# Transmission and Distribution - Line parameters.pptx

Professor em Engineering College
2 de Jun de 2023
1 de 49

### Transmission and Distribution - Line parameters.pptx

• 2. UNIT - I TRANSMISSION LINE PARAMETERS
• 3. Course Outcome Compute the transmission line parameters
• 4. Introduction • The energy is neither be created nor be destroyed but it can be converted from one form to another. • The various energy sources 1. Burning coal oil 2. Natural gas 3. Water stored in dams 4. Diesel oil 5. Nuclear power 6. Other non conventional energy sources
• 5. Introduction • Depending upon the source of energy used, these stations are called thermal power station, hydroelectric power station, diesel power station, nuclear power station etc. • The generated electric power is to be supplied to the consumers. • Generally the power stations are located too far away from the town and cities where electrical energy is demanded. • Hence there exists a large network of conductors between the power stations and the consumers. • The network is broadly classified into two parts 1. Transmission 2. Distribution
• 6. A Typical Transmission and Distribution Scheme • The flow of electrical power from the generating station to the consumer is called an electrical power system or electrical supply system. • It consists of the following important components 1. Generating station 2. Transmission network 3. Distribution network
• 8. Structure of electrical power system
• 9. Components of Distribution • The distribution scheme consists of following important components. 1. Substation 2. Local distribution scheme 3. Feeders 4. Distributors 5. Service mains
• 12. Types of Transmission • Overhead System
• 15. Types of Transmission • Underground System
• 16. S.No. Underground System Overhead System 1. Transmission is by using cables Transmission is by using the transmission lines 2. All the cables must be properly insulated from each other The appropriate spacing provided between the conductors acts as an insulation. No external insulation is necessary 3. The insulation cost is very high No transmission cost as air acts as an insulator 4. Transmission over long distance is not possible as laying of cables is difficult, costly and complicated Transmission over long distance is possible with the help of transmission lines. 5. The voltage level used is below 66 kV due to insulation difficulties The voltage level used can as high as 400 kV 6. The maintenance cost is less The maintenance cost is high 7. The faults due to lightning, short circuit, storms etc. are eliminated The occurrence of faults due to lightning, short circuits, storms and abnormal weather conditions are possible. 8. It is very safe due to insulation used The conductors are bare without insulation hence dangerous
• 17. S.No. Underground System Overhead System 9. Maximum stress is on the insulation between the conductors Maximum stress is between conductor and earth 10. The beauty of the area, towns etc. is well maintained The beauty of the area gets affected due to overhead lines. Sometimes trees are required to be cut 11. The size of the cables is high The size of the conductors is less 12. The voltage drop is less The voltage drop is more
• 19. Constants of a Transmission Line • Resistance • Inductance • Capacitance
• 20. Constants of a Transmission Line Resistance: • It is the opposition of line conductors to current flow. The resistance is distributed uniformly along the whole length of the line as shown in Fig. (i). • However, the performance of a transmission line can be analysed conveniently if distributed resistance is considered as lumped as shown in Fig.(ii).
• 21. Constants of a Transmission Line • Inductance: • When an alternating current flows through a conductor, a changing flux is set up which links the conductor. • Due to these flux linkages, the conductor possesses inductance. • Mathematically, inductance is defined as the flux linkages per ampere i.e.,
• 22. Constants of a Transmission Line • Capacitance: • We know that any two conductors separated by an insulating material constitute a capacitor. • As any two conductors of an overhead transmission line are separated by air which acts as an insulation, therefore, capacitance exists between any two overhead line conductors. • The capacitance between the conductors is the charge per unit potential difference i.e., • Capacitance, C = q/v farad
• 23. Constants of a Transmission Line • Capacitance:
• 24. Factors to be considered while Designing Transmission Line • Type and size of conductors • Voltage level • Line regulation and control of voltage • Efficiency of transmission • Corona loss • Power flow capability and stability • Requirement of compensation • Levels of faults at various bus bars and requirement of new circuit breakers • Grounding needs • Protection schemes for new lines • Coordination of insulation
• 25. Factors to be considered while Designing Transmission Line • Mechanical design aspects which include stress and sag calculations, compensation of conductor, spacing of conductor and configuration for insulators. • Design of power system structure • Economical aspects
• 26. Requirements of Transmission Line Conductors • They should have low weight • They should have high tensile strength and fatigue strength • They must have high conductivity • They should have low co-efficient of expansion, low corona loss • They should have less resistance and low cost The conductors used in practice are made up from the materials such as copper, aluminium and their alloys.
• 27. Aluminum Transmission Line Conductors • The advantages of using aluminium conductors over copper conductors are 1. They have low cost 2. Less resistance and corona loss 3. Less weight • But aluminium has less tensile strength, high co- efficient of expansion and large area which restricts it use alone as a conductor.
• 28. Stranded Conductors • Stranded conductors have three or more strands of conductor material twisted together to form a single conductor. • Stranded can carry high currents and are usually more flexible than solid conductors
• 29. Types of Aluminum Transmission Line Conductors • AAC - All aluminium conductors • AAAC - All aluminium alloy conductor (Silmalec- 0.5% of silicon & 0.5% of magnesium) • ACSR - Aluminium conductors with steel reinforcement • ACAR - Aluminium conductors with alloy reinforcement
• 30. Types of Aluminum Transmission Line Conductors
• 31. Types of Aluminum Transmission Line Conductors
• 32. ACSR
• 39. Transposition of Transmission line conductors
• 40. Transposition of Transmission line conductors
• 42. SKIN EFFECT • When a conductor is carrying steady direct current (d.c.), this current is uniformly distributed over the whole X-section of the conductor. • However, an alternating current flowing through the conductor does not distribute uniformly, rather it has the tendency to concentrate near the surface of the conductor as shown in Fig. This is known as skin effect.
• 43. SKIN EFFECT • The tendency of alternating current to concentrate near the surface of a conductor is known as skin effect.
• 44. SKIN EFFECT • Due to skin effect, the effective area of cross- section of the conductor through which current flows is reduced. • Consequently, the resistance of the conductor is slightly increased when carrying an alternating current. • The cause of skin effect can be easily explained. A solid conductor may be thought to be consisting of a large number of strands, each carrying a small part of the current.
• 45. SKIN EFFECT • The inductance of each strand will vary according to its position. Thus, the strands near the centre are surrounded by a greater magnetic flux and hence have larger inductance than that near the surface. • The high reactance of inner strands causes the alternating current to flow near the surface of conductor. • This crowding of current near the conductor surface is the skin effect.
• 46. SKIN EFFECT • The skin effect depends upon the following factors : 1. Nature of material 2. Diameter of wire − increases with the diameter of wire. 3. Frequency − increases with the increase in frequency. 4. Shape of wire − less for stranded conductor than the solid conductor. • It may be noted that skin effect is negligible when the supply frequency is low (< 50 Hz) and conductor diameter is small (< 1cm).
• 47. PROXIMITY EFFECT • The current distribution may be non-uniform because of another effect known as proximity effect.
• 48. PROXIMITY EFFECT • Let each of the line conductor is assumed to be divided into 3 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 the conductor. • Due to this non-uniform distribution of current, the effective conductor resistance increases. As the distance between the conductors goes on reducing, this distribution of current becomes more and more non-uniform.
• 49. PROXIMITY EFFECT • For normal spacing of overhead lines this proximity effect is negligible. For underground cables this effect is significant as the conductors are located close to each other. • The proximity effect also depends on the same factors as that of skin effect.