How are power towers arranged?
Power line (PTL) is one of the components of the electrical network, a system of power equipment designed to transmit electricity through electric current. Also, the electric line in the composition of such a system, beyond the power plant or substation. There are overhead and cable power lines. Recently, gas insulated lines (GIL) have become popular. Power transmission lines also transmit information using high-frequency signals (according to expert estimates, in the CIS, about 60,000 HF channels are used over power transmission lines) and VOLS. They are used for dispatcher control, telemetry data transmission, relay protection signals and emergency control. It is also noteworthy that in the 1985s, the development of transmission lines reaching a height of 70 meters were carried out.
An overhead power line pylon (power line pylon) is a structure for holding wires and, if there are ground lightning protection cables of an overhead power line and fiber-optic communication lines, at a given distance from the ground surface and from each other.
What could be the ordinary power lines? Power transmission towers - one of the most common engineering structures, and they are all the time before our eyes. However, this area also has its own technological subtleties and even room for technical progress. Not very noticeable for us overhead power lines acquire a new look and a new design.
Most often, we imagine a power transmission line support in the form of a lattice structure. About 30 years ago it was the only option, and even today they continue to be built. A set of metal corners is brought to the construction site and, step by step, a support is screwed out of these typical elements. Then comes the crane and puts the structure vertically. Such a process takes quite a lot of time, which affects the timing of the laying of lines, and these supports themselves with dull lattice silhouettes are very short-lived. The reason is poor corrosion protection. The technological imperfection of such a support complements the simple concrete foundation. If it is done in bad faith, for example using a solution of inadequate quality, then after a while the concrete will crack, water will fall into the cracks. Several cycles of freezing and thawing, and the foundation must be redone or seriously repaired.
Tubes instead of corners
We asked the representatives of PJSC ROSSETI that the alternative is replacing traditional supports made of ferrous metal. “In our company, which is the largest power grid operator in Russia,” says a specialist of this organization, “we have long tried to find a solution to the problems associated with lattice supports, and in the late 1990s, we began to switch to faceted supports. These are cylindrical racks of a curved profile, actually pipes, having a polyhedron shape in cross section. In addition, we began to apply new methods of corrosion protection, mainly the method of hot-dip galvanizing. This is an electrochemical method of applying a protective coating on the metal. In an aggressive environment, the zinc layer becomes thinner, but the carrier part of the support remains intact. ”
Electricity pylons, we usually imagine that way. However, the classic lattice design is gradually giving way to more progressive versions - multifaceted supports and supports made of composite materials.
In addition to greater durability, new supports are also distinguished by ease of installation. No corners need to be screwed anymore: the tubular elements of the future support are simply inserted into each other, then the connection is fixed. Mount such a design can be eight to ten times faster than to collect lattice. The corresponding transformations have also undergone foundations. Instead of the usual concrete began to use the so-called pile-shell. The design is lowered into the ground, the counter flange is attached to it, and the support itself is already placed on it. The estimated service life of such supports is up to 70 years, that is, approximately two times longer than that of lattice ones.
Why wires are buzzing
And the wires? They hang high above the ground and from a distance look like thick monolithic cables. In fact, high-voltage wires are twisted from wire. Conventional and ubiquitous wire has a steel core, which provides structural strength and is surrounded by aluminum wire, the so-called external layers, through which the current load is transmitted. Grease is laid between steel and aluminum. It is needed in order to reduce the friction between steel and aluminum - materials with different thermal expansion coefficients. But since the aluminum wire has a circular cross section, the coils do not abut one another, the surface of the wire has a pronounced relief. This deficiency has two consequences. First, moisture penetrates into the gap between the coils and washes away lubricant. Friction increases and conditions for corrosion are created. As a result, the service life of such a wire is not more than 12 years. To extend the service life, the wire is sometimes put on repair cuffs, which can also cause problems (more on this later). In addition, this design of the wire contributes to the creation near the air line well-distinguishable hum. It occurs because the alternating voltage of 50 Hz gives rise to an alternating magnetic field, which causes the individual wires in the wire to vibrate, which causes them to collide with each other, and we hear a characteristic buzz. In the EU, this noise is considered acoustic pollution, and is struggling with it. Now this struggle has begun with us.
“We now want to replace the old wires with wires of a new design that we are developing,” said a representative of Rosseti PJSC. - This is also steel-aluminum wire, but the wire there does not apply a circular cross section, but rather a trapezoid. Having turned it turns out dense, and the surface of a wire smooth, without cracks. There is almost no moisture to get inside, the lubricant does not wash out, the core does not rust, and the service life of such a wire is approaching thirty years. Wires of similar construction are already used in countries such as Finland and Austria. There are lines with new wires in Russia - in the Kaluga region. This line "Orbit-Sputnik" length of 37 km. And there the wires have not just a smooth surface, but also another core. It is made not of steel, but of fiberglass. Such a wire is lighter, but stronger in tearing than ordinary steel-aluminum. ”
However, the latest design achievement in this area can be considered a wire created by the American concern 3M. In these wires, the carrying capacity is provided only by conductive layers. There is no core, but the poviv themselves are reinforced with aluminum oxide, thus achieving high strength. This wire has an excellent carrying capacity, and with standard supports it can withstand spans up to 700 m long (standard 250x300 m) due to its strength and low weight. In addition, the wire is very resistant to heat loads, which leads to its use in the southern states of the United States and, for example, in Italy. However, the 3M wire has one significant drawback - the price is too high.
The original "designer" supports serve as an undoubted decoration of the landscape, but they are unlikely to be widely distributed. The priority of power grid companies is the reliability of power transmission, rather than costly “sculptures”.
Ice and strings
Overhead power lines have their natural enemies. One of them is wire icing. Especially this disaster is typical for the southern regions of Russia. At a temperature of about zero, drizzle frost falls on the wire and freezes on it. A crystal cap is formed on the top of the wire. But this is only the beginning. The cap under its weight gradually turns the wire, substituting the other side to the freezing moisture. Sooner or later, an ice coupling will form around the wire, and if the coupling weight exceeds 200 kg per meter, the wire will break and someone will be left without light. Rosseti has its own ice-fighting know-how. The line section with icy wires is disconnected from the line, but connected to a DC source. When using DC, the ohmic resistance of the wire can be practically ignored and currents can be passed, say, twice as strong as the calculated value for alternating current. The wire heats up and the ice melts. Wires dump unnecessary freight. But if there are repair clutches on the wires, then additional resistance occurs, and then the wire may burn out.
Another enemy is high-frequency and low-frequency vibrations. The tensioned wire of an overhead line is a string that, when exposed to wind, begins to vibrate at a high frequency. If this frequency coincides with the natural frequency of the wire and the amplitude coincides, the wire may break. To cope with this problem, special devices are installed on the lines - vibration dampers, having the form of a cable with two weights. This design, which has its own oscillation frequency, upsets the amplitudes and dampens vibrations.
With the low-frequency oscillations associated with such a harmful effect as the "wire dancing." When a break occurs on the line (for example, due to the formation of ice), there are oscillations of wires that go a wave further, through several spans. As a result, five to seven supports that make up the anchor span (the distance between two supports with rigid wire fastening) may bend or even fall. A well-known means of combating "dancing" is to establish interfacial struts between adjacent wires. In the presence of a spacer wires will mutually dampen their vibrations. Another option is the use of supports made of composite materials on the line, in particular of fiberglass. Unlike metal supports, the composite has the property of elastic deformation and can easily “play back” the oscillations of the wires, bending down and then restoring the vertical position. Such a support can prevent the cascade fall of a whole line segment.
The photo clearly shows the difference between the traditional high-voltage wire and the wire of a new design. Instead of round wire, a pre-deformed wire was used, and the core of the steel core was taken by a composite core.
Of course, there are all sorts of unique cases associated with the laying of overhead lines. For example, when installing supports in flooded soil or in permafrost conditions, ordinary piles for the foundation will not work. Then screw piles are used, which are screwed into the ground as a screw, in order to achieve the strongest possible foundation. A special case is the passage of power lines wide water barriers. They use special high-rise supports, which weigh ten times more than usual and have a height of 250x270 m. Since the span length can be more than two kilometers, a special wire with a reinforced core is used, which is additionally supported by a load line. This is how, for example, the transition of power lines through the Kama with a span of 2250 m.
A separate group of supports are structures designed not only to hold the wires, but also to carry a certain aesthetic value, such as sculpture-supports. In 2006, Rosseti initiated a project to develop supports with an original design. There were interesting works, but their authors, designers, often could not assess the feasibility and adaptability of the engineering embodiment of these structures. In general, it must be said that supports in which an artistic concept is embedded, such as figure supports in Sochi, are usually installed not on the initiative of grid companies, but on the order of some third-party commercial or government organizations. For example, in the United States popular support in the form of the letter M, stylized logo of the fast food chain "McDonald's".
Via popmech.ru & wiki