Different types of conductors in transmission .ppt
- 1. Unit II Electrical Design of Transmission Lines
- 2. Electrical parameters • The performance of transmission line depends on the parameters of the line. • The transmission line has mainly four parameters, resistance, inductance, capacitance and shunt conductance. • These parameters are uniformly distributed along the line. Hence, it is also called the distributed parameter of the transmission line.
- 3. Lumped V.S. Distributed Circuits Lumped circuit: • In circuit theory, we assume the physical dimensions of a circuit element are much smaller than the electrical wavelength. • Resistor, Capacitor, Inductor, Independent and dependent sources are lumped circuit elements The voltages and currents in such a circuit are functions of time only.
- 4. Lumped V.S. Distributed Circuits Distributed Circuit: • In a distributed circuit, for example in a transmission line circuit, The size of the transmission line may be a considerable fraction of a wavelength, or many wavelengths. • Thus a transmission line can’t be modeled as a lumped circuit element. • It should be modeled as a distributed parameter network, where voltages and currents are functions of position as well as time
- 9. Skin Effect • The non-uniform distribution of electric current over the surface or skin of the conductor carrying a.c is called the skin effect. • In other words, the concentration of charge is more near the surface as compared to the core of the conductor. • The ohmic resistance of the conductor is increased due to the concentration of current on the surface of the conductor.
- 10. • Skin effect increases with the increase in frequency. • At low frequency, such as 50Hz, there is a small increase in the current density near the surface of the conductor; but, at high frequencies, such as radio frequency, practically the whole of the currents flows on the surface of the conductor. • If d.c current (frequency=0) is passed in a conductor, the current is uniformly distributed over the cross-section of the conductors.
- 11. Why skin effect occurs? • Let us consider the conductor is made up of a number of concentric cylinders. • When a.c is passed in a conductor, the magnetic flux induces in it. • The magnetic flux linking a cylindrical element near the center is greater than that linking another cylindrical element near the surface of the conductor. • This is due to the fact that the center cylindrical element is surrounded by both the internal as well as the external flux, while the external cylindrical element is surrounded by the external flux only.
- 12. • The self-inductance in the inner cylindrical element is more and, therefore, will offer a greater inductive reactance than the outer cylindrical element. • This difference in the inductive reactance gives a tendency to the current to concentrate towards the surface or skin of the conductor. • The current density is maximum at the surface of the conductor and minimum at the center of the conductor. • The effect is equivalent to a reduction of the cross-section area of the conductor and, therefore the effective resistance of the conductor is increased.
- 13. Factors affecting skin effect • Frequency – Skin effect increases with the increase in frequency. • Diameter – It increases with the increase in diameter of the conductor. • The shape of the conductor – Skin effect is more in the solid conductor and less in the stranded conductor because the surface area of the solid conductor is more. • Type of material – Skin effect increase with the increase in the permeability of the material
- 14. Proximity Effect • The alternating magnetic flux in a conductor caused by the current flowing in the neighboring conductor gives rise to circulating currents • This causes apparent raise in the value of resistance and this is known as Proximity Effect. This also produces non – uniformity of current • For normal spaced transmission lines, proximity effect is dominant whereas if the conductor spacing is increased, this effect decreases
- 15. • When two or more conductors are placed near to each other, then their electromagnetic fields interact with each other. • Due to this interaction, the current in each of them is redistributed such that the greater current density is concentrated in that part of the strand most remote from the interfering conductor. • If the conductors carry the current in the same direction, then the magnetic field of the halves of the conductors which are close to each other is cancelling each other and hence no current flow through that halves portion of the conductor. The current is crowded in the remote half portion of the conductor.
- 16. Factors Affecting the Proximity Effect • Frequency – The proximity increases with the increases in the frequency. • Diameter – The proximity effect increases with the increase in the conductor. • Structure – This effect is more on the solid conductor as compared to the stranded conductor (i.e., ASCR) because the surface area of the stranded conductor is smaller than the solid conductor. • Material – If the conductor is made up of high ferromagnetic material then the proximity effect is more on their surface.
- 18. Solid Conductor • It consists of single piece of metal wire. It is cheap for manufacturing. • Skin effect is higher in solid conductors as at higher frequencies current flow on the surface of the conductors results in the increase in the effective resistance. • The main disadvantage of the solid wire is its more rigid property. • It cannot be bent easily
- 20. Stranded or composite Conductors: • Stranded wire consists of sub conductors touch each other. It is costlier to manufacture compared to solid wire. • For the given current carrying capacity, the size of the stranded conductor is large compared to solid wire. • Different elements of strands can be wound together to get the transmission line of desired property (eg: ACSR conductor contains Aluminum and Steel stands wound together). • Proximity and skin effect is reduced using stranded conductors.
- 22. Bundle Conductors • Bundled conductor are the conductors which form from two or more stranded conductors, bundled together to get more current carrying capacity. • we use two or more stranded conductors per phase. Also, to increase the current carrying capacity of the system. • A bundled conductor reduces the reactance of the electric transmission line. • It also reduces voltage gradient, corona loss, radio interference, surge impedance of the transmission lines. Two conductor bundle Three conductor bundle Four conductor bundle
- 24. Types of Conductors • All Aluminum Conductor (AAC) • All Aluminum Alloy Conductor (AAAC) • Aluminum Conductor Steel Reinforced (ACSR) • Aluminum Conductor Aluminum-Alloy Reinforced(ACAR) • Bundle Conductors • AAC and ACSR are the most common type of conductors which use in the transmission line.
- 25. ACSR conductors • Copper - best conductors of electricity - durability - natural choice for manufacturing transmission lines. • the copper transmission line was not reliable as copper has a huge weight compared to other metals like Aluminum - support structure like cross-arms got costlier. • Also creates unwanted sag - copper itself is costly - increases the initial cost of the entire project. • copper was replaced - lighter metal Aluminum - provides good conductivity and has a low weight .
- 26. ACSR conductors • Being a light metal, the tensile strength of the aluminum conductor is low and it keeps working satisfactorily in all weathers - came the role of Aluminum Conductor Steel Reinforced (ACSR). • It has a steel core that provides the cable with the necessary tensile strength and the core is surrounded by aluminum conductors through which the electrical power is transmitted. • Aluminum has lower power loss which therefore increases the efficiency of the system. Thus, ACSR conductors are now widely used.
- 30. ACAR ( Aluminium Conductor Alloy Reinforced) • Aluminium Alloy conductor got great mechanical strength and overall electrical conductivity of the ACSR (Aluminium Conductor Alloy Reinforced) conductivity is between 56% to 60%.
- 31. AACSR (Aluminum Alloy Conductor Steel Reinforced) • Aluminum Alloy Conductor Steel Reinforced (AACSR) conductor consist of the high mechanical strength high tensile galvanized steel core covered with Aluminum alloy wires. This type of conductors can use for any rough mechanical circumstances.
- 32. ACSR (Aluminium Conductor Steel Reinforced) Conductors • Aluminum Conductor Steel Reinforced (ACSR) Conductors consist of more than seven Aluminum and steel conductors. • Center of the conductors comprised galvanized steel and outer layers of the galvanized steel comprise Aluminum conductors. • These types of conductors are much use for long spans of transmission lines because these lines got high tensile strength.
- 33. Types of circuit • Single Circuit line Single Circuit Transmission Line refers to an arrangement of conductor over the Transmission Tower. In Single Circuit Transmission Line, three conductors corresponding to three distinct phases i.e. R, Y & B phase are run on the Transmission Tower.
- 34. Double Circuit line • Refers to the arrangement in which a total of six conductors are provided to make two different set of Transmission Circuit. • In Double Circuit Transmission Line, there are two circuits each consisting of three conductors corresponding to three phases. • Both the circuits in Double Circuit Transmission Line are mounted or run through the same Transmission Line. • In Double Circuit Transmission Line, bundle conductors are mostly used.
- 35. Single and Double circuit
- 36. Ground Wire / Sky Wire / Shield Wire
- 37. Horizontal and vertical line
- 38. Multi circuit
- 41. Horizontal circuit with vertical Phases
- 42. vertical circuit with vertical Phases
- 43. Horizontal circuit with horizontal Phases