home › BY › Icing of power lines. De-icing power lines, pak fa and other best letters of the month. The computer will choose the optimal system

Icing of power lines. De-icing power lines, pak fa and other best letters of the month. The computer will choose the optimal system

The invention relates to electrical engineering, in particular to devices that prevent the formation of ice on the wires of overhead high-voltage power lines (power lines) without disconnecting consumers. The technical result consists in the simplicity and efficiency of the claimed device, and, if possible, the removal of existing ice formations without disconnecting consumers and without complicating the power transmission line, i.e. without adding redundant or bypass wires. The device includes a current source external to the power line, configured to connect to the current-carrying wires of the power line, wherein the current source is made in the form of a high-frequency generator, made to provide power calculated by the formula P Г =q·A·ΔT, where q is the heat transfer coefficient of the upper hot layer of the wire to the air, A is the surface area of the wires, ΔT is the heating temperature of the wire relative to the ambient temperature; in this case, the output of the generator is connected to the input of a capacitive-type matching device, designed to match the output resistance of the high-frequency generator with the input resistance of the power line and having the number of outputs corresponding to the number of wires of the power line. 2 n.p. f-ly, 7 ill.

Power engineers consider icing of power lines as one of the most serious disasters. This phenomenon is characterized by the formation of a dense ice deposit when supercooled drops of rain, drizzle or fog freeze predominantly at temperatures from 0 to -5 ° C on power transmission line wires. The thickness of ice on overhead high-voltage power lines can reach 60-70 mm, significantly weighing down the wires. Simple calculations show that, for example, the mass of an AC-185/43 wire with a diameter of 19.6 mm, a length of 1 km and a mass of 846 kg increases by 3.7 times with an ice thickness of 20 mm, and by 9 times with a thickness of 40 mm, with a thickness of 60 mm - 17 times. At the same time, the total mass of a power transmission line of 8 wires 1 km long increases to 25, 60 and 115 tons, respectively, which leads to breakage of wires and breakdown of load-bearing supports.

Such accidents cause significant economic damage, interrupting the power supply to businesses and homes. Eliminating the consequences of such accidents sometimes takes considerable time and huge amounts of money are spent. Such accidents occur annually in many countries in the northern and central zone. In Russia alone, major accidents due to ice during the period from 1971 to 2001 occurred repeatedly in 44 power systems (see Diagnostics, reconstruction and operation of overhead power lines in icy areas. / I.I. Levchenko, A.S. Zasypkin, A.A. Alliluyev, E.I. Satsuk. - M.: MPEI Publishing House, 2007). Only one accident in the Sochi power grid in December 2001 led to damage to 2.5 thousand km of overhead power lines with voltages up to 220 kV and the cessation of power supply to a huge region (see).

Numerous methods are known to combat this phenomenon, based on mechanical or thermal effects on the ice crust. In this case, preference is given in various ways melting ice, since mechanical means often cannot be used in hard-to-reach mountainous and forested areas. Electric melting is the most common way to combat ice on overhead high-voltage power lines. Ice is melted by heating the supporting or auxiliary wires with direct or alternating current with a frequency of 50 Hz to a temperature of 100-130 ° C (see, and also Dyakov A.F., Zasypkin A.S., Levchenko I.I. Prevention and elimination ice accidents in electrical networks. - Pyatigorsk, from RP “Yuzhenergotekhnadzor”, 2000 and Rudakova R.M., Vavilova I.V., Golubkov I.E. Fighting ice in power grid enterprises. - Ufa, Ufa State Aviation Technical University, 1995).

There is a known method for removing ice by passing short-circuit current through the split-phase wires of a power transmission line (see A.S. No. 587547). Short circuit current is an emergency mode for a power line and with a high degree of probability can lead to annealing of wires with subsequent irreversible loss of strength, which is unacceptable. The problem is aggravated by the fact that a single short-circuit current may not be sufficient to complete removal ice, and short circuits will have to be repeated several times, which will further aggravate the consequences.

Let's consider theoretical basis a way to combat ice by short-circuiting wires.

Let the required current for melting ice due to heating the wire on which it is frozen is I PL. Then, when melting with direct current, the required voltage of the power source is

where R PR is the active resistance of the wires, and when melting with alternating current from the network

where X PR =2πFL PR =314L PR - reactance due to the inductance of the wires L PR at a frequency of F=50 Hz. For the ratio of these two voltages at the same melting currents, according to (1) and (2), we obtain

Since the value of K U in lines of considerable length and cross-section, due to the relatively large inductance of the wires, can reach 5-10, it is more economically profitable to perform melting with direct current, at which the voltage of the power source, and, accordingly, its power according to (3) is reduced by 5-10 times compared to AC source. True, this requires the use of special powerful high-voltage rectifier units. Therefore, alternating current melting is usually used on high-voltage lines with voltages of 110 kV and below, and direct current - above 110 kV. As an example, we point out that the melting current at a voltage of 110 kV can reach 1000 A, the required power is 190 million volt-amperes, the melting temperature is 130 ° C (see and).

Thus, melting ice by electric current is a rather complex, dangerous and expensive undertaking with the shutdown of all consumers. In addition, once the wires have been cleared of ice, if the climatic conditions have not changed, they will become covered with ice again, and melting will have to be carried out again and again.

Sometimes heating the wires is combined with mechanical stress. For example, RF patent No. 2166826 proposes a method for removing ice from overhead wires and power lines, which involves passing alternating current or current pulses with a frequency close to mechanical resonance and an amplitude sufficient to overcome external and internal forces friction, and the change in the transmitted alternating current can be strictly periodic, have a swinging frequency, change according to a harmonic law, have the form of pulse trains with given laws of change in frequency, amplitude and duty cycle. The parameters of the electric current passed through double or multiple wires of the contact network and power lines are selected so as to set the wires into oscillatory motion. As you know, conductors with unidirectional current flow attract each other. At the same time, when the wires hit each other, potential energy accumulates in the form of elastic deformation. Consequently, an oscillatory system is obtained, which, with appropriate selection of the frequency, amplitude and duty cycle of the current pulses, can begin to oscillate and enter into resonance. Acceleration of ice removal is achieved due to the fact that heating of the wires will be accompanied by mechanical impacts of the wires against each other. Reducing energy costs is achieved by significantly reducing the time required to remove ice from wires and reducing the amount of current passed. Increased safety is achieved by eliminating short circuit conditions. Reducing the impact on communication lines and preventing failures of electronic equipment also occurs due to the elimination of short circuit modes. This method is very difficult to implement, and in addition, as in other considered methods, it is necessary to disconnect consumers during the defrosting procedure.

The closest to the claimed device is the technical solution described in RF patent No. 2316866. The prototype is characterized by the fact that the device consists of two groups of wires insulated from each other, which at one end are connected to each other and to the wire of the subsequent section of the overhead line, and at the other end the first group of wires is connected to the wire of the previous section of the overhead line, and between the first and second groups of wires turn on an independent voltage source.

The prototype device for preventing the formation of ice on an overhead line is shown in Figure 1 and consists of the first 1 and second 2 groups of wires insulated from each other, which are connected at one end to each other and to the wire of the subsequent section of the power line 3, and at the other - the first group The wire is connected to the wire of the previous section of the power line 4, and an independent voltage source 5 is connected between the first 1 and second 2 groups of wires.

The main current of the line passes from the wire of the previous section of the power line 4 to the first group of wires 1 and then to the wire of the next section of the power line 3. Voltage is applied from an independent source 5 between the first group of wires 1 and the second group of wires 2.

From the theoretical calculations given by the authors of the prototype, it follows that in order to prevent the formation of ice, for example, on the ASU 95/16 wire, the temperature rise of the wire relative to the environment should be equal to 5 ° C at a wind speed of 3 m/s. In this case, 36 kW/10 km should be released on the wire. At rated current of this wire, the active losses over a length of 10 km are 28 kW/10 km. Therefore, the power from an independent voltage source 5 should be 8 kW/10 km. If there is no line load, then the power of independent source 5 should be 36 kW/10 km.

If the second group of wires is an insulated steel wire with a diameter of 4.5 mm, then with the loss power of this wire being 36 kW/10 km, the voltage of the independent source 5 will be 2.1 kV and the current 17 A. With an insulated second group of wires made of aluminum, with a power loss of 36 kW/10 km, the voltage of the independent source will be 0.8 kV and the current will be 45 A.

The independent voltage source can be a voltage transformer fed from the 0.38 kV mains with 63 kV insulation to ground for a 110 kV substation, or a transformer away from the substation fed directly from the 110 kV overhead lines.

The most attractive feature of this solution is the ability to use it without disconnecting consumers. However, the disadvantage this method is to complicate the design of the entire power line due to the creation of “bypass” groups of wires that take on the load during the defrosting period of the main wire.

The problem to be solved by the claimed invention is to develop a fairly simple and economical device for preventing the formation of ice on overhead high-voltage power lines and, if possible, removing existing ice formations without disconnecting consumers and without complicating the power transmission line, i.e. without adding redundant or bypass wires. Moreover, to achieve such results, it is desirable that such a device be based on a new, more effective way. As a prototype of the method, it makes sense to point to a solution that uses wire heating using an external current source without disconnecting consumers.

The technical result in relation to the method is achieved due to the fact that an improved method has been developed for heating current-carrying wires, at least two wires, by applying high-frequency voltage to them, the distinctive characteristic of which is the use of the skin effect and the traveling wave effect to heat the wires. In this case, the proposed method involves performing the following operations:

A high-frequency voltage in the range of 50-500 MHz is supplied between two wires of the power line with a power P G =q·A·ΔT, where q is the heat transfer coefficient of the upper hot layer of the wire to the air, A is the surface area of the wires, ΔT is the heating temperature of the wire relative to the temperature environment.

The technical result in relation to the device is achieved due to the fact that the claimed device includes a high-frequency generator with power calculated by the formula: R G =q·A·ΔT,

where q is the heat transfer coefficient of the upper hot layer of the wire to the air, A is the surface area of the wires, ΔT is the heating temperature of the wire relative to the ambient temperature, while the output of the generator is connected to the input of a capacitive-type matching device, designed to match the output resistance of the high-frequency generator with the input power line resistance and having a number of outputs corresponding to the number of power line wires.

For a better understanding of the essence of the claimed invention, its theoretical justification is given below with links to relevant graphic materials.

Fig.1. Prototype device.

Fig.2. Electrical line: 2.1) short circuit in the line, 2.2) equivalent circuit with direct current, 2.3) equivalent circuit with alternating current with a frequency of 50 Hz.

Fig.3. Current distribution over the conductor cross-section: 3.1) at constant current and low frequency; 3.1) at high frequency.

Fig.4. Two-wire line: 4.1) appearance, 4.2) graph of the voltage amplitude for a traveling wave, 4.3) for a traveling and reflected wave.

Fig.5. Connection diagram of a high-frequency generator to a power line.

Fig.6. Dependency graphs: 6.1) surface layer of current penetration into the conductor, 6.2) relative resistivity of wires depending on frequency: 601 - steel, 602 - aluminum, 603 - copper.

Fig.7. Dependence of the coefficient of conversion of electromagnetic energy of a traveling wave into thermal energy on the line length.

As you know, the term “skin effect” comes from the English word “skin”, i.e. "leather"; Moreover, in electrical engineering this means that in certain circumstances electricity concentrates on the “skin” of the conductor (see ru.wikipedia.org/wiki/Skin effect). It was found that in a homogeneous conductor, alternating current, unlike direct current, is not distributed evenly over the cross-section of the conductor, but is concentrated on its surface, occupying a very thin layer (see Fig. 3), the thickness of which at alternating current frequency f>10 kHz determined by the formula

where σ (Ohm mm 2 /m) - specific electrical resistance at constant current; µ o =1.257·10 6 (V·s/A·m) - magnetic constant; µ - relative magnetic permeability (for non-magnetic material µ=1) f - frequency in MHz.

Graphs of the function δ(f) according to (4) for three materials (steel - 601, aluminum - 602 and copper - 603) are shown in Figure 6.1. Thinning of the layer through which alternating current flows leads to an increase in the resistance of the conductor with radius r (mm), determined at (r/2δ)>10 by the formula

where R o =σ/πr 2 is the resistance of the same conductor 1 m long to direct current.

Graphs of the function R f (f)//R o at r=10 mm, showing how the conductor resistance increases with frequency for three materials (steel - 601, aluminum - 602 and copper - 603), are shown in Fig. 6.2. From them, for example, it follows that at a frequency of 100 MHz and higher, the resistance of aluminum wires increases by 600 times or more.

Regarding the “running” effect electromagnetic wave", then, as is known (see, for example, izob.narod.rn/p0007.html), there are two main ways of propagating electromagnetic waves: in free space when emitted by an antenna and using waveguides and feeder or so-called long lines - coaxial , stripline and two-wire - (see Kaganov V.I. Oscillations and waves in nature and technology. Computerized course. - M.: Hotline - Telecom, 2008). In the second case, the electromagnetic wave, as if on rails, slides along the line. Since two wires of a power line can be considered as a two-wire line (Fig. 4.1), we will focus on its analysis. The line itself is characterized by three main parameters: characteristic impedance ρ, attenuation constant α and phase constant β. Characteristic impedance of a two-wire line stretched in the air

where a is the distance between the centers of the wires, r is the radius of the wire (see Fig. 4.1) Attenuation constant

where R f is the resistance of one wire at high frequency, determined according to (5).

Phase constant β=2π/λ, (1/m), where λ (m) is the wavelength propagating in the line.

In the two-wire line itself, like other feeder lines, two main modes of operation are possible: with only a traveling wave in one direction and with two waves - traveling and reflected from the end or obstacle in the line. Suppose the line is infinitely long. Then only a traveling wave mode is possible in it, the voltage of which depends on time t and distance x from the generator (Fig. 4.2):

where U 0 is the voltage amplitude at the input of the line to which the generator is connected with frequency f.

According to (8), the amplitude of a traveling wave propagating along the line decreases exponentially (Figures 6 and 7). Consequently, the power of a traveling electromagnetic wave at a distance L from the generator will be:

where R G =(U 0)) 2 /2ρ is the wave power at the beginning of the line, equal to the output power of the high-frequency generator.

The difference between the power of the traveling wave at the beginning of the line and at a distance L will determine the thermal heating of the line along which the wave propagates

The conversion coefficient of electromagnetic energy of a traveling wave W into thermal energy in a line of length L (m), taking into account (10), will be:

Graphs of the function η(L) for three values of the attenuation constant α (1/km) are plotted in Fig.7. It follows from them that the greater the resistance of the line wires Rf, defined by (5), and, accordingly, the attenuation constant α, defined by (7), the greater the energy electromagnetic field The traveling wave along the line is converted into heat. It is this effect of converting electromagnetic energy into thermal energy, used to heat wires at a high signal frequency, that forms the basis of the proposed method for preventing ice on power lines.

In the case of limited dimensions of the line or any high-frequency obstacle, such as a capacitance, in addition to the incident wave, a reflected wave will also propagate in the line, the energy of which will also be converted into heat as it propagates from the obstacle to the generator. The amplitudes of change along the line of both waves - incident and reflected - are shown in Figure 4.3.

To calculate thermal output, we define specific example, what power

The R G of a high-frequency generator with a frequency f connected to the power line will be required to heat the two wires by ΔT degrees. Let's take into account the following circumstances. Firstly, the thin top layer of the wire, under the influence of an electromagnetic wave, warms up almost instantly with a high volumetric heat release. Secondly, this heat is spent on heating the entire wire (O M) and the air surrounding the wire by convection (Q B) (see Fig. 3.2).

Let us accept the following initial data: wire material - aluminum with a diameter of 10 mm, cross-section S = 78.5 mm 2, length L = 5000 m, density p = 2710 kg/m 3, resistivity at direct current σ = 0.027 Ohm mm 2 /m, specific heat c = 896 J/kg K, heat transfer coefficient of the upper hot layer of the wire to the air q = 5 W/m K.

Weight of two wires:

Surface of two wires:

The amount of heat required to heat two wires at ΔT=13°C:

Heat transfer of two wires to the environment at a temperature difference ΔТ=13°С:

where t is time in seconds.

From the last expression we obtain for the required power of the high-frequency generator R G = 20.4 kW, i.e. 2 W of high-frequency vibration power per 1 m of wire with a volumetric heat release in the upper layer of the wire of 8 MW/m 3. In passing, we note that with the same type of wire, to free it from ice by melting with a cycle of up to 40 minutes, a power of 100 VA per 1 meter is required (see and).

Equating the expressions for energy, we find the time value for establishing a stationary mode of heating the wires:

To test the theoretical principles stated above and prove the industrial applicability of the proposed method and device, a laboratory experiment was conducted.

From preliminary calculations, it was concluded that powerful VHF FM radio transmitters operating in the frequency range 87.5...108 MHz can be used as a high-frequency signal generator by changing only the load matching device and connecting them to the power line according to the diagram in Fig. .5.

In the experimental version, a 30 W, 100 MHz generator 502 was connected through a matching device 501 to a two-wire line 50 m long, open at the end, with wires with a diameter of 0.4 mm and a distance between them of 5 mm. The characteristic impedance of such a line according to (6):

Under the influence of a traveling electromagnetic wave, the heating temperature of the two-wire line was 50-60°C at an ambient air temperature of 20°C. The results of the experiment coincided with satisfactory accuracy with the results of the calculation performed according to the given mathematical expressions.

The following conclusions were formulated:

The inventive method of heating power lines by an electromagnetic wave propagating along it, the energy of which, as it spreads, turns into heat, allows the wires to be heated by 10-20°C, which should prevent the formation of ice;

The most appropriate is the use of the proposed method and device to prevent the formation of ice on wires, since removing an already formed ice “coat” will require significantly greater energy consumption and a longer procedure;

Compared to the currently used method of melting ice, the proposed method has a number of advantages, in particular, given the fact that the method is implemented without disconnecting consumers, it is possible, for preventive purposes, to heat the line until a dense ice deposit forms on the wires, which allows them to be heated up to 10-20°C, and not up to the temperature of 100-130°C required for melting ice;

The resistance of the wires, which increases as the frequency of alternating current increases (in the given example, at a frequency of 100 MHz, the resistance increases by three orders of magnitude compared to a frequency of 50 Hz) allows us to obtain a high conversion coefficient of electrical energy into thermal energy and, thereby, reduce the power of the generator.

1. A method of combating ice on power lines, which consists in the fact that without disconnecting consumers, a current is supplied to the current-carrying wires from an external source, a heating wire, characterized in that a high frequency voltage in the range of 50-500 MHz is supplied between two wires of the power line. power R Г =q·A·ΔT, where q is the heat transfer coefficient of the upper hot layer of the wire to the air, A is the surface area of the wires, ΔT is the heating temperature of the wire relative to the ambient temperature.

2. A device for combating ice, including a current source external to the power line, configured to connect to the current-carrying wires of the power line, characterized in that external source current is designed in the form of a high-frequency generator, designed to provide power calculated by the formula R G =q·A·ΔT, where q is the heat transfer coefficient of the upper hot layer of the wire to the air, A is the surface area of the wires, ΔT is the heating temperature of the wire relative to the temperature environment; in this case, the output of the generator is connected to the input of a capacitive-type matching device, designed to match the output resistance of the high-frequency generator with the input resistance of the power line and having the number of outputs corresponding to the number of wires of the power line.

The invention relates to electrical engineering, in particular to devices that prevent the formation of ice on the wires of overhead high-voltage power lines without disconnecting consumers

Methods for combating icing of power lines

Scientific supervisor – Doctor of Technical Sciences, Professor

1. Introduction

Despite many years of efforts by power engineers and scientists, ice accidents in the electrical networks of many power systems still cause the most severe consequences and periodically disrupt the power supply to the regions of the country.

De-icing of power line wires is carried out using 3 methods:

1 – mechanical; 2 – physical and chemical; 3 – electromechanical.

1) Mechanical method

The mechanical method involves the use of special devices that knock ice off the wires. The easiest way to mechanically remove ice is to knock it down using long poles. The upholstery is carried out with side impacts, causing wave-like vibrations of the wire. But this method requires access to power lines, which violates normal work plot. In addition, mechanical action does not prevent icing, but eliminates it.

https://pandia.ru/text/80/410/images/image006_24.jpg" align="left" width="292" height="271 src=">

Removing ice from wires with poles is practically impossible without a large number of workers. This method is time-consuming and is only used on short sections of lines, which is why it is considered impractical in most cases. Therefore, at present, the most common way to combat ice on power line wires is to melt ice with alternating or direct current of large magnitude for a long period of time (about 100 minutes or more). This consumes a significant amount of energy and requires disconnecting the line from consumers for a long period of time.

2) Electrothermal method

Electrothermal methods of ice removal involve heating the wires with an electric current, which prevents the formation of ice - preventive heating or its melting.

Preventative heating of wires consists of artificially increasing the current in the power transmission line network to such a value that the wires heat up to a temperature above 0°C. At this temperature, ice does not form on the wires. Preventive heating must begin before ice forms. During preventive heating, power supply circuits should be used that do not require disconnecting consumers.

Melting of ice on wires is carried out when ice has already formed by artificially increasing the current of the power line network. The wires are heated with direct or alternating current with a frequency of 50 Hz to a temperature of 100-130°C. It is easier to do this by short-circuiting two wires, in which case all consumers have to be disconnected from the network.

Ice melting with alternating current is used only on lines with voltages below 220 kV with wires with a cross-section of less than 240 mm2. For overhead lines with a voltage of 220 kV and higher with wires with cross-sections of 240 mm2 or more, melting ice with alternating current requires significant large capacities power supply.

The advantage of this method is that it reduces energy costs. However, the disadvantages of this method include the following: the need for constant heating of the wires to prevent ice formation, the high cost of high-frequency current sources of the required power.

3) Physico-chemical method

The physico-chemical method, unlike others, prevents the occurrence of icing on the wires. The results obtained allow us to speak about a new physical and chemical method in the fight against icing of power line wires, the effectiveness of which significantly exceeds the capabilities traditional methods. Also, this method does not require any large economic costs. Therefore, it is more promising. The only drawback of the physicochemical method is that the lifespan of such liquids is short-lived, and it is unrealistic to regularly apply them to hundreds and thousands of kilometers of wires.

4) Replacement of wires.

The method is not to invent any minor devices for cleaning wires from ice, but to create new high-tech wires. These wires must meet the following requirements:

Increase throughput existing lines;

Reduce mechanical loads applied to power transmission line supports due to the dancing of wires;

Increasing the corrosion resistance of wires and cables;

Reducing the risk of wire breakage when several external wires are partially damaged due to external influences, including a lightning strike;

Improving the mechanical properties of wires during snow accumulation or ice formation

To do this, the outer layers of the wire must be made of conductors that will fit tightly to each other.

Thus, due to the tighter twist of the conductors and the smoother outer surface, it is possible to use thinner and lighter wires. This, in turn, leads to a reduction in electrical losses in wires by 10–15%, including corona losses, and an increase in the mechanical strength of the structure. Also, thanks to the tight twisting, the penetration of water and contaminants into the internal layers is practically eliminated, therefore the corrosion of the internal layers of the wire is reduced.

3. Conclusion

Due to the ineffectiveness of the mechanical and physical-chemical method over long distances, we will not talk about the economic side.

IN this moment, the formed ice on the wires is cleaned by heating. This is not the cheapest method, as this method requires powerful and expensive power supplies. Thus, melting ice by electric current is a rather inconvenient, complex, dangerous and expensive undertaking. In addition, cleaned wires under the same climatic conditions again become covered with ice, which must be melted again and again.

It should be noted that ice melting should be carried out in areas of intense ice formation with frequent dancing of wires. In other cases, the use of ice melting should be justified by technical and economic calculations.

The service life of the wires is 45 years. We need to switch to new high-tech wires. Foreign wires are very expensive, the cost is 10 times higher than the cost of AC wires. It is proposed to develop domestic high-tech wires and begin replacing old ones with new ones.

Bibliography

1. Method for removing icing from power line wires / ,: Pat. 2442256 C1 Ross. Federation, IPC H 02 G 7/16.; No. 000/07; application 10/29/2010; publ. 02/10/2012, Bulletin. No. 4. 4 p.: ill.

2. , Emelyanov combating icing of power lines: prospects and advantages of new superhydrophobic coatings. //Electro Magazine No. 6/2011. http://www. ess. ru/.

3. Dyakov and the elimination of ice accidents in electrical networks. Pyatigorsk: Publishing house RP "Yuzhenergotekhnadzor", 2000. 284 p.

4. Abzhanov P. S. Study of aerosol deposition in relation to the process of ice formation on power line wires / Dis. Ph.D. tech. Sciences Alma - Ata, 1973.

5. , On the issue of combating ice formation on power line wires // Scientific. Tr. CHIMZSH - Chelyabinsk, 1973, issue 83, pp. 34-36.

6. AUTOMATIC SYSTEM FOR REMOVING ICE FROM POWER LINE WIRES

Doctor of Technical Sciences V. KAGANOV, Professor of MIREA.

Over the past fifteen years, ice on high-voltage lines has begun to occur more and more often. When there is slight frost, in mild winter conditions, droplets of fog or rain settle on the wires, covering them with a dense ice “coat” weighing several tons over a length of a kilometer. As a result, wires break and power line supports break. The increasing frequency of accidents on power lines is apparently associated with general climate warming and will require a lot of effort and money to prevent them. You need to prepare for them in advance, but the traditional method of melting ice on wires is ineffective, inconvenient, expensive and dangerous. Therefore, the Moscow Institute of Radio Electronics and Automation (MIREA) has developed a new technology not only for destroying already frozen ice, but also for preventing its formation in advance.

Science and life // Illustrations

Ice patches on wires, insulators and supporting structures sometimes reach significant sizes and weight.

Multi-ton layers of ice on wires even break steel and reinforced concrete supports.

Experimental generator at 100 MHz with a power of 30 W, assembled at MIREA.

Ice is a disaster for power lines

According to Dahl's dictionary, ice has another name - ice or ice. Ice, that is, a dense ice crust, is formed when supercooled drops of rain, drizzle or fog freeze at a temperature of 0 to –5 ° C on the surface of the earth and various objects, including high-voltage power lines. The thickness of the ice on them can reach 60-70 mm, significantly weighing down the wires. Simple calculations show that, for example, an AS-185/43 wire with a diameter of 19.6 mm and a kilometer length has a mass of 846 kg; with an ice thickness of 20 mm it increases by 3.7 times, with a thickness of 40 mm - by 9 times, with a thickness of 60 mm - by 17 times. At the same time, the total mass of a power transmission line consisting of eight kilometer-long wires increases to 25, 60 and 115 tons, respectively, which leads to wire breakage and breakage of metal supports.

Such accidents cause significant economic damage; their elimination takes several days and huge amounts of money are spent. Thus, according to materials from the OGRES company, major accidents due to ice during the period from 1971 to 2001 occurred many times in 44 power systems of Russia. Only one accident in Sochi power grids in December 2001 led to damage to 2.5 thousand km of overhead power lines with voltages up to 220 kV and the cessation of power supply to a huge region. There were many ice-related accidents last winter.

High-voltage power lines are most susceptible to ice in the Caucasus (including in the area of the upcoming Sochi Winter Olympics in 2014), in Bashkiria, Kamchatka, and in other regions of Russia and other countries. This scourge has to be dealt with in a very expensive and extremely inconvenient way.

Electric melting

Ice crust on high-voltage lines is eliminated by heating the wires with direct or alternating current with a frequency of 50 Hz to a temperature of 100-130°C. The easiest way to do this is to short-circuit two wires (in this case, you have to disconnect all consumers from the network). Let a current of I pl be required to effectively melt the ice crust on the wires. Then, when melting with direct current, the power source voltage

U 0 = I pl R pr,

where R pr is the active resistance of the wires, and the alternating current from the network is

where X pr = 2FL pr - reactance at frequency F = 50 Hz, due to the inductance of the wires L pr.

In lines of considerable length and cross-section, due to their relatively large inductance, the voltage of the alternating current source at a frequency of F = 50 Hz, and accordingly its power, should be 5-10 times greater compared to a direct current source of the same power. Therefore, it is economically profitable to melt ice with direct current, although this requires powerful high-voltage rectifiers. Alternating current is usually used on high-voltage lines with voltages of 110 kV and below, and direct current - above 110 kV. As an example, we point out that at a voltage of 110 kV, the current can reach 1000 A, the required power is 190 million VA, and the wire temperature is 130°C.

Thus, melting ice by electric current is a rather inconvenient, complex, dangerous and expensive undertaking. In addition, cleaned wires under the same climatic conditions again become covered with ice, which must be melted again and again.

Before we present the essence of our proposed method for combating ice on high-voltage power lines, let us dwell on two physical phenomena, the first of which is associated with the skin effect, the second with a traveling electromagnetic wave.

Skin effect and traveling waves

The name of the effect comes from the English word “skin” - skin. The skin effect is that high-frequency currents, unlike direct current, are not distributed evenly over the cross-section of the conductor, but are concentrated in a very thin layer of its surface, the thickness of which at a frequency f > 10 kHz is already fractions of a millimeter, and the resistance of the wires increases hundreds of times.

High-frequency electromagnetic oscillations can propagate in free space (when emitted by an antenna) and in waveguides, for example, in the so-called long lines along which the electromagnetic wave slides as if on rails. Such a long line could be a pair of power line wires. The greater the resistance of the line wires, the greater part of the energy of the electromagnetic field of the wave traveling along the line is converted into heat. It is this effect that forms the basis of a new method for preventing ice on power lines.

In the case of limited dimensions of the line or any high-frequency obstacle, for example a capacitance, in addition to the incident wave, a reflected wave will also propagate in the line, the energy of which will also be converted into heat as it propagates from the obstacle to the generator.

Calculations show that to protect a power line about 10 km long from ice, a high-frequency generator with a power of 20 kW is needed, that is, delivering 2 W of power per meter of wire. The stationary mode of heating the wires occurs after 20 minutes. And with the same type of wire, the use of direct current requires a power of 100 W per meter with ramp-up in 40 minutes.

High-frequency currents are generated by powerful VHF FM radio transmitters operating in the range 87.5-108 MHz. They can be connected to power line wires through a load matching device - a power line.

To test the effectiveness of the proposed method, a laboratory experiment was conducted at MIREA. A 30 W generator with a frequency of 100 MHz was connected to a two-wire line 50 m long, open at the end, with wires with a diameter of 0.4 mm and a distance of 5 mm between them.

Under the influence of a traveling electromagnetic wave, the heating temperature of the two-wire line was 50-60°C at an air temperature of 20°C. The experimental results coincided with the calculation results with satisfactory accuracy.

conclusions

The proposed method, of course, requires careful testing under real conditions of an operating power grid with full-scale experiments, since a laboratory experiment only allows us to give a first, preliminary assessment of a new method of combating ice. But some conclusions can still be drawn from all that has been said:

1. Warming up power lines with high-frequency currents will prevent the formation of ice on the wires, since they can be heated to 10-20°C without waiting for dense ice to form. There is no need to disconnect consumers from the electrical network - the high-frequency signal will not penetrate to them.

Let us emphasize: this method allows you to prevent ice from appearing on the wires, and not to start fighting it after the ice “coat” envelops them.

2. Since the wires can be heated by only 10-20°C, electricity consumption is significantly reduced compared to melting, which requires heating the wires to 100-130°C.

3. Since the resistance of wires to high-frequency currents compared to industrial (50 Hz) increases sharply, the conversion coefficient of electrical energy into thermal energy turns out to be high. This in turn leads to a reduction in the required power. At first, apparently, you can limit yourself to a frequency of about 100 MHz of a generator with a power of 20-30 kW, using existing broadcast radio transmitters.

Literature

Dyakov A.F., Zasypkin A.S., Levchenko I.I. Prevention and elimination of ice accidents in electrical networks. - Pyatigorsk: Publishing house RP "Yuzhenergotekhnadzor", 2000.

Kaganov V.I. Oscillations and waves in nature and technology. Computerized course. - M.: Hotline - Telecom, 2008.

Levchenko I. I., Zasypkin A. S., Alliluyev A. A., Satsuk E. I. Diagnostics, reconstruction and operation of overhead power lines in icy areas. - M.: MPEI Publishing House, 2007.

Rudakova R. M., Vavilova I. V., Golubkov I. E. Fighting ice in power grid enterprises. - Ufa: Ufimsk. state aviation tech. University, 1995.

Yavorsky B. M., Detlaf A. A. Handbook of physics. - M.: Nauka, 1974.

Use: in the field of electrical engineering. The technical result consists in preventing the formation of ice on the wires of power lines without the need to disconnect the line for maintenance. The method consists in connecting double wires of a power line connected to one phase with elastic jumpers, for example, springs, providing mechanical vibrations wires at standard parameters of the electric current flowing through them. In normal operation, power transmission lines, when alternating current passes, pairs of wires of the same phase connected by a spring constantly perform oscillatory movements, which ensures continuous shaking off drops of moisture and snow from them and thereby prevents icing. 1 salary f-ly, 2 ill.

The invention relates to the electric power industry and can be used in the operation of alternating current power lines. There are known mechanical, electrical and chemical methods for removing ice from power line wires.

Mechanical methods involve the use of special devices to remove ice from wires. The disadvantage of such devices is low productivity and the possibility of damage and deformation of wires in the process of removing ice, which leads to network breaks and is accompanied by accelerated wear of the wires.

Chemical methods involve applying special substances to the wires that prevent the formation of ice or ensure its destruction. The application process is characterized by great labor intensity. In addition, such substances are short-lived and therefore require periodic renewal throughout the entire ice season.

Electrical methods for removing ice involve heating or shaking wires with pulses of current to melt ice or prevent it from forming.

As a prototype, a method was chosen for removing ice from contact network wires and power lines, which consists of passing alternating current or current pulses with a frequency close to their mechanical resonance through double or multiple power line wires. The resulting mechanical vibrations of the wires ensure the removal of moisture and ice from them. The disadvantages of this method are:

The need to disconnect the power line for maintenance due to the fact that the current parameters required to ensure mechanical resonance of the wires may differ significantly from the standard current;

The need for an auxiliary source of pulsed or alternating current with the pulse frequency adjusted to the resonance frequency of the wires;

The need to use mobile teams to deliver equipment to icing areas, which can be associated with significant costs when working in hard-to-reach areas and in conditions of intense ice formation;

The impossibility of frequent use of this method requires an increase in the power of current pulses that shake the wires, which can lead to mechanical damage and rupture of the wires.

The purpose of the invention is to prevent the formation of ice on the wires of power lines during their normal operation without the need to shut down for maintenance.

This goal is achieved by the fact that in the proposed method, pairs of power line wires connected to the same phase are connected by elastic jumpers, for example, springs, the parameters of which are selected in such a way as to ensure continuous mechanical vibrations of the wires at standard parameters of the current passing through the power line. The layout of wires and jumpers is shown in Fig.1.

The method for preventing icing is presented in Fig. 2 and consists in the fact that in the normal operating mode of a power transmission line, when alternating current passes, pairs of wires of the same phase connected by elastic jumpers constantly perform oscillatory movements, repelling under the action of the elastic force of the jumper F Y and being attracted under the influence of the Lorentz force F L:

where d is the distance between the wires; I 1, I 2 - current strength in the wires; µ, µ 0 - magnetic permeability of the medium and vacuum; l is the length of the wires.

Continuous vibration of the wires leads to shaking off drops of water, snow and ice from them and thereby prevents icing, and also leads to the splitting of the ice crust when it forms.

Thus, in normal operation of a power transmission line, the causes of icing of wires are eliminated, and not its consequences, which eliminates the need for shutdowns for maintenance and reduces the required costs of resources and energy.

Information sources

1. Device for removing ice deposits. MKI H02G 7/16. A.S. No. 957332, 09/07/1982.

2. Wire shaker. IPC H02G 7/16. Russian Federation, pat. No. 2318279, 06/20/2006.

3. Power line. IPC H02G 7/16. Russian Federation, Pat. No. 2076418, 03/27/1997.

4. A method for removing ice from overhead wires and power lines. IPC H02G 7/16, V60M 1/12. Russian Federation, Pat. No. 2166826, 04/27/2001.

5. Device to prevent the formation of ice on the overhead line. IPC H02G 7/16. Russian Federation, Pat. No. 2316866, 02/10/2008.

6. Method and device for combating ice on power lines. IPC H02G 7/16. Russian Federation, Pat. No. 2356148, 05.20.2009.

7. High voltage network. IPC H02G 7/16, H02J 3/18. Russian Federation, Pat. No. 2365011, 08/20/2009.

8. Koshkin N.I., Shirkevich M.G. Handbook of elementary physics. - M.: Nauka, 1976.

9. Marquardt K.G. Contact network. - M.: Transport, 1994.

1. A method for preventing icing of the wires of overhead AC power lines, which consists of passing alternating current through double or multiple wires of the power line, characterized in that the wires connected to one phase are connected by elastic jumpers that provide mechanical vibrations of the wires at the normal parameters of the flow through them electric current.

2. The method according to claim 1, characterized in that the transmitted electric current has standard parameters, which ensures the continuity of the process of removing drops of water, snow and ice from the wires.

Similar patents:

The invention relates to the field of electrical engineering, in particular to a device for removing ice from overhead power line wires, and contains a housing that can be installed on the wire, and is also equipped with means of movement and removal of ice.

The invention relates to energy and can be used in areas with harsh winter climates. Protection against icing of wires is known, which consists in melting the ice by directly heating the wires of an overhead power line by passing current through them.

The invention relates to a device for flexible power transmission and for de-icing of a high-voltage line having several phases using direct current, comprising an alternating current connection of the high-voltage line, which has a number of phases corresponding to the phases of the high-voltage line, each phase having at least one inductance and one valve circuit connected in series with each inductance, wherein the valve circuit is connected via a node point to the AC connection and has a first current circuit branch with a first power semiconductor valve and a second current circuit branch with a second power semiconductor valve, wherein the power semiconductor valves are connected opposite to each other relative to the node point and wherein the first and second branches of the current circuit are designed to be connected by at least one zero point switch to the TCR zero point.

The invention relates to energy, in particular to electrical cables/wires, including high-voltage power lines mounted on supports, when the problem is completely solved full protection cables from snow accumulation, icing and, as a consequence, breakage

The invention relates to electrical engineering. The method includes placing a suspended temperature sensor on a wire, and under the wire - control device. Using the first and second ultrasonic transceivers, the sag and horizontal deflection of the wire across the power line are measured by means of a control device together with a suspended temperature sensor. The ultrasonic pulse is emitted, the ultrasonic pulse is received at the ultrasonic transceivers, and the position of the wire in the plane is calculated based on the time of propagation of the ultrasonic pulse from the suspended temperature sensor to the first and second ultrasonic transceivers. The technical result is to increase the accuracy of sag determination. 2 ill., 1 tab.

Usage: in the field of electrical energy. The technical result is increased efficiency while simplifying the design. The device contains impact elements installed on the wire, each of them made in the form of a cylindrical sleeve (2) loosely placed on the wire (1) made of large ferromagnetic material such as soft magnetic rubber, having conical sockets on both edges with longitudinal slots (3) along the generatrices , dividing the bells into separate petals (4), characterized by a natural frequency of bending vibrations relative to the place of their cantilever attachment to the end of the bushing, approximately coinciding with the frequency of alternating current in the wires. 1 ill.

The invention relates to the electric power industry and can be used in the operation of AC power lines

Use: in the field of electrical engineering. The technical result consists in preventing the formation of ice on the wires of power lines without the need to disconnect the line for maintenance. The method consists in connecting double wires of a power transmission line connected to one phase with elastic jumpers, for example, springs, which ensure mechanical vibrations of the wires at the standard parameters of the electric current flowing through them. In normal operation, power transmission lines, when alternating current passes, pairs of wires of the same phase connected by a spring constantly perform oscillatory movements, which ensures continuous shaking off drops of moisture and snow from them and thereby prevents icing. 1 salary f-ly, 2 ill.

Drawings for RF patent 2474939