JPS6226556B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a stabilizer having a relatively low thermal resistivity that is particularly effective in providing a thermally stable environment for buried power transmission and distribution equipment such as cables and transformers. Nowadays, for ecological and operational reasons, high voltage transmission and distribution power lines, electrical equipment such as transformers are buried underground. One of the most severe limitations placed on the capabilities of such devices is the dissipation of heat caused by the power flow. If the thermal resistivity of the environment surrounding buried equipment is sufficiently high, the heat generated while the equipment is functioning can increase the temperature of the equipment beyond permissible limits, and the equipment cannot be kept at such temperatures for long periods of time. Equipment deterioration or destruction may occur during operation. For this reason, underground facilities must be designed according to the generally expected thermal environment. Furthermore, since most of the thermal impedance from a heat source or electrical conductor to air is present in the intervening ground, the ground becomes an overwhelming factor in calculating device dimensions. Such calculations must take into account limitations arising from the heterogeneity of the surrounding soil environment. For example, soils found along the route of underground cables typically vary widely in thermal conductivity properties, and therefore cable sizing will be required to be compatible with the region of soil that has the highest thermal resistivity. . To alleviate this situation, current commercial practice requires the use of prepared backfill materials with known resistivity properties to replace the natural pot. This backfill material is generally a well-sorted substrate that exhibits resistivity within a satisfactory range for the assumed thermal history, ie, expected period of subsurface temperature and moisture availability. However, this backside filler often has to be transported to the installation site, which increases the cost of the project. Furthermore, in many cases the original soil jar that is replaced must be transported from the installation site. Therefore, the installation cost relative to the usability is greatly increased. One solution to the problem of heat dissipation for buried electrical transformers is disclosed in U.S. Pat. No. 3,212,563, which teaches a jacketed transformer in which cooling water is piped to the transformer jacket. Heat generated during normal operation is dissipated. Although the cooling water does serve to dissipate the heat generated, such designs greatly increase transformer costs, and maintenance problems with such systems tend to make them commercially unviable. Other solutions to this problem, such as those disclosed in US Pat. No. 3,719,511, utilize weak mix concrete to house electrical equipment. However, once the concrete mixture has been utilized, reintroduction presents certain difficulties and the concrete system may develop certain cracks, thus reducing its potential as an effective backfill material. Other backside fill materials, such as those defined in U.S. Pat. Optimize rates. Such materials do not provide the cost savings associated with transporting backfill materials to the installation site. It has now been discovered that a backfill composition with improved thermal resistivity properties can be produced by simply treating the clay with a clay, preferably a kaolinite clay or a montmorillonite clay, and a stabilizer containing a dispersant for the clay. Ta. Depending on the nature of the natural soil excavated during trenching operations, the same soil can often be treated and returned to the trench as backfill material. According to the invention, about 90 to about 99% by weight of the clay,
and from about 1.0 to about 10.0% by weight of a stabilizer comprising a mixture of clay and its dispersant, the dispersant comprising at least about 0.25% by weight of the mixture. The clay/dispersant mixture unexpectedly reduces the thermal resistivity of the backfill material below that found when the components of the mixture are used separately from the clay. Heat transfer through a clay pot is of course a complex phenomenon due to the complexity of the clay pot itself. In this text, soil is composed of solid substances such as sand, clay or fine sand, and finally air or water. Thermal resistivity, which is the main concern in this paper, generally depends on soil composition, density, water content, particle size, particle size distribution, etc. The main physical characteristic of thermally stabilizing media for the backside filling of buried electrical devices, for example cables, is the resistivity unit known as the "thermal ohm", which measures the amount of heat applied to a cube 1 cm on a side by 1 watt or 1 joule/joule. It is defined as the temperature drop in °C when flowing at a speed of seconds. It is denoted by the Greek letter "ρ" or "rho". A high solids content is of course desirable since solids have the lowest thermal resistivity. For example, solid quartz, the main component of siliceous sand, has a thermal resistivity of about 11°C-cm/watt. Water, on the other hand, has a resistivity of about 165°C-cm/watt, and air has a resistivity of about 4000°C-cm/watt. From these figures it is clear that in order to obtain a minimum resistivity, the soil should contain a maximum amount of solid particles and a minimum amount of air. Of course, it is not possible to fill the solid particles without gaps. In fact, it was an object of the aforementioned U.S. Pat. be. From a physical composition standpoint, an ideal backfill material for thermal stabilization would have a low thermal resistivity that is stable over a wide range of climatic conditions, have good moisture retention properties, and be rewetted to capacity. It also needs to be easily handled. Such properties are obtained due to the high solids content of materials with inherently low resistivity. Currently, one of the most suitable such materials is quartz sand, which consists of a wide range of grain sizes graded to give a dense mixture. However, sand has low water retention. Also, the high density of such mixtures depends on the particles of each size being thoroughly mixed. However, relatively dry sand particles will separate very quickly during handling. Currently, compensation for such deficiencies is accomplished by including a small amount of clay in the composition, preferably from about 5 to about 10% by weight, sufficient to provide a thin coating to the individual sand particles. This provides the mixture with the water retention capacity of the clay, increases the contact area between adjacent sand particles, and provides sufficient adhesion between the particles to reduce segregation. Clay is one of the effective ingredients in the heat-stable compositions of the present invention.
There is also one. It has been determined that up to about 10% by weight of clay in the clay will sufficiently reduce resistivity when used in conjunction with the dispersants described below. Exemplary preferred clays include kaolinite clays, such as commercially available Dixie Clay (manufactured by R.I. Vanderbilt Company), and montmorillonite, with kaolinite clay being most preferred. It has been unexpectedly discovered that a synergistic effect on the thermal stability of the clay can be obtained by including a dispersant for the clay along with the clay. It has been found that the inclusion of such agents with clay and clay reduces the thermal resistivity below that found when either component alone is used with clay. Apparently, the dispersant acts to disperse the clay particles so that they do not settle in the aqueous medium by imparting an electric charge to the clay particles. Electrostatic repulsion between these charged particles causes the particles to separate, preventing settling and allowing more effective mixing with the soil. Additionally, it is believed that a secondary effect of including a dispersant in the composition may be a reduction in surface tension, which tends to promote more effective particle wetting. Examples of preferred dispersants that have been found to work effectively in the present invention include anionic materials such as Durban No. 1 and Durban No. 2, commercially available from R.T. Vanderbilt Corporation. Durban No. 1 consists of a sodium salt of a polymerized alkylnaphthalene sulfonic acid, and Durban No. 2 consists of a sodium salt of a polymerized substituted benzoid alkyl sulfonic acid. An exemplary cationic dispersant is Atlas G-3570, available from Atlas Chemical Corporation, and an exemplary nonionic dispersant is Atlas G-1441, available from Atlas Chemical Corporation.
It is. Anionic dispersants are preferred. At least about 0.25% by weight of the clay/dispersant mixture to effectively reduce the thermal resistivity of the composition.
It was confirmed that it must be a dispersant.
Although an upper limit for dispersant has not been found, dispersant concentrations of about 2.0% by weight and above only marginally effective reductions in soil resistivity are observed. By using such a simple treatment composition to perform thermal stabilization of the soil, many of the natural soils removed from trenching sites can be mixed with clay/dispersant combinations at the installation site. It can be reused, thereby effectively eliminating the need for transportation of stabilized backfill material and removal of natural soil from the site. The method of addition of the clay/dispersant stabilizer is not critical as long as thorough mixing occurs. In fact, clay and dispersant can be added separately to the clay to stabilize it. Of course, water is used to help disperse the stabilizer. Water can be present in the clay or added with stabilizers. The invention is illustrated by the following non-limiting examples. All parts are by weight unless otherwise specified. Example 1 Measure thermal resistivity using a hot needle. In this case, the relationship that actually exists between the thermal resistivity of the material and the temperature rise of the heat source within the material is utilized. A.I.E.
E.Trans. (Power Apparatus and Systems),
Vol. 79, pp. 836-843 (1960), the thermal needle contains a heater element and a thermocouple by which the temperature-time characteristics resulting from a given heat input can be observed. . According to the discussion in the above literature, a 4" length laboratory hot needle was created. By using this device, thermal resistivity was measured using a technique known as the temporal method. The temporal method is It is based on the theory that the rate of temperature rise of an object generally depends on the thermal properties of the materials around it.The basis of this method is the AIEE
Trans. (Power Apparatus and Systems),
Volume 71, part 3, pp 570-577 (1952). By utilizing a data acquisition system, the millivolt output of the hot needle thermocouple was automatically recorded at preselected time intervals. Generally, 10 second time intervals were used and experiments were run for no more than 8 minutes. The current and voltage to the needle was monitored every 2 minutes and the average of these readings was used to calculate the power input thereto. Analysis of the data was performed using a least squares fit computer programmer and the temperature rise of the sample was plotted mathematically against time. The particular soil used in many of the tests described below is called Otsutawa sand, which is an ASTM C-
satisfy the instructions contained in § 109. This sand is a natural silica sand from Otsutawa, Illinois, and is generally uniform in grain size and round in shape. According to the foregoing discussion, both of these properties give sand a high thermal resistivity, on the order of 270°C-cm/watt. Soil samples were generally compacted prior to testing. The compression method used is detailed in ASTM D698-70. In addition, samples were thoroughly dried before testing to ensure uniformity during testing and measured based on maximum thermal impedance. In order to confirm the effect of the present invention on Otsukwa sand, Otsukwa sand samples containing 5% by weight of water were prepared.
Compressed according to ASTM D698-70. After drying the sample to remove water, its thermal resistivity was measured using a hot needle, and the thermal resistivity was found to be 275°C-cm/watt. A second sample of Otsutawa sand was thoroughly mixed with 2.94 parts by weight of Deixie clay in a Hobart mixer. Deixie clay requires 5 parts water.
It was given as an aqueous suspension by mixing with 2.94 parts of clay and adding it to dry Otsutawa sand. The thermal resistivity of the sample was confirmed to be 137°C-cm/watt. A similar sample was prepared by removing the Dixie clay from the formulation and replacing it with 0.06 parts by weight of Durban #1 in 5 parts of water and thoroughly mixing the clay pot with a Hobart mixer. The thermal resistivity of the sample is 270
It was ℃-cm/watt. Finally, 5 parts by weight of water, 2.94 parts by weight of Dixie clay, and 0.06 parts by weight of Durban #1 were added to the dry Otsutawa sand of the fourth sample. The thermal resistivity of the sample was 94.3°C-cm/watt. The effect of the ingredients on the thermal stabilization of the soil was also tested using a soil referred to as a Class 5 soil, which is a relatively high quality soil commonly used in subgrade construction. Class 5 clay itself, dried to remove water and compacted without the addition of clay or dispersants, is 68.2
It has a thermal resistivity of °C-cm/watt, which points to a greater effect on resistivity when using soils with substantially uniform particle size, i.e., fine soils versus Otsutawa sands. . When tested by adding 2.94 parts by weight of Deixie clay to the clay pot,
Its thermal resistivity was 70.7°C-cm/watt, indicating that the mere addition of clay to a fine Class 5 clay has only a very modest effect. When 0.06 part of Durban #1 is added to the soil and thoroughly mixed in a Hobart mixer, its thermal resistivity is 69.7°C-cm/watt, and in this case, the effect of adding a dispersant on the soil is also very large. It was pointed out that it was small.
However, when the Class 5 clay was well mixed with 2.94 parts of Deixie clay and 0.06 parts of Durban #1, its thermal resistivity decreased to 57.0 °C-cm/watt, which is clearly a synergistic effect of the dispersant and clay additions. This was to point out the effects. Example 2-13 To confirm the effect of the clay/dispersant combination on other clays, clay samples having the analytical values shown in Table 1 below were obtained. The clay jars tested are representative of the various clay jar types found in the United States as classified by the United States Department of Agriculture.

【table】

TABLE The results obtained by treating each pot with the clay/dispersant mixture provided resistivity data as shown in Table 2.

【table】

Table 2 As can be seen from Table 2, treatment of the various clays with the clay/dispersant mixture resulted in a decrease in thermal resistivity in most cases. The water content of all control and stabilized samples was chosen to maximize compaction of the sample and thus optimize its resistivity. For the dispersant-only samples, the control water content was used.

Claims (1)

[Claims] 1. A method for treating soil comprising a mixture of a clay selected from kaolinite and montmorillonite clays and a dispersant for the clay, the dispersant comprising about 0.25 to about 2.0% by weight of the mixture. stabilizer to reduce its thermal resistivity.