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| Transmission Line |
A transmission line is a pair of electrical conductors that carry electrical signals from one place to another. Examples are coaxial cable and twisted cable.
The length of two conductors is per unit, which we can measure based on their size and shape. They have capacitance per unit length, which we can calculate from the dielectric constant of insulation. In the early days of cable manufacturing, leakage from insulation existed, but in modern cables, such leakage is negligible.
The electrical resistance of the conductor, however, is important because it increases with frequency. The magnetic fields generated by the high-frequency current carry those currents to the conductor’s conductor, so that the higher the frequency, the thinner the layer of metal, and the more effective resistance of the cable.
In this discussion we explore and demonstrate these equations that control the transmission of waves down a transmission line and explain how the frequency-dependent resistance of these cables leads to attenuation and distortion of high frequency signals .
In radio frequency engineering, a transmission line is a special cable or other structure designed to handle the alternating current of the radio frequency, that is, the frequency current must take into account their wave nature.
Broadcast lines are used for the purpose of connecting radio transmitters and receivers to their antennas (they are then called feed lines or feeders), cable television signal distribution, telephone switching centers, computer network connections, and high-speed computer data data. Routing the trunkline between.
The distance between the line and the land is greater for security purposes. Electrical towers are used to support the conductors of the transmission line.
The conductor is made of steel to provide high strength. For high voltage transmissions, high voltage direct current over long distances is used in the transmission line.
Constants of a Transmission Line
A transmission line no longer most effective has an ohmic resistance but in addition inductance and capacitance between its conductors. These are often called the constants of a transmission line. At the same time calculating the drop in a.C. Transmission and distribution circuits, we can need to do not forget (i) resistive or ohmic drop—in section with the present (ii) inductive drop—leading the present by means of ninety° and (iii) the capacitive drop and charging present taken by using the capacitance of the line. The capacitance and hence the charging present is frequently negligible for brief transmission traces.
Capacitance of a Single-phase Transmission Line
We know that any two conductors which might be separated via an insulating medium represent a capacitor. When a capabilities difference is headquartered throughout two such conductors, the present flows in at one conductor and out on the different as long as that p.D. Is maintained. The conductors of an overhead transmission line fulfil these stipulations, therefore when an alternating talents change is applied across a transmission line, it draws a leading current even when it is unloaded. This leading current is in quadrature with the utilized voltage and is often called the charging present. Its value relies on voltage, the capacitance of the road and the frequency of alternating present.
Effect of Capacitance
Thus far now we have neglected the influence of capacitance on the line regulation when you consider that the capacitances of short lines transmitting at quite low voltages (as much as 20 kV) are negligible. However as the voltage and length of the transmission line increase, the capacitance gradually becomes of higher importance. In a similar way, the leakage throughout insulators additionally assumes bigger value. Consequently, distinct calculations of regulation for lengthy lines take into consideration the capacitance and leakage reactance of the traces and are relatively problematic, the amount of elaboration depending on the transmitting voltage. (i) in the case of brief lines, frequently, the capacitance is negligible. But when in a crisis, the line capacitance is given and if the line is less than eighty km, then the road capacitance can be lumped at the receiving or load end. (a) despite the fact that this process of localizing the road capacitance on the load finish over-estimates the result of capacitance. If so, the road current IS is the vector sum of the weight current IR and the charging current IC of the capacitance.
“Nominal” π-method
In this method, the line-to-neutral capacitance is divided into two halves ; one half being concentrated or localized at the sending-end and the other half at the receiving-end. The capacitance at the sending or generating end has no effect on line drop or line regulation but its charging current must be added to the line current in order to obtain the total sending-end current IS.
Ferranti Effect
A long or medium transmission line has giant capacitance and so attracts leading charging current from the generating-end even when unloaded. Furthermore, receiving-end voltage VR beneath no-load situation is discovered to be bigger than sending-finish voltage VS. This phenomenon is known as Ferranti result.
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