HVDC system.

2. (i) Draw and explain the structure of modern power systems with typical voltage levels.

(ii) What is the highest voltage level available in India?

3. (i). Explain the effect of high voltage on volume of copper and on efficiency.

(ii) Explain why the transmission lines are 3 phase 3-wire circuits while distribution lines are 3

phase 4-wire circuits.

4. (i) Draw the model power system with single line representation. Show its essential

constituent sections.

(ii) What are the AC transmission and distribution level voltages we have in India?

(iii) What are the different kinds of DC links? Draw relevant diagrams.

5. (i) Explain why EHV transmission is preferred? What are the problems involved in EHV AC

transmission?

(ii) With neat schematic, explain the principle of HVDC system operation.

6. Explain about FACTS and its controllers with neat diagram

7. (i) Compare EHVAC and HVDC transmission.

(ii) Explain the applications of HVDC transmission System.

8. Explain TCSC and SVC systems .

9. Explain with neat diagram about STATCOM and UPFC.

10. A transmission line conductor at a river crossing is supported from two towers at a height of

50 and 80 meters above water level. The horizontal distance between towers is 300m. If tension

in conductor is 200kg, find clearance between conductor and water at a point midway between

towers. Weight of conductor/meter = 0.844kg. Derive formula used.

11. An overhead line has a span of 336m. The line is supported at a water crossing from two

towers whose heights are 33.6m and 29m above water level. The weight of conductor is 8.33N/m

and tension in the conductor is not to exceed 3.34*104N.Find 1)Clearance between lowest point

on conductor and water 2) Horizontal distance of this point from lower support.

12. Explain the principle of operation of compensators used for voltage control. (6)

13. What are the advantages of high transmission voltage for the transmission of electric power ?

Explain. (8)

14. A 50km long transmission line supplies a load of 5MVA at 0.8pf lagging at 33kV.The

efficiency of transmission line is 90%. Calculate the volume of Al conductor required for the line

when 3 phase 3 wire system is used. The specific resistance of Al is 2.85*10-8 m.

15.Derive an expression for sag calculation in a transmission line

(i) When the supports are at equal heights (8)

(ii) When the supports are at unequal heights (8)

Assume shape of overhead line is a parabola.

UNIT- II

TRANSMISSION LINE PARAMETERS

PART-A

1. Define Skin effect. On what factors does the skin effect depend.

2. What is meant by proximity effect?

3. Differentiate the stranded conductor and bundled conductor.

4. List out the advantages of double circuit lines.

5. Define - Self and mutual G.M.D.

6. What is meant by inductive interference?

7. What is transposition of conductors?

8. What is ACSR conductor?

9. What is fictitious conductor radius?

10. Define unsymmetrical and symmetrical spacing.

11. State why transposition of line conductors are needed?

12. List the advantages of bundled conductors.

13. What are the factors that affect the skin effect?

14. Why the effective resistance is more than the static resistance of a transmission line?

15. Why does a transmission lines have resistance, inductance, and capacitance?

16. List the factors that governing the capacitance of a transmission line.

17. State the advantages of double circuit line over single circuit line.

18. What do you understand by inductive interference?

19. What is corona? State its advantages & disadvantages.

20. Define critical disruptive voltage.

21. What are the factors which affect corona?

22. Define transmission efficiency.

PART-B

1. From the fundamentals derive an expression for inductance of a single phase transmission

system.

2. Derive an expression for capacitances of a single phase transmission system and discuss the

effect of earth on capacitance with suitable equation.

3. Derive an expression for inductance

i) Of a single-phase overhead line.

ii) A conductor is composed of seven identical copper strands each having a radius r. Find

the self-GMD of the conductor.

4. i) Derive an expression for the capacitance between conductors of a single phase overhead

line.

ii) Find the capacitance between the conductors of a single-phase 10 km long line. The

diameter of each conductor is 1.213 cm. The spacing between conductors is 1.25 m. Also find

the capacitance of each conductor neutral.

5. i) Derive the expression for inductance of a two wire 1 transmission line. ii) Derive the expression for capacitance of a 1 transmission line. 6. (i) What are the advantages of bundled conductors?

(ii) Derive the expression for capacitance of a double circuit line for hexagonal spacing.

(iii) Why is the concept of self GMD is not applicable for capacitance?

7. (i) Explain clearly the skin effect and the proximity effects when referred to overhead lines.

ii) Write a short note on the inductive interference between power and communication lines.

8. i) Derive the expression for the capacitance per phase of the 3 phase double circuit line flat

vertical spacing with transposition.

ii) A 3 overhead transmission line has its conductors arranged at the corners of an equilateral triangle of 2 m side. Calculate the capacitance of each line conductor per km. Given

the diameter of each conductor is 1.25 cm.

9. Find the capacitance per km per phase of a 3 line arrangement in a horizontal plane spaced 8 metres apart. The height of all conductors above the earth is 13 metres. The diameter of each

conductor is 2.6 cm. The line is completely transposed and takes the effect of ground into

account.

10. Discuss the concept of GMR and GMD in the calculation of transmission line inductance.

11.i) Derive the expression for the voltage induced in communication lines due to current in

power lines. (8)

ii) Explain the various factors affecting corona loss and methods of minimizing those (8)

12. Derive the expression for inductance of a 3 phase line with Unsymmetrical & symmetrical

spacing.

13. A 220KV, 50Hz, 200Km long three phase line has its conductors on the corners of a triangle

with sides 6m,6m and 12m. The conductor radius is 1.81cm. Find the capacitance per phase per

km, capacitive reactance per phase, charging current and total charging Mega volt amperes.

14. Derive the equation of capacitance of a 3 phase unsymmetrically spaced & symmetrically

spaced overhead lines.

15. Calculate the loop inductance per km of a single phase line comprising of 2 parallel

conductors 1m apart and 1 cm in diameter, when the material of the conductor is

i) Copper ii) Steel of relative permittivity 50

16. Calculate the capacitance of a 100km long 3 phase,50 Hz overhead transmission line

consisting of 3 conductors each of diameter 2 cm and spaced 2.5m at the corners of an equilateral

triangle.

UNIT-III

MODELLING AND PERFORMANCE OF TRANSMISSION LINES

PART-A

1. Classify overhead transmission lines.

2. Define transmission efficiency.

3. List out the methods of representation of medium transmission lines.

4. What is Ferranti effect?

5. Define regulation of power transmission line.

6. What is the use of power circle diagram?

7. What is meant by the receiving end power circle diagram?

8. What is the cause of Ferranti effect?

9. What is the use of power circle diagram?

10. What are the causes of voltage drop and line loss in a transmission line?

11. What are the advantages of using series compensation?

12. What are the factors which govern the performance of a transmission line?

13. What is shunt compensation?

14. Distinguish attenuation and phase constant.

15. Define surge impedance

16. Draw the phasor representation of short transmission line.

17. For controlling reactive power what adjustment should be done in transformer present in

the system.

PART-B

1. Determine the efficiency and regulation of a 3phase, 100 Km, 50 Hz transmission line

delivering 20 MW at a power factor of 0.8 lagging and 66 kV to a balanced load. The conductors

are of copper, each having resistance 0.1 / Km, 1.5 cm outside dia, spaced equilaterally 2 meters between centres.Use nominal T method.

2. A three phase 5 km long transmission line, having resistance of 0.5 / km and inductance of 1.76 mH / km is delivering power at 0.8 pf lagging. The receiving end voltage is 32kV. If the

supply end voltage is 33 kV, 50 Hz, find line current, regulation and efficiency of the

transmission line.

3. Derive the expressions for sending end voltage in nominal T method and end Condenser

method.

4. i) What is an equivalent circuit of long line? Derive expression for parameters of this circuit

in terms of line parameters.

ii) A 50Hz transmission line 300 km long total series impedance of 40 + j25 and total shunt admittance of 10-3 mho. The 220 KV with 0.8 lagging powerfactor. Find the sending end

voltage, current, power and power factor using nominal method.

5. i) Define regulation of a transmission line and derive the approximate expression for the

regulation of a short transmission line.

ii) What is corona loss? How do you determine this loss?

6. A 220 kV, 3 transmission line has an impedance per phase of (40 + j200) and an admittance of (0 + j0.0015) mho. Determine the sending end voltage and sending end current

when the receiving end current is 200 A at 0.95 pf lagging. Use nominal T method.

7. Determine the efficiency and regulation of a three phase 200 km, 50 Hz transmission line

delivering 100 MW at a pf of 0.8 lagging and 33 kV to a balanced load. The conductors are of

copper, each having resistance 0.1 / km, and 1.5 cm outside diameter, spaced equilaterally 2 m between Centers. Neglect leakage reactance and use nominal T and methods. 8. i) Explain the Ferranti effect with a phasor diagram and its causes.

ii) Explain the classification of lines based on their length of transmission.

iii) What are ABCD constants.

9. A 3 phase line having an impedance of (5+j20) per phase delivers a load of 30MW at a power factor of 0.8 lag and voltage of 33 kV. Determine the capacity of the phase modifier to be

installed at the receiving end if the voltage at the sending end is to be maintained at 33kV.

Assume the shunt admittance is neglected.

10. Write short notes on

i) Shunt compensation ii) Series compensation

11. A 3 phase, 50Hz, 150 km line has a resistance, inductive reactance and capacitive shunt

admittance of 0.1, 0.5 and 3*10-6 mho per km per phase. If the line delivers 50MW at 110kV and 0.8pf lagging. Determine the sending end voltage and current. Assume nominal circuit for the line.

12. A 15 km long 3 phase overhead line delivers 5 MW at 11kV at 0.8 lagging pf line loss is

12% of power delivers. Line inductance is 1.1mH per km per phase. Find the sending end

voltage and regulation.

13.i) Explain surge impedance loading with respect to an overhead transmission line .

ii) Explain the end condenser method for medium transmission lines.

14. The A,B,C,D constants of a 3 phase transmission line are A=D=0.936+j0.016,

B=33.5+j138, C=(-0.9280+j901.223)*10-6 mho. The load at the receiving end is 40MW at 220kV with power factor of 0.86 lagging. Find the magnitude of the sending end voltage,

current, power, line efficiency and voltage regulation. Assume the magnitude of the sending end

voltage remains constant.

15. Deduce an expression for the sending end and receiving end power of a line in terms of

voltage and ABCD constants. Show that the real power transferred is dependent on the power

angle and reactive power transferred is dependent on the voltage drop in the line.

UNIT-IV

INSULATORS AND CABLES

PART-A

1. What is the purpose of insulator?

2. What is the main purpose of armouring?

3. What is meant by efficiency of an insulator string?

4. List out various types of insulators used for overhead transmission lines.

5. Mention the advantages of the pin type insulator

6. What are the main causes for failure of insulators?

7. What are the different tests that are conducted on an insulator?

8. Define string efficiency and what are the methods for improving string efficiency?

9. Write short notes on puncture test.

10. Define impulse ratio.

11. State advantage of polymeric insulators over porcelain insulators.

12. What are the routine tests conducted on insulators?

13. What are the performance tests conducted on insulators?

14. What are the merits of under ground cables?

15. How are cables classified based on operating voltage.

16. What is the main purpose of bedding?

17. What are the common materials used for insulation?

18. What is the main purpose of armouring?

19. What is serving?

20. What is dielectric stress?

21. What is grading of cables and give the methods of grading.

22. What are the main advantages of suspension type insulators over pin type ones?

23. Why the potential distribution across the string units of insulator is not uniform.

24. Name the two methods of locating cable faults.

25. State two types of faults in a cable.

26. Show that insulation resistance of cable is inversely proportional to its length.

27. What are the advantages of string insulators?

28. Why loss angle of cable should be very small?

PART-B

1. Discuss any two methods to increase the value of string efficiency, with suitable sketches.

2. Explain any two methods of grading of cables with necessary diagrams.

3. i) What are different methods to improve string efficiency of an insulator?

ii) In a 3-unit insulator, the joint to tower capacitance is 20 % of the capacitance of each unit.

By how much should the capacitance of the lowest unit be increased to get a string efficiency of

90 %. The remaining two units are left unchanged.

4. i) Derive the expression for insulator resistance, capacitance and electric stress in a single core

cable. Where is the stress maximum and minimum?

ii) A single core 66 kV cable working on 3-phase system has a conductor diameter of 2cm and

sheath of inside diameter 5.3 cm. If two inner sheaths are introduced in such a way that the stress

varies between the same maximum and minimum in the three layers find:

a) position of inner sheaths

b) voltage on the linear sheaths

c) maximum and minimum stress

5. i) Draw the schematic diagram of a pin type & suspension type insulator and explain its

function.

ii) A 3 phase overhead transmission line is being supported by three disc insulators. The

potential across top unit (i.e. near the tower) and the middle unit are 8 kV and 11 kV

respectively. Calculate,

a) The ratio of capacitance between pin and earth to the self capacitance of each unit

b) Line Voltage

c) String Efficiency

6. i) Describe with the neat sketch, the construction of a 3 core belted type cable.

ii) A conductor of 1cm diameter passes centrally through porcelain cylinder of internal

diameter 2 cms and external diameter 7 cms. The cylinder is surrounded by a tightly fitting metal

sheath. The permittivity of porcelain is 5 and the peak voltage gradient in air must not exceed 34

kV / cm. Determine the maximum safe working voltage.

7.i) What are the various properties of insulators? Also briefly explain about suspension type

insulators.

ii) Calculate the most economical diameter of a single core cable to be used on 132 kV, 3

phase system. Find also the overall diameter of the insulation, if the peak permissible stress does

not exceed 60 kV / cm. also derive the formula used here.

8. i) Briefly explain about various types of cables used in underground system.

ii) A string of 4 insulator units has a self capacitance equal to 4 times the pin to earth

capacitance. Calculate,

a) Voltage distribution as a % of total voltage

b) String efficiency

9. i) Give any six properties of a good insulator.

ii) With a neat diagram, explain the strain and stay insulators.

iii) A cable is graded with three dielectrics of permittivities 4,3 and 2. The maximum

permissible potential gradient for all dielectrics is same and equal to 30 kV/cm. The core

diameter is 1.5cm and sheath diameter is 5.5 cm. Determine the working voltage.

10. Explain the constructional features of various types of cables

11. i) Compare and contrast overhead lines and underground cables.

ii)List out the properties of insulating materials used for cables

12. An insulator string consist of three units, insulator nearest to the line having a safe working

voltage of 20kV. The ratio of self to shunt capacitance is 6:1. Determine the line voltage and

string efficiency.

UNIT-V

SUBSTATION GROUNDING SYSTEM AND DISTRIBUTION SYSTEM

PART-A

1. What is substation?

2. What are the classifications of substation according to service?

3. What are the types of transformer substations?

4. What are the factors to be considered for busbar design?

5. What is neutral grounding or neutral earthing?

6. What are the equipments used in a transformer substation?

7. What are the different types of bus bar arrangements in substations?

8. What is bus bar and what are its components?

9. What are the materials mainly used in busbars?

10. What are the factors to be considered for busbar design?

11. Which tests are necessary on station busbars?

12. What is neutral grounding or neutral earthing?

13. What is equipment grounding?

14. What are the advantages of neutral grounding?

15. What is earth resistance?

16. What are the devices used for DC power at the substation by using converting

machinery?

17. Define distribution substation.

18. Define service mains?

19. What are the types of nature of current in distribution system?

20. What is interconnected system.

21. State the advantage of ring main distributor.

22. Give the disadvantage of single bus scheme.

23. State the role of circuit breaker in power system.

24. Define the term feeders and service mains.

25. What are the various methods of earthing in substations?

26. Why are transmission lines 3 phase 3 wire circuits while distribution lines are 3 phase 4

wire circuits?

27. Give the difference between disconnector switch and isolator.

28. Give the protective device present in substation.

29. State the advantages of outdoor substation over indoor substation.

30. What are the objectives of earthing?

PART-B

1. With a neat sketch explain double bus with double breaker and double bus with single breaker.

State their advantages and disadvantages.

2. Explain the following:

(i) Neutral grounding

(ii) Resistance grounding.

3. Explain about the various types of substations

4. Write short notes on

i. Sub mains

ii. Stepped and tapered mains

5. Explain the various types of bus bar arrangements in a substation.

6. Write short notes on

i. Busbar arrangement in substation

ii. Grounding grids

7. i) Explain the design principles of substation grounding system.

ii) Explain the equipments in a transformer substation.

8. Draw the circuit arrangement and explain the various elements of the following bus bar

arrangements.

i)Single bus scheme

ii)Double bus bar scheme

iii) Double bus bar with bypass isolators

iv)Main and transfer bus bar

v)Mesh scheme

9. Discuss briefly each of the following

i)Feeders

ii)Radial distribution

iii)Ring main distribution

iv)Interconnected system

10. A DC ring main distributor is fed at A and the load is tapped at points B,C,D. The distributor

length is 400m long and points B,C,D are 50m,250m,375m from A. Loads are 150A,40A,200A

respectively. If resistance/100 m of single conductor is 0.04 and VA = 220V. Calculate i) Current in each distributor ii) Voltage at points B,C,D.

11. Discuss and compare radial and ring main distribution system. What is the role of

interconnectors in distribution system.

12. Discuss the design of primary distribution system with respect to following i) Selection of

voltage ii)Choice of scheme iii)Size of feeders