Each of us is aware of how important power transmission lines (power lines) play in our lives. We can say that the energy that they carry nourishes our lives. Almost any work is impossible without the use of electricity.

Power lines - one of the foundations of the energy complex

The main advantage of transmitting precisely electric energy is the minimum time during which the receiving device will receive power. This is explained by the propagation velocity of the electromagnetic field and provides widespread transmission lines. Electricity is transmitted over fairly long distances. This requires additional tricks to reduce losses.

Types of power lines

For the convenience of perceiving information, as well as for proper documentation in the field of electric power, transmission lines are classified according to several indicators. Here are some of them.

Mounting method

The main criterion by which power lines are classified is a constructive method of energy transfer. The lines are divided into the following types:

• aerial - electric current is transmitted through wires suspended on special supports;
• cable - electric current is transmitted by means of power cables laid in the ground, cable duct or engineering structures of a different kind.

Line voltage

Depending on the characteristics of the network, the length of the line, the number of consumers and their needs, power lines are divided into the following voltage classes:

• lowest (voltage less than 1 kV);
• medium (voltage in the range from 1 kV to 35 kV);
• high (voltage in the range from 110 kV to 220 kV);
• ultra-high (voltage in the range from 330 kV to 750 kV);
• ultra-high (voltage above 750 kV).

Type of transmitted current

According to this criterion, power lines are divided into the following types:

1. aC lines
2. dC lines.

DC lines are not widespread, although they have lower costs when transmitting energy over long distances. This is primarily due to the high cost of equipment.

The composition of power lines

The composition of the cable and overhead lines are different. For differentiation, we consider each type of power line separately.

Overhead Power Line Components

VL in its composition have many devices and structures. We list the main ones:

1. supports;
2. fittings and insulators;
3. grounding devices;
4. wires and cables;
5. bit devices;
6. wire markers;
7. substations.

In addition to direct use, overhead lines are used as engineering structures for suspending a fiber optic communication cable. In this regard, on some lines the number of constituent elements is constantly growing.

Cable Power Line Components

Cable lines are used to transfer electric energy in places inaccessible for suspension along the overhead lines. The structure includes a power cable and input nodes at substations and to end consumers.

High voltage justification

It is customary for consumers to deliver an electric current of 220 and 380 volts. However, in conditions of long lines, this is not profitable, since losses in sections longer than 2 km may not be comparable with the required power consumption.

In order to reduce losses over long distances, they increase power and transmit high voltage current. For this, step-up substations are used before transmission, and step-down transformers are placed in front of the consumer. Thus, the transmission line is as follows:

How can you indicate the meaning of power lines? Is there an exact definition of the wires through which electricity is transmitted? Intersectoral Rules technical operation consumers' electrical installations have an accurate definition. So, a power line is, firstly, an electric line. Secondly, these are sections of wires that go beyond substations and power plants. Thirdly, the main purpose of power lines is the transmission of electric current at a distance.

According to the same rules of MPTEP, power lines are divided into air and cable. But it should be noted that high-frequency signals are also transmitted along power lines, which are used to transmit telemetric data, for dispatch control of various industries, for emergency control signals and relay protection. According to statistics, 60,000 high-frequency channels today go through power lines. Let's face it, the figure is significant.

Aerial power lines

Overhead power lines, they are usually denoted by the letters "VL" - these are devices that are located outdoors. That is, the wires themselves are laid through the air and fixed on special fittings (brackets, insulators). Moreover, their installation can be carried out on poles, and on bridges, and overpasses. It is not necessary to consider “VL” those lines that are laid only on high-voltage poles.

What is included in overhead power lines:

• The main thing is the wires.
• Traverses, with the help of which the conditions of impossibility of contact of wires with other elements of supports are created.
• Insulators.
• The supports themselves.
• Ground loop
• Lightning rods.
• Arresters.

That is, a power line is not just wires and supports, as you can see, it is a rather impressive list of various elements, each of which carries its own specific load. Fiber optic cables and their accessories can also be added here. Of course, if high-frequency communication channels are conducted along the transmission line poles.

The construction of the power transmission line, as well as its design, plus the structural features of the supports are determined by the rules for the installation of electrical installations, that is, PUE, as well as various construction rules and norms, that is, SNiP. In general, the construction of power lines is not an easy and very responsible matter. Therefore, their construction is carried out by specialized organizations and companies, where the state has highly qualified specialists.

Classification of Overhead Power Lines

The high-voltage overhead power lines themselves are divided into several classes.

By type of current:

• Variable
• Permanent.

At its core, air overhead lines are used to transmit alternating current. Rarely can you find the second option. Usually it is used to power a contact or connected network to provide several power systems with communication, there are other types.

By voltage, overhead power lines are divided by the nominal value of this indicator. For information, we list them:

• for alternating current: 0.4; 6; ten; 35; 110; 150; 220; 330; 400; 500; 750; 1150 kilovolt (kW);
• for constant, only one type of voltage is used - 400 kV.

At the same time, power lines with voltages up to 1.0 kV are considered to be of the lower class, from 1.0 to 35 kV - medium, from 110 to 220 kV - high, from 330 to 500 kV - ultra-high, above 750 kV ultra-high. It should be noted that all these groups differ from each other only in requirements for design conditions and design features. In all other respects, these are ordinary high-voltage power lines.

Power line voltage corresponds to their purpose.

• High-voltage lines with voltages above 500 kV are considered ultra-long, they are designed to connect separate power systems.
• High-voltage line voltage of 220, 330 kV are considered trunk. Their main purpose is to interconnect powerful power plants, separate power systems, as well as power plants within these systems.
• 35-150 kV overhead power transmission lines are installed between consumers (large enterprises or settlements) and distribution points.
• Overhead lines up to 20 kV are used as power lines that directly supply electric current to the consumer.

Classification of power lines by neutral

• Three-phase networks in which the neutral is not grounded. Typically, such a circuit is used in networks with a voltage of 3-35 kV, where small currents flow.
• Three-phase networks in which the neutral is grounded through inductance. This is the so-called resonant-grounded type. In such overhead lines, a voltage of 3-35 kV is used, in which large currents flow.
• Three-phase networks in which the neutral bus is fully grounded (effectively grounded). This neutral mode of operation is used in overhead lines with medium and ultra-high voltage. Please note that in such networks it is necessary to use transformers, not autotransformers, in which the neutral is grounded tightly.
• And, of course, networks with earthed neutral. In this mode, overhead lines operating below 1.0 kV and above 220 kV operate.

Unfortunately, there is such a separation of power lines, which takes into account the operational state of all power transmission line elements. This is a power line in the normal state, where the wires, supports and other components are in good condition. The main emphasis is on the quality of wires and cables, they should not be torn off. An emergency condition where the quality of wires and cables leaves much to be desired. And the mounting state when repairing or replacing wires, insulators, brackets, and other power line components is performed.

Elements of an overhead power line

There are always conversations between specialists in which special terms are applied to power lines. Uninitiated in the subtleties of slang to understand this conversation is quite difficult. Therefore, we offer a breakdown of these terms.

• The route is the axis of the transmission line, which runs along the surface of the earth.
• PC pickets. In fact, these are segments of the power transmission line. Their length depends on the terrain and the rated voltage of the route. Zero picket is the beginning of the track.
• The construction of the support is indicated by a center sign. This is the center of the support.
• Picket - in fact, this is a simple installation of pickets.
• Span is the distance between the supports, or rather, between their centers.
• The sag arrow is the delta between the lowest point of the wire sag and the strictly taut line between the supports.
• The size of the wire is again the distance between the lowest point of the sag and the highest point of the engineering structures running under the wires.
• Loop or loop. This is the part of the wire that connects the wires of adjacent spans on the anchor support.

Cable power lines

So, we turn to the consideration of such a thing as cable power lines. To begin with, these are not bare wires that are used in overhead power lines, these are cables closed in insulation. Typically, cable lines are several lines installed next to each other in a parallel direction. Cable lengths are not enough for this, so connecting couplings are installed between the sections. By the way, it is often possible to meet cable power lines with oil filling, so such networks are often equipped with special low-filling equipment and an alarm system that responds to oil pressure inside the cable.

If we talk about the classification of cable lines, then they are identical to the classification of overhead lines. There are distinctive features, but not many. Basically, these two categories differ in the way they are laid, as well as design features. For example, according to the type of installation, cable power lines are divided into underground, underwater and by structures.

The first two positions are understandable, but what about the “buildings” position?

• Cable tunnels. These are special closed corridors in which the cable is laid according to the installed supporting structures. In these tunnels you can walk freely, carrying out installation, repair and maintenance of the power line.
• Cable channels. Most often they are buried or partially buried channels. They can be laid in the ground, under the floor, under the ceilings. These are small channels in which it is impossible to walk. To check or install the cable, you have to dismantle the ceiling.
• Cable shaft. This is a vertical corridor with a rectangular cross section. A mine can be a walk-through, that is, with the ability to fit a person into it, for which it is equipped with a ladder. Or impassable. In this case, you can get to the cable line only by removing one of the walls of the structure.
• Cable floor. This is a technical space, usually 1.8 m high, equipped with bottom and top slabs.
• It is possible to lay cable power lines in the gap between the floor slabs and the floor of the room.
• The cable block is a complex structure consisting of laying pipes and several wells.
• The chamber is an underground structure, closed from above with reinforced concrete or slab. In such a chamber, couplings of sections of a cable power line are connected.
• An overpass is a horizontal or inclined structure open type. It can be above ground or above ground, walk-through or impassable.
• The gallery is almost the same as the flyover, only of a closed type.

And the last classification in cable power lines Is a type of insulation. In principle, there are two main types: solid insulation and liquid. The first includes insulating braids made of polymers (polyvinyl chloride, crosslinked polyethylene, ethylene-propylene rubber), as well as other types, for example, oiled paper, rubber-paper braid. Liquid insulators include petroleum oil. There are other types of insulation, for example, special gases or other types of solid materials. But they are used very rarely today.

Conclusion on the topic

A variety of power lines comes down to the classification of two main types: air and cable. Both options are used everywhere today, so you should not separate one from the other and give preference to one over the other. Of course, the construction of overhead lines is fraught with large investments, because the laying of the route is the installation of supports mainly metal, which have a rather complicated structure. This takes into account which network, under what voltage will be laid.