1. What are the transmission system voltages used in India? 33kV, 66 kv For medium high voltage

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1 UNIT I POWER GENERATION Structure of electric power system; Sources of Electric Energy; Load Characteristics and Economic Aspects; Power Plants: Steam, Hydroelectric, Nuclear, Gas, Wind and Solar(Qualitative Treatment Only). TWO MARKS 1. What are the transmission system voltages used in India? 33kV, 66 kv For medium high voltage 132 kv, 220 kv For high voltage 400 kv For extra high voltage 765 kv For Ultra high voltage 2. What are the parts of the transmission system network? i) Transmission system ii) Sub transmission system iii) Primary distribution system iv) Secondary distribution system 3. Define an electric power supply system? The system of generation, transmission and distribution of electrical power is called the electrical power system. 4. What are service mains? Service mains are conductors which connect the consumers terminals to the distributor 5. What is the usable voltage for secondary distribution? V (415 volts for 3-phase loads and 240 volts for 1-phase loads) 6. What are the main technical problems of long distance power transmission using ac? i) Voltage regulation associated with reactive power balance ii) Steady state, transient state and dynamic stability of the system under different load conditions and under outage conditions 7. What are the advantages of hydroelectric power plant? i) Water is the cheapest and reliable source of generation of electric power. ii) No fuel transportation problem. iii) Maintenance problem. iv) No ash disposal problems and no smoke is produced. v) Running cost is low. 8. What is the main purpose of the reservoir? Storage used to retain excess water from periods of high flow and supplies the retained water during low flow is commonly known as reservoir. The storage of water during high flow period (Flood) may also reduce flood damage to the area below the reservoir in addition to conserving water for later use. 9. What is the use of surge tank?

2 The main purpose of providing surge tank is to reduce the distance between the free water space and turbine thereby reducing the water-hammer effect on penstock and also protect upstream tunnel from high pressure rises. It also serves as a supply-tank to the turbine when the water in the pipe is accelerating during increased load conditions and as a storage tank when the water is decelerating during reduced load conditions. 10. What are the disadvantages of hydroelectric power plant? i) The power produced by the plant depends upon quantity of water which in turn is dependent upon the rainfall. ii) iii) Capital cost of the plant is high. The hydroelectric power plants are generally situated away from the load centres. This requires long transmission lines to deliver power. Therefore the cost of transmission lines and losses will be more. iv) It takes long time for the erection. 11. What is the purpose of regeneration? What are its advantages? To preheat the air entering the combustion chamber by means of heat from the exhaust gases of the turbine. Its advantages are: i. The quantity of the fuel supplied is substantially reduced as the temperature of the air entering the combustion chamber is increased. ii. Thermal efficiency and specific output of the open cycle gas iii. turbine power plant are increased by regeneration. 12. What are the advantages of gas turbine plant over steam power plant? i. The handling of ash is a major problem in steam plants which is completely eliminated in open cycle gas turbine plants using gas or liquid as fuel. ii. The cubic capacity of buildings and total weight of the materials required for gas turbine plants is about 50% to 60% of steam plant. iii. Capital cost is less. iv. The site of the steam power plant depends on availability of large cooling water whereas on open cycle gas turbine plant can be located near load centers as no cooling water is required. v. 13. What are the advantages of closed cycle gas turbine over open cycle gas turbine? i. The disadvantage of open cycle gas turbine is the atmospheric back pressure at the turbine exhaust. With close cycle gas turbine plants the back pressure can be increased thus unit rating can be increased. ii. The closed cycle avoids the erosion of the turbine blades due to the contaminated gases and fouling of compressor blades due to the dust. iii. The need for filtration of the incoming air, which is a severe problem in a open cycle plant is completely eliminated. 14. What are the advantages of steam power plant? i) Fuel is cheaper. ii) Less space is required compared with hydroelectric plant.

3 iii) Capital cost is low. iv) It can be located at any place, located near the load centre. v) Response quickly to change in load. 15. What are the disadvantages of steam power plant? i) Maintenance and operating costs are high. ii) Atmosphere is polluted. iii) Large quantity of water is required. iv) Handling of ash is difficult. v) Time required for erection and put into operation is more. 16. What are the advantages of Nuclear power plant? i) The amount of fuel required is very small. ii) There is no problem of transportation and storage. iii) Less space is required. iv) Can be located near the load centre. v) Most economical. 17. What are the disadvantages of Nuclear power plant? i) Capital cost is very high. ii) Erection and commissioning of the plant requires greater technical know-how. iii) The by products are generally radio active and may cause a large amount of radio active pollution. iv) The fuel is expensive and difficult to recover. v) Maintenance costs are high. vi) The disposal of radio active waste is a big problem. 18. What do you meant by chain reaction? Nuclear fission is done by bombarding uranium nuclei with slow moving neutrons. This splits the uranium nuclei with the release of huge amount of energy and emission of neutrons (called fission neutrons).this fission neutrons cause further neutrons. If this process continues, then in a very short time huge amount of energy will be released which may cause explosion. This is known as explosive chain reaction. 19. What are the components of nuclear Reactor? i. Fuel ii. Moderator iii. Reflector iv. Coolant v. Control rods vi. Shielding vii. Reactor vessel 20. Name the components of diesel power plant. The essential components of diesel electric power plants are; i. Engine ii. Air-filter and supercharger. iii. Exhaust system. iv. Fuel system. v. Cooling system. vi. Lubrication System. vii. Starting system. viii. Governing system.

4 21. Name the fuels used in gas turbines. Natural gas,blast furnace gas,producer gas, coal gas and solid fuels distillate oils and residual oils;paraffins used in gas turbine are methane,ethane,propane,octane. 22. Define diversity factor. It is defined as the ratio of sum of individual maximum demands to maximum demand on power station. 23. What is meant by connected load? It is the sum of continuous ratings of all the equipment s connected to supply system 24. Define plant capacity factor. It is defined as the ratio of actual energy produced to the maximum possible energy that could have been produced during a given period. 25. Define plant use factor It is defined as the ratio of kwh generated to the product of plant capacity and the numbers of hours for which the plants was in operation. 26. Mention the different types of load. a.motor devices b. Heatingequipments c. Lighting equipment 27. Define load curve. The curve showing the variation of load on the power station with respect to time is known as a load curve. 28. What is meant by load duration curve? When the load elements of a load curve are arranged in the order of descending magnitudes, the curve thus obtained is called a load duration curve. 29. What is meant by utilization factor? It is defined as the ratio of maximum demand to plant capacity. 30. What is meant by peak load and base load on power station? The unvarying load which occurs almost the whole day on the station is known as the base load. The various peak demands of load over and above the base load of the station is known as peak load. 31. Write down the classification of cost of energy. i. Fixed cost ii. Running cost 32. Write down the objectives of Tariff. i. Cost of operation, supplies, maintenance and losses must be recovered. ii. Cost of capital investment in generation, transmission and distribution equipment must be recovered. iii. Cost of billing, metering, collection and miscellaneous services must be recovered. iv. A satisfactory net return on the capital investment must be ensured. v. It should have a provision of penalty for low power fctors. 33. What ate the classification of tariff?

5 i. Simple tariff ii. Flat rate tariff iii. Block rate tariff iv. Two part tariff v. Maximum demand tariff vi. Power factor tariff vii. Three part tariff 16 Mark QUESTIONS: 1. Draw and explain the line diagram of a typical transmission and distribution scheme. Indicate clearly the voltage levels used at different stage. Structure of power system Mention the voltage level Transmission system I. Primary transmission II. Secondary transmission Distribution system I. Primary distribution II. Secondary distribution 2. A generating station has the following daily load cycle Draw the load curve and find i) Maximum Demand ii) Units generated per day iii)averageloadiv)load factor. Load curve Maximum demand Units generated per day Average load Load factor 3. Draw and explain the Schematic arrangement of steam power plant? Introduction to the steam power plant Schematic block diagram

6 Explain each component Advantage & Disadvantage 4. Explain the factors for selection of site for Nuclear power plant? Introduction to the nuclear power plant Availability of water Disposal of waste Distance from populated area Transportation facilities advantage over other power plant 5. Explain the Schematic arrangement of gas turbine power station along with the neat diagram. Introduction to the steam power plant Schematic block diagram

7 Explain each component Advantage 6. Draw and explain the Schematic arrangement of Hydro Electric power plant? Introduction to the steam power plant Schematic block diagram Explain each component Advantage

8 UNIT II TRANSMISSION LINE PARAMETERS Parameters of single and three phase transmission lines with single and double circuits: Resistance, inductance and capacitance of solid, stranded and bundled conductors:symmetrical and unsymmetrical spacing and transposition; application of self and mutualgmd; skin and proximity effects; interference with neighboring communication circuits. TWO marks 1. Define inductance of a line. It is defined as the loop inductance per unit length of the line.its unit is henrys per meter. 2. Define capacitance of a line. It is defined as shunt capacitance between the two wires per unit line length. Its unit is farads per meter. 3.What is skin effect? The steady current when flowing through the conductor,does not distribute uniformly, rather it has the tendency to concentrate near the surface of the conductor. This phenomenon is called skin effect. 4.Why skin effect is absent in dc system? The steady current when flowing through a conductor distributes itself uniformly over the whole cross section of the conductor.that is why skin effect is absent in dc system. 5.What is the effect of skin effect on the resistance of the line? Due to skin effect the effective area of cross section of the conductor through which current flow is reduced. Hence the resistance of the line is increased when ac current is flowing. 6.On what factors the skin effect depend? Nature of the material, Diameter of the wire, Frequency and shape of the wire. 7.Define symmetrical spacing. In 3 phase system when the line conductors are equidistant from each other then it is called symmetrical spacing. 8.What is the necessity for a double circuit line? To reduce the inductance per phase and to increase the efficiency. 9.Mention the factors governing the inductance of a line. Radius of the conductor and the spacing between the conductors. 10.Define a neutral plane. It is a plane where electric field intensity and potential is zero.

9 11.Define proximity effect. The alternating magnetic flux in a conductor caused by the current flowing in a neighbouring conductor gives rise to a circulating current which cause an apparent increase in the resistance of the conductor.this phenomenon is called as proximity effect. 12.What is the effect of proximity effect? It results in the non uniform distribution of current in the cross section, and the increase of resistance. 13.What is a composite conductor? A conductor which operates at high voltages and composed of 2 or more subconductors and run electrically in parallel are called composite conductors. 14.What is a bundle conductor? It is a conductor made up of 2 or more sub conductors and is used as one phase conductors. 15.Mention the advantages of using bundled conductors. Reduced reactance, reduced voltage gradient, reduced corona loss.reduced interference 16.What is meant by transposition of line conductors? Transposition means changing the positions of the three phases on the line supports twice over the total length of the line.the line conductors in practice,are so transposed that each of the three possible arrangements of conductors exit for one-third of the total length of the line. 17.Define bundled conductors? The use of more than one conductor per phase is called bundled conductors. 18.What is skin effect? The phenomenon of concentration of an ac current near the surface of the conductor is known as skin effect. 19.On what factors does the skin effect depends? The skin effect depends upon the 1, type of the material 2, frequency of the current 3, diameter of conductor& shape of conductor. It increases with the increase of cross-section, permeability and supply frequency. 20.Define voltage regulation. Voltage regulation is defined as the change in voltage at the receiving (or load) end when the full-load is thrown off, the sending-end (or supply) voltage and supply frequency remaining unchanged.. % voltage regulation= ((Vs-Vr)/Vr)*100

10 Where, Vs is the voltage at the sending end Vr is the receiving end voltage. 21.Define transmission efficiency. Efficiency defined as the ratio of power delivered at the receiving end to the power sent from the sending end. 22.Define Ferranti effect. The phenomenon of rise in voltage at the receiving end of the open circuited or lightly loaded line is called the Ferranti effect. 23.What are the units of ABCD (generalised) constants of a transmission line? A and D are dimensionless B is in ohms and C is in Siemens (mhos) 24.Mention the range of surge impedance in underground cables ohms 25.Mention the range of surge impedance in overhead transmission lines ohms 16 Mark QUESTIONS: 1. From the fundamentals derive an expression for inductance of a single phase transmission system. single phase two wire system model flux linkages with A conductor flux linkages with B conductor

11 total flux linkages inductance of conductor A Loop inductance 2. Derive an expression for of a single phase transmission system and discuss the effect of earth on capacitance with suitable equation. Capacitance of single phase two wire system model potential difference between the conductor A and neutral infinite plane is potential difference between the conductor Band neutral infinite plane is capacitances of conductor Effect of earth on capacitance.

12 3. Derive the expression for the capacitance per phase of the 3 Φsingle circuit with symmetrical spacing capacitance of 3 phase single circuit model potential difference between the conductor A and neutral infinite plane is Capacitance of a conductor A with respect to the neutral 4. Find the inductance per km of a double circuit, 3-phase system as in fig. The conductor radius is 2.5 cm. a 4 m c b 6 m 10 m b GMR of c a conductor GMR=0.7788r

13 Equivalent self GMD of onephase is Equivalent mutual GMD is inductance of per phase per metre 5. Calculate the inductance per phase per metre for a three-phase double circuit linewhose phase conductors have a radius of 5.3cm with the horizontal conductorarrangement as shown in fig. GMR of conductor GMR=0.7788r Equivalent self GMD of onephase is Equivalent mutual GMD is inductance of per phase per metre 6. Discuss the concept of GMR and GMD in the calculation of transmission line inductance. Self GMD(D s ) of 3 phase single circuit Double circuit Mutual GMD(D m ) of 3 phase single circuit Double circuit UNIT-III-ANALYSIS OF TRANSMISSION LINES Classification of lines: Short line, medium line and long line; equivalent circuits, attenuation constant, phase constant, surge impedance; transmission efficiency and

14 voltage regulation; real and reactive power flow in lines: Power-angle diagram; surge impedance loading, load ability limits based on thermal loading, angle and voltage stability considerations; shunt and series compensation; Ferranti effect and corona loss -Calculation of sag and tension. TWO MARKS 1. Define transmission efficiency It is defined as the ratio of power delivered at the receiving end to the power at the sending end. Mathematically it is defined as, Efficiency = Power delivered at the receiving end / Power sent from the sending end = Power delivered at the receiving end / (Power delivered at the receiving end+losses) 2. Define the regulation of a transmission line It is defined as the ratio of change in voltage at the receiving end, from no load to full load keeping the sending end voltage and frequency constant, to the full load voltage. Mathematically, percentage regulation is defined as, *100 % regulation = ((No load voltage Full load voltage)/ Full load voltage) 3. Give the length wise classification of the transmission lines i) Short lines (length less than 80 km) ii) Medium lines ( Between 80 km and 200 km) iii) Long lines (More than 200 km) iv) 4. Define characteristic impedance and surge impedance Characteristic impedance is defined as the square root of the ratio of series impedance to shunt impedance, which is a complex quantity. Mathematically, Z C z y r g jl jc r resistance of the transmission line L inductanceof the transmission line g conductance of the transmission line C capacitance of the transmission line If the line is lossless, (r = 0 and g = 0), the characteristic impedance is known as surge impedance. 5. What do you mean by surge impedance loading (or natural loading) of a transmission line?

15 Surge Impedance Loading (SIL) of a line is the power transmitted when a lossless line operating at its nominal voltage, is terminated with a resistance equal to surge impedance of the line. It can be written as, PSIL V Z V Nominal voltage Z 0 Surge impedance What do you mean by Ferranti effect? In long transmission lines and cables, receiving end voltage is greater than sending end voltage during light load operation. This occurs due to high charging current. This effect is known as Ferranti effect. 7. What are the factors restricting the power transfer capability of a transmission line? i) Thermal limit of conductors ii) Voltage drop limit iii) Stability limit 8. What do you mean by compensation of transmission lines? Compensation of transmission lines means, modification of the electrical (not physical) characteristics of transmission line in order to increase its power transfer capacity and satisfying the following fundamental requirements of transmission: i) Major synchronous machines must remain stable in synchronism ii) Voltage must be kept to rated values iii) 9. What are the objectives of compensation of the system? i) To produce a substantially flat voltage profile at all the level of power transmission ii) To improve the stability of the system iii) To meet the economical way for reactive power requirement of the system 10. How the compensation techniques are classified? According to the device control operation, the compensation is classified as, i) Active compensation(control variables are continues and voltage is maintained) ii) Passive compensation(quantities are not continuously controlled) According to the devices used, the compensation is classified as, i) Series compensation ii) Shunt compensation 11. Define Corona It is defined as a self sustained electric discharge in which the field intensified ionization is localized only over a portion of distance between the electrodes (lines). 12. Explain the Phenomenon Corona

16 If the potential difference is increased between two conductors spaced some distance apart in air, at some potential a faint luminous glow of violet color will appear adjacent to the conductor surface with a hissing noise. There is also formation of ozone gas. If the potential is further increased, the intensity of glow and noise will increase. This phenomenon is known as corona, which is due to the ionization of air near power conductor. 13. Define Critical Disruptive voltage It is a voltage at which complete disruption of dielectric occurs. It corresponds to the gradient at the surface of conductors equal to the breakdown strength of air. 14. Define Visual Critical Disruptive voltage At critical disruptive voltage corona occurs, but is not visible because the charged ions in air must receive some finite energy to cause further ionization by collision. When the voltage further increases at some point, the corona becomes visible. This voltage is called visual critical disruptive voltage 15. Define Energy distance The value of potential gradient at which ionization takes place under normal temperature(25 C) and pressure (76 cm of Hg) and without impurities is equal to 30 kv (peak)/ cm or 21.1 kv (rms)/cm and is denoted by g 0. The gradient for critical visual corona is denoted by g v. The distance between g o and g v is called energy distance. 16. Write about corona loss The ionized charges near the conductor surface take energy from the supply system and thus there is a loss of some energy due to corona. This is resistive loss. It is not possible to derive any formula for the exact loss that occurs due to corona. 17. Give the advantage sand disadvantages of corona Advantages of corona i) It works as safety valve in the event of high voltage steep waves due to switching or lightning surges. The energy of these waves is dissipated in air as corona loss. ii) Corona does have several beneficial applications as in Van de Graff generator, electrostatic precipitators, electro printing, electrostatic deposition and ionization counting. Disadvantages of corona i) The main disadvantage of corona is the power loss which occurs. It reduces the efficiency of the lines. This loss is significant in the case of extra/ ultra high voltage (EHV/UHV) lines especially in bad weather conditions. ii) The capacitance of transmission lines increases due to increase in effective diameter of conductors. The ionized air near conductor surface works as a conducting medium. The increase in capacitance results in increased charging current, which reduces the surge impedance loading of the line. iii) Triple frequency corona current induces the triple frequency voltage in the system and these currents and voltages interfere with the communication system.

17 18. List the factors which affects corona Atmospheric factors i) Temperature ii) Pressure iii) Dust and dirt iv) Rain, snow, hail and fog Electrical factors i) Frequency ii) Supply voltage Line configurations i) Conductor configurations ii) Diameter of conductor iii) Profile of conductor iv) Surface condition v) Number of conductor per phase vi) Heating of conductor by load current vii) Conductor spacing 19. What are the effects of corona on line design If a line has a critical disruptive voltage of about 10% above the operating voltage, then it is quite satisfactory even though some corona loss will take place under a foul weather condition. An increase in spacing and diameter of conductors increase the critical disruptive voltage thus reduces the corona loss but it also increases the cost. In properly designed transmission lines, the corona loss is usually insignificant in a fair weather condition 20. What is shunt compensation? Shunt compensation is the use of shunt capacitors and shunt reactors is the line to avoid voltage instability. 21. Mention any two advantages of series compensation improves system stability. are generally self regulatory and requires little or no control equipment 22. Why series compensation is used in long series? to increase transmission capacity to improve system stability. to obtain correct load division between parallel circuits. 23. Mention the components used in series compensation? Series capacitors Spark gap protection Metal oxide resistor (for protection ) Current limiting reactor Bypass switch Control & protection equipment. 24. List the four parameters by which the performance of transmission lines aregoverned. Series resistance Series inductance Series capacitance Series conductance. 25. Explain the term voltage stability. The ability of the system to maintain the voltage level within its acceptable limits is called as voltage stability.

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19 16 Mark QUESTIONS 1. What is an equivalent πcircuit of long line? Derive expression for parameters of this circuit in terms of line parameters. Equivalent circuit phasor Diagram sending end voltage sending end current 2. Define regulation of a transmission line and derive the approximate expression for the regulation of a short transmission line. voltage regulation Equivalent Circuit and Phasor Diagram Sending end voltage Sending end power factor

20 Percentage of transmission efficiency Percentage of voltage regulation 3. Derive the expressions for sending end voltage in nominal T method and endcondensermethod. Equivalent Circuit and Phasor Diagram of end condenser method percentage voltage Transmission efficiency Equivalent Circuit Nominal T method phasor diagram of Nominal T method sending end voltage

21 Sending end current 4. Determine the efficiency and regulation of a 3phase, 100Km, 50 Hztransmission 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 Ω / Km, 1.5 cm outside dia, spaced equilaterally 2 metres between centres. Use nominal T method. total resistance/phase total Reactance/phase phase Impedance/phase Find the voltage regulation total line losses for the three phases transmission efficiency 5. A 50Hz transmission line 300 km long total series impedance of 40+j25 Ωand 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 π method. total resistance/phase total Reactance/phase phase Impedance Sending end voltage Sending end current sending end power factor sending end power 6. Deduce an approximate expression for sag in over head lines when I. Supports are at equal levels

22 II. Supports are at unequal levels. Define sag Supports are at equal levels Sag Supports are at unequal levels Sag

23 UNIT IV- INSULATORS AND CABLES 9 Insulators Types Voltage distribution in insulator string and grading Improvement of string efficiency Underground cables Constructional features of LT and HT cables Capacitance Dielectric stress and grading Thermal characteristics. TWO MARKS 1. What are the characteristics of an ideal insulator? i) There should not be any pores or air spaces ii) There should not be any impurities iii) There should be perfectly homogeneous material iv) Leakage current through insulators should be minimum v) Insulators should be able to withstand over voltage and normal working voltage vi) It should be mechanically strong to bear the conductor load. vii) 2. Write the advantages and disadvantages of glass insulators over the porcelain insulators Advantages i) High dielectric strength ii) Longer life iii) High thermal sock resistant thus reduced damage from the flashover iv) Lower coefficient of thermal expansion v) Greater mechanical strength under the compression but in tension it is same as porcelain vi) Fault can be easily seen from the naked eyes Disadvantages i) Moistures are readily condensed on the surface ii) It is expensive than porcelain iii) Its resistance to continuous mechanical load and temperature changes is poor compared to porcelain and toughened glass 3. Define working voltage, flashover voltage and puncture voltage Working voltage It is the voltage at which an insulator is designed to bear the steady state voltage stress. Flashover voltage It is the voltage at which flashover occurs through air surrounding the insulator Puncture voltage It is the voltage at which the insulator breaks through between conductor and pin. It destroys the insulator. 4. Define safety factor A safety factor is defined relating the flashover and working voltages. Mathematically,

24 Safety factor = Flashover voltage / Working voltage 5. What are the types of insulators used in overhead transmission lines i) Sackle type( V lines) ii) Pin type iii) Suspension type iv) Strain type 6. What are the advantages of suspension type insulators? i) Economical for voltage above 33 kv ii) Each insulator is designed for 11 kv and hence for any operating voltage, a string can be made. iii) Failure of any unit can be replaced without changing the whole string iv) Since it is allowed to swing in the air, mechanical stress at a point of attachment is reduced v) Flexible in extension of voltage rating by adding more units vi) Since the conductors lay below the cross arm, the line outages due to lightening strokes are reduced. 7. Define String efficiency It is a measure of utilization of material in the string. If the number of units in the string is n, the string efficiency is defined as, Stiring efficiency = Voltage across the n strings ( n x Voltage across the unit near to the power conductor) = Spark over voltage of n strings n x spark over voltage of one disc 8. What are the methods to improve the string efficiency? i) Increasing the value of m M= Mutual Capacitance Capacitance between each link pin and the earth ii) iii) iv) Grading of unitsstatic shielding Conducting glazes Conducting glazes 9. What do you mean by capacitance grading Since the current in each unit is different which is not possible to eliminate, voltages across each unit can be equalized using the different capacity units. As the current in the lowest string is highest, the low impedance unit (or high capacitance units) near to the conductor will improve the string efficiency. This shows that if discs are arranged in decreasing order of capacitance from bottom (near to the conductor) to top, the voltage across each unit can be equalized, which improves the string efficiency. This is called capacitance grading or grading of units.

25 10. Where the cables are preferred over the overhead transmission lines? i) Public safety is involved ii) Scenic beauty of a city is important iii) Submarine crossing is there iv) Connections of substations, transformers, etc., are required 11. Write the properties of insulating materials used in cables i) High insulation resistance ii) High dielectric strength iii) Good mechanical properties(elasticity and tenacity) iv) Immunity to chemical attacks over wide range of temperatures v) Non hygroscopic (i.e. free from moisture) vi) Being economical vii) Easy handling, manufacture and installation viii)reasonably long life ix) Sufficiently low thermal resistivity x) Low relative permittivity and less tangent angle when used in ac cables 12. Give various insulating materials used for cable i) Vulcanized rubber ii) Varnished cambric iii) Polyvinyl chloride iv) Impregnated paper i) Polythene 13. What do you mean by grading of cables? Grading means distribution of dielectric material such that the difference between E max and E min is reduced. Thereby a cable of same size can be operated for high voltage or for the same operation voltage, the size can be reduced. 14. What are the grading methods available for a cable? i) Capacitance grading(more than one dielectric materials are used) ii) Intersheath grading( the same dielectric material is used but potentials at certain radius are held constant by using sheaths) 15. What are the difficulties in practical system grading of cables? i) Non availability of varying permittivity of insulating materials ii) Change in the permittivity with time, which changes the distribution of stress that lead to rapture of insulating material at normal working voltage. iii) Damage of Intersheath during laying or due to aging may lead to severe stress iv) Charging current flows through the Intersheath which may damage the cable due to overheating v) There may be resonance problem in Intersheath grading due to inductance of transformer and capacitance of cable vi) Grading may not be economical in low voltage cables 16. Give the reasons of high capacitance in cables than the overhead transmission lines? i) High value of permittivity of insulating materials ii) Distance between the core and the earthed sheath is small iii) Small distances between the cores (phases) itself 17. Differentiate the supply PF and the dielectric PF The dielectric PF, which is different from the supply factor, represents the loss and therefore tried to reduce it, whereas it is tried to increase the PF of supply near to unity.

26 18. Why cables are not used for long distance transmission? Cables are not used for long distance transmissions due to their large charging 19. What is the purpose of insulation in a cable? The insulation or dielectric withstands the service voltage and isolates the conductor with other objects. 20. What is the function of sheath in a cables? The sheath does not allow the moisture to enter and protects the cable from all external influences like chemical or electrochemical attack fire etc. 21. Mention the conductor materials in cables? Copper,Aluminium 22. What is the purpose of stranding of conductors? Stranding increases the resistance of the cable.it has flexibility. 23. Why protective covering is done in cables? To protect the cables from mechanical damage, corrosion and electrolytic action when laid direct in the ground the protective covering is made. 24. Why armouring is not done in single core cables? The presence of magnetic material within the alternating magnetic field of a single core cable produces excessive losses. Hence single core cables are left unarmoured with non-magnetic materials like tin-bronze or silicon-bronze tapes or wires. 25. What is meant by charging current of a cable? The capacitance of a cable determines the charging current. The charging current restricts the use of cables on EHV lines. The current carrying capacity of an a.c cable is also reduced by the charging current. 16 MARK QUESTIONS 1. Discuss any two methods to increase the value of string efficiency, withsuitable sketches. String Efficiency types of string efficiency By using longer cross arms By using a guard ring By grading the insulator longer cross arms- Explanation

27 Guard Ring- Explanation 2. Explain any two methods of grading of cables with necessary diagrams. Define grading of cables methods of grading of cables capacitance grading intersheath grading capacitance grading potential difference between core and earthed sheath is

28 intersheath grading Maximum stress in each layer is same voltage between conductor and earthed lead sheath 3. Derive the expression for insulator resistance, capacitance and electric stress in a single core cable. Where is the stress maximum and minimum? insulation resistance of a single core cable Capacitance of a single core cable

29 dielectric stress in a single core cable Potential Gradient of the cable is Maximum potential gradient is Minimum potential gradient is 4. What are the various properties of insulators? Also briefly explain about Various type of insulators. Define insulator properties of insulator types of insulator Pin type insulator Suspension insulator-explanation

30 Strain insulator-explanation Shackle insulator-explanation 5. Describe with the neat sketch, the construction of a 3 core Pressure typecable. pressure cables i) oil filled cables ii) Gas pressure cables Oil filled cables Gas pressure cables

31 6. 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 8kV and 11kV respectively. Calculate, a) The ratio of capacitance between pin and earth to the selfcapacitance of each unit b) Line Voltage c) String Efficiency Apply kirchoffs current law to at junction A, find K value Apply kirchoffs current law to at junction B, Find V3 value voltage between line and earth string efficiency UNIT - V DISTRIBUTION SYSTEM & FACTS TECHNOLOGY 9 Radial and ring-main distributors; inter-connectors; AC distribution: AC distributor with concentrated load; three-phase, four-wire distribution system; DC distribution; submains;stepped and tapered mains.facts (qualitative treatment only): TCSC, SVC, STATCOM, UPFC.Introduction, Application, Merits & Demerits of HVDC and EHV AC transmission TWO MARKS 1. List the advantages of high voltage power transmission iii) Cost of conductor is reduced for given power iv) Voltage drop in lines is reduced v) Efficiency of transmission line is increased 2. What do you mean by a radial distribution system If a distributor is connected to the supply system from one end only, it is called radial system of distribution. This is also true for the feeders i.e. if a feeder is connected to the supply system from one end only that feeder is called radial feeder.

32 3. What are the drawbacks of a radial distribution system i) Distributor nearest to the substation is highly loaded ii) Severe voltage variation to the consumers far away from the substation due to load variations iii) Consumers are dependent on a single feeder and a single distributor and a fault on either of them causes interruption of supply to all the consumers away from the fault 4. What do you mean by a ring main distribution system A ring main is the name given to a distributor or feeder, which is arranged to form a closed loop. It may have one or more feeding points. 5. What is the purpose of an interconnector? Sometimes between the two points of a ring main, the potential difference becomes very high which can be reduced by increasing the cross section of the feeder ring or by joining those points which have high potential difference by an interconnector. Since increasing the cross section requires the replacement of older ring main and also more volume of conductopr, interconnectors provide economy and are frequently used. 6. What are the methods available for feeding the distributors? A distributor may fed at one end or at both ends. If it is fed at both ends, it may have either equal or unequal voltages at both the ends. 7. Differentiate Service mains and sub-mains Service mains are conductors between a distributor and the metering point of the consumers premises. There are possibilities of several connections from one service mains. It is called sub-mains. The diameter of conductors of sub-mains is more than the normal service mains. 8. What is a substation? Normally large power generating stations are built far away from load centres. There are a number of transformations and switching stations built between generating stations and the ultimate consumers. These are generally known as substations. 9. List the substation equipments Transformers, circuit breakers, disconnecting switches, station buses and insulators, reactors, capacitors, current and potential transformers, grounding system, lightning arrestors and spark gaps, wave traps, protective relays, station batteries. 10. Classify the substations, depending upon the purpose i) Generating or step-up substations ii) Grid substations iii) Secondary substations iv) Distribution substations v) Special purpose substations 11. Classify the substations, depending upon the physical features i) Outdoor type ii) Indoor type

33 iii) Pole mounted or open or kiosk type iv) Underground type 12. What are the advantages and disadvantages of rigid type bus compared to the strain type bus Advantages: i) The rigid bus design employs less steel and simple low level structures ii) The rigid conductors are not under constant strain iii) The pedestal type bus supports are usually easier in maintenance and cleaning iv) The rigid bus has low profiles, which provides good visibility of the conductors and apparatus v) Due to large diameter of pipes, corona loss is extremely less Disadvantages i) It is comparatively expensive due to higher cost of tubing and the connections ii) It usually needs more supports and insulators iii) It is more sensitive to structural deflections, which may lead to possible damage iv) It requires usually more ground space than strain type 13. What are the bus bar schemes available? i) Single bus scheme ii) Double bus with double breaker iii) Double bus with single breaker iv) Main and transfer bus v) Ring bus vi) Breaker and a half with two main buses vii) Double bus bar with bypass isolators 14. List the advantages and disadvantages of single bus scheme Advantage: Low cost Disadvantages: i) Dependence on a single bus can cause a serious outage in the event of bus failure ii) Difficult to do any maintenance iii) Bus cannot be extended without completely de-energizing the substation iv) It can be used only where loads can be interrupted or other supply arrangements 15. List the advantages of double bus with double breaker i) Each circuit has two dedicated breakers ii) It has flexibility in permitting feeder circuits to be connected to either bus iii) Any breaker can be taken out for maintenance iv) It is more reliable than single bus scheme 16. List the advantages and drawbacks of double bus with single breaker Advantages

34 i) It permits some flexibility with two operating buses ii) Either bus 1 or bus 2 may be isolated for maintenance iii) Circuit can be transferred readily by use of bus tie breaker and the isolators Drawbacks i) One extra breaker is required ii) Four isolators are required per circuit iii) Bus protection may cause loss of substation when it operates if all circuits are connected to that bus iv) High exposure to bus fault v) Bus tie breaker fault takes entire substation out of service vi) It does not permit breaker maintenance without causing stoppage of supply 17. List the advantages and drawbacks of main and transfer bus Advantages i) Low initial and ultimate cost ii) Any breaker can be taken out of service for maintenance and potential devices may used on the main bus for relaying Drawbacks i) Switching is somewhat complicated when maintaining a breaker ii) Failure of a bus or any circuit breaker results in shutdown of entire substation, and requires an extra breaker 18. List the advantages and disadvantages of ring bus (or) mesh scheme Advantages i) Low initial cost ii) Flexible operation for breaker maintenance iii) Any breaker can be taken out for maintenance without interrupting load iv) It requires only one breaker per circuit v) It does not use main bus vi) Each circuit is fed by two breakers vii) All switching is done through breakers Disadvantages i) If fault occurs during a breaker maintenance period, the ring will be divided into two sections ii) Automatic reclosing and protective relaying circuitry is complex iii) It requires potential devices on all the circuits since there is no definite potential reference point. These devices may be required in all the cases for synchronizing, live line or voltage indication iv) Breaker failure during a fault on one of the circuit causes loss of one additional circuit owing to operation of breaker failure relay 19. What are the types of HVDC links? i) Monopolar link ii) Bipolar link iii) Homopolar link 20. List the advantages and disadvantages of HVDC transmission system? Advantages i. Asynchronous operation is possible

35 ii. Less corona loss and radio interference iii. No compensation problem iv. Cheaper for long distance transmission v. No charging current vi. No technical limit for power transfer except thermal limit vii. No skin and Ferranti effect viii. No transmission of short circuit power incase of fault ix. Low short circuit current x. Require less space compared to ac for same voltage rating and size xi. Fast fault clearing time. Disadvantages i) Point to point transmission not possible ii) Introduction of harmonics iii) Blocking of reactive power iv) High cost of terminal equipment 21. What are the main components of HVDC transmission system? i) Converters ii) Converter transformers iii) Smoothing reactors iv) Reactive power source v) Harmonic filters vi) Overhead lines vii) Earth electrodes 22. What are the applications of HDC transmission system? i) Long distance bulk power transmission ii) Underground or submarine cables iii) Asynchronous connection of ac system with different frequencies iv) Control and stabilize the power system with power flow control 23. What are the main objectives of FACTS technology i) To increase the power transfer capability of transmission systems (up to thermal limit) ii) To keep power flow over designated routes 24. Define a FACTS controller It is defined as a controller which can control the interrelated parameters that govern the operation of transmission systems including series impedance, shunt impedance, current, voltage, phase angle and the damping of oscillations at various frequencies below the rated frequency. 25. What are the advantages of FACTS controllers? i) Control of power flow by controlling line impedance, angle and voltage ii) Optimum power flow iii) Reduce reactive power flows iv) Reduce loop flows v) Increase the loading capability of lines to their thermal capabilities vi) Greater flexibility

36 vii) Increase system security by limiting short circuit currents and overloads

37 16 MARK QUESTIONS 1. Draw and Explain the 3Φ, 3-wire&3 Φ, 4-wire Transmission and distribution system. 3 phase 3 wire system- Explanation 3 phase 4 wire system- Explanation 2. Explain why EHV transmission is preferred? What are the problems involved in EHV AC transmission? need for EHV transmission system Increase in transmission voltage Decrease in transmission current Installation cost of the transmission line cost/km decreases problems involved in EHV transmission line corona loss and radio interference Line supports Erection difficulties Insulation needs 3. Explain the following system of distribution. i) Radial system ii) Ring main system radial distribution system

38 advantage and disadvantage- any two ring main system advantage and disadvantage- any two 4. With neat schematic, explain the principle of HVDC system and explain any two types of systems. schematic block diagram of HVDC system advantage any two Monopolar HVDC system-explanation Multiterminal HVDC sytem-explanation

39 5. Explain with neat diagram about TCSC and SVC systems by TCSC controller-explanation SVC controller- Explanation 6. Explain with neat diagram about STATCOM and UPFC systems. STATCOM controller-explanation UPFC controller-explanation

40

41 UNIVERSITY QUESTIONS ANNA UNIVERSITY OF TECHNOLOGY, COIMBATORE B.E/B.TECH.DEGREE EXAMINATIONS: NOV/DEC 2011 REGULATIONS: 2008 FIFTH SEMESTER-EEE TRANSMISSION AND DISTRIBUTION PART- A(10*2=20 MARKS) ANSWER ALL QUESTIONS 1. List the sources of electric energy Renewable Source Biogas, tidal energy, geothermal energy, wind energy solar energy, etc. Non Renewable Source Natural gas, Coal, Petroleum (they are also called as fossil fuels.) 2. Draw the block diagram of wind energy conversion system 3. Why skin effect occurs in a a.c system An alternating current flowing through the conductor does not distribute uniformly. Rather it has the tendency to concentrate near the surface f the conductor. A solid conductor may be thought to be consisting of a large no.of strands. Each carrying the small part of current. The inductance of each strand will be varying according to its position. Thus the strands near the centre are surrounded by a Greater magnetic flux and hence have large inductance than that near surface. The high reactance of inner strands causes the alternating current to flow near the surface of conductor. This crowing of current near the conductor surface is the skin effect. 4. What is Ferranti effect? The phenomenon of rise in voltage at the receiving end of the open circuited or lightly loaded line is called the Ferranti effect.

42 5. Draw the Equivalent circuit and phasor representation of long transmission line 6. Write the expression for corona loss 7. Define Dielectric strength. The voltage at which the insulating qualities of a material break down. 8. What is String efficiency in insulator? It is a measure of utilization of material in the string. If the number of units in the string is n, the string efficiency is defined as, Stiring efficiency = Voltage across the n strings (n x Voltage across the unit near to the power conductor) 9. Name any 4 advantage of HVDC transmission i) Less corona loss and radio interference ii) No compensation problem iii) Cheaper for long distance transmission iv) No charging current 10. List the merits of a ring main distribution system i) Low initial cost ii) Flexible operation for breaker maintenance iii) Any breaker can be taken out for maintenance without interrupting load iv) It requires only one breaker per circuit PART-B(5*16=80 MARKS) 11. (a) Draw the neat diagram of structure of electric power system and explain its operation. (16) Mention the voltage level Transmission system Primary transmission Secondary transmission Distribution system Primary distribution Secondary distribution

43 (or) (b) Sketch the diagram of thermal power station and explain its working(16) Explain each component Advantage & Disadvantage 12. (a)a 3 phase 345 KV, 50HZ transposed transmission line is 150 KM long and composed of two conductor per phase with flat horizontal spacing of 15m. The bundle spacing 50cm. the conductors are made aluminium and have diameter of 4cm. The resistivity of aluminium is 26.5nΩ-m. Find the resistance, inductive reactance and susceptance per phase of the line. total resistance/phase total Reactance/phase phase Impedance finally find out Resistance, inductive reactance &susceptnce (or) (b) Derive the expression for the capacitance of a 3 phase transmission line with unsymmetrical spacing. Unsymmetrical Spacing

44 Average voltage on the conductor A is Capacitance from conductor to neutral is 13. (a) A 3 phase 50 Hz, 100 km long over head line has the following constants:resistance per phase per km= 0.153Ω, inductance per phase per km=1.21 mh, Capacitance per phase km= µf. The line supplies a load of 20MW at o.9 pf lagging at the line voltage 0f 110kv at the receiving end. Using nominal π representations calculate the sending end voltage,current,power factor, regulation and efficiency. total resistance/phase total Reactance/phase phase Impedance Sending end voltage Sending end current sending end power factor voltage regulation Transmission efficiency

45 (b) Derive the values of Generalized network constants A,B,and D in nominal T Equivalent circuit for medium transmission line. Also draw the respective phasor diagram. Equivalent model of Medium line- Nominal T method Phasor diagram 14. (a) i)what are the types of insulators used for over head lines? With neat diagram explain any one type of insulator. Types of insulator Pin type insulator Suspension type insulator Strain insulator Shackle insulator Suspension type insulator

46 Mention the voltage level Advantage- ant two iii) A 3 unit insulator String is fitted with a guard ring. The capacitance of the link pins to metal work and the guard ring can be assumed to be 15% and 5% of capacitance of each unit. Determine the voltage distribution and string efficiency, if V1+V2+V3=100. Apply Kirchhoff s current law, Find the voltage across each insulator Sting efficiency (b) Calculate the capacitance and charging current of a single core cables used on three phase 66KV systems. The cable is 1KM long having a core diameter of 15 cm and impregnated paper insulation of thickness 22.5cm. The relative permitivity of the insulation is 3.5 and supply at 50 Hz. Capacitance of a cable is Charging current 15.(a) Explain the following connection scheme of distribution system with neat diagram. i) Radial system ii) interconnected system

47 radial distribution system- Explanation Interconnected system- Explanation (or) (b) Explain the principle operation of following FACTS devices i)svc ii)upfc SVC controller- Explanation

48 UPFC controller-explanation ANNA UNIVERSITY OF TECHNOLOGY, COIMBATORE B.E/B.TECH.DEGREE EXAMINATIONS: MAY/JUNE 2012 REGULATIONS: 2008 FIFTH SEMESTER-EEE TRANSMISSION AND DISTRIBUTION PART- A(10*2=20 MARKS) ANSWER ALL QUESTIONS 1. Draw the static characteristics of lighting load.

49 2. List the different types of Hydro electric power plant i) Hydraulic Structure ii) Water turbine iii) Electrical Equipment 3. What are the advantages of bundled conductors? i) Reduced reactance, ii) reduced voltage gradient, iii) reduced corona loss. iv) reduced interference 4. What is meant by proximity effect? The alternating magnetic flux in a conductor caused by the current flowing in a neighboring conductor gives rise to a circulating current which cause an apparent increase in the resistance of the conductor.this phenomenon is called as proximity effect. 5. Define surge impedance. The characteristic impedance of a lossless line is called as surge impedance 6. What are the factors on which the corona loss depends? Atmosphere, conductor size, spacing between conductors and line voltage. 7. Define string efficiency. Stiring efficiency = Voltage across the n strings ( n x Voltage across the unit near to the power conductor) 8. List the advantages of underground cables. It requires less maintenance The voltage drop in underground cables is less The life of underground cable is long compared to the overhead lines 9. What is meant by sub mains? There are possibilities of several connections from one service mains. It is called sub-mains. The diameter of conductors of sub-mains is more than the normal service mains. 10. What are the functions of STATCOM? It is shunt connected static VAR compensator whose capacitive or inductive output current can be controlled independently of the a.c system voltage.

50 PART-B(5*16=80 MARKS) 11. (a) i) Draw neatly the structure of power system ii)explain the characteristics of different kinds of load. Write about the charcteristics of following loads Domestic load Commercil load Industrial load Municipal lod Irrigation load Traction load (or) (b) With neat sketch explain briefly about the power generation by nuclear and gas power plants. Schematic arrangement of nuclear power plant- Wxplanation

51 Main stageg of nuclear power plant Nuclear reactor, Heat exchanger,steam turbine, Alternator Advantage- any two Schematic arrangement of Gas power plant- Explanation Advantage- any two 12. (a) i)derive the inductance formula for a 3 phase transmission line with double circuits. 3 phase double circuit with symmetrical spacing The inductance of conductor A will be, 3 phase double circuit with unsymmetrical spacing The inductance of conductor A will be,

52 iii) Derive the expression for the inductance of a 3 phase transmission line with symmetrical spacing. 3 phase Symmetrical Spacing The inductance of conductor A will be, (or) (b) i)derive the expression for capacitance in a 3 phase single circuit (10) 3 phase Symmetrical Spacing Capacitance of conductor A w.r.t to neutral, 3 phase unsymmetrical Spacing Capacitance of conductor A w.r.t to neutral,

53 iii) Write short notes on skin effect (6) Define Skin Effect- Explanation 13. (a) i) Derive the ABCD parameters of a medium line with nominal π model Equivalent model of Nominal π model ii) A 345 KV 3 phase transmission line is 130 km long. The resistance per phase is 0.036Ω per km and the inductance per phase is 0.8 mh per km. The shunt capacitance is 0.012µF per km. The receiving end load is 270 MVA with 0.8 p.f lagging at 325 KV. Use the medium line model to find the voltage and power at the sending end and the voltage regulations. Sending end voltage Sendind end power Voltage regulation (or) (b) Discuss the following: i) Voltage stability (4) ii) Shunt compensation (6) iii) Series compensation (6) Define te voltage stability What is the need for compensation Draw the shunt and series compensation model

54 Give the explanation of compensation tecniques 15. (a) Draw and explain about briefly about the different types of insulator types of insulator Pin type insulator-explanation Suspension insulator-explanation Strain insulator-explanation Shackle insulator-explanation

55 (or) (b) Explain briefly about constructional features of LT and HT cables. Low tension cables- upto 1000V Construction-Explanation High Tension Cables upto 11,000V (Belted Cables) Construction-Explanation 15.(a) Discuss briefly about the ring- main distributors and 3 phase 4 wire distribution systems. Ring main distribution system- Explanation