Types of Overhead Power Lines

An overhead power line is a structure used in the distribution and transmission of electric electricity across long distances. It consists of one or more uninsulated electric wires stretched from towers or poles, typically in multiples of three for three-phase power.

For huge amounts of electric energy, overhead power lines are typically the least expensive type of power transmission because the majority of the insulation is provided by the surrounding air.

Construction:

Concrete, steel, or aluminum (in the form of lattice structures or tubular poles), and occasionally reinforced plastics are used to construct towers that support the lines. The bare wire conductors on the line are normally constructed of aluminum, despite the fact that various types of wire, particularly copper, are used in medium-voltage distribution and low-voltage connections to customer premises (either plain or reinforced with steel or composite materials such as carbon and glass fiber). Maintaining sufficient distance between energized conductors and the ground is important for preventing unsafe contact with the line and for providing the conductors with dependable support that is resilient to storms, ice loads, earthquakes, and other potential damage-causing factors. Currently, voltages are commonly used to operate overhead lines.

The transmission system

The transmission system connects the load and the power plant. The transmission lines of the power system network span a considerable area. The analysis and design of the transmission network is the most crucial duty.

Resistance (R), inductance (L), and capacitance (C) are the three constants that make up an overhead transmission line (C). Over the whole transmission line's length, these parameters are distributed evenly. The series impedance is made up of resistance and inductance. Capacitance exists between the conductors and between the conductor and the natural in a single-phase line. The capacitance creates a shunt route along the entire length of a three-phase transmission line. As a result, the modeling and calculation of transmission lines are made more difficult by the capacitance effects.

Based on how capacitance is considered, there are three different types of overhead transmission lines.

Short transmission line

A line is regarded as a short transmission line when its length is less than 50 km. The line voltage is 20 kV, which is extremely low. Short overhead lines ignore the capacitance effect. Because the length is short and the voltage is low, the capacitance impact is minimal. Therefore, the capacitance impact on overhead transmission lines is ignored. Therefore, only resistance and inductance are considered while planning, modeling, and researching the performance of the short line.

Medium transmission line

This type of overhead line is regarded as a medium transmission line when the line's length is between 50 km and 150 km and the voltage is between 20 kV and 100 kV. The capacitance impact in this kind of line cannot be disregarded. Therefore, the capacitance impact must be taken into account when analyzing the line's performance.

The medium transmission line is further divided into three sections based on the distribution of the effect of capacitance: the end condenser method, the nominal T method, and the nominal PI method.

long transmission line

A transmission line is said to be a long transmission line if its length exceeds 150 km. The voltage in this type of transmission line is greater than 100 kV. The capacitance effect is assumed to be evenly distributed along the full length of the line when modeling and designing a long overhead transmission line. the exact process used to solve a complex transmission line mathematical model.

Additional applications

In some cases, transmitting antennas are supplied by overhead lines, particularly for the effective transmission of the long, medium, and short waves. A staggering array line is frequently used for this purpose. The conductor cables for the transmitting antenna's earth net supply are joined to the outside of a ring. The conductor inside the circle is fastened to insulators going to the antenna's high-voltage standing feeder.

Conductor:

One of the most crucial parts of overhead cables is the conductor. As crucial as choosing a reasonable conductor size and reasonable transmission voltage is choosing the right type of conductor for overhead lines.

Characteristics of a good conductor ought to possess:

● high conductivity of electricity

● to endure mechanical forces, the material must have a high tensile strength.

● relatively lower cost without compromising much of other properties

● lower weight per unit volume

Types of conductor

The type of material utilized determines how the conductors are categorized.

Homogeneous conductor (i.e. copper, AAC, AAAC)

Non-homogeneous conductor (i.e. ACAR, ACSR, ACSS, AACSR)

AAC (All Aluminum Conductor)

Features

● One or more strands of hard-drawn aluminum alloy make up AAC.

● Due to the huge spans used, it has a restricted application in transmission lines and rural distribution

● Good Conductivity 61.2% IACS

● Good Corrosion Resistance

● High Conductivity to Weight Ratio

● Moderate Strength

Application

● When a maximum current transmission is required over a short spans, it is employed.

● Aluminum's superior resistance to corrosion has made AAC a popular conductor in coastal environments.

● It has been extensively used in urban areas where spans are often short but high conductivity is necessary because to its relatively low strength to weight ratio.

● All voltage levels of a transmission line require these conductors. It can be utilized in overhead transmission lines with low, medium, and high voltages.