JP4575895B2 - Ground fault prevention method for OF cable connection - Google Patents

Description

The present invention relates to a ground fault disaster how the OF cable connection, in particular, relates to a ground fault disaster how the OF cable connection using a ground fault prevention sheet made of aramid fibers.

  In general, a connecting portion of an OF cable used as a high-voltage underground power transmission line is provided with a disaster prevention function for preventing a secondary disaster such as a fire caused by a ground fault.

  For example, the conventional OF cable connection part is covered with a box-shaped FRP trough or rubber disaster prevention tape to ensure airtightness, so the cable is ignited due to a ground fault. The fire is immediately extinguished by the suffocation effect of the trough and disaster prevention tape, and the occurrence of secondary disasters such as fire is prevented.

  In addition, when a ground fault occurs, not only ignition but also a sudden rise in pressure around the blast will occur.For example, the trough and the disaster prevention tape are bound at equal intervals by a high tension band such as stainless steel or aramid. In order to improve the pressure resistance against the blast, it has been devised.

In addition, when an ultra-high-pressure OF cable is used, the pressure and ignition power caused by the blast at the time of a ground fault will increase, so that better pressure resistance and airtightness can be secured and sufficient suffocation effect can be exhibited. There is a need. As a method for this, for example, the OF cable connecting portion is surrounded by a trough so that a constant pressure-reducing space is formed around the OF cable connecting portion, and a belt-like aramid fiber sheet is directly wound around the entire outer peripheral surface of the trough in a roll shape. A ground fault that uniformly covers the entire outer peripheral surface, and further covers the entire periphery of the aramid fiber sheet with a ground fault disaster prevention sheet composed of a double sheet of an inner sheet and an outer sheet made of an aramid fiber that is directly sleeved. A disaster prevention method is known (see Patent Document 1).
Japanese Patent No. 3663103

  However, according to the ground fault prevention method for the OF cable connection part described in Patent Document 1, in order to ensure sufficient pressure resistance and airtightness, a large number of disaster prevention sheets to be used is set, which is disadvantageous in terms of cost. There is a case.

  Moreover, the method of taking out the ground wire, the cross bond wire, the oil sampling pipe, etc. from the inside of the disaster prevention sheet to the outside is not uniform and takes time, and there are cases where the pressure resistance and air tightness of the disaster prevention sheet are affected.

  Further, the method of discharging leaked oil, water entering the sheet, etc. from the inside of the sheet to the outside is not uniform and takes time, and there are cases where the pressure resistance and airtightness of the disaster prevention sheet are affected.

  Accordingly, an object of the present invention is to provide a ground fault disaster prevention method for an OF cable connecting portion using an appropriate number of sheets for ground fault disaster prevention. The object of the present invention is to discharge a grounding wire, a cross bond wire, an oil sampling pipe, etc. from the inside of the disaster prevention sheet to the outside, or to discharge leaked oil or water that has entered the sheet from the inside of the disaster prevention sheet to the outside. It is providing the OF cable connection part provided with the ground fault disaster prevention sheet | seat which has the mechanism for doing.

In order to achieve the above object, the present invention surrounds an OF cable connecting portion with a trough so that a constant pressure-reducing space is formed around the OF cable connecting portion, and a roll sheet made of aramid fibers directly on the entire outer peripheral surface of the trough. A ground fault disaster prevention method for an OF cable connecting portion, in which the entire outer peripheral surface of the roll sheet is uniformly covered and the entire periphery of the roll sheet is directly covered with a ground fault disaster prevention sheet made of an aramid fiber. The sheet is wound with a number of sheets selected so as to correspond to the pressure calculated by the formula (1) described later based on the design limit pressure for each number of roll sheets, and the ground fault disaster prevention sheet is the ground fault disaster prevention sheet. oF cable being characterized in that to cover overlapping a number chosen to accommodate the pressure calculated by the equation (2) described later on the basis of the number by the design limit pressure It provides a ground fault prevention method of Le connection.

Further, the present invention in order to achieve the above object, before Symbol ground fault prevention sheet provides OF cable connections ground disaster method of the present invention characterized by having a slit having a suture mechanism .

The present invention includes an invention having one or more of the following features.
(1) The slit has a cut surface covered with a fraying prevention tape.
(2) The said slit is provided in the terminal part of the said ground fault disaster prevention sheet.
(3) The suturing mechanism includes a binding band part attached to each of both ends of the slit, a bolt passed through a bolt hole formed in the binding band part, and a nut paired with the bolt, A plate-like suture metal fitting sandwiched between the bolt and the nut;

The present invention also land of OF cable connection of the present invention which is characterized in that it comprises a oil drain mechanism having oil drain drain provided for achieving the above object, before Symbol ground fault prevention sheet To provide a disaster prevention method .

The present invention includes an invention having one or more of the following features.
(1) The oil drain mechanism includes the oil drain, a string-like oil absorber connected to the oil drain, and a spiral tube wound around the oil absorber, and the spiral The tube is in contact with the inner wall surface of the trough.
(2) The spiral tube has a shape-maintaining hose in which all or part of the portion from the location where the oil absorber comes out of the trough to the connecting portion of the oil absorber and the oil drainage drain. Covered with.

  According to the present invention, in the ground fault prevention method for the OF cable connecting portion, it is possible to prevent wasteful costs while maintaining excellent pressure resistance and airtightness. Moreover, according to the present invention, in the OF cable connecting portion provided with the ground fault disaster prevention sheet, the grounding wire, the cross bond line, the oil collecting pipe, etc. can be easily taken out from the inside of the ground fault disaster prevention sheet, or The leaked oil or the water that has entered the sheet can be discharged from the inside of the sheet to the outside.

[Embodiments of the present invention]
[Configuration of OF cable connection part]
FIG. 1 is a schematic side view for explaining the configuration of an OF cable connecting portion according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line AA of FIG.

  The OF cable connecting portion 12 is surrounded by a trough 1 so that a constant pressure-reducing space is formed around the OF cable connecting portion 12, and a roll sheet 2 made of aramid fiber that is directly rolled on the entire outer peripheral surface of the trough 1 is provided. The entire outer peripheral surface of the roll sheet 2 is wound and uniformly covered, and the entire periphery of the roll sheet 2 is directly covered with a sleeve-shaped ground fault disaster prevention sheet 5 made of aramid fibers. The ground fault disaster prevention sheet 5 includes an inner sheet 3 and an outer sheet 4 made of aramid fibers.

  The trough 1 has, for example, a box shape and is manufactured using fiber reinforced plastic (FRP).

  The roll sheet 2 is made of an aramid fiber excellent in strength and heat resistance, and this aramid fiber is an aromatic polyamide fiber which is a kind of nylon. Specifically, DuPont Kevlar (registered trademark), Nomex (registered trademark), Teijin Techno Products Limited Conex (registered trademark), and the like can be used. The roll sheet 2 may be used by superimposing one sheet in a double layer or more (two or more troughs 1). The roll sheet 2 is bound by winding an aramid band 6 or the like around it.

  The ground fault disaster prevention sheet 5 is made of an aramid fiber like the roll sheet 2, and the inner sheet 3 and the outer sheet 4 made of aramid fiber are used in an overlapping manner. The surface of the outer sheet 4 is coated with flame retardant polyvinyl chloride resin (PVC) or the like in order to achieve high airtightness. The ground fault disaster prevention sheet 5 may use only the outer sheet 4 alone without using the inner sheet 3. In addition, two or more inner sheets 3 and the outer sheet 4 may be used in an overlapping manner.

  Drawing 3 is an appearance side view of a ground fault disaster prevention sheet, (a) shows an inner sheet and (b) shows an outer sheet. The outer sheet 4 is produced with a slightly wider lateral width than the inner sheet 3. The inner sheet 3 and the outer sheet 4 are respectively formed with slit portions 3a and 4a, knob stitch portions 3b and 4b, and belt reinforcement portions 3c and 4c at both ends in the longitudinal direction.

  The slit portions 3a and 4a are provided to bring out a ground wire, a cross bond wire, an oil collection pipe, and the like, and it is desirable to provide a plurality of slit portions. When the OF cable connection part 12 has a wall on one side and the other side is a surrounding environment, it is located on the wall side when the ground fault disaster prevention sheet 5 is attached to the OF cable connection part 12. A grounding wire or the like is taken out from the slit and an oil drain, which will be described later, is attached to the slit located at the lower part of the passage. A method for forming the slit portions 3a and 4a will be described later.

  Knob stitch portions 3b and 4b are formed from a wide rectangular aramid fiber sheet in the shape shown in FIG. 3 (a wide central portion (for example, length 2430 mm) located on the outer periphery of the trough 1), and both end portions (for example, a long length). 470mm), the middle part of the center part and the end part (for example, length 540mm)), when the middle part of the narrowing and the sheet bumps generated at both end parts are pinched and stitched together Yes, the knob stitches are sewn together with a weak thread, and have a structure that expands greatly due to the pressure at the time of ground fault.

  The belt reinforcement portions 3c and 4c are portions obtained by sewing a band of aramid fibers and reinforcing the band. A hole is formed in this portion, and the belt reinforcement portions 3c and 4c are used for joining with an offset sheet of a cable portion installed next to the connection portion sheet. .

4 and 5 are side views for explaining the installation procedure of the disaster prevention sheet for the OF cable connecting portion.
First, the OF cable 11 is placed on the cable cradle 13 and the OF cable connection part 12 is placed on the connection part cradle 14, and the trough 1 surrounds the OF cable connection part 12 so as to form a constant pressure-reducing space. (FIG. 4A).

Next, the connecting portion 12 and the trough 1 are temporarily suspended by the lever block (registered trademark) 15, and the roll sheet 2 is wound around the entire outer circumferential surface of the trough 1 two or more times to uniformly cover the entire outer circumferential surface (see FIG. 4 (b)). After the roll sheet 2 is wound, the periphery thereof is bound with an aramid band 6 (FIG. 4C). The ground wire and the cross bond wire are drawn out from the open end of the roll sheet 2.

Then, the split plastic hose 7 is put on the OF cables 11 at both ends of the ground fault disaster prevention sheet 5, and the entire periphery of the roll sheet 2 is directly covered with the ground fault disaster prevention sheet 5 including the inner sheet 3 and the outer sheet 4 (see FIG. 5 (d)), the respective side end portions are sutured using a suture fitting (FIG. 5 (e)).

FIG. 6 is a perspective view showing a stitched portion of the ground fault disaster prevention sheet side end portion, and FIG. 7 is a side view thereof.
As shown in FIGS. 6 and 7, the end portions of the inner sheet 3 and the outer sheet 4 are folded back and overlapped with each other, and rope holes 3d and 4d are formed in the folded portions. The rope 8 is passed through the holes 3d and 4d.

  The overlapped portions of the inner sheet 3 and the outer sheet 4 are overlapped, the plate-like suture metal fitting 21 is applied to the lowermost surface and the uppermost surface, and the side edges of the inner sheet 3 and the outer sheet 4 by the bolts 22 and 23. Suture.

[Number of roll sheets 2 and ground fault disaster prevention sheets 5]
In determining the number of roll sheets 2 and ground fault disaster prevention sheets 5 to be used, the following is considered.

  In the protective tube of the OF cable connecting part 12, the oil in the connecting part is gasified and expanded by the first-wave arc power, and the pressure rises. The protective tube breaks, this pressure is released into the trough 1, spreads into the space in the trough 1, and the pressure in the trough 1 rises (temperature changes are ignored). Furthermore, the pressure in the trough 1 (in the roll sheet 2) is released and spreads into the ground fault disaster prevention sheet 5, and the pressure in the ground fault disaster prevention sheet 5 increases.

Therefore, the roll sheet 2 is wound around the number (number of windings) obtained based on the following formula (1). PJT is the pressure (MPa) in the trough 1. V _aj is a cross-sectional area (mm ² ) in the protective tube of the OF cable connecting portion 12 (the cross-sectional area in the protective tube is a cross-sectional area inside the protective tube of the OF cable connecting portion 12. V _aT is the effective cross-sectional area (mm ² ) in the trough 1 (the effective cross-sectional area in the trough 1 is the inside of the trough 1 and the outside of the OF cable connection portion 12). It refers to the cross-sectional area.)

Moreover, the ground fault disaster prevention sheet 5 is made to overlap and cover the number calculated | required based on following formula (2). PJS is the pressure (MPa) in the ground fault disaster prevention sheet 5. V _aS is a cross-sectional area (mm ² ) in the ground-fault disaster prevention sheet 5 (a cross-sectional area in the ground-fault disaster prevention sheet 5 refers to a cross-sectional area inside the ground-fault disaster prevention sheet 5 and outside the roll sheet 2. .)

  here,

Pj _max : Maximum generated pressure (MPa) in the protective tube of the OF cable connecting portion 12
E _m : Maximum pressure increase rate in the protective pipe of the OF cable connection part P ₀ : Initial hydraulic pressure in the protective pipe of the OF cable connection part 12 (kgf / m ² )
α: Pressure wave propagation speed of oil in protective tube of OF cable connection 12 (m / s)
KW: Energy given by arc KW = k ・ β ・ W _1S
k: constants of oil k = (C ₀ · G / 9.8) × {Gt / (4.186 · Gq)}
C ₀ : Specific gravity of oil (kg / m ³ )
G: Gas constant (m / K)
Gq: Energy required for gasification (kcal / kg)
Gt: Gas temperature (° C)
β: Ratio related to increase in arc power hydraulic pressure (varies depending on conditions, and is 0.1 in this embodiment)
W _1S : Arc power average value (MW) of ground fault first wave (until protection tube destruction)
A: The cross-sectional area occupied by the oil in the protective tube of the OF cable connecting portion with respect to the cross-sectional area in the protective tube (the cross-sectional area of the oil involved) (m ² )
C _L : Coefficient (It is a coefficient related to the transmission of pressure, etc., and is 2 for the ground fault of the connection part)
It is.

  Since the breaking pressure P of the aramid fiber sheet is determined by P = F / r (F is the design strength of the aramid fiber sheet (280 kN / m), r is the inner diameter of the sheet), the roll sheet 2 and the ground fault disaster prevention sheet The design limit pressure for each of the five sheets is as shown in Table 1 below.

The arc current at the ground fault current of 31.5 kA is assumed to be about 91 MW. At this time, the pressure in the trough 1 (pressure applied to the roll sheet 2) PJT and the pressure in the ground fault disaster prevention sheet 5 (pressure applied to the ground fault disaster prevention sheet 5) ) PJS is calculated from the above formulas (1) and (2) as follows.
PJT = about 1.69 MPa
PJS = about 0.87 MPa
From this, it is considered that two roll sheets 2 and one ground fault disaster prevention sheet 5 (only the outer sheet 4) can be used.

Further, the arc current at the ground fault current of 45 kA is assumed to be about 127 MW. At this time, the pressure in the trough 1 (pressure applied to the roll sheet 2) PJT and the pressure in the ground fault disaster prevention sheet 5 (pressure applied to the ground fault disaster prevention sheet 5) ) PJS is calculated from the above formulas (1) and (2) as follows.
PJT = about 1.99 MPa
PJS = about 1.03 MPa
From this, it is considered that two roll sheets 2 and two ground fault disaster prevention sheets 5 (inner sheet 3 and outer sheet 4) can be handled.

In the calculation, the following numerical values were used.
V _aj = 0.0452 mm ²
V _aT = 0.134 mm ²
V _aS = 0.196 mm ²
ε ₁ = 0.9
ε ₂ = 0.75
P ₀ = 2.0 × 10 ⁴ kgf / m ²
α = 1300 m / s
KW = k ・ β ・ W _1S
k = (C ₀ · G / 9.8) × {Gt / (4.186 · Gq)}
= 1.467 × 10 ³
C ₀ = 999.7 kg / m ³
G = 47.06 m / K
Gq = 626 kcal / kg
Gt = 800 ° C
β = 0.1
W _1S : When the ground fault current is 31.5 kA, 90.9 MW
127 MW for ground fault current of 45 kA
A = 0.0226 m ²
C _L = 2

<Example>
Actually, when a test was performed with the number of sheets according to the above calculation results using an intermediate connection portion of a 275 kVOF cable (1400 mm ² ), good results were obtained as shown in Table 2. In the calculation, each numerical value described above was used.

[Method of forming slit portions 3a, 4a]
A method for forming the slit portion will be described with reference to FIGS. 8 to 10 by taking the inner sheet 3 as an example (the same applies to the outer sheet 4). FIG. 8 is a perspective view for explaining a procedure for forming the slit portion. 9A is a cross-sectional view of part A in FIG. 8, and FIG. 9B is a cross-sectional view of part B in FIG. FIG. 10 is an enlarged view of a portion C in FIG.

  First, the inner sheet 3 is cut, and a slit 31 is provided (FIG. 8A), and a reinforcing tape 32 made of aramid fiber is sewn along the cut surface (FIGS. 8B and 9A). ). Thereafter, the reinforcing tape 32 is folded back to the back surface of the inner sheet 3 with the sewn portion as an axis so that the cut surface is covered with the reinforcing tape 32 (FIGS. 8C and 9B). Further, the cable tie part 33 is sewn on the reinforcing tape 32 sewn on the back surface of the inner sheet 3 (FIG. 8D).

  The tying band part 33 is formed by folding one aramid fiber sheet into a double, and is stitched so that a rope hole 3d is formed in the folded part (stitched part 3f), and the rope is inserted into the rope hole 3d. 8 is passed. In addition, the two ends overlapped with each other are folded inward and overlapped four times and sewn on the reinforcing tape 32.

  Bolt holes 3e are formed in the binding band part 33 (FIGS. 8 (e) and 10), and the slit portion 3a that does not draw out the grounding wire or the like is sewn using the above-described suture fitting 21, bolt 22 and nut 23. .

[Oil release mechanism]
FIG. 11 is a schematic side view of an OF cable connecting portion having an oil draining mechanism. 12 is an enlarged view of a D portion in FIG. 11, and FIG. 13 is an enlarged view of an E portion in FIG.

  The OF cable connecting portion 12 includes an oil drain mechanism having an oil drain (SUS pipe 44) provided on the ground fault disaster prevention sheet 5. The SUS pipe 44 is desirably installed by providing an insertion hole for the SUS pipe 44 in the above-described suture fitting 21 (and the ground fault disaster prevention sheet 5). Alternatively, as shown in FIG. 12, a stopper 46 provided with an insertion hole for the SUS pipe 44, a bolt 47 and a nut 48 are used at a position different from the attachment position of the suture fitting 21 on the ground fault disaster prevention sheet 5. Then, the SUS pipe 44 may be installed.

  As the SUS pipe 44, for example, an 8A size pipe can be used, and an openable / closable lid is attached to the outer end of the ground fault disaster prevention sheet 5.

  In addition to the SUS pipe 44, the oil draining mechanism is wound around the nylon string 41 and a string-like oil absorber (for example, a nylon string 41 (about 1 to 6 mm in diameter)) connected to the SUS pipe 44. The spiral tube 42 (having a diameter of about 20 mm) is provided, and the spiral tube 42 is in contact with the inner wall surface (the lower surface at the time of installation) of the trough 1.

  From the gap between the spiral tubes 42, the oil is absorbed by the nylon string 41, and the oil moves to the SUS pipe 44 through the string 41 and is discharged.

  The spiral tube 42 has a shape holding hose from the portion where the nylon string 41 does not contact the inner wall surface of the trough 1 (where it goes out of the trough 1) to the connection portion between the nylon string 41 and the SUS pipe 44. It is covered with an insulating lock 45 at the end of the SUS pipe 44. As the shape-maintaining hose, PVC or the like can be used. For example, a soft PVC hose (High Plus Hose 43 (manufactured by Toyo Tire & Rubber Co., Ltd.)) using a reinforcing yarn can be used.

  Using the oil draining mechanism, water or the like that has entered the sheet can be discharged to the outside.

[Effect of the embodiment of the present invention]
(1) Since the roll sheet and the ground fault disaster prevention sheet can be used in an appropriate number in the ground fault prevention method for the OF cable connecting portion, it is possible to prevent wasteful costs while maintaining excellent pressure resistance and airtightness.
(2) In the OF cable connection part equipped with the ground fault disaster prevention sheet, the grounding wire, the cross bond line, the oil sampling pipe, etc. are taken out from the inside of the ground fault disaster prevention sheet while maintaining excellent pressure resistance and airtightness. Can do. Further, since the cut surface of the slit is covered and stitched with the fraying prevention tape (reinforcing tape), fraying is prevented.
(3) In the OF cable connection part equipped with the ground fault disaster prevention sheet, while maintaining excellent pressure resistance and air tightness, leaked oil or water that has entered the sheet is discharged from the inside of the ground fault disaster prevention sheet to the outside. can do.

It is a schematic side view for composition explanation of an OF cable connection part concerning an embodiment of the invention. It is AA sectional drawing of FIG. It is an external appearance side view of a ground fault disaster prevention sheet, (a) shows an inner side sheet and (b) shows an outer side sheet. It is a side view for demonstrating the installation procedure of the disaster prevention sheet for OF cable connection parts. It is a side view for demonstrating the installation procedure of the disaster prevention sheet for OF cable connection parts. It is a perspective view which shows the stitching | suture site | part of a ground fault disaster prevention sheet side edge part. It is a side view which shows the stitching | suture site | part of a ground fault disaster prevention sheet side edge part. It is a perspective view for demonstrating the formation procedure of a slit part. (A) is sectional drawing of the A section of FIG. 8, (b) is sectional drawing of the B section of FIG. It is an enlarged view of the C section of FIG. It is a schematic side view of the OF cable connection part which has an oil draining mechanism. It is an enlarged view of the D section of FIG. It is an enlarged view of the E section of FIG.

Explanation of symbols

1: trough 2: roll sheet 3: inner sheet 4: outer sheet 3a, 4a: slit part 3b, 4b: knob stitching part 3c, 4c: belt reinforcing part 3d, 4d: rope hole 3e: bolt hole 3f: stitching part 3g : Terminal folding part 5: Ground fault disaster prevention sheet 6: Aramid band 7: Back split plastic hose 8: Rope 10: Disaster prevention sheet for OF cable connection part 11: OF cable 12: OF cable connection part 13: Cable cradle 14: Connection part Base 15: Lever block 21: Suture fitting 22: Bolt 23: Nut 31: Slit 32: Reinforcement tape 33: Cable tie part 41: Nylon string 42: Spiral tube 43: High plus hose 44: SUS piping 45: Insulok 46: Fastener 47: Bolt 48: Nut

Claims (8)

The OF cable connection part is surrounded by a trough so that a constant pressure-reducing space is formed around the OF cable connection part, and an aramid fiber roll sheet is wound directly around the entire outer circumferential surface of the trough to uniformly cover the entire outer circumferential surface. Furthermore, it is a ground fault disaster prevention method of the OF cable connecting part that is directly covered with the ground fault disaster prevention sheet made of aramid fiber, all around the roll sheet,
The roll sheet is wound around a number selected so as to correspond to the pressure calculated by the following formula (1) based on the design limit pressure for each number of the roll sheets, and the ground fault disaster prevention sheet is the ground fault disaster prevention The ground fault disaster prevention of the OF cable connecting portion characterized in that the selected number of sheets is overlapped and covered so as to correspond to the pressure calculated by the following formula (2) based on the design limit pressure for each number of sheets. Method.
here,
PJT: Pressure in the trough (MPa)
PJS: Pressure in the ground fault disaster prevention sheet (MPa)
V _aj : _Cross- sectional area in the protective tube of the OF cable connection part (mm ² )
(The cross-sectional area in the protective tube refers to the cross-sectional area inside the protective tube of the OF cable connecting portion.)
V _aT : Effective sectional area in trough (mm ² )
(The effective cross-sectional area in the trough refers to the cross-sectional area inside the trough and outside the OF cable connecting portion.)
V _aS : _Cross- sectional area in the ground fault disaster prevention sheet (mm ² )
(The cross sectional area in the ground fault disaster prevention sheet refers to the cross sectional area inside the ground fault disaster prevention sheet and outside the roll sheet.)
ε ₁ : Pressure reduction coefficient in consideration of elongation of aramid sheet (= 0.9)
ε ₂ : Pressure reduction coefficient in consideration of elongation of aramid sheet and pressure release in the longitudinal direction (= 0.75)

Pj _max : Maximum generated pressure (MPa) in the protective tube of the OF cable connection
E _m : Maximum pressure increase rate in the protective pipe of the OF cable connection part P ₀ : Initial hydraulic pressure in the protective pipe of the OF cable connection part (kgf / m ₂ )
α: Pressure wave propagation speed of oil in protective tube of OF cable connection (m / s)
KW: Energy given by arc KW = k ・ β ・ W _1S
k: constants of oil k = (C ₀ · G / 9.8) × {Gt / (4.186 · Gq)}
C ₀ : Specific gravity of oil (kg / m ³ )
G: Gas constant (m / K)
Gq: Energy required for gasification (kcal / kg)
Gt: Gas temperature (° C)
β: Ratio of arc power related to hydraulic pressure increase W _1S : Arc power average value (MW) of ground fault first wave (until protection tube breakage)
A: The cross-sectional area occupied by the oil in the protective tube of the OF cable connecting portion with respect to the cross-sectional area in the protective tube (the cross-sectional area of the oil involved) (m ² )
C _L : Coefficient (It is a coefficient related to pressure transmission, etc., and is 2 for the ground fault of the connection)
It is. Before Symbol ground fault prevention sheet, ground fault prevention method of OF cable connection of claim 1, wherein further comprising a slit having a suture mechanism. The ground fault disaster prevention method for an OF cable connecting portion according to claim 2, wherein the slit has a cut surface covered with a fray prevention tape. The said slit is provided in the terminal part of the said ground fault disaster prevention sheet, The ground fault disaster prevention method of the OF cable connection part of Claim 2 characterized by the above-mentioned. The suturing mechanism includes a binding band part attached to each cut end of the slit, a bolt passed through a bolt hole formed in the binding band part, a nut paired with the bolt, and the bolt The ground fault disaster prevention method of the OF cable connection part according to claim 2, further comprising a plate-like suture metal fitting sandwiched between the nuts. OF cable connections ground disaster method according to claim 1, characterized in that it comprises a oil drain mechanism having oil drain drain provided before Symbol grounding disaster sheet. The oil drain mechanism includes the oil drain, a string-like oil absorber connected to the oil drain, and a spiral tube wound around the oil absorber, the spiral tube The ground fault disaster prevention method for the OF cable connecting portion according to claim 6, wherein the ground wall is in contact with an inner wall surface of the trough. In the spiral tube, all or a part of the portion from the location where the oil absorber comes out of the trough to the connecting portion between the oil absorber and the oil drainage drain is covered with a shape-retaining hose. The ground fault disaster prevention method for an OF cable connecting portion according to claim 7.