Transmission and Distribution.

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Transmission and Distribution.

  1. 1. EE 1302 TRANSMISSION AND DISTRIBUTION BY M.VALAN RAJKUMAR, L/ EEE N.P.R. COLLEGE OF ENGINEERING AND TECHNOLOGY, NATHAM.
  2. 2. ANNA UNIVERSITY TIRUCHIRAPPALLI, Tiruchirappalli Regulations 2008 Curriculum SEMESTER V S. No. Subject Subject L T P C Code Theory 1 MG1301 Total Quality Management 3 0 0 3 2 EE1301 Electrical Machines II 3 1 0 4 3 EE1302 Transmission and Distribution Engineering 3 1 0 4 4 EC1307 Digital Signal Processing 3 1 0 4 5 EC1308 Principles of Communication Engineering 3 0 0 3 6 CS1312 Object Oriented Programming 3 0 0 3 Practical 7 EE1303 Electrical Machines II Laboratory 0 0 3 2
  3. 3. 8 EC1309 Digital Signal Processing Laboratory 0 0 3 2 9 CS1313 Object Oriented Programming Laboratory 0 0 3 2 Total 27 EE1302 – TRANSMISSION AND DISTRIBUTION ENGINEERING L T P C 3 1 0 4 UNIT I TRANSMISSION SYSTEMS 9 Structure of electric power system – Various levels Generation, Transmission and distribution – HVDC and EHV AC transmission – Comparison of economics of transmission – Technical performance and reliability – Application of HVDC transmission system – FACTS (qualitative treatment only) – TCSC – SVC – STATCOM – UPFC UNIT II TRANSMISSION LINE PARAMETERS 9 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 – Transposition – Application of self and mutual GMD – Skin and proximity effects – Interference with neighboring communication circuits – Typical configuration– Conductor types and electrical parameters of 400, 220, 110, 66 and 33 kV lines UNITIII MODELLING AND PERFORMANCE OF TRANSMISSION LINES 9 Classification of lines – Short, medium and long line – Equivalent circuits, attenuation constant – Phase constant – Surge impedance – Transmission efficiency and voltage regulation – Real and reactive power flow in lines – Power-angle diagram – Surge-impedance loading – Loadability limits based on thermal loading – Angle and voltage stability considerations – Shunt and series compensation – Ferranti effect and corona loss 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 –
  4. 4. Dielectric stress and grading – Thermal characteristics UNIT V SUBSTATION GROUNDING SYSTEM AND DISTRIBUTION SYSTEM 9 Types of substations – Bus-bar arrangements – Substation bus schemes – Single bus scheme – Double bus with double breaker – Double bus with single breaker – Main and transfer bus – Ringbus – Breaker-and-a-half with two main buses – Double bus-bar with bypass isolators – Resistanceof grounding systems – Resistance of driven rods, resistance of grounding point electrode –Grounding grids – Design principles of substation grounding system – Neutral grounding L: 45 T: 15 Total: 60 TEXT BOOKS 1. Gupta, B.R., “Power System Analysis and Design”, S.Chand, 2003 2. Singh, S.N., “Electric Power Generation, Transmission and Distribution”, Prentice Hall of India, 2002 REFERENCES 1. Luces M. Fualkenberry, Walter Coffer, “Electrical Power Distribution and Transmission”, Pearson Education, 1996 2. Hadi Saadat, “Power System Analysis”, Tata McGraw Hill Publishing Company, 2003 3. Wadhwa, C.L., “Electric Power Systems”, New Age International (P) Ltd., 2000 4. Turan Gonen, “Electric Power Distribution Engineering”, 2nd Edition, CRC Press, 2007
  5. 5. UNIT I TRANSMISSION SYSTEMS Structure of electric power system – Various levels Generation, Transmission and distribution – HVDC and EHV AC transmission – Comparison of economics of transmission – Technical performance and reliability – Application of HVDC transmission system – FACTS (qualitative treatment only) – TCSC – SVC – STATCOM – UPFC
  6. 6. • Various levels such as generation, transmission and distribution.
  7. 7. INTRODUCTION • HVDC High voltage direct current (HVDC) is used to transmit large amounts of power over long distances or for interconnections between asynchronous grids. When electrical energy is required to be transmitted over very long distances, it is more economical to transmit using direct current instead of alternating current • EHV AC transmission Hydro-electric and coal or oil-fired stations are located very far from load centres for various reasons which requires the transmission of the generated electric power over very long distances.
  8. 8. This requires very high voltages for transmission. The very rapid strides taken by development of dc transmission since 1950 is playing a major role in extra-long-distance transmission, complementing or supplementing EHV AC transmission. Technical performance and reliability Considerations in the design of a power line: • • The amount of active power it has to transmit • • The distance over which the power must be carried • • The cost of the power line • • Aesthetic considerations, urban congestion, ease of installation, expected load growth • Application of HVDC transmission system • HVDC Light, is utilising state of the art semiconductors,
  9. 9. control and cable insulation and can offer many new transmission opportunities as has been demonstrated by actual projects above. It offers a lot of possibilities to enhance the power systems. • Wind power, even big parks, can easily be connected to the grid. In many cases HVDC Light can give new opportunities to trade electric energy in the new deregulated markets. • As HVDC Light has been developed to minimise environmental impact and impact on the connecting grids, the licence procedure is generally more favourable than more traditional solutions. FACTS:
  10. 10. • TCSC The Thyristor Controlled Series Capacitor (TCSC) seems to be one of the members within the FACTS family, beside the SVC that was established long ago, which has attracted the most interest so far. One reason may be that a distinctive quality of the TCSC concept is that it uses an extremely simple main circuit topology.
  11. 11. The capacitor is inserted directly in series with the transmission line and the thyristor controlled inductor is mounted directly in parallel with the capacitor. Thus no interfacing equipment like e.g. high voltage transformers is required. This makes TCSC much more economical than some other competing FACTS technologies • SVC • Static variable capacitor Parallel-connected static var generator or absorber Output is adjusted to exchange capacitive or inductive current. Maintain or control specific parameters of the electrical power system (typically bus voltage). Thyristor-based Controllers Lower cost alternative to STATCOM • STATCOM
  12. 12. Static Synchronous Compensator (STATCOM) • Parallel-connected static var compensator • Capacitive or inductive output current controlled independently of the ac system voltage • UPFC Unified power flow controller (UPFC) is one of the FACTS devices, which can control power system parameters such as terminal voltage, line impedance and phase angle. Therefore, it can be used not only for power flow control, but also for power system stabilizing control.
  13. 13. UNIT-I TRANSMISSION SYSTEM – INTRODUCTION PART-A 1. What is meant by power supply system? (2) 2. What is meant by Transmission and Distribution system? (2) 3. What are the different types of Power supply system? (2)
  14. 14. 4. What are the various components of power supply system? (2) 5. What are the different types of power plants? (2) 6. What are the different operating voltages used for generation, primary and secondary transmission in AC power supply systems in India? (2) 7. Define feeder, distributor and service mains. (2) 8. List the advantages of high voltage transmission. (2) 9. State Kelvin’s law. (2) 10. What are the limitations of Kelvin’s law? (2) PART-B 1. (i) Discuss various types of HVDC links. (8) (ii) List out the main components of a HVDC system. (8) 2. (i) Draw and explain the structure of modern power systems with typical voltage levels (13) (ii) What is the highest voltage level available in India? (3) 3. (i) Explain the effect of high voltage on volume of copper and on efficiency. (8) (ii) Explain why the transmission lines are 3 phase 3-wire circuits while
  15. 15. distribution lines are 3 phase 4-wire circuits. (8) 4. (i) Draw the model power system with single line representation. Show its essential constituent sections. (6) (ii) What are the AC transmission and distribution level voltages we have in India? (4) (iii) What are the different kinds of DC links? Draw relevant diagrams. (6) 5. (i) Explain why EHV transmission is preferred? What are the problems involved in EHV AC transmission? (8) (ii) With neat schematic, explain the principle of HVDC system operation. (8) 6. Explain about FACTS with neat diagram (16) 7. Explain TCSC and SVS systems (16) 8. Explain with neat diagram about STATCOM and UPFC (16) 9. (i) Compare EHVAC and HVDC transmission (8) (ii) Explain the applications of HVDC transmission system (8)
  16. 16. 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 – Transposition – Application of self and mutual GMD – Skin and proximity effects – Interference with neighboring communication circuits – Typical configuration – Conductor types and electrical parameters of 400, 220, 110, 66 and 33 kV lines „ Parameters in the transmission line „ resistance r, inductance L, capacitance C „ L and C are due to the effects of magnetic and electric fields around the conductor „ Overhead transmission line „ ANSI voltage standard: 69kV, 115kV, 138kV, 161kV, 230kV, 345kV, 500kV, 765kV line-to-line „ extra-high-voltage (EHV): >230kV, ultra-high-voltage (UHV): ≥765kV „ bundling: use more than one conductor per phase, usually used at voltage > 230kV „ advantage of bundling: increase effective radius of line conductor, reduce electric field strength and
  17. 17. reduces corona power loss, audio loss and radio interference, and reduces line reactance
  18. 18. LINE RESISTANCE „ Transmission line resistance „ dc flow: resistance of solid round conductor is given by R dc =ρl/A „ ac flow: the current distribution is not uniform, the current density is greatest at surface of the conductor, this is called skin effect, therefore, R ac > R dc „ temperature: resistance increases when temperature increases „ Transmission line inductance „ definition of inductance L: L=λ/I, λ is flux linkage „ magnetic field density: H x =I x /2πx, x is the radius of circle, I x induces magnetic field density H x
  19. 19. INTERNAL INDUCTANCE „ Derivation of internal inductance L int „ consider the flux linked by the portion x ≤ r of current I a flowing inside a cylinder of radius x, the magnetic intensity: ∫ Hdl = I enclosed 2 2 „ Since Ia = πx I, πr 2 therefore 2πxHx πx = I πr 2 „ magnetic flux density B x : B x =µ o H x =µ o xI /2πr 2 „ µ o is the permeability of free space: 4π×10 -7 H/m „ since current flowing into the circuit of x is only a fraction of I a , the effective turn is equivalent to the fraction N = πx 2 /πr 2
  20. 20. ∫ INTERNAL INDUCTANCE „ Derivation of internal inductance L int „ πx 2 /πr 2 turns of the current I a linked by flux: „ dλ x = (πx 2 /πr 2 ) dφ x = (πx 2 /πr 2 ) (B x ×1dx) = (πx 2 /πr 2 ) (µ o xI/2πr 2 ) ×1dx = (µ o I) x 3 /(2πr 4 ) dx „ total flux linkage in the inductor: λ int = µ o I r 2πr 4 0 x 3 dx = µ o I 8π „ inductor due to the internal flux: L int =µ o /8π=(1/2)×10 -7 H/m „ inductor L int is independent of the conductor radius r
  21. 21. ∫ EXTERNAL INDUCTANCE „ Derivation of external inductance L ext „ consider H x external to conductor at x>r, since the circle at radius x enclose entire current, I x =I ( see Fig.4.4 ): B x =µ o H x =µ o I/2πx „ the entire current I is linked by the flux outside the conductor, dλ x =dφ x = B x dx*1=µ o I/(2πx)*dx „ external flux linkage between D 1 and D 2 : λext = µoI 2π D2 1 dx D1 x = 2×10 −7 I ln D2 D1 Wb/m „ inductance between two points D 1 and D 2 due to the external flux: Lext = 2×10 −7 ln D2 D1 H/m
  22. 22. UNIT- II TRANSMISSION LINE PARAMETERS PART-A 1. Define Skin effect. (2) 2. What is meant by proximity effect? (2) 3. Differentiate the stranded conductor and bundled conductor. (2) 4. List out the advantages of double circuit lines. (2) 5. Define - Self and mutual – G.M.D. (2) 6. What is meant by inductive interference? (2) 7. What is transposition of conductors? (2) 8. What is ACSR conductor? (2) 9. What is fictitious conductor radius? (2) 10. Define unsymmetrical and symmetrical spacing. (2) PART-B 1. From the fundamentals derive an expression for inductance of a single phase transmission system. (16)
  23. 23. 2. Derive an expression for capacitances of a single phase transmission system and discuss the effect of earth on capacitance with suitable equation. (16) 3. Derive an expression for inductance i) Of a single-phase overhead line. (8) ii) A conductor is composed of seven identical copper strands each having a radius r. Find the self-GMD of the conductor. (8) 4. i) Derive an expression for the capacitance between conductors of a Single phase overhead line. (8) ii) Find the capacitance between the conductors of a single-phase 10 km long line. The diameter of each conductor is 1.213cm. The spacing between conductors is 1.25m. Also find the capacitance of each conductor neutral. (8) 5. i) Derive the expression for inductance of a two wire 1Φ transmission line (8) ii) Derive the expression for capacitance of a 1Φ transmission line (8) 6. i) What are the advantages of bundled conductors? (4) ii) Derive the expression for capacitance of a double circuit line for hexagonal spacing. (8) iii) Why is the concept of self GMD is not applicable for capacitance? (4) 7. i) Explain clearly the skin effect and the proximity effects when referred to
  24. 24. overhead lines. (8) ii) Write a short note on the inductive interference between power and communication lines. (8) 8. i) Derive the expression for the capacitance per phase of the 3 Φ double circuit line flat vertical spacing with transposition. (8) ii) A 3 Φ overhead transmission line has its conductors arranged at the corners of an equilateral triangle of 2m side. Calculate the capacitance of each line conductor per km. Given the diameter of each conductor is 1.25cm. (8) 9. Find the capacitance per km per phase of a 3Φ 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. (16) 10. Discuss the concept of GMR and GMD in the calculation of transmission line inductance. (16)
  25. 25. UNIT IV INSULATORS AND CABLES 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 Insulators: • An insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate electrical conductors without passing current through themselves. • The term is often used more specifically to refer to insulating supports that attach electric power transmission wires to utility poles or pylons.
  26. 26. • Some materials such as glass or Teflon are very good electrical insulators. • A much larger class of materials, for example rubber-like polymers and most plastics are still "good enough" to insulate electrical wiring and cables even though they may have lower bulk resistivity. • These materials can serve as practical and safe insulators for low to moderate voltages (hundreds, or even thousands, of volts). • Insulators are used for high-voltage power transmission are made from glass, porcelain, or composite polymer
  27. 27. materials. Porcelain insulators are made from clay, quartz or alumina and feldspar, and are covered with a smooth glaze to shed dirt. • Insulators made from porcelain rich in alumina are used where high mechanical strength is a criterion. • Porcelain has a dielectric strength of about 4-10 kV/mm. Glass has a higher dielectric strength, but it attracts condensation and the thick irregular shapes needed for insulators are difficult to cast without internal strains. • Some insulator manufacturers stopped making glass insulators in the late 1960s, switching to ceramic materials. • Recently, some electric utilities have begun converting to polymer composite materials for some types of insulators. • These are typically composed of a central rod made of fibre reinforced plastic and an outer weathershed made of silicone rubber or EPDM. • Composite insulators are less costly, lighter in weight, and have excellent hydrophobic capability. This combination makes them ideal for service in polluted areas.
  28. 28. • However, these materials do not yet have the long-term proven service life of glass and porcelain. • Design • Cap and pin insulator string (the vertical string of discs) on a 275 kV suspension pylon. • The electrical breakdown of an insulator due to excessive voltage can occur in one of two ways:Puncture voltage is the voltage across the insulator(when installed in its normal manner) which causes a breakdown and conduction through the interior of the insulator. • The heat resulting from the puncture arc usually damages the insulator irreparably. • Flashover voltage is the voltage which causes the air around or along the surface of the insulator to break down and conduct, causing a 'flashover' arc along the outside of the insulator. • They are usually designed to withstand this without damage. High voltage insulators are designed with a lower flashover voltage than puncture voltage, so they will flashover before they puncture, to avoid damage.
  29. 29. • Dirt, pollution, salt, and particularly water on the surface of a high voltage insulator can create a conductive path across it, causing leakage currents and flashovers. • The flashover voltage can be more than 50% lower when the insulator is wet. High voltage insulators for outdoor use are shaped to maximise the length of the leakage path along the surface from one end to the other, called the creepage length, to minimize these leakage currents. • To accomplish this the surface is molded into a series of corrugations or concentric disk shapes. These usually include one or more sheds; downward facing cup-shaped surfaces that act as umbrellas to ensure that the part of the surface leakage path under the 'cup' stays dry in wet weather. Minimum creepage distances are 20-25 mm/kV, but must be increased in high pollution or airborne sea- salt areas. Cables • A cable is one or more strands bound together. Electrical cables may contain one or more metal conductors, which may be individually insulated or covered. • An optical cable contains one or more optical fibers in a protective jacket that supports the fibers.
  30. 30. • Mechanical cables such as wire rope may contain a large number of metal or fiber strands. • Electrical cables may be made flexible by stranding the wires. The technical issue is to reduce the skin effect voltage drop while using with alternating currents. • In this process, smaller individual wires are twisted or braided together to produce larger wires that are more flexible than solid wires of similar size. Bunching small wires before concentric stranding adds the most flexibility. • A thin coat of a specific material (usually tin-which improved striping of rubber, or for low friction of moving conductors, but it could be silver, gold and another materials and of course the wire can be bare - with no coating material) on the individual wires. • Tight lays during stranding makes the cable extensible (CBA - as in telephone handset cords). • Bundling the conductors and eliminating multi-layers ensures a uniform bend radius across each conductor. • Pulling and compressing forces balance one another around the high-tensile center cord that provides the necessary inner stability.
  31. 31. • As a result the cable core remains stable even under maximum bending stress. Cables can be securely fastened and organized, such as using cable trees with the aid of cable ties or cable lacing. Continuous-flex or flexible cables used in moving applications within cable carriers can be secured using strain relief devices or cable ties. Copper corrodes easily and so should be layered with Lacquer UNIT-IV INSULATORS AND CABLES
  32. 32. PART-A 1. What is the purpose of insulator? (2) 2. What is the main purpose of armouring? (2) 3. What is meant by efficiency of an insulator string? (2) 4. List out various types of insulators used for overhead transmission lines. (2) 5. Mention the advantages of the pin type insulator. (2) 6. What are the main causes for failure of insulators? (2) 7. What are the different tests that are conducted on an insulator? (2) 8 What are the methods for improving string efficiency? (2) 9. Write short notes on puncture test. (2) 10. Define impulse ratio. (2) PART-B 1. Discuss any two methods to increase the value of string efficiency, with suitable sketches. (16) 2. Explain any two methods of grading of cables with necessary diagrams. (16) 3. i) What are different methods to improve string efficiency of an insulator? (8) 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. (8)
  33. 33. 4. i) Derive the expression for insulator resistance, capacitance and electric stress in a single core cable.Where is the stress maximum and minimum?(8) ii) A single core 66kv cable working on 3-phase system has a conductor diameter of 2cm and sheath of inside diameter 5.3cm. 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 (8) 5. i) Draw the schematic diagram of a pin type insulator and explain its function. (8) 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 8kV and 11kV respectively. Calculate, a) The ratio of capacitance between pin and earth to the self capacitance of each unit (4) b) Line Voltage (2) c) String Efficiency (2) 6. i) Describe with the neat sketch, the construction of a 3 core belted type cable. (8) ii) A conductor of 1cm diameter passes centrally through porcelain cylinder of internal diameter 2 cms and external diameter 7cms. 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 34kV/cm. Determine
  34. 34. the maximum safe working voltage. (8) 7. i) What are the various properties of insulators? Also briefly explain about suspension type insulators. (8) ii) Calculate the most economical diameter of a single core cable to be used on 132kV, 3 phase system. Find also the overall diameter of the insulation, if the peak permissible stress does not exceed 60kV/cm. also derive the formula used here. (8) 8. i) Briefly explain about various types of cables used in underground system.(8) 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 (8) 9. i) Give any six properties of a good insulator. (4) ii) With a neat diagram, explain the strain and stay insulators. (4) 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 5.5cm. (8) 10. i) Explain the constructional features of one LT and HT cable (8) ii) Compare and contrast overhead lines and underground cables. (8)
  35. 35. UNIT V SUBSTATION GROUNDING SYSTEM AND DISTRIBUTION SYSTEM Types of substations – Bus-bar arrangements – Substation bus schemes – Single bus scheme – Double bus with double breaker – Double bus with single breaker – Main and transfer bus –Ring bus – Breaker-and-a-half with two main buses – Double bus-bar with bypass isolators – Resistance of grounding systems – Resistance of driven rods, resistance of grounding point electrode –Grounding grids – Design principles of substation grounding system – Neutral grounding
  36. 36. UNIT-V SUBSTATION GROUNDING SYSTEM AND DISTRIBUTION SYSTEM PART-A 1. What is substation? (2) 2. What is earth resistance? (2) 3. What are the classifications of substation according to service? (2) 4. What are the types of transformer substations? (2) 5. What are the factors to be considered for busbar design? (2) 6. What is neutral grounding or neutral earthing? (2) 7. What are the equipments used in a transformer substation? (2) 8. What are the different types of bus bar arrangements in substations? (2) 9. What is bus bar? (2) 10. What are the materials mainly used in busbars? (2) PART-B 1. With a neat sketch explain double bus with double breaker and double bus with single breaker. State their advantages and disadvantages. (16) 2. Explain the following: (i) Neutral grounding (ii) Resistance grounding. (16) 3. Explain about the various types of substations (16)
  37. 37. 4. Write short notes on I. Sub mains (4) II. Stepped and tapered mains (12) 5. Explain the substation bus schemes. (16) 6. Write short notes on i. Busbar arrangement in substation (8) ii. Grounding grids (8) 7. i) Explain the design principles of substation grounding system. (8) ii) Explain the equipments in a transformer substation.

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