JPWO2015152252A1 - Fireproof coating structure of power cable and its construction method - Google Patents

Abstract

The fireproof covering structure of the power cable includes a power cable, a container, and a plurality of layers of fireproof coverings covering the container, each of the fireproof coverings being a heat absorbing pack, a fire resistant heat insulating material, and these heat absorbing packs, Each of the refractory coatings, the heat-absorbing pack is located on the container side, the refractory heat-insulating material is located outside the heat-absorbing pack, and the jacket material is inorganic with metal foil. The thickness of the refractory insulation of the outermost refractory coating is greater than the thickness of each refractory insulation of all the refractory coatings inside the outermost refractory coating.

Description

  The present invention relates to a fireproof coating structure for a power cable and a construction method thereof.

  For power cables installed at power stations, etc., especially power cables installed in fire-proof areas within nuclear power plants, power should be supplied during a safe shutdown such as emergency shutdown of the reactor and securing of a cooling system. It is considered essential to ensure this, and for this reason, it is required to provide a fireproof coating that can withstand a long-term fire.

  On the other hand, when electricity flows through the power cable, heat is generated by the electric resistance of the power cable. When this heat accumulates and the temperature of the power cable rises, the current that can flow through the power cable decreases, and there is a risk that the necessary power cannot be secured. Therefore, in such a fireproof coating for a power cable, it is necessary to be able to prevent the temperature of the power cable from rising excessively by mitigating the accumulation of heat caused by the current flowing through the power cable.

  In other words, heat accumulation caused by the current flowing through the power cable is alleviated to prevent the temperature of the power cable from rising excessively, and in the event of a fire, in addition to that, the power cable is protected from fire and the power cable due to the heat of the fire The contradictory function of suppressing the temperature rise is required.

  As a fireproof coating for a general electric wire that is not a power cable, a technique is known in which a wire tube is covered with a heat-absorbing pack and a fireproof heat insulating material such as an inorganic fiber mixed mat (Patent Document 1). However, if such a fire-resistant coating structure is applied to a power cable as it is and an attempt is made to provide a fire-resistant coating that can withstand a long-term fire, the thickness of the fire-resistant coating layer increases, and electricity flows through the power cable. Since the generated heat is accumulated, the power cable is overheated, and there is a problem that the current that can be flowed is reduced.

JP-A-7-135716

  That is, the present invention has been made in view of the above, and can protect the power cable from the heat at the time of a fire, and can reduce the accumulation of heat caused by the current flowing through the power cable, thereby reducing the temperature of the power cable. An object of the present invention is to provide a fireproof covering structure for a power cable and a method for constructing the same, which can prevent an excessive rise.

In order to achieve the above-described object, a fireproof coating structure for a power cable according to the present invention includes a power cable, a housing that houses the power cable, and a multi-layer fireproof coating that covers the housing that houses the power cable, Each of the refractory coverings includes an endothermic pack, a refractory heat insulating material, and a jacket material. In each of the refractory coverings, the endothermic pack is located on the container side, and the refractory insulating material is It is provided so that it may be located in the outside of the endothermic pack, the jacket material is an inorganic fiber cloth with metal foil, and the thickness of the refractory insulation of the outermost refractory coating is the outermost pack. It is thicker than the thickness of each of the refractory insulation materials of all the refractory covers inside the refractory cover.
Furthermore, the construction method of the fireproof coating structure of the power cable of the present invention for achieving the same object, repeatedly wrapping and fixing the fireproof coating one layer at a time on the outside of the container, By obtaining the fireproof covering, the construction of the fireproof covering structure of the power cable according to the present invention described above is performed.

  According to the present invention, the power cable can be protected from heat at the time of fire, and the accumulation of heat caused by the current flowing through the power cable can be relaxed to prevent the temperature of the power cable from rising excessively. .

It is a perspective view which shows the fireproof coating | cover structure of the power cable of Embodiment 1 of this invention. It is a figure which shows the structure of a fireproof covering. It is a figure which shows the structure of an endothermic pack. It is a figure of the same aspect as FIG. 1 regarding Embodiment 2 of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

Embodiment 1 FIG.
FIG. 1 is a perspective view showing a fireproof covering structure for a power cable according to Embodiment 1 of the present invention. The power cable fireproof covering structure 1 includes a power cable 3, a housing 5 that houses the power cable 3, and a plurality of layers of fireproof coverings 7, 9, 11, and 13 that cover the housing 5 that houses the power cable 3. Is provided.

  In the first embodiment, an example in which a four-layer fireproof covering is used is shown as an example. Moreover, in this Embodiment 1, the container 5 is a conduit tube in which the power cable is accommodated.

  FIG. 2 is a diagram showing the configuration of the fireproof covering. Each of the fireproof coverings 7, 9, 11, and 13 has flexibility including a heat absorbing pack 21 and a fireproof heat insulating material 23 that are stacked on each other, and a covering material 25 that covers the heat absorbing pack 21 and the fireproof heat insulating material 23. It is a sheet-like (futon-like) member. And each of the fireproof coverings 7, 9, 11, and 13 is used in a front-back relationship in which the heat absorption pack is located on the inner side (covering target side) and the fireproof heat insulating material 23 is located on the outer side when covering the covering target. Having flexibility means that the fireproof covering can be applied by being wound around a conduit (container 5) in which the power cable 3 is arranged or a cable tray (container 105) described later. In the first embodiment, Aqua cover (registered trademark) is used as each of the fireproof coverings 7, 9, 11, and 13.

  In each of the fireproof coverings 7, 9, 11, and 13, the surface of the fireproof heat insulating material 23 (surface opposite to the heat absorbing pack 21 side) and the surface of the heat absorbing pack 21 (surface opposite to the fireproof heat insulating material 23 side) ) (A portion in the vicinity of the end constituting the peripheral end of the fireproof covering) is covered with the jacket material 25. The jacket material 25 is for protecting the surface of the refractory heat insulating material 23, and is obtained by integrating a metal foil that reflects radiant heat from the outside due to a fire and the like and an inorganic fiber cloth that reinforces the metal foil. Preferably used. As a metal foil used for the jacket material, for example, an aluminum foil is suitable, and a thickness of 0.01 mm to 0.1 mm is suitable. As the inorganic fiber cloth, a glass fiber or ceramic fiber cloth is preferably used, and the thickness is preferably 0.1 mm to 0.5 mm. The jacket material is laminated with the refractory heat insulating material so that the inorganic fiber cloth comes into contact with the refractory heat insulating material described later.

  The refractory heat insulating material 23 needs to have flexibility as described above. Therefore, as the refractory heat insulating material 23, a refractory heat insulating material made of mat-like, blanket-like or felt-like inorganic fibers is preferably used. Moreover, as inorganic fiber, glassy fibers, such as rock wool, ceramic fibers, etc. are used suitably. Specifically, for example, a ceramic fiber blanket conforming to JIS R 3311 is suitable. The refractory heat insulating material 23 has a role of making it difficult for heat from the outside such as a fire to be transmitted to the inside. However, if the fireproof covering structure is formed only by the fireproof heat insulating material 23, the heat generated by the current flowing through the power cable is stored. Therefore, in the present invention, the heat generated from the power cable is suppressed from being stored by stacking and using the refractory heat insulating material 23 and the heat absorbing pack 21 described later.

Insulating refractory material 23, it is preferable density of ^{90kg / m 3 ~160kg / m 3} . When the density is less than 90 kg / m ³ , the heat insulating performance may be insufficient. Moreover, since a softness | flexibility will fall when a density exceeds 160 kg / m < ³ >, it becomes difficult to wind and construct the fireproof covering 7, 9, 11, 13 around the electric power cable 3 or the accommodating body 5. FIG. The thickness of the refractory insulation 23 differs depending on the required refractory performance. However, when the refractory performance is a three-hour refractory performance that is required in the refractory area in the nuclear power plant as the refractory covering structure of the power cable, The total thickness of each refractory insulation used in the refractory coating structure is preferably 40 mm or more. The thicker the refractory insulation 23 is, the higher the fire resistance performance is. However, the heat resistance in the thickness direction increases, so that heat generated from the power cable is stored and the temperature of the power cable is likely to rise. In consideration of this, it is preferable that the total thickness of the refractory heat insulating materials of the plurality of layers of the refractory coating is 60 mm or less regardless of the desired refractory performance.

  The fireproof covering structure 1 of the power cable is formed by laminating fireproof coverings 7, 9, 11, and 13. And the main role of the fireproof heat insulating material in the fireproof coverings 7, 9, 11, and 13 is to make it difficult to transfer heat from the outside such as a fire to the inside. Therefore, of the total thickness of the above-mentioned fireproof insulation material 23, the thickness of the fireproof insulation material 13 of the fireproof coating body 13 forming the outermost layer is set to the thickness of the fireproof coating body 7 forming the inner layer. , 9, 11 is preferably thicker than the thickness of the refractory heat insulating material 23. However, since the total thickness of the refractory insulation 23 has an upper limit as described above, if the thickness of the refractory insulation 23 of the refractory covering 13 that forms the outermost layer is too thick, the inner side of the refractory insulation 23 may be increased. The thickness of the refractory heat insulating material 23 becomes too thin, and the effect of disposing the heat absorbing packs described later in multiple layers is reduced. In order to effectively exhibit the effect of disposing the heat absorbing packs 21 in multiple layers, it is preferable that the thickness of the fireproof insulation material 23 of each of the fireproof coverings 7, 9, 11, and 13 is at least 5 mm.

  FIG. 3 is a diagram illustrating a configuration of the heat absorption pack. The endothermic pack 21 is a material in which an endothermic material 33 is sealed in a cell defined between two sealing films 31, and sealing is performed when the temperature rises due to heat from the outside such as a fire. The endothermic material that has been unwound and sealed acts to suppress an internal temperature rise. As the sealing film 31, a film in which a metal foil 43 such as an aluminum foil is sandwiched between a synthetic resin film 41 such as a nylon film or a polyethylene film can be used.

  The endothermic pack 21 is formed by sealing the endothermic material 33 in a cell partitioned between the two sealing films 31 and heat-sealing the periphery. As the endothermic material 33 to be sealed, water or a polymer impregnated with water, or a substance that causes a dehydration reaction at a predetermined temperature, such as aluminum hydroxide, can be used, but a polymer impregnated with water or water. Is preferred. The cell is preferably a square having a side of 5 cm to 10 cm. The sealing of the endothermic pack 21 is released at least at 90 ° C. or higher, preferably 95 ° C. or higher. If the temperature at which the sealing is released is low, the sealing is released by the heat generated from the power cable, and the heat absorbing material may not sufficiently act in the event of a fire. Further, when the endothermic material 33 to be sealed is water or a polymer impregnated with water, it is preferable that the endothermic material 33 is unsealed at 100 ° C. or lower. If the temperature at which the sealing is released exceeds 100 ° C., the cell is ruptured by the water vapor pressure inside the cell and the sealing is released, so that the surrounding refractory insulation 23 may be damaged and the fire resistance performance may be reduced. Because there is sex.

  The thickness of the endothermic pack 21 is preferably 5 mm to 10 mm. When the thickness of the endothermic pack 21 is less than 5 mm, the ratio of the sealing film 31 occupying the cross section in the thickness direction of the endothermic pack 21 is increased, and the entire endothermic pack 21 in the fireproof covering structure for obtaining desired fireproof performance is obtained. This is not preferable because the thickness is increased. Moreover, when the thickness of the heat absorption pack 21 exceeds 10 mm, it becomes difficult to wrap the fireproof coverings 7, 9, 11, and 13 around the housing 5 in which the power cable 3 is disposed.

The amount of the endothermic material 33 sealed in the endothermic pack 21 varies depending on the required fire resistance and the type of the endothermic material 33, but the fire resistance is required in the fire prevention area in the nuclear power plant as the fireproof covering structure of the power cable 3. If the heat absorbing material 33 is made of water or a polymer impregnated with water, the fireproof coverings 7 and 9 per 1 m ² of the construction area 5 of the container 5 in which the power cable 3 is arranged , 11 and 13, the amount of water sealed in the endothermic pack 21 is required to be at least 16 kg when fire resistance of 3 hours is required.

  The thickness of the entire fireproof coating structure is preferably 80 mm or less in consideration of workability. Usually, the fireproof coating of the power cable is performed after the power cable is installed. This is because the work space is often limited. Therefore, in this embodiment, the balance between the refractory heat insulating material 23 included in the entire laminate of the refractory coverings 7, 9, 11, and 13 and the heat absorbing material 33 sealed in the heat absorbing pack 21 is important. When the number of the refractory heat insulating materials 23 is excessive, the heat generated by the current flowing in the power cable is likely to be stored, and the temperature rise suppressing effect by the heat absorbing material 33 is reduced. On the other hand, when the amount of the heat absorbing material 33 sealed in the heat absorbing pack 21 is increased, the thickness of the refractory heat insulating material 23 is reduced. The sealing is released, and the temperature rise of the power cable 3 due to heat from the outside is accelerated. In addition, in this specification, thickness and total thickness are seen by the radius unit centering on a container. In other words, it is not the dimension seen from the range from one outer end to the other outer end, but the dimension seen from the center to the outer end in any one direction. In addition, the description of the thickness and the total thickness indicates the dimensions of the general part, and does not include a part having a greatly different thickness from the general part, such as a joint portion of joints generated in the working process.

Moreover, in order to suppress the heat storage of the heat generated by the current flowing in the power cable 3, the total thermal resistance in the thickness direction of the laminated fireproof coverings 7, 9, 11, 13 is set to 1.3 m ² · K / It is preferable to set it to W or less. In addition, the total thermal resistance in the thickness direction of the laminated refractory coating is the state in which the individual refractory coatings constituting the refractory coating structure extend in a plane before being wound or laminated. The thermal resistance in the thickness direction is obtained, and the individual thermal resistances are values obtained by summing up the layers, and are used as a guideline when examining the configuration of the fireproof coating in the fireproof coating structure of the present invention. As the total thermal resistance in the thickness direction is smaller, heat storage of heat generated by the current flowing through the power cable 3 can be suppressed. On the other hand, there is a problem that external heat such as a fire is easily transmitted to the power cable 3. In the present embodiment, when heat from the outside is transferred to the inside of the fireproof coating structure 1 of the power cable and reaches a predetermined temperature, the heat absorbing pack 21 is unsealed, and the heat absorbing material 33 that has been unsealed is released. Due to the endothermic effect, heat from the outside is further prevented from being transmitted to the inside. In order to fully exhibit this endothermic effect, the endothermic packs 21 are arranged in multiple layers, and a refractory heat insulating material 23 is provided between the endothermic packs 21 and is first arranged on the outermost side by heat from the outside. The endothermic pack 21 is unsealed, and the endothermic effect of the outermost endothermic material 33 is suppressed by suppressing the temperature rise inside by the endothermic effect of the endothermic material 33 of the endothermic pack 21 that has been unsealed. After the loss, it is preferable that the endothermic pack 21 disposed on the inside of the layer is unsealed, and this is repeated so that the endothermic material 33 of each layer has an endothermic effect over time. Therefore, in the present embodiment, a plurality of mat-like fireproof coverings 7, 9, 11, and 13 each having flexibility including a jacket material 25, a refractory heat insulating material 23, and an endothermic pack 21 are respectively provided. Regarding the fireproof coverings 7, 9, 11, and 13, the heat absorbing pack 21 is laminated in multiple layers to form a fireproof covering structure in a front-back relationship where the heat-absorbing pack 21 is positioned closer to the covering target side (inner side) than the fireproof insulating material 23. In addition, the jacket material 25 and the fireproof heat insulating material 23 constituting the fireproof covering 7, 9, 11, 13 are laminated in contact with the inorganic fiber cloth of the jacket material 25 and the fireproof heat insulating material 23, The ends of the mat-shaped fireproof covering may be covered with a jacket material.

  In the present embodiment, the above-described fireproof coverings 7, 9, 11, and 13 are repeatedly wound around and fixed to the outer periphery of the housing 5 where the power cable 3 is disposed in order, and the desired layers are repeatedly formed. The numbers are stacked to form a fireproof coating structure 1 for the power cable. Here, fixing of the wound fireproof coverings 7, 9, 11, and 13 is performed with metal foil such as a glass cloth tape with aluminum foil by overlapping the ends of the fireproof coverings 7, 9, 11, and 13, for example. After being fastened with an inorganic fiber cloth tape, a wire or the like may be wound around the fireproof coverings 7, 9, 11 and 13.

  It is preferable that the outer surface of the outermost layer fireproof covering 13 formed in this way is covered with a metal net 51 (for example, a turtle shell metal net) or a metal plate. This is because it is possible to prevent a part of the fireproof covering from falling off during the fire and reducing the fireproof performance. A wire mesh is sufficient for fireproof coating of indoor power cables, but it is preferable to cover with a metal plate in places where there is a possibility of decontamination at a nuclear power plant even outdoors or indoors. It is.

  Hereinafter, as an example of a specific implementation scene, a more detailed description will be given of a fireproof covering structure for a power cable that satisfies the fire resistance performance of 3 hours required in a fireproof area in a nuclear power plant, and a construction method thereof.

The fireproof covering structure 1 of the power cable that satisfies the fireproof performance of the three-hour fireproof in the first embodiment includes the first layer of the fireproof covering 7 and the second layer of the fireproof covering 9 from the inner side (side closer to the housing 5). Each of the third layer of the fireproof covering 11 is an Aqua Cover (registered trademark) having a thickness of 13 mm (ceramic fiber blanket: thickness 6 mm, heat absorption pack: thickness 7 mm, containing a highly water-absorbing polymer impregnated water, amount of water 4.8 kg) / M ² , outer jacket material: glass cloth with aluminum foil thickness 0.2 mm), fourth layer (outermost layer) fireproof covering 13 is 32 mm thick Aqua Cover (registered trademark) (ceramic fiber blanket) : thickness of 25 mm, an endothermic pack: thickness 7 mm, superabsorbent polymers impregnated water enclosed-water 4.8 kg / m ^2, the enveloping member: an aluminum structure of the foil glass cloth thickness 0.2 mm), About these joints, the circumferential direction and the longitudinal direction are both wrapped 50 mm or more, and the joints are fixed with glass cloth tape 55 (thickness 0.1 mm to 0.3 mm, width 50 mm to 100 mm) with aluminum foil. After tightening with a stainless steel wire 53 (wire diameter 0.5 mm to 1.5 mm) at intervals of 300 mm or less, the outermost layer is stainless steel turtle wire mesh 51 (wire diameter 0.3 mm to 1.5 mm, mesh 8 mm) Finish with ~ 40mm). In addition, it is necessary to construct the joints of the second and subsequent layers of the fireproof coating material so as not to overlap with the joints of the previous layer.

A test specimen having the configuration of Example 1 shown in Table 1 was prepared by the following procedure. First, a steel conduit tube having an outer diameter of 104 mm and a length of 2 m was used as a container, and four cable wires (diameter of about 20 mm) simulating a power cable were passed therethrough. Next, as a fireproof covering for the first layer, Aqua Cover (registered trademark) having a thickness of 13 mm (ceramic fiber blanket: thickness 6 mm, heat absorbing pack: thickness 7 mm, containing highly water-absorbing polymer-impregnated water, amount of water 4.8 kg / m ² , jacket material: a glass cloth with aluminum foil having a thickness of 0.2 mm). At the time of attachment, it was attached as closely as possible to the container so as not to form an air layer. Further, the joint portion was wrapped 50 mm or more in both the circumferential direction and the longitudinal direction, and a glass cloth tape with aluminum foil (thickness: about 0.15 mm, width: 75 mm) was attached to the joint. Stainless steel wire (wire diameter 0.66 mm) was used for binding the fireproof covering, and the interval between the bindings was 200 mm to 300 mm. The knot of the stainless steel wire was covered with a glass cloth tape with aluminum foil. Furthermore, the fireproof coverings of the second to fourth layers were sequentially attached in the same procedure as the first layer. The second layer and the third layer fireproof coverings use the same 13 mm thick Aquacover (registered trademark) as the first layer, and only the fourth layer fireproof coverings have a 32 mm thick Aquacover (registered trademark). (Ceramic fiber blanket: 25 mm thick, heat absorption pack: 7 mm thick, high water absorption polymer impregnated water enclosed, water volume 4.8 kg / m ² , jacket material: glass cloth with aluminum foil 0.2 mm thick) did. Finally, it was finished with a stainless steel turtle shell wire mesh (wire diameter 0.4 mm, mesh 16 mm) as a reinforcing material. Moreover, as a test body having the configuration of Reference Example 1 shown in Table 1, the third layer of the fireproof covering of Example 1 is an Aqua Cover (registered trademark) having a thickness of 32 mm, and the fourth layer of the fireproof covering is thick. The same procedure as in Example 1 was performed except that a 25 mm ceramic fiber blanket (JIS R 3311: 1) was used alone and a glass cloth with aluminum foil was wound once as a protective material on the outside. Furthermore, as a test body having the configuration of Reference Example 2 shown in Table 1, a steel conduit tube and cable wire similar to those of Example 1 were used, and a ceramic fiber blanket (JIS R 3311: 1 No. 1) having a thickness of 25 mm as a fireproof covering. ) Is used as a single piece, wrapped in 6 layers (total thickness 300 mm) and fixed, and once wrapped with a glass cloth with aluminum foil as a protective material on the outside, it was finished with a reinforcing stainless steel turtle wire mesh Things were made. Each layer was fixed in the same procedure as in Example 1.

  Next, the verification test result of the fireproof performance of the fireproof coating structure of the power cable according to the present embodiment will be described. For power cables installed at power stations, etc., especially power cables installed in fire-proof areas within nuclear power plants, power should be supplied during a safe shutdown such as emergency shutdown of the reactor and securing of a cooling system. Since it is considered essential to ensure, it is required to provide a fireproof coating that can withstand a long-term fire. According to the review standards (established on June 19, 2013) concerning the fire protection of practical power reactors and their associated facilities established by the Nuclear Regulatory Commission, a cable that has a fire resistance performance of 3 hours or more for a cable subject to fire protection Therefore, the target fire resistance in the present invention is set to be capable of withstanding heating for 3 hours.

  For Example 1, Reference Example 1 and Reference Example 2 shown in Table 1, a 3-hour heating and fire test was performed in accordance with the ISO 834 standard heating curve used in the fire resistance test for evaluating the fire resistance required for general building parts. It was. The specific contents are as follows.

<Pass / fail of fire resistance test>
In the fire resistance test, the measured values satisfy the following <determination criteria> by the following <heating method> and the following <measuring method> by the following <heating method> for each of the above test specimens. To pass.

<Heating furnace>
(1) The heating is such that the temporal change in temperature defined in the following <heating conditions> is applied almost uniformly to the entire surface of the test specimen.
(2) Heat with a burner.
(3) A thermocouple for measuring the temperature in the furnace is installed in the furnace so as to be uniform inside the heating furnace. At that time, the thermosensitive point (tip) of each thermocouple is set at a position 100 mm away from the surface of the specimen.

<Heating conditions>
Heating is performed so that the time lapse of the temperature measured by the thermocouple installed in the furnace becomes a numerical value represented by the following formula within an allowable error.
T = 345log10 (8t + 1) +20
In this equation, T is the average furnace temperature (° C.), and t is the elapsed time (minutes) of the test. In addition, the said average furnace temperature means the temperature which averaged the temperature measured with each thermocouple installed in the furnace.

<Measurement method>
The temperature is measured every minute or less, and the temperature of the surface of the power cable placed in the conduit at the center of the specimen is measured.

<Criteria>
Heating for 3 hours was carried out, and the first judgment criterion was that the surface temperature of the power cable was 150 ° C. or lower until the end of the test. However, in the test to evaluate the fire resistance performance of such structures, considering the variation of construction materials and construction, as a judgment standard to ensure more reliable performance, 10% safety against the set first judgment standard temperature. The idea of setting and evaluating a second determination criterion that takes a value is widespread. Therefore, in this test, the second criterion was set to be 135 ° C. or lower. Therefore, the satisfaction of the first criterion is set as the minimum condition for passing the 3-hour fire resistance test, and it is further evaluated according to the second criterion whether the safety can be secured. The first criterion of 150 ° C. was set with reference to the temperature at which the heat-resistant vinyl used for the insulating material of a general power cable softens.

  The test results are shown in Table 2 below.

  The test body of Example 1 has a maximum power cable surface temperature of 117.0 ° C. from the start of the test to the end of heating for 3 hours, satisfies the first determination criterion of the above <determination criterion>, and further Since the judgment criteria were also satisfied, it was a pass judgment at a level ensuring safety. The test sample of Reference Example 1 has a maximum power cable surface temperature of 135.2 ° C. until the end of heating for 3 hours, satisfies the first determination criterion of the above <determination criterion>, and is a pass determination. Since it did not satisfy the second criterion, the evaluation result remained a little uneasy about safety. The test sample of Reference Example 2 was rejected because the power cable surface temperature up to the end of heating for 3 hours was 161.9 ° C. and did not satisfy the first determination criterion of the above <determination criterion>.

  Next, for Example 1, Reference Example 1 and Reference Example 2, the calculation results of the total thermal resistance (20 ° C.) in the thickness direction in each fireproof coating structure are shown in Table 3.

In order to alleviate the heat accumulation caused by the current flowing through the power cable during normal use and prevent the temperature of the power cable from rising excessively, the total thermal resistance in the thickness direction of the fireproof coating structure is 1.3 m. ² · K / W or less is considered preferable. This is because when the total heat resistance in the thickness direction exceeds 1.3 m ² · K / W, there is a high possibility of adversely affecting the temperature rise of the power cable during normal use. Both Example 1 and Reference Example 1 had a fireproof protective performance that satisfied the first criterion in the results of the 3-hour fireproof test, but the fireproof coating structure of Reference Example 1 had a total thermal resistance in the thickness direction. Since it is as large as 1.35 m ² · K / W, heat dissipation for preventing overheating of the power cable during normal use cannot be maintained at a desirable level. In addition, for Reference Example 2, in addition to failing the 3-hour fire resistance test, the total thermal resistance in the thickness direction was a large value of 3 times or more of the standard 1.3 m ² · K / W. It became. In order to pass the above three-hour fire resistance test using only the fireproof insulation material as in Reference Example 2, the total thickness of the fireproof coating must be further increased, and as a result, the power cable that is the subject of the present invention is overheated. In a fireproof coating structure that needs to be prevented, sufficient heat dissipation performance cannot be ensured. That is, in order to achieve both high fire resistance in the event of fire and prevention of overheating of the power cable during normal use, the book by laminating the heat-absorbing pack, the fire-resistant heat insulating material, and the jacket material as in the first embodiment. It can be said that the fireproof coating structure of the invention is extremely effective.
In addition, the thermal resistance in the thickness direction in a state where each fireproof covering was extended in a plane was calculated by the following equation.

In the calculation of the thermal resistance, the following values were used as the thermal conductivity (λ) at 20 ° C. of each fireproof covering.
Aqua cover (registered trademark) with a thickness of 13 mm: λ = 0.0735 W / m · K
Aqua cover (registered trademark) with a thickness of 32 mm: λ = 0.0524 W / m · K
Ceramic fiber blanket with a thickness of 25 mm: λ = 0.0646 W / m · K

As described above, according to the fireproof covering structure of the power cable according to the first embodiment, in the event of a fire, the fireproof action is exhibited sequentially from the outer fireproof covering in relation to the multiple layers of fireproof covering, that is, the outer fireproof covering. Sequentially, the endothermic pack is released from the cover, moisture in the endothermic pack oozes into the refractory insulation and the temperature rise is suppressed by latent heat of vaporization, while the endothermic pack of the refractory cover inside is held. . That is, whether or not a suitable fire resistance can be obtained depends on how the endothermic pack of the inner fireproof coating can be made to last for as long as possible without being unsealed. By providing the fireproof covering, the fireproof action is exhibited sequentially from the outer fireproof cover, and the fireproof insulation of the outer fireproof cover is the thickest so that a suitable fireproof action can be obtained. It has become. In addition, the configuration in which a plurality of layers of fireproof coverings using a combination of an endothermic pack and a fireproof insulation material can suppress the thickness of the entire fireproof covering structure for the required fireproof performance, and the thermal resistance in the thickness direction is relatively Since it can be made small, it is also possible to ensure the heat radiation action necessary as a fireproof coating structure for power cables. That is, it is possible to achieve both fire resistance and heat dissipation, that is, the power cable can be protected from heat during a fire, and the temperature of the power cable rises by mitigating the accumulation of heat caused by the current flowing through the power cable. Too much can be prevented.
In the case of fire resistance performance for 3 hours, a fireproof covering structure in which fireproof coverings are laminated in three to four layers is preferable, and four layers are particularly preferable.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a diagram of the same mode as FIG. The second embodiment is assumed to be the same as the first embodiment described above except for portions specifically described below.

  In the fireproof covering structure 101 of the power cable, a cable tray having an open top is used as the container 105. A plurality of power cables 3 are placed side by side on the bottom surface of a cable tray having a substantially U-shaped longitudinal section. And the fireproof covering 7, 9, 11, 13 similar to the said Embodiment 1 is provided in these outer sides. Thus, the present invention can be implemented not only in a tube type container but also in a tray type container. In addition, when constructing the fireproof coating structure according to the present embodiment on a tray-type container, an inorganic fiber cloth with a metal foil such as a glass cloth with an aluminum foil is accommodated as a base so as to protect the open part of the upper part of the tray. It is more preferable to wrap around the body and fix it in order from the first layer of the fireproof covering.

Further, the fire-resistant covering structure 101 of the tray-type power cable of the second embodiment was also subjected to the same 3-hour fire resistance test as in Example 1, and the maximum temperature of the power cable surface during the 3-hour heating test was as follows. It was 102.9 ° C. (arrival time: 180 minutes), which met the determination criteria. Moreover, as a result of calculating the total thermal resistance in the thickness direction of the fireproof coating, the target value was 1.3 m ² · K / W or less.

  Although the contents of the present invention have been specifically described above with reference to the preferred embodiments, those skilled in the art can adopt various modifications based on the basic technical idea and teachings of the present invention. It is self-explanatory.

  DESCRIPTION OF SYMBOLS 1,101 Fire-resistant covering structure of power cable, 3 Power cable, 5 Housing, 7, 9, 11, 13 Fire-resistant covering, 21 Heat-absorbing pack, 23 Fire-resistant heat insulating material, 25 Outer covering material, 31 Sealing film, 33 Heat-absorbing Material, 43 metal foil, 51 wire mesh.

Claims (9)

A power cable, a container that houses the power cable, and a multi-layered fireproof covering that covers the container that houses the power cable,
Each of the fireproof coverings includes an endothermic pack, a fireproof heat insulating material, and a jacket material,
In each of the fireproof coverings, the endothermic pack is located on the container side, and the fireproof heat insulating material is provided on the outside of the endothermic pack,
The jacket material is an inorganic fiber cloth with metal foil,
The thickness of the refractory insulation of the outermost refractory coating is greater than the thickness of each of the refractory insulations of all the refractory coatings inside the outermost refractory coating,
Fireproof coating structure for power cables. The total thermal resistance in the thickness direction of the multi-layered fireproof coating is 1.3 m ² · K / W or less,
The fireproof covering structure for a power cable according to claim 1. The endothermic pack is formed by sealing an endothermic material in a cell partitioned between two sealing films composed of a metal foil and a synthetic resin film,
The endothermic material sealed in the endothermic pack is water or a polymer impregnated with water,
The fireproof covering structure for a power cable according to claim 1 or 2. Both the metal foil contained in the endothermic pack and the metal foil contained in the inorganic fiber cloth with metal foil of the jacket material are aluminum foils,
A fireproof covering structure for a power cable according to claim 3. The thickness of the refractory heat insulating material of the outermost refractory covering is 25 mm to 50 mm, and the heat absorbing pack included in the entire laminate of the refractory covering per 1 m ² of the refractory covering construction area of the container. The amount of sealed water is 16 kg or more, thereby having a fire resistance performance of 3 hours,
The fireproof covering structure for a power cable according to any one of claims 1 to 4. The fireproof covering is laminated in four layers,
The fireproof covering structure for a power cable according to any one of claims 1 to 5. A wire mesh or a metal plate is further provided outside the outermost fireproof covering,
The fireproof covering structure for a power cable according to any one of claims 1 to 6. A construction method for forming a fireproof coating structure of a power cable according to any one of claims 1 to 7,
Repetitively winding and fixing the fireproof covering one layer at a time on the outside of the container to obtain the multiple layers of fireproof covering,
Construction method of fireproof coating structure for power cables. After wrapping and fixing the outermost fire-resistant coating, further wrapping and fixing a wire mesh or metal plate on the outside,
The construction method of the fireproof covering structure of the electric power cable of Claim 8.

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