WO2014081096A1 - Fire resistant cable for medium or high voltage - Google Patents
Fire resistant cable for medium or high voltage Download PDFInfo
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- WO2014081096A1 WO2014081096A1 PCT/KR2013/004770 KR2013004770W WO2014081096A1 WO 2014081096 A1 WO2014081096 A1 WO 2014081096A1 KR 2013004770 W KR2013004770 W KR 2013004770W WO 2014081096 A1 WO2014081096 A1 WO 2014081096A1
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- layer
- fire resistant
- semiconducting
- cable
- insulation layer
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B9/00—Power cables
- H01B9/02—Power cables with screens or conductive layers, e.g. for avoiding large potential gradients
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
- H01B7/29—Protection against damage caused by extremes of temperature or by flame
Abstract
Disclosed is a fire resistant cable for high voltage. According to the fire resistant cable for high voltage of the present invention, both fire resistant performance and electrical features are satisfied. It is possible to prevent creation of curvatures and gaps, which are formed due to a small radius of curvature for winding a mica tape which forms a fire resistant layer, and partial discharge generated by the curvatures and gaps can be suppressed. Since the fire resistant layer is formed at a position having optimum electric field strength considering insulation thickness, withstand voltage, partial discharge and the like, convenience in installing the cable and electrical features of the cable can be improved.
Description
The present invention relates to a fire resistant cable for medium or high voltage and a method of manufacturing the same, and more specifically, to a fire resistant cable for medium or high voltage which can satisfy fire resistance performance and improve electrical features of a medium or high voltage class cable.
Recently, an important issue in the cable manufacturing industry is improving behaviors and performance of a cable in a situation where an extreme temperature state is confronted, particularly, when a fire breaks out. It is absolutely necessary to maximize the capability of the cable for delaying spread of fire and enduring flames in order to secure safety.
If fire resistance of the cable is improved furthermore, the capability of the cable for flowing electricity can be sustained furthermore when a fire breaks out, and spread of the fire is delayed, and thus the time needed for evacuating people or dispatching appropriate means for extinguishing the fire can be secured.
Requirements on properties of fire resistance tend to be strict furthermore, and particularly, cables used for on and off shore plants, building infrastructures or the like require high fire resistance properties. It is required to provide a cable which can maintain operation of a fire and disaster prevention system of a main facility, including emergency power supplies, fire alarms, sprinklers and the like, for a minimum period of time in order to evacuate people when a fire breaks out in a plant or a building.
Although fire resistant cables are mainly used for low voltage in the prior art, as the prevention of fire and disaster is emerged as an important issue recently, fire resistant cables of a medium or high voltage class are required furthermore, and fire resistant cable products for high voltage are required to satisfy performance of IEC 60331-21 (750oC for 90 minutes), which is a general fire resistance specification.
Here, the fire resistant cables of a medium or high voltage class refer to cables for a medium voltage (MV) or high voltage (HV) class, and the fire resistant cables of a medium or high voltage class are generally referred to as high voltage cables.
Among general cables not for fire resistance, cables for low voltage of less than 3kV may sufficiently satisfy electrical features by insulating a conductor with only one layer thereon, whereas cables of a medium or high voltage class apply a three-layer structure of 'conductor-inner semiconducting layer-insulation layer-outer semiconducting layer'.
Here, the insulation layer insulates the conductor from outside so that current may not flow to the outside of the cable, and the inner semiconducting layer mitigates concentration of electrical field inside the cable by uniformly distributing charges on the surface of the conductor and minimizes degradation of the insulator through ionization by filling the gaps formed between the conductor and the insulator. In addition, the outer semiconducting layer uniformly distributes electrical stress inside the insulator and minimizes external corona.
When a voltage of 6kV or higher is applied, it is highly probable that a partial discharge (PD) value, which is one of important electrical features, increases and dielectric breakdown gradually occurs since electrical treeing occurs in the insulator. Therefore, the inner and outer semiconducting layers should be formed by applying the three-layer structure as described above in order to satisfy the characteristics of the partial discharge and minimize the dielectric breakdown by uniformly distributing the electrical field and the electrical stress.
The cables of a medium or high voltage class exhibit fire resistance performance by applying a fire resistant layer, and the fire resistant layer is manufactured by winding a mica tape having characteristics of high heat resistance and maintains cable functions for a predetermined period of time at a high temperature of 700 to 800oC. At this point, the mica tape is manufactured by applying mica powder on a glass fiber or a Poly Ethylene (PE) tape, and although the cable is burnt to the insulator when a fire breaks out, the mica tape performs the functions of the insulator since it wraps around the conductor.
As described above, since a fire resistant cable for low voltage has a simple structure, the fire resistant layer can be formed by winding the mica tape right on the conductor. However, in manufacturing a fire resistant cable of a medium or high voltage class, the fire resistant layer should be formed considering electrical features and fire resistance performance to satisfy both of them.
In relation to such a fire resistant cable of the prior technique, fire resistant cables of a two-layer structure including a first (inner) fire resistant layer provided right on a conductor and a second (outer) fire resistant layer provided outside of an insulation layer or on a sheath layer are proposed in Japanese Utility Model Reg. No. 2521343 and Korean Laid-opened Patents No. 2011-0105563 and 2012-0005246.
Specifically, as shown in FIG. 1, a structure sequentially stacking a conductor 4, an inner fire resistant layer 5, an insulation layer 6, an outer fire resistant layer 9 and a sheath layer 10 is proposed, and although there is a slight difference among the prior techniques, they have a structure similar to the structure shown in FIG. 1.
However, the aforementioned prior techniques do not mention a structure for implementing electrical features of the cable for medium or high voltage described above, i.e., the three-layer structure of 'conductor-inner semiconducting layer-insulation layer-outer semiconducting layer', and a method of applying the fire resistant layer in the three-layer structure.
Furthermore, the mica tape can be damaged when the mica tape is wound right around a conductor having a small radius of curvature, and the insulation layer can be damaged in a process thereafter due to the damage of the mica tape. If the insulation layer is damaged as described above, electrical treeing occurs, and thus a partial discharge value is increased, and performance of the cable can be degraded.
In addition, the damage of the mica tape itself may invite degradation of insulation strength performance of the mica tape, and as a result, fire resistance performance of the cable may not be satisfied.
Japanese Laid-opened Utility Model No. 1993-182532 discloses a fire resistant cable having a structure including a thermal insulation layer (a fire resistant layer) and a foam-based fireproof layer on a cable core sequentially containing a conductor, an inner semiconducting layer, an insulation layer, an outer semiconducting layer and a metallic shield layer.
However, if the insulation layer inside the cable is burnt down by a high temperature when a fire breaks out, the fire resistant layer should function as an insulator between the conductor and the metallic shield layer. However, the fire resistant layer cannot perform such a function since the fire resistant layer is provided outside of the metallic shield layer and the sheath layer, and thus the fire resistant cable is difficult to be applied as a fire resistant cable of a medium or high voltage class.
Although Japanese Laid-opened Utility Model No. 1994-033319 discloses a heat resistant coaxial cable of a structure forming an insulation layer of a two-layer structure on an inner conductor and forming a first fire resistant layer thereon, since the structure, electrical features, usage and the like of the coaxial cable are different from those of a medium or high voltage cable, the structure of the coaxial cable is inappropriate to be applied as the medium or high voltage cable.
Meanwhile, it is possible to consider a fire resistant cable applying a four-layer structure of 'conductor-inner semiconducting layer-fire resistant layer-insulation layer-outer semiconducting layer'. However, since a mica tape used as a fire resistant layer is applied between the inner semiconducting layer and the insulation layer, the surface between the inner semiconducting layer and the insulation layer is not smooth relatively, and thus the partial discharge value can be increased or the dielectric breakdown may easily occur due to electrical treeing. In addition, important features of a cable such as specifications of withstand voltage and partial discharge cannot be satisfied.
Furthermore, since the radius of curvature is still small although the mica tape is wound around the inner semiconducting layer, it is still possible as described above that the mica tape can be damaged, or the fire resistant layer can be additionally damaged while passing through a plurality of processes such as forming the insulation layer, the outer semiconducting layer, and the like after winding the mica tape.
Accordingly, it is required to provide a fire resistant cable for high voltage which can satisfy fire resistance performance and improve electrical features of the cable at a medium or high voltage.
An object of the present invention is to satisfy fire resistance performance and improve electrical features of a medium or high voltage class cable.
Another object of the present invention is to prevent curvatures and gaps formed due to a small radius of curvature for winding a mica tape which forms a fire resistant layer, thereby suppressing partial discharge.
Another object of the present invention is to improve electrical features and promote convenience of installing cables by forming a fire resistant layer at a position having optimum electric field strength, considering insulation thickness, withstand voltage, partial discharge and the like.
To accomplish the above objects, according to a first aspect of the present invention, there is provided a fire resistant cable for medium or high voltage comprising a conductor; a first semiconducting layer formed outside of the conductor; a first insulation layer formed outside of the first semiconducting layer; a second semiconducting layer formed outside of the first insulation layer; a shield layer formed outside of the second semiconducting layer; and a fire resistant layer provided between the first insulation layer and the second semiconducting layer.
The first semiconducting layer and the first insulation layer contact with each other.
The cable further comprises a sheath layer formed outside of the shield layer.
The cable further comprises a second insulation layer provided between the fire resistant layer and the second semiconducting layer.
The second insulation layer is formed through a silicon coating process.
The cable is formed as a multi-layer structure wherein a separate fire resistant layer and a separate insulation layer are additionally formed outside of the second insulation layer.
The first semiconducting layer is formed through extrusion and the second semiconducting layer is formed by winding a semiconducting tape.
The fire resistant layer is formed by winding a mica tape two or more times.
To accomplish the above objects, according to a second aspect of the present invention, there is provided a fire resistant cable for medium or high voltage comprising a conductor; a first semiconducting layer formed outside of the conductor; a first insulation layer formed outside of the first semiconducting layer; a second semiconducting layer formed outside of the first insulation layer; a shield layer formed outside of the second semiconducting layer; and a fire resistant layer for protecting and insulating the conductor when a fire breaks out, wherein the fire resistant layer is positioned in an area where electric field strength is between 1 to 3kV/mm.
The first semiconducting layer and the first insulation layer contact with each other.
The cable further comprises a second insulation layer provided between the fire resistant layer and the second semiconducting layer.
The embodiments of the present invention may satisfy fire resistance performance and improve electrical features of a medium or high voltage class cable.
The embodiments of the present invention may prevent curvatures and gaps formed due to a small radius of curvature for winding a mica tape which forms a fire resistant layer, thereby suppressing partial discharge.
The embodiments of the present invention may improve electrical features and promote convenience of installing cables by forming a fire resistant layer at a position having optimum electric field strength, considering insulation thickness, withstand voltage, partial discharge and the like of the fire resistant layer.
FIG. 1 is a cross-sectional view showing the structure of a fire resistant cable of the prior art.
FIG. 2 is a cross-sectional view showing a single-phase high-voltage fire resistant cable according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a three-phase high-voltage fire resistant cable according to an embodiment of the present invention.
FIG. 4 is a cross-sectional view showing a single-phase high-voltage fire resistant cable according to another embodiment of the present invention.
FIG. 5 is a cross-sectional view showing a three-phase high-voltage fire resistant cable according to another embodiment of the present invention.
FIG. 6 is a view showing differences in the structure of a high-voltage fire resistant cable according to another embodiment of the present invention, before and after forming an insulation layer.
FIG. 7 is a view showing changes of electric field according to the distance from a conductor.
The preferred embodiments of the present invention will be hereafter described in detail, with reference to the accompanying drawings. Furthermore, in the drawings illustrating the embodiments of the present invention, elements having like functions will be denoted by like reference numerals and details thereon will not be repeated.
FIG. 2 is a cross-sectional view showing a single-phase high-voltage fire resistant cable according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view showing a three-phase high-voltage fire resistant cable according to an embodiment of the present invention.
Referring to FIGs. 2 and 3, a fire resistant cable for high voltage according to an embodiment of the present invention largely includes a conductor 111, a first semiconducting layer 112 formed outside of the conductor 111, an insulation layer 113 formed outside of the first semiconducting layer 112, a second semiconducting layer 115 formed outside of the insulation layer 113, a shield layer 116 formed outside of the second semiconducting layer 115 and a fire resistant layer 114 formed between the insulation layer 113 and the second semiconducting layer 115.
A class 2 or class 5 conductor satisfying the specification of IEC 60228 can be used as the conductor 111. The first semiconducting layer 112 is formed outside of the conductor 111 by extruding a semiconducting compound or winding a semiconducting tape, or the first semiconducting layer 112 can be formed as multiple layers by applying both of these.
The first semiconducting layer 112 is an inner semiconducting layer for mitigating concentration of electric field inside the cable by uniformly distributing charges on the surface of the conductor and minimizing degradation of the insulator, which is caused by ionization, by filling the gaps formed between the conductor and the insulator.
The insulation layer 113 is made of a material having fire and impact resistant properties and insulates the conductor from outside by covering and protecting the conductor 111 so that current may not flow to outside of the cable. Here, the insulation layer 113 can be formed of a polymer, such as silicone rubber, cross-linked polyethylene (XLPE), cross Linked polyolefin (XLPO), ethylene-propylene rubber (EPR), high ethylene-propylene rubber (EPR), polyvinyl chloride (PVC) or the like, or a mixture of these.
The second semiconducting layer 115 formed outside of the insulation layer 113 is an outer semiconducting layer which is formed by extruding a semiconducting compound or winding a semiconducting tape like the inner semiconducting layer, or the second semiconducting layer 115 can be formed as multiple layers by applying both of these.
The second semiconducting layer 115 uniformly distributes electrical stress inside the insulator and minimizes external corona.
The shield layer 116 can be configured in the form of a metallic tape or a metallic braid using a material such as copper, aluminum, a copper alloy, an aluminum alloy or the like. The shield layer 116 should contact with the second semiconducting layer 115 because if the shield layer 116 does not contact with the second semiconducting layer 115, a ground should be provided separately.
The fire resistant layer 114 can be formed by winding a mica tape, which is manufactured in the form of a tape by applying mica powder on a PE film or a glass fiber texture, around the insulation layer 113. At this point, although the number of windings may vary according to the required fire resistance performance or the structure and usage of the cable, generally, it is preferable to wind the mica tape two or more times in order to implement basic fire resistance performance.
Meanwhile, in the fire resistant cable for high voltage according to an embodiment of the present invention, the fire resistant layer 114 is preferably provided between the insulation layer 113 and the second semiconducting layer 115. If the fire resistant layer 114 is formed immediately outside of the conductor 111 or immediately outside of the first semiconducting layer 112 like the prior art, the radius of curvature for winding the mica tape is small, and thus it is highly probable that the mica tape is damaged in or after the process of winding the mica tape.
Then, if the fire resistant layer 114 is close to the conductor 111, it is highly probable that curvatures and gaps can be formed, after winding the mica tape, near the conductor 111, i.e., where the electrical field is high, and thus the problem of partial discharge may occur.
In addition, if the mica tape is formed between the first semiconducting layer 112 and the insulation layer 113, the surface between the first semiconducting layer 112 and the insulation layer 113 is not smooth relatively, and thus the partial discharge value can be increased or the dielectric breakdown may easily occur due to electrical treeing.
Meanwhile, since the conductor 11 may contact with the shield layer 116 if the insulation layer 113 is burnt up by a high temperature when a fire breaks out, it should be considered that the fire resistant layer 114 is formed inside the shield layer 116 so as to function as the insulation layer 113.
In addition, as described above, since the second semiconducting layer 115 and the shield layer 116 should be placed in the neighborhood due to the problem of grounding, the fire resistant layer 114 is preferably placed between the insulation layer 113 and the second semiconducting layer 115 in order to satisfy electrical features and fire resistance performance while satisfying all the conditions described above.
Accordingly, unlike the low voltage cable of the prior art in which the fire resistant layer 114 is formed outside of the conductor 111 or outside of the first semiconducting layer 112 without seriously considering the electrical features or structural characteristics, in the fire resistant cable for high voltage 100 of the present invention, both the electrical features and the fire resistant features can be satisfied by forming the fire resistant layer 114 between the insulation layer 113 and the second semiconducting layer 115.
As a result, since the fire resistant layer 114 is formed between the insulation layer 113 and the second semiconducting layer 115, the fire resistant layer 114 is not intervened outside of the first semiconducting layer 112, and the first semiconducting layer 112 contacts with a first insulation layer 113a.
Then, the conductor 111 and the first semiconducting layer 112 contact with each other in order to satisfy the conditions described above, and at least a part of the second semiconducting layer 115 contacts with a part of the shield layer 116 for the purpose of grounding.
As described above, the fire resistant cable for high voltage 100 according to an embodiment of the present invention configures a cable core 110 basically including the conductor 111, the first semiconducting layer 112, the insulation layer 113, the fire resistant layer 114, the second semiconducting layer 115 and the shield layer 116, and the fire resistant cable for high voltage 100 can be completed by forming a sheath layer and performing an exterior work on the outside of the cable core 110.
Specifically, an inner sheath layer 120 can be formed outside of the cable core 110, and the inner layer 120 can be configured in the form of an extruded layer of polyvinyl chloride (PVC), polychloroprene rubber (CR), chloro sulfonated polyethylene (CSPE), chlorinated polyethylene (CPE), ethylene vinyl acetate (EVA) or a mixture of these, which are halogen free materials having high impact resistance.
An exterior layer 130 is formed outside of the inner sheath layer 120, and the exterior layer 130 can be configured in the form of a metallic braid, a metallic tape, a metallic wire or the like using a metallic material such as copper, aluminum, iron, a copper alloy, an aluminum alloy or the like.
Then, an outer sheath layer 140 is formed outside of the exterior layer 130, and like the inner sheath layer 120, the outer sheath layer 140 is configured in the form of an extruded layer of polyvinyl chloride (PVC), polychloroprene rubber (CR), chloro sulfonated polyethylene (CSPE), chlorinated polyethylene (CPE), ethylene vinyl acetate (EVA) or a mixture of these, which are halogen free materials having high impact resistance, and protects the cable from external impact or corrosion.
The structure of the inner sheath layer 120, the exterior layer 130 and the outer sheath layer 140 may vary according to the usage of the cable.
Meanwhile, the fire resistant cable for high voltage 100 can be configured as a single-core product including one cable core 110 as shown in FIG. 2 or a multi-core product including two or more cores as shown in FIG. 3.
In the case of the multi-core product, a plurality of cable cores 110 is aggregated at a predetermined pitch, and a filling material 150 is applied into the gaps. Then, the inner sheath layer 120, the exterior layer 130 and the outer sheath layer 140 described above are formed to complete the product. The fire resistant cable for high voltage 100 shown in FIG. 3 is a three-phase cable, and a cable including three cable cores 110 is shown as an example.
The electrical features and fire resistance performance of the fire resistant cable for high voltage 100 according to an embodiment of the present invention configured as described above are compared with those of the prior art as shown in Table 1.
Table 1
| Items | 3.6/6KV | 6/10KV | 8.7/15KV | |||
| Existing | Invention 1 | Existing | Invention 1 | Existing | Invention 1 | |
| Conductor | Anealed copper | Anealed copper | Tinned anealed copper | Tinned anealed copper | Anealed copper | Anealed copper |
| Inner Semiconducting layer | Semiconducting tape | Semiconducting extrusion | Semiconducting tape | Semiconducting extrusion | Semiconducting tape | Semiconducting extrusion |
| Fire resistant layer | Mica tape | X | Mica tape | X | Mica tape | X |
| Insulation layer | XLPE | XLPE | EPR | EPR | XLPE | XLPE |
| Fire resistant layer | X | Mica tape | X | Mica tape | X | Mica tape |
| Outer semiconducting layer | Semiconducting extrusion | Semiconducting tape | Semiconducting extrusion | Semiconducting tape | Semiconducting extrusion | Semiconducting tape |
| Shield layer | Copper tape | Copper tape | Copper tape | Copper tape | Copper tape | Copper tape |
| Sheath layer | SHF1 | SHF1 | SHF2 | SHF2 | SHF1 | SHF1 |
| Exterior layer | Tinned Copper Wire Braid | Tinned Copper Wire Braid | Tinned Copper Wire Braid | Tinned Copper Wire Braid | Tinned Copper Wire Braid | Tinned Copper Wire Braid |
| Sheath layer | SHF1 | SHF1 | SHF2 | SHF2 | SHF1 | SHF1 |
| Partial discharge(=<5pC) | 2pC | 2pC | 7pC | 2pC | 15pC | 3pC |
| Withstand voltage(voltage test) | 12.5KV, 5min Pass | 12.5KV, 5min Pass | 21KV, 5min Fail | 21KV, 5min Pass | 30.5KV, 5min Fail | 30.5KV, 5min Pass |
| Fire resistance test(IEC 60331-21 750℃, 90minutes) | Pass(90minutes) | Pass(90minutes) | Pass(90minutes) | Pass(90minutes) | Fail(67minutes) | Pass(90minutes) |
The configuration of the prior art in which the fire resistant layer 114 is formed to be adjacent to the outside of the first semiconducting layer 112, i.e., the inner semiconducting layer, is compared with the configuration of the present invention in which the fire resistant layer 114 is formed between the insulation layer 113 and the second semiconducting layer 115 to make an experiment on electrical features and fire resistance performance.
Since the semiconducting layer of a portion adjacent to the fire resistant layer 114, i.e., a portion where the mica tape is wound, can be easily formed by winding a semiconducting tape, rather than extruding a semiconducting compound, in the present invention, for the convenience of processing, the inner semiconducting layer, i.e., the first semiconducting layer 112, is formed by extrusion, and the second semiconducting layer 115 adjacent to the fire resistant layer 114, i.e., the outer semiconducting layer, is formed by winding the semiconducting tape.
Contrarily, in the configuration of the prior art, the first semiconducting layer 112 adjacent to the fire resistant layer 114 is formed by winding the semiconducting tape, and the second semiconducting layer 115 is formed by extruding a semiconducting compound.
Although the semiconducting layer adjacent to the fire resistant layer 114 is formed by winding the semiconducting tape as described above for the convenience of work, it is not limited thereto, and the semiconducting layer adjacent to the fire resistant layer 114 can be formed through extrusion.
Comparing the electrical features and fire resistance performance of a cable configured in the prior art with those of the fire resistant cable for high voltage 100 of the present invention, as is confirmed from Table 1, the electrical features (partial discharge and withstand voltage) and the fire resistance performance of the product of 6kV class or lower are satisfied regardless of the position of the fire resistant layer 114. However, if the voltage rises to 10kV or higher, although the existing product satisfies the fire resistance performance, the electrical features thereof, such as partial discharge, withstand voltage or the like, are degraded.
In addition, when the voltage rises to 15kV or higher, the existing product does not satisfy the fire resistance performance, as well as the electrical features. Contrarily, it is confirmed that the product applying the technique of the present invention satisfies the electrical features and the fire resistance performance for all voltage classes of 6 to 15kV.
FIG. 4 is a cross-sectional view showing a single-phase high-voltage fire resistant cable according to another embodiment of the present invention, FIG. 5 is a cross-sectional view showing a three-phase high-voltage fire resistant cable according to another embodiment of the present invention, and FIG. 6 is a view showing differences in the structure of a high-voltage fire resistant cable according to another embodiment of the present invention, before and after forming an insulation layer.
Another embodiment of the present invention will be described with reference to FIGs. 4 to 6.
As shown in FIG. 4, the fire resistant cable for high voltage 100 according to the present invention may further includes a second insulation layer 113b provided between the fire resistant layer 114 and the second semiconducting layer 115. For the convenience, the insulation layer 113 of the previous embodiment is referred to as a first insulation layer 113a, and it will be described to be distinguished from the second insulation layer 113b.
Although the fire resistant cable for high voltage 100 according to the previous embodiment satisfies the electrical features and the fire resistance performance as shown in Table 1, since the fire resistant layer 114 is configured in the form of taping a mica tape 114a or the like, gaps are formed between the first insulation layer 113a and the fire resistant layer 114, and the fire resistant layer 114 and the second semiconducting layer 115, and thus air pockets 114b are formed. Accordingly, dielectric breakdown may occur due to concentration of electrical field caused by the uneven surface of the insulator.
In order to solve the problem of degrading electrical features caused by the uneven contact between the second semiconducting layer 115 and the taped fire resistant layer 114, in the present invention, a second insulation layer 113b is additionally formed by extrusion on the fire resistant layer 114 so that the second semiconducting layer 115 may not directly contact with the fire resistant layer 114, but the second insulation layer 113b having a sleek surface may be contact with the second semiconducting layer 115.
Here, the second insulation layer 113b can be formed through a silicon coating process, and it may reduce the air pockets 114b formed by the existing taped fire resistant layer 114 between the fire resistant layer 114 and the first insulation layer 113a, and the fire resistant layer 114 and the second semiconducting layer 115. Since the fire resistant layer 114 can be configured in the form of a sleek layer as shown in FIG. 6 (b), the electrical features can be improved furthermore.
Furthermore, the fire resistant cable for high voltage 100 can be configured as a multi-layer structure, in which a fire resistant layer 114 and an insulation layer 113 are additionally formed outside of the second insulation layer 113b to improve the fire resistance performance.
The electrical features and fire resistance performance of the fire resistant cable 100 for high voltage in which the second insulation layer 113b is provided between the fire resistant layer 114 and the second semiconducting layer 115 are compared with those of the prior art as shown in Table 2.
Table 2
| Items | 6/10KV | 8.7/15KV | 18/30KV | |||
| Existing | Invention 2 | Existing | Invention 2 | Invention 1 | Invention 2 | |
| Conductor | Tinned anealed copper | Tinned anealed copper | Anealed copper | Anealed copper | Anealed copper | Anealed copper |
| Inner semiconducting layer | Semiconducting tape | Semiconducting extrusion | Semiconducting tape | Semiconducting extrusion | Semiconducting extrusion | Semiconducting extrusion |
| Fire resistant layer | Mica tape | X | Mica tape | X | X | X |
| First insulation layer | EPR | EPR | XLPE | XLPE | XLPE | XLPE |
| Fire resistant layer | X | Mica tape | X | Mica tape | Mica tape | Mica tape |
| Second insulation layer | X | EPR | X | XLPE | X | XLPE |
| Outer semiconducting layer | Semiconducting extrusion | Semiconducting tape | Semiconducting extrusion | Semiconducting tape | Semiconducting tape | Semiconducting tape |
| Shield layer | Copper tape | Copper tape | Copper tape | Copper tape | Copper tape | Copper tape |
| Sheath layer | SHF2 | SHF2 | SHF1 | SHF1 | SHF1 | SHF1 |
| Exterior layer | Tinned Copper Wire Braid | Tinned Copper Wire Braid | Tinned Copper Wire Braid | Tinned Copper Wire Braid | Tinned Copper Wire Braid | Tinned Copper Wire Braid |
| Sheath layer | SHF2 | SHF2 | SHF1 | SHF1 | SHF1 | SHF1 |
| Partial discharge(=<5pC) | 7pC | 1pC | 15pC | 1pC | 5pC | 1pC |
| Withstand voltage(voltage test) | 21KV, 5min Fail | 21KV, 5min Pass | 30.5KV, 5min Fail | 30.5KV, 5min Pass | 63KV, 5min Pass | 63KV, 5min Pass |
| Fire resistance test(IEC 60331-21 750℃, 90minutes) | Pass(90minutes) | Pass(90minutes) | Fail(67minutes) | Pass(90minutes) | Pass(90minutes) | Pass(90minutes) |
In the voltage classes of 6/10kV and 8.7/15kV, the configuration of the prior art in which the fire resistant layer 114 is formed to be adjacent to the outside of the first semiconducting layer 112, i.e., the inner semiconducting layer, is compared with the configuration of the present invention in which the fire resistant layer 114 is formed between the insulation layer 113 and the second semiconducting layer 115 to make an experiment on electrical features and fire resistance performance. In the voltage class of 18/30kV, an embodiment of the previous embodiment in which the second insulation layer 113b does not exist is compared with a case where the second insulation layer 113b is formed to make an experiment.
As is shown from the comparisons in the voltage classes of 6/10kV and 8.7/15kV, the configuration of the prior art does not satisfy the electrical features, such as partial discharge and withstand voltage, and the fire resistance performance, whereas the configuration of the present invention satisfies both the electrical features and the fire resistance performance.
Meanwhile, in the case of the previous embodiment in which the second insulation layer 113b is not formed on the fire resistant layer 114, the partial discharge value is at a level of 5pC as shown in Table 1, which is a level barely satisfying the specification of 5pC or lower. However, the present invention in which the second insulation layer 113b is additionally formed on the fire resistant layer 114 shows a further stable electrical quality, particularly, the partial discharge value of less than 1pC.
Accordingly, it needs to pay more attention to the electrical features as the voltage class of a cable is increased, and this is confirmed from the fact that it is preferable to additionally form the second insulation layer 113b between the fire resistant layer 114 and the second semiconducting layer 115.
FIG. 7 is a view showing changes of electric field according to the distance from a conductor.
Referring to FIGs. 2 to 7, the relation between electric field strength according to the distance from the conductor 111 and an optimum position for forming the fire resistant layer 114 will be described below. In FIG. 7, ri denotes a radius between the inner semiconducting layer and the insulation layer, R denotes a radius between the outer semiconducting layer and the insulation layer, and t denotes insulation thickness.
As shown in FIG. 7, when the electric field strength is calculated, further higher electric field strength is observed at a point further closer to the surface of the conductor 111. Accordingly, when the fire resistant layer 114, i.e., a mica tape, is applied on the inner semiconducting layer having a relatively high electrical field like a cable product of the prior art, the phenomena such as partial discharge, dielectric breakdown and the like caused by unevenness of the wound mica tape can be intensified.
Meanwhile, Table 3 shows a result of comparing electrical field strength between the inner semiconducting layer and the insulation layer with electrical field strength between the insulation layer and the outer semiconducting layer through experimental products of 10kV and 15kV of 70SQ.
Table 3
| Products | Electrical field strength(kV/mm) | Remarks | |
| Inner semiconducting layer-Insulator(ri) | Insulator-Outer semiconducting layer(R) | ||
| 6/10kV 3CX70SQ(Applied voltage 10kV) | 3.30 | 1.91 | Diameter of conductor: 10.14mmThickness of insulator: 3.638mm |
| 8.7/15kV 3CX70SQ(Applied voltage 15kV) | 4.09 | 2.10 | Diameter of conductor: 10.14mmThickness of insulator: 4.815mm |
As shown in Table 3, it is understood that when electrical field strength is calculated for the cables of 10kV and 15kV classes, the electrical field strength between the insulation layer and the outer semiconducting layer is reduced by a half of the electrical field strength between the inner semiconducting layer and the insulation layer. That is, it is actually confirmed that the effect of electrical field is reduced by half if the fire resistant layer 114 is formed between the insulation layer and the outer semiconducting layer, compared with a structure in which the fire resistant layer 114 is positioned between the inner semiconducting layer and the insulation layer.
Meanwhile, when the fire resistant layer 114 is applied in an area where the electric field strength is 3kV/mm or higher, electrical features such as withstand voltage, partial discharge and the like are degraded. Accordingly, the electric field strength is reduced furthermore as the distance is farther from the conductor in the radius direction of the insulation layer, and the fire resistant layer 114 should be applied at a distance farther than a point where the electric field strength is reduced to be less than 3kV/mm.
Contrarily, if the position of the fire resistant layer 114 is farther from the conductor, the insulation thickness is increased although the electrical quality is improved. Therefore, since the outer diameter and weight of the cable is increased, work convenience is lowered in installing the cable.
Accordingly, it is preferable to form the fire resistant layer 114 in an area where the electric field strength is at least 1kV/mm from the viewpoint of optimizing the electrical quality and the outer diameter, and as a result, placing the fire resistant layer 114 in an area where the electric field strength is 1 to 3kV/mm corresponds to the optimum condition.
As described above, the present invention is advantageous in that since the fire resistant layer 114 is formed between the insulation layer 113 and the second semiconducting layer 115, i.e., an outer semiconducting layer, in which the electric field strength is formed to be relatively low, while protecting the conductor 111, the electrical performance such as partial discharge, dielectric breakdown and the like is improved while maintaining the fire resistance performance.
In addition, since the fire resistant layer 114 is applied between the insulation layer 113 and the second semiconducting layer 115, in which the radius of curvature is larger than that of placing the fire resistant layer 114 between the first semiconducting layer 112 and the insulation layer 113, the cable can be stably manufactured in case of applying a brittle material such as a mica tape, and as a result, it is confirmed that fire resistance performance is also improved compared with that of existing products.
While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.
Claims (11)
- A fire resistant cable for medium or high voltage, the cable comprising:a conductor;a first semiconducting layer formed outside of the conductor;a first insulation layer formed outside of the first semiconducting layer;a second semiconducting layer formed outside of the first insulation layer;a shield layer formed outside of the second semiconducting layer; anda fire resistant layer provided between the first insulation layer and the second semiconducting layer.
- The cable according to claim 1, wherein the first semiconducting layer and the first insulation layer contact with each other.
- The cable according to claim 1, further comprising a sheath layer formed outside of the shield layer.
- The cable according to claim 1, further comprising a second insulation layer provided between the fire resistant layer and the second semiconducting layer.
- The cable according to claim 4, wherein the second insulation layer is formed through a silicon coating process.
- The cable according to claim 4, formed as a multi-layer structure wherein a separate fire resistant layer and a separate insulation layer are additionally formed outside of the second insulation layer.
- The cable according to claim 1, wherein the first semiconducting layer is formed through extrusion and the second semiconducting layer is formed by winding a semiconducting tape.
- The cable according to claim 1, wherein the fire resistant layer is formed by winding a mica tape two or more times.
- A fire resistant cable for medium or high voltage, the cable comprising:a conductor;a first semiconducting layer formed outside of the conductor;a first insulation layer formed outside of the first semiconducting layer;a second semiconducting layer formed outside of the first insulation layer;a shield layer formed outside of the second semiconducting layer; anda fire resistant layer for protecting and insulating the conductor when a fire breaks out, wherein the fire resistant layer is positioned in an area where electric field strength is between 1 to 3kV/mm.
- The cable according to claim 9, wherein the first semiconducting layer and the first insulation layer contact with each other.
- The cable according to claim 9, further comprising a second insulation layer provided between the fire resistant layer and the second semiconducting layer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR10-2012-0132527 | 2012-11-21 | ||
| KR1020120132527A KR102038707B1 (en) | 2012-11-21 | 2012-11-21 | fire resistant cable for medium or high voltage and manufacturing method of the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2014081096A1 true WO2014081096A1 (en) | 2014-05-30 |
Family
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/KR2013/004770 WO2014081096A1 (en) | 2012-11-21 | 2013-05-30 | Fire resistant cable for medium or high voltage |
Country Status (2)
| Country | Link |
|---|---|
| KR (1) | KR102038707B1 (en) |
| WO (1) | WO2014081096A1 (en) |
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| KR20140065241A (en) | 2014-05-29 |
| KR102038707B1 (en) | 2019-10-30 |
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