WO2014187053A1

WO2014187053A1 - Power transmission line for preventing snow and ice disaster

Info

Publication number: WO2014187053A1
Application number: PCT/CN2013/084075
Authority: WO
Inventors: 谢迎军; 张大华; 于振; 黄娜
Original assignee: 国家电网公司; 中国电力科学研究院
Priority date: 2013-05-23
Filing date: 2013-09-24
Publication date: 2014-11-27
Also published as: CN103337295A

Abstract

A power transmission line for preventing snow and ice disasters. The power transmission line is provided with a conductor, a heat-insulating layer and a supporting layer successively from inside to outside, wherein the supporting layer comprises rubber. The heat transfer process between the lost heat of the power transmission line and the surrounding environment is changed by adding the heat-insulating layer and the supporting layer around the surface of the conductor, thereby changing the distribution of the temperature field of the power transmission line and the surrounding environment, and preventing and delaying the coagulation of snow and ice on the power transmission line, so as to prevent snow and ice disasters.

Description

Transmission line for preventing snow and ice disaster

Technical field

The invention belongs to the technical field of disaster prevention and mitigation, and particularly relates to a power transmission line for preventing ice and snow disasters. Background technique

Rain, snow, ice and often accompanied by strong wind disasters are one of the major disasters facing the power grid. Such disasters often cause the transmission line to dance at the same time, which causes the towers of the transmission line to fall down, the lines to trip, the line bolts loose, the jumpers fall off, and the lines are broken. Serious damages such as strand breakage, damage to connecting fittings, damage to towers, flashover of ice, etc., the direct consequence is that it is easy to cause secondary failure due to grid disconnection, large-scale power grid outage, local grid grid operation, power rail power outage, etc. Disasters cause great difficulties to the social economy and people's livelihood. Such disasters occur frequently in China, Russia, Canada, the United States, Japan, the United Kingdom, Finland, Iceland, etc. It can be said that snow and ice disasters are common to many countries in the world. problem.

At present, the main methods for the power industry to deal with snow and ice disasters are:

1 External force tapping method, which is called "ad hoc" method in foreign countries, that is, it is processed by the operator on site, and the processing method is ever-changing. External force tapping is simple and easy, but it can only de-ice a small part of the ice-covered line. It is slow, heavy and uneconomical, so it is only used in emergency situations where there is no other more effective method.

2 high current ice melting methods, including over-current melting ice, short-circuit current melting ice, DC current melting ice, etc. These methods are more efficient, but generally require the preparation of additional equipment, high cost, huge energy consumption, operation Complex, has a greater impact on system safety, and is also prone to local overheating and damage to grid equipment. In particular, limited to system short-circuit capacity, ice melting power supply, etc., for 500kV and above, short-circuit melting ice is almost impossible to achieve.

3 With load ice melting method, this technology mainly uses the double-split wire line itself, after the auto-transformer is boosted to form a loop in the double-split wire and generate current or change the operation mode of the power grid to adjust the power flow distribution of the power grid to increase the icing line. The current, the wire heats up to melt the ice. The ice melting effect of this technology is better, but the limitation of the circuit design, supporting facilities construction or grid operation mode adjustment is relatively large, and the scope of use is narrow.

4 Passive deicing method, this method is to install a snow block, balance hammer and other devices on the wire, so that ice and snow are not easy to coalesce on the wire and fall off by itself. Although it does not require basic input and the operation price is low, the efficiency of this method Low, limited by natural conditions and limited to certain types of ice, this method cannot be guaranteed to be reliable.

5 laser ice melting method, there are generally two cases, the first is to use the high-energy melting ice of the laser to de-ice, the second is to use the pulse of the laser, the stress wave to produce the impact, so as to achieve the purpose of melting ice. Such methods, on the one hand, high power laser sources are difficult On the other hand, power lasers are also more harmful to objects such as ceramics and metals, and are rarely used in practical work.

6 chemical deicing method, such methods include ice coating, heat absorbing coating, spraying deicing fluid, etc., and have been applied in the anti-icing and snow-proofing of airplanes, automobiles and trains. However, the deicing operation range of the transmission line is too large, and it is difficult to apply it in the power system considering the influence on the environment and the corrosion effect on the tower.

7 New high-voltage overhead conductor (AERO-Z) method (Yunnan Zhaotong), this kind of wire cross-section is arranged in a star Z shape, which is stronger and compact than the stranded cable. The smooth surface of the AE O-Z wire can greatly reduce the accumulation of snow and frost. Due to the high cost, only the smooth surface reduces the accumulation of ice and snow. As the wire ages, the effect is weakened and the promotion is limited.

8 Others include the robot snow shoveling method, the electromagnetic force deicing method, and the electric pulse deicing method. Most of them are still in the exploratory research stage.

The above methods are basically methods of elimination after the formation of ice and snow disasters, and often losses have been caused, both in terms of losses and countermeasures, the cost is relatively large. In fact, the formation process of ice and snow disasters is "not a cold day", and the accumulation of disasters is not abrupt. The conditions for disasters are very narrow. If you start from the prevention link, in the process of ice and snow disaster formation, "anti-micro-duration", then, snow and ice prevention effect and cost It will be very different. Summary of the invention

In order to overcome the above deficiencies of the prior art, the present invention provides a power transmission line for preventing snow and ice disasters, which increases the heat conduction layer and the heat insulation support layer around the surface of the conductor, thereby changing the heat loss of the power transmission line and the heat conduction and convection heat exchange around the power transmission line. The process is artificially caused to overflow the "diffuse dam", thereby changing the temperature distribution of the transmission line, the insulation layer and the support layer, the thin layer of the transmission line to the ambient air, and the air environment layer around the transmission line. Therefore, it blocks the passages caused by ice storms such as rain and snow, and plays a role in preventing and controlling the transmission line ice and snow disaster.

In order to achieve the above object, the present invention adopts the following technical solutions:

Provided is a power transmission line for preventing snow and ice disasters, wherein the power transmission line is provided with a conductor, an insulation layer and a support layer in order from the inside to the outside, and the support layer comprises rubber.

When the ambient temperature is around 0 °C, the inner and outer surfaces of the insulation layer have a temperature difference of about 5 °C. At high temperatures, the wire heat balance satisfies the national standard insulation layer.

HOkV The following power transmission and distribution conductors, the surrounding transmission conductors are tightly wrapped around a layer of soft, insulating polymer material, and a layer of corrosion-resistant, flexible and insulating support layer rubber is placed outside the insulation layer.

In order to overcome the influence of strong electric field dielectric loss, corona and partial discharge on the supporting material, the transmission line of HOkV and above power grid is placed in the middle of the single wire layer of the wire, and the outer wire serves as the supporting layer.

The use of insulation layer and support layer in one, using insulation coating, etc., to produce the same function of ice disaster prevention Governance of transmission lines.

The power transmission line is a power line in a power distribution network for each voltage level.

During the transmission of the power transmission line, the line loss energy lost by the transmission line is radiated to the atmosphere in the form of heat exchange and heat radiation; the heat exchange includes thermal motion due to internal atoms and free electron microscopic particles. The resulting conduction heat exchange, as well as the convective heat exchange caused by the relative displacement between the transmission line and the ambient air and inside the air.

In the conducted heat exchange, according to the Fourier heat conduction law, the conduction heat loss thermal power follows the following rules: dQ = -AdS— ( 1 )

Dx

Where Q is the heat transfer rate, S is the heat transfer area, X is the temperature field position variable, λ is the thermal conductivity, t is the temperature field temperature, and the thermal conductivity λ is the material per unit thickness under stable heat transfer conditions, both sides The unit temperature difference is the unit of heat transferred per unit area in watts per meter. The thermal conductivity λ characterizes the thermal conductivity of the material. The larger the thermal conductivity, the better the value and the substance. Composition, structure, density, temperature and pressure are related.

In the convective heat exchange, according to Newton's law of cooling, the fluid heat exchange power Q is calculated by the following formula:

Q = aS(ti - t ₂ ) (2)

Where t^nt ₂ is the solid wall temperature and the fluid temperature, respectively, in degrees Celsius; S is the heat transfer area, the unit is square meters, a is the convective heat transfer coefficient, the unit is watts/square meter·degree Celsius; and a represents convection The heat transfer capacity, the value is equal to the heat transferred per unit area when the temperature between the fluid and the wall is different. The shape and position of the heat transfer surface, the heat transfer coefficient, heat capacity, density and viscosity of the fluid. The coefficient, the laminar or turbulent state of the fluid, and the state of motion of the fluid's free or forced motion.

In the thermal radiation, the radiant energy Q of the object is calculated by:

Q = εΑσ(Τ! ⁴ - Τ ₂ ⁴ ) (3 )

Wherein, [epsilon] is the emissivity of the object, the object is the surface area of [alpha], [sigma] is the Stefan - Boltzmann constant, which is 5.67 Χ 10- ⁸ w / m ² · ⁴ Kelvin, and 1 ^ are object temperature And ambient temperature.

Compared with the prior art, the invention has the beneficial effects that: the power transmission wire provided by the invention increases the heat conduction layer and the heat insulation support layer around the surface of the conductor, thereby changing the heat loss of the power transmission line and the heat conduction and convection heat exchange process around the power transmission line. Artificially caused the overflow of the "diffuse dam", thereby changing the temperature field distribution of the transmission line, the insulation layer and the support layer, the thin layer of the transmission line and the surrounding ambient air, and the air environment layer around the transmission line. Thereby blocking the channels caused by rainstorms, snow shovel and other ice disasters caused by transmission lines, and playing a role in preventing and controlling the transmission line ice and snow disaster. DRAWINGS

1 is a schematic cross-sectional view showing the structure of a power transmission line for preventing ice and snow disasters in an embodiment of the present invention;

2 is a schematic cross-sectional view showing a structure of a transmission line for preventing ice and snow disasters in the embodiment of the present invention; FIG. 3 is a schematic cross-sectional view showing a structural change of a transmission line for preventing ice and snow disasters in the embodiment of the present invention. Specific form

The invention will be further described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the present invention provides a power transmission line for preventing snow and ice disasters. The power transmission line is provided with a conductor, an insulation layer and a support layer in order from the inside to the outside, and the support layer comprises rubber. According to different climatic conditions and theoretical transmission wire loss heat, the material and thickness of the insulation layer and the insulation support layer are adjusted to construct a suitable "diffuse heat dam", thereby blocking the formation process of the transmission line ice coating. Since the heat in the transmission line "diffuse dam" is slowly released (heat potential) through the surface, a small amount of ice coating on the transmission line disappears or falls off due to melting.

Using the objective fact that the ice disaster is formed in a very narrow interval of o°c, without relying on external energy input, control or intervention, using only the transmission wire loss heat, by slightly changing the transmission line and the surrounding temperature field, slightly shifting the transmission line upwards The isotherm of its surface is thus staggered from the temperature of the ambient freezing rain, so that under the freezing rain conditions (about o°c), there is no ice on the surface of the transmission line; when the temperature is further lowered, the external environment has no freezing rain formation condition. (dry or cold), no ice on the surface of the transmission line. When the ambient temperature is around 0 °C, the inner and outer surfaces of the insulation layer have a temperature difference of about 5 °C. At high temperatures, the wire heat balance meets the national standard insulation layer.

As shown in Fig. 2, the insulation layer and the support layer are combined into one, and the thermal insulation coating is used to produce the ice fault prevention transmission wire with the same function.

In order to overcome the influence of strong electric field dielectric loss, corona and partial discharge on the supporting material, the transmission line of HOkV and above power grid is placed in the middle of the single wire layer of the wire, and the outer wire serves as the supporting layer, as shown in Fig. 3.

The temperature field is the temperature distribution of each point in space at a certain moment. The temperature distribution of the object is space sitting. The function of the label and time, ie

t = f(x,y, z,x)

Where: t is temperature; x, y, z are spatial coordinates; τ is time.

The surface composed of the same temperature at the same time in the temperature field is an isothermal surface.

Characteristics of the isothermal surface: 1 The isothermal surface cannot intersect; 2 There is no heat transfer along the isothermal surface. There is no heat transfer along the isothermal surface, and there is heat transfer in any direction that intersects the isothermal surface due to temperature changes. The temperature varies with distance to the maximum along the vertical direction from the isothermal surface.

The temperatures of the isothermal surfaces X and X + Δχ are t( _X , _T ) and t(x + Δχ, τ), respectively, and the average temperature change rate between the two isothermal surfaces is:

t(x + Δχ, τ) - t(x, τ)

― Δχ

The temperature gradient is: gradt =

The temperature gradient is a vector whose direction is perpendicular to the isothermal surface and is positive in the direction of temperature increase.

In the temperature space, the heat transfer rate (heat flow rate) is the amount of heat per unit time passing through the heat transfer area, expressed in Q, in watts (W), or joules per second (J/s).

In conduction heat exchange, according to Fourier's law of heat conduction, the conduction heat loss thermal power follows the following rules:

dQ = -AdS— ( 1 )

Dx

Where Q is the heat transfer rate, S is the heat transfer area, X is the temperature field position variable, λ is the thermal conductivity, t is the temperature field temperature, and the thermal conductivity λ is the unit thickness (1 m) under stable heat transfer conditions. Material, unit temperature difference between the two sides (1 degree (Κ, °0) The amount of heat transferred per unit area (1 square meter) per unit time (1 square meter), in watts/meter* degrees (w/mk And the thermal conductivity λ characterizes the physical properties of the thermal conductivity of the material. The larger the thermal conductivity, the better the thermal conductivity is related to the composition, structure, density, temperature and pressure of the material.

Here, it does not affect the judgment and can obtain accurate results through experiments. Theoretically, it can be roughly considered: The heat conduction speed of the wire is proportional to the average thermal conductivity and temperature difference of the transmission wire and inversely proportional to the insulation layer. That is: Q = - s^ Δχ, ie: dx = — λ ds .

dQ

The heat transfer caused by the relative displacement of the particles during the movement is called convective heat transfer. The heat exchange process between the fluid and the solid wall in direct contact with both the convection generated by the displacement of the fluid and the thermal conduction between the fluid molecules is a common result of heat conduction and convection.

In convective heat exchange, according to Newton's law of cooling, the fluid heat transfer power Q is calculated by: Q = aS(ti - t ₂ ) (2)

Where t^nt ₂ is the solid wall temperature and fluid temperature, respectively, in degrees Celsius rc ); S is the heat transfer area, the unit is square meters (m ² ), a is the convective heat transfer coefficient, the unit is watts / square meter · Celsius (w/m ² * °C ); and a represents the convective heat transfer capacity, the value is equal to the temperature difference between the fluid and the wall surface per unit time C, the heat transferred per unit area, and the shape of the heat exchange surface And position, fluid heat transfer coefficient, heat capacity, density and viscosity coefficient, laminar or turbulent state of the fluid, and the motion state of the fluid free motion or forced motion.

In the thermal radiation, the radiant energy Q of the object is calculated by:

Q = εΑσ(Τ! ⁴ - Τ ₂ ⁴ ) (3 )

Wherein, [epsilon] is the emissivity of the object, the object is the surface area of [alpha], [sigma] is the Stefan - Boltzmann constant, which is 5.67 Χ 10- ⁸ w / ^m2 Kelvin ^{4 (w / m2 - K4)} , 1\ and 1^ are the object temperature and the ambient temperature, respectively, and the temperature is the Kelvin temperature.

Through the above analysis, the following conclusions can be drawn:

In the application scenario of heat conduction of transmission lines, among many factors, heat transfer power Q and temperature difference A t are the key and goals of the problem.

Through the above analysis, it is known that the ambient temperature, weather conditions, wind speed, wire surface area, etc. are uncontrollable due to the environment and specific applications. Therefore, the convective heat exchange and radiant heat exchange processes cannot be artificially controlled, that is, the variables cannot be passed. The regulation changes the distribution of the energy temperature (temperature field) of the transmission line and its surroundings. However, the conduction heat exchange process of the transmission wire can change the average (equivalent) 输 of the transmission wire by changing the material of the insulation and supporting materials, and adjust the heating loss and the wrapping manner and thickness of the support layer to regulate the transmission wire loss heat. The conduction speed makes the internal energy of the transmission wire have high internal energy, and there is always a "hot potential" between the surface of the transmission wire. It can be used as the reverse process (or feedback process) of the transmission wire to cover ice, effectively preventing and delaying ice and snow. Condensation in the transmission line.

Material and process conditions, the thermal conductivity of the aluminum wire of the transmission line material is about 237 w/mk, and the thermal conductivity of asbestos is about 0.15 w/mk. Currently, there is a new type of ultra-fine glass wool with a heat transfer coefficient of 0.008 w/ Mk, light weight, low thermal conductivity, good elasticity, non-toxic, non-polluting, high temperature resistance (can be used for 600-105CTC for a long time), high pressure resistance, tensile strength and high bending strength. Through testing, it is possible to manufacture a transmission line insulation and insulation support layer that meets the requirements.

The following LGJ500/35 is used as an example to estimate the following:

Prerequisites: Since the steel core wire resistance is greater than the aluminum wire, plus the skin effect, the steel core interface size does not affect the following analysis conclusions, so the steel core section is not considered.

Calculate the parameters as follows:

Unit transmission wire resistance (1 m): The theoretical calculation of the transmission line resistance is complicated, including AC resistance and DC resistance. Involving temperature, twisting factor, number of aluminum wire, single wire diameter, eddy current, hysteresis, skin effect, etc. Here, the theoretical resistance has guiding significance, the actual resistance can be accurately obtained through the test, without losing the generality of analysis, the transmission wire resistance According to the standard "aluminum and aluminum alloy drawn round wire" (GB/T 3195-2008), the aluminum wire resistivity is 0.028 Ω · mm ² /m, since the wire cross section is S cut = 500mm ² , the unit length (1 The resistance of the wire) is r = p X丄 = 0.028/500 = 0.000056 ohms (Ω).

Unit wire surface area: Ignore the thickness of the insulation layer and the insulation support layer, the surface area of the unit wire is 5 = πά χ 1 =

Maximum use temperature of the conductor: According to the Design Code for Overhead Transmission Lines of 110kV-750kV (GB 50545 - 2010), the maximum operating temperature of the conductor is 70 °C.

Current carrying capacity: Calculate the current carrying capacity (maximum operating temperature 70 °C) according to the “Design Specification for 110kV-750kV Overhead Transmission Lines” (GB 50545 - 2010). The calculated carrying capacity of the LGJ500/35 is approximately 670 amps (A).

According to the "Design Specification for 110kV - 750kV Overhead Transmission Lines" (GB 50545 - 2010), other parameters are as follows: At high temperature, the ambient temperature is 40 °C, and the sunshine intensity is 1000 (w/m ² ). The surface emissivity of the wire is 0.9, and the heat absorption coefficient of the wire is 0.9.

From this, the line loss power is calculated as the power consumption = I ² r = 670 ² X 0.000056 - 25 (W). At low temperatures (about zero degrees), ignoring heat radiation, assuming that the internal temperature and surface temperature difference of the wire is controlled at 5 °C, according to formula (6), assuming ultra-fine glass wool insulation material with a heat transfer coefficient of 0.008 w/mk is used. It can be calculated that the thickness of the insulation layer is dx = -0.008 X 79 X 10- ³ x 5 ÷ (—25) = 0.13 x 10- ³ m = 0.13 mm, that is, as long as 0.13 is added to the surface or inner layer of the transmission line The insulation layer of millimeters maintains a temperature difference of approximately 5 °C inside and outside the wire, that is, there is a "heat potential". (The actual situation and theoretical calculation of the temperature field show that if the thermal conductivity of the aluminum wire is too small, the heat capacity is too small and the heat transfer coefficient is too large, the wire temperature is slightly lower than the ambient temperature, and there is no "heat potential"), thereby preventing or delaying ( According to weather conditions and icing rate, the occurrence of ice disaster.

At high temperatures, according to extreme conditions, the wire temperature is 70 ° C, the ambient temperature is 40 ° C, then the wire thermal radiation power P _ft = 0.9

X 79 X 10-3 X 5.67 X [ ( 343/100) ⁴ - ( 313/100) ⁴ ]=17.1 (W); Conductor heat transfer power P = 4 X ( 70-40)

=120 (W); Receive sunlight for 1/2 of the wire area, power P _p = 0.5 X 79 X 10-3 X 1000 = 39.5 (W); Line loss power P consumption = / ² r=25 ( W). Obviously, P pass +/3⁄4 > P _p day + P consumption. The heat dissipation power of the wire is greater than the power generated by the heat. That is to say, below 70 ° C, the heat generated by the wire and the power lost by heat can be balanced, that is, the maximum temperature of the wire does not exceed 70 ° C. The modified transmission line can meet national standards at high temperatures. Further calculations show that: the current main specification of steel core aluminum stranded wire (1 meter length) has a loss thermal power of about 20 watts (W), which can meet the requirements of the present invention.

According to the specific climatic conditions, plan the transmission capacity, determine the temperature difference between the inside and the surface of the transmission line (for example, 5 ° C), and calculate and test the insulation insulation, insulation support material, weaving, wrapping method, etc. according to the design specifications of the transmission line, thereby reducing The comprehensive thermal conductivity of the transmission line adjusts the thickness of the insulating insulation layer and the insulating support layer so that the conducted heat exchange satisfies the target requirement of maintaining the temperature difference, and thereby manufactures a transmission line that satisfies the demand.

It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limited thereto. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be The invention is to be construed as being limited to the scope of the appended claims.

Claims

Rights request

A power transmission line for preventing snow and ice disaster, characterized in that: the power transmission line is provided with a conductor, an insulation layer and a support layer in order from the inside to the outside, and the support layer comprises rubber.

2. The power transmission line for preventing ice and snow disaster according to claim 1, wherein: when the ambient temperature is around 0 ° C, the inner and outer surfaces of the thermal insulation layer have a temperature difference of about 5 ° C, and at a high temperature, the thermal balance of the electric wire meets the state. Standard insulation layer.

3. The power transmission line for preventing ice and snow disaster according to claim 1, characterized in that: l lOkV power transmission and distribution line below, the surrounding transmission line is tightly wrapped around a layer of soft, insulating polymer material, in the insulation layer. A layer of corrosion-resistant, flexible, and insulating support layer rubber is provided.

4. The power transmission line for preventing ice and snow disaster according to claim 1, characterized in that: l lOkV and above power transmission lines, in order to overcome the influence of strong electric field dielectric loss, corona, partial discharge on the supporting material, the thermal insulation layer Placed in the middle of the single wire layer of the wire, the outer wire serves as a support layer.

5. The power transmission line for preventing ice and snow disaster according to claim 1, wherein: the thermal insulation layer and the support layer are combined into one, and a thermal insulation coating is used to produce an ice disaster prevention transmission wire with the same function.

6. The power transmission line for preventing ice and snow disaster according to claim 1, wherein the power transmission line is a power line in a power distribution network for each voltage level.

7. The power transmission line for preventing ice and snow disaster according to claim 6, wherein: during the transmission of the power transmission line, the line loss energy lost by the power transmission line is dissipated in the form of heat exchange and heat radiation. In the atmospheric environment; the heat exchange includes conductive heat exchange due to thermal motion of internal atoms and free electron microscopic particles, and convective heat exchange caused by relative displacement between the power transmission line and the ambient air and inside the air.

8. The power transmission line for preventing ice and snow disaster according to claim 7, wherein: in the conduction heat exchange, according to the Fourier heat conduction law, the conduction heat loss thermal power follows the following rules:

dQ = -AdS— ( 1 )

Dx

9. The power transmission line for preventing ice and snow disaster according to claim 7, wherein: in the convection heat exchange, according to Newton's law of cooling, the fluid heat exchange power Q is calculated by: Q = aS(ti - t ₂ ) (2)

10. The power transmission line for preventing ice and snow disaster according to claim 7, wherein: in the thermal radiation, the radiant energy Q of the object is calculated by:

Q = εΑσ(Τ! ⁴ - Τ ₂ ⁴ ) (3 )

Wherein, [epsilon] is the emissivity of the object, the object surface area [alpha], [sigma] is the Stefan - Boltzmann constant, which is 5.67 Χ 10- ⁸ w / m ² · ⁴ Kelvin,! ^ and ^ are the object temperature and the ambient temperature, respectively.