It has already been mentioned that transmission of electrical power is completed by 3-phase, 3-wire overhead lines. An a.c. the conductor has resistance, inductance, and capacitance uniformly distributed on its length. These are called constants or parameters of the road.
The performance of a conductor depends to a substantial extent upon these constants. for example, these constants verify whether or not the potency and voltage regulation of the road are going to be sensible or poor.
Therefore, a sound thought of those constants is important so as to form the electrical style of a conductor a technical success. during this chapter, we tend to shall focus our attention on the strategies of scheming these constants for a given conductor. Out of those 3 parameters of a conductor, we tend to shall pay the greatest attention to inductance and capacitance. Resistance is actually of equal importance however needs less clarification since it’s not a perform of conductor arrangement.
Constants of a Transmission Line:
A line has resistance, inductance, and capacitance uniformly distributed on the complete length of the road. Before we tend to pass away to the strategies of finding these constants for a line, it’s profitable to know them totally.
- Resistance: It is the opposition of line conductors to current flow. The resistance is distributed uniformly on the complete length of the road. However, the performance of a line is often analyzed handily if distributed resistance is taken into account as lumped.
- Inductance: When associate degree electricity flows through a conductor, a dynamic flux is ready up that links the conductor. because of these flux linkages, the conductor possesses inductance. Mathematically, inductance is outlined because of the flux linkages per ampere.
- Capacitance: We know that associate degree 2 conductors separated by an insulant represent a capacitance. As associate degree 2 conductors of associate degree overhead line area unit separated by air that acts as an insulation, therefore, capacitance exists between any 2 overhead line conductors.
The capacitance is uniformly distributed on the total length of the road and should be regarded as a consistent series of capacitors connected between the conductors When an alternating voltage is affected on a cable, the charge on the conductors at any purpose increases and reduces with the rise and reduce of the instant price of the voltage between conductors at that time.
When a conductor is carrying steady electricity (d.c.), this current is uniformly distributed over the full X-section of the conductor. However, Associate in Nursing AC flowing through the conductor doesn’t distribute uniformly, rather it’s the tendency to concentrate close to the surface of the conductor.
Due to the electrical phenomenon, the effective space of crosswise of the conductor through that current flows is reduced. Consequently, the resistance of the conductor is slightly inflated once carrying Associate in Nursing AC. The reason for the electrical phenomenon will be simply explained. A solid conductor could also be thought to be consisting of an oversized variety of strands, each carrying a tiny low a part of this. The inductance of every strand can vary in line with its position. Thus, the strands close to the center area unit enclosed by a bigger magnetic flux and thus have larger inductance than that close to the surface.
causes the alternating current to flow near the surface of the conductor. This crowding of current near the conductor surface is the skin effect. The skin effect depends on the following factors:
- Nature of material
- Diameter of wire
- Shape of wire
As explicit earlier, the inductance of a circuit is outlined because of the flux linkages per unit current. Therefore, so as to search out the inductance of a circuit, the determination of flux linkages is of primary importance. we tend to shall discuss 2 necessary cases of flux linkages.
1. Flux linkages due to a single current carrying conductor:
Consider a protracted straight cylindrical conductor of radius r meters and carrying a current I amperes (r.m.s.). This current can found out the magnetic flux. The magnetic lines of force can exist within the conductor also as outside the conductor. each these fluxes can contribute to the inductance of the conductor.
Flux linkages due to internal flux:
where the X-section of the conductor is shown exaggerated for clarity. The magnetic flux intensity at a degree x meter from the center is given.
Flux linkages due to external flux:
Now allow us to calculate the flux linkages of the conductor thanks to external flux. The external flux extends from the surface of the conductor to time. concerning Fig. 9.5, the sphere intensity at a distance x meters (from center) outside the conductor.
2. Flux linkages in the parallel current carrying conductors:
We shall currently confirm the flux linkages in an exceeding cluster of parallel current carrying conductors. the conductors A, B, C, etc. carrying currents Iowa, IB, IC, etc. allow us to take into account the flux linkages with on conductor, say conductor A. there’ll be flux linkages with conductor A because of its own currency as mentioned antecedently. Also, there’ll be flux linkages with this conductor because of the coefficient effects of IB, IC, ID, etc. we tend to shall currently confirm the entire flux linkages with conductor A.