Resistance and inductance together is called transmission line impedance. In this article we will discuss about the line resistance and inductance. In the next article we will discuss about line capacitance and conductance.
Construction[ edit ] A man working on powerlines in Nauru Towers for support of the lines are made of wood as-grown or laminatedsteel or aluminum either lattice structures or tubular polesconcrete, and occasionally reinforced plastics.
The bare wire conductors on the line are generally made of aluminum either plain or reinforced with steelor composite materials such as carbon and glass fiberthough some copper wires are used in medium-voltage distribution and low-voltage connections to customer premises.
A major goal of overhead power line design is to maintain adequate clearance between energized conductors and the ground so as to prevent dangerous contact with the line, and to provide reliable support for the conductors, resilience to storms, ice loads, earthquakes and other potential damage causes.
Low voltage LV — less than volts, used for connection between a residential or small commercial customer and the utility. Medium voltage MV; distribution — between volts 1 kV and 69 kV, used for distribution in urban and rural areas.
Ultra high voltage UHV — higher than kV. The Financial Times reported UHV lines are a "game changer", making a global electricity grid potentially feasible. StateGrid said that compared to conventional lines, UHV enables the transmission of five time more power, over six times the distance.
Transmission tower Structures for overhead lines take a variety of shapes depending on the type of line. Structures may be as simple as wood poles directly set in the earth, carrying one or more cross-arm beams to support conductors, or "armless" construction with conductors supported on insulators attached to the side of the pole.
Tubular steel poles are typically used in urban areas. High-voltage lines are often carried on lattice-type steel towers or pylons. For remote areas, aluminum towers may be placed by helicopters. Each structure must be designed for the loads imposed on it by the conductors.
Where conductors are in a straight line, towers need only resist the weight since the tension in the conductors approximately balances with no resultant force on the structure. Flexible conductors supported at their ends approximate the form of a catenaryand much of the analysis for construction of transmission lines relies on the properties of this form.
Depending on the design criteria for a particular line, semi-flexible type structures may rely on the weight of the conductors to be balanced on both sides of each tower.
More rigid structures may be intended to remain standing even if one or more conductors is broken. Such structures may be installed at intervals in power lines to limit the scale of cascading tower failures.
Each structure may be stabilized considerably by the use of guy wires to counteract some of the forces applied by the conductors.
In some cases the lines are buried to avoid this, but this " undergrounding " is more expensive and therefore not common. For a single wood utility pole structure, a pole is placed in the ground, then three crossarms extend from this, either staggered or all to one side.
The insulators are attached to the crossarms. For an "H"-type wood pole structure, two poles are placed in the ground, then a crossbar is placed on top of these, extending to both sides.
The insulators are attached at the ends and in the middle.
Lattice tower structures have two common forms. One has a pyramidal base, then a vertical section, where three crossarms extend out, typically staggered. The strain insulators are attached to the crossarms.
Another has a pyramidal base, which extends to four support points.The conductors of the transmission lines have small resistance. For short lines, resistance plays an important role.
As the line current increases so do the ohmic loss (I 2 R loss). When the current exceed a certain value the heat generated due to ohmic loss starts to melt the conductor and the conductor becomes longer that results in more sag.
Table: Wave Velocity and Characteristic Impedance of Various Mediums. Each medium acts as a transmission line. The velocity is v and the characteristic impedance is Z..
The high-frequency resistance of wires is proportional to √ω, due to the skin effect, which we will discuss lausannecongress2018.com now, the table gives R for f = ω/2π ≤ 1 kHz.
We obtained R for . Determining Characteristic Impedance of Transmission Lines with the MSA Sam Wetterlin 11/26/09 This document demonstrates methods of using the MSA to determine the characteristic. Time domain reflectometer circuit.
Time Domain Reflectometer (TDR) Copyright Tomi Engdahl Summary of circuit features. Power Transmission.
Long distance transmission of electrical power is one of the major challenges of the electrical age. The goals which engineers have been working towards have remained the same despite many other things changing over the years. The conductors of the transmission lines have small resistance.
For short lines, resistance plays an important role. As the line current increases so do the ohmic loss (I 2 R loss). When the current exceed a certain value the heat generated due to ohmic loss starts to melt the conductor and the conductor becomes longer that results in more sag.