De-icing of power lines in Sweden. Removing ice deposits from overhead power line wires using modern semiconductor systems. Methods for combating icing of power lines
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.
Fuse electric shock
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 source voltage alternating current at a frequency F = 50 Hz, and accordingly its power should be 5-10 times greater compared to the source direct current the same strength. 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 with preserved climatic conditions again overgrown with ice, which needs to 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 requires, of course, careful testing in real conditions operating power grid with full-scale experiments, because 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 - high frequency signal will not penetrate 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 electrical energy in thermal it turns out to be great. 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. univ., 1995.
Yavorsky B. M., Detlaf A. A. Handbook of physics. - M.: Nauka, 1974.
Since efficient operation of wind power plants is only possible where strong and constant winds blow, large wind farms in Europe are concentrated mainly in the north and northwest of the continent. The winds there are actually quite suitable. But the climate is not very good.
The harsh winters that are so typical of Scandinavia create very serious problem- icing of the blades. And it is fraught with several troubles at once, says Swedish meteorologist Stefan Söderberg, Researcher Weathertech company in Uppsala: “When ice forms on the blades, their aerodynamic characteristics deteriorate noticeably - just as sometimes happens with airplanes. As a result, the performance of a wind power plant drops. This is the first thing. Secondly, the ice disrupts the balance wind wheels, which leads to increased wear of the bearings and the wind generator as a whole. And finally, one cannot ignore the dangers associated with the fact that pieces of ice from the ends of the rotating blades can break off and fly over considerable distances.”
The computer will choose the optimal system
Operators in northern Europe face this kind of trouble every day every winter. It is clear that engineering thought has not been dormant all this time, but has been developing various technical solutions to the problem of icing of blades. Actually, there are not so many of these solutions; the only question is which of them is most effective in certain specific operating conditions. Until now, one had to answer it intuitively, that is, almost at random.
Now Stefan Söderberg, together with a group of colleagues, have developed a computer model that allows one to virtually test different strategies for combating icing of the blades of wind power plants and select the optimal one for each individual wind farm. The scientist explains: “Both de-icing systems and anti-icing systems usually consist of three components: a detector, a control unit and the heating system itself. In de-icing systems, the heating of the blades is turned on as soon as the detector registers the formation of ice. In prevention systems, icing, the heating is turned on at the moment when weather conditions make the formation of ice likely, that is, without waiting for the formation of an actual ice crust."
A helicopter is an expensive but effective means
All this, of course, is wonderful, but what if wind power plants are not equipped with a blade heating system at all - and so far the majority are? At least in northern Sweden, many hundreds of wind turbines do not have built-in de-icing systems. For such cases it is very interesting idea put forward by Hans Gedda, an engineer at the consulting firm H Gedda Consulting in Buden.
Context
He proposed to combat wind wheel icing using a helicopter. Of course, this pleasure, frankly speaking, is not cheap, but under certain conditions it can pay for itself, the author believes unusual idea: “If you expect optimal weather conditions in the coming days, that is, strong and stable winds, and your wind generators are turned off due to icing and cannot produce electricity, then freeing them from ice, even from a helicopter, makes direct sense.”
The blades are sprayed with hot anti-icing liquid not all at once, but one after another. The blade subjected to this procedure should always be directed vertically downward, that is, after processing one blade is completed, the wind wheel should be rotated so that the next blade takes the same position. This is necessary and very important, emphasizes Hans Edda, otherwise pieces of melted ice, falling from a great height, can damage the remaining blades or the hub when falling.
Icing is an almost universal phenomenon
“We hope that this whole procedure will take no more than two hours, otherwise it will be too expensive,” says the engineer. “But if the installations, freed from ice, then operate in good wind for at least two days, this will be enough for this helicopter operation paid for itself."
Where wind turbine icing is not dealt with, the average annual loss - or rather, the average annual lost profit - ranges from five to ten percent, and in some regions reaches 20 percent.
Moreover, this problem does not only apply to Scandinavia, says Stefan Söderberg: “Icing occurs in many regions of the world - almost everywhere where it snows in winter. All that is needed for this effect is a temperature below zero and high humidity. And supercooled water can be present in the atmosphere at temperatures up to minus twenty degrees. That is, the probability of icing of wind turbine blades is also high in Germany. When I first started working on this topic, we were always talking only about regions with a very harsh climate - like Scandinavia. Indeed, here in our country. Sweden, like Norway and Denmark, has very cold winters, but icing can occur at temperatures only slightly below zero.”
However, in Germany, it seems that no one has yet taken this issue seriously. Therefore, here, unlike Scandinavia, at the first signs of icing on the blades, wind generators are supposed to simply be turned off. There is only one wind turbine equipped with a heating system - for the whole country.
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
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 highly labor intensive. 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;
Inability to use frequently 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 attracting 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.
CLAIM
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.
Icing- a dangerous phenomenon that worsens the characteristics and quality of structures, their strength and, ultimately, durability and safety. Icing significantly increases wind resistance, which can lead to the destruction of structures and mechanisms.
Icing causes breakdowns of power lines, which gives another reason to think about the means of protecting them and taking measures. The main means of protection against icing are heating or special anti-icing compounds.
In world practice, organosilicate compositions are most widely used to create anti-icing coatings. They are used to combat icing of various instruments and devices used in the industrial and economic complex, for example, power lines.
In some areas of the north there is ice and different kinds icing of power line wires disrupts their normal operation. Power line wires are often subject to icing, which disrupts the integrity of the unified system, leading to accidents and even disasters.
The traditional main measures to combat ice on power lines are: removing ice from wires and cables using electric current or mechanical means, as well as preventive heating of the wires.
The mechanical method requires a lot of time and significant labor costs, and in most cases is not considered appropriate. Melting ice by electric current, in most cases, is dangerous for the integrity of wires and support structures. The energy consumption of such schemes is very high.
The proposed method of combating ice on a line wire with an induction current of the same line, by moving "induction torpedo" from one wire attachment point to another, within one span, is a new direction in the fight against icing of high-voltage lines.
Advantages of this method:
Full autonomy of movement of the “torpedo” within one flight;
Possibility of choosing to install “torpedoes” in the areas of high-voltage lines most vulnerable to icing;
Incommensurably lower energy consumption compared to existing methods;
The ability to remotely start and stop a “torpedo” at the command of a dispatcher using a coded signal via HF communication. Between these signals there is complete self-control through a system of limit switch contacts;
Reducing the likelihood of wire breaks in high-voltage lines and destruction of load-bearing elements of supports, eliminating the “dance of wires”;
Reliability in operation and durability, simplicity of design and low cost of manufacture;
There is no need to maintain the “torpedo” during the entire time of its use.
Line wires cannot withstand the weight of snow and ice, which leads to their damage and even rupture. As a result, it will be necessary to carry out electrical installation work to restore power lines. A controlled ice melting device using a thyristor controlled rectifier is effectively used. It is specially designed to combat ice formation on high-voltage power lines. It should be noted that previously an unregulated rectifier was used to melt ice at the station. A feature of the modern device is that it instantly responds to the melting current of ice, thereby preventing overheating of wires and lightning cables, since the fiber-optic communication lines built into the lightning protection cables of power lines do not accept such influence. In addition, operating this device is much simpler than its predecessor. It speeds up the smelting process by an order of magnitude, without requiring an increase in the power of the installed transformer equipment. The operation of installations can be monitored from the Network Control Center in real time.
3.3 Operation of cable lines up to 35 kV
Supervision of cable line routes is carried out in order to check their condition by periodic walk-through and inspection by installers specially allocated for this within the time limits stipulated by the PTE, and by engineering and technical personnel within the time limits provided for by local instructions.
1. Extraordinary rounds and inspections are carried out during floods and after rainstorms, as well as when lines are disconnected by relay protection.
2. When walking around and inspecting cable line routes laid in open areas, it is necessary to:
· check that no work is being carried out on the route that is not coordinated with the operating organization (construction of structures, excavation of land, planting, arrangement of warehouses, driving piles, poles, etc.), and also that there are no blockages of the routes with snow, garbage, slag , waste, there were no failures or landslides;
· inspect the intersections of cable routes with railways, paying attention to the presence of warning posters;
· inspect the intersections of cable routes with highways, ditches, and ditches;
· inspect the condition of devices and cables laid across bridges, dams, overpasses and other similar structures;
· check, in places where cables exit the walls of buildings or supports of overhead power lines, the presence and condition of cable protection from mechanical damage, the serviceability of end couplings;
3. When walking around and inspecting cable line routes laid in closed areas, in addition to fulfilling the requirements of clause 2, it is necessary to:
· involve in the inspection of the route a representative of the organization responsible for the protection of cables and other related structures;
· when defects are identified on line routes, issue orders for their elimination;
· if deficiencies are identified that were not eliminated within the period established during the previous inspection, draw up a protocol on the violation.