JP5528306B2 - Water tree generation test method and water tree generation test specimen manufacturing method - Google Patents

Description

The present invention relates to a water tree generation test method of generating water tree in a polymer material, water tree generation test method and test piece preparation how for the test.

  Some cables that can be placed in water include a copper wire as a conductor covered with an insulating portion made of a polymer material or the like. Here, for the polymer material, for example, a thermosetting resin such as cross-linked polyethylene (hereinafter referred to as XLPE) is often used.

  Some insulated cables arranged in water are used for propagating inverter voltage (AC voltage) and the like. When such an insulated cable is used for several years in a state where an AC voltage including an inverter surge is applied, a water tree may be generated in an insulating part such as XLPE. The water tree is a phenomenon that finally induces a dielectric breakdown due to an insulation deterioration phenomenon that occurs in an insulator when an electric field is applied in a state where water coexists for a long time.

  As a water tree diagnosis method, there is known an insulation diagnosis system or the like for performing an insulation diagnosis of a lightning arrester and a power cable by interrupting the power system (see Patent Document 1).

  On the other hand, in order to design a material used for an insulating portion used for an insulating cable disposed in water and a structure thereof, it is necessary to grasp in advance a generation state of a water tree. For this reason, it is necessary to perform a test for generating a water tree experimentally in a short time, that is, for reproducing it.

JP 2010-151576 A

  In order to generate a water tree, a water electrode method or the like is used. In this water electrode method, a plurality of electrode holes are formed in a flat plate of XLPE serving as a test piece, and the test piece is immersed in a liquid to generate a relatively high electric field in the vicinity of each electrode hole. Thereby, the water tree can be reproduced in XLPE around each electrode hole.

  Each electrode hole is usually formed by pressing a mold member having a plurality of protrusions into a plate material of XLPE. The electrode holes formed in this way often have variations in shape. When evaluating the water tree generated around each electrode hole, it is necessary to remove the cause of shape variation. For this reason, this variation in shape complicates the evaluation of the water tree.

  Moreover, the operation | movement which pushes in a protrusion destroys the molecular structure of XLPE around each electrode hole. For this reason, the molecular structure of XLPE around each electrode hole is different from the molecular structure of other parts related to XLPE. In the test piece in which the electrode hole is manufactured by such a method, there is a high possibility that the water tree generated in the insulated cable using XLPE is not faithfully reproduced.

  The present invention has been made in view of such circumstances, and an object of the present invention is to make it possible to reproduce a water tree in a state closer to a water tree generated in an insulated cable actually used in the liquid.

In order to achieve the above object, the water tree generation test method according to the present invention includes a water tank part in which a flat test piece in which an electrode part is embedded in a polymer material can be immersed, and a water tank part disposed outside the water tank part. In the water tree generation test method for generating a water tree on the test piece using a water tree generation device having an electric field generator capable of applying an electric field to the electrode part, the test piece has one flat surface. A plurality of holes formed so that the cross section becomes smaller toward the bottom and perpendicular to the surface thereof, and the electrode portion has a predetermined hole depth direction distance from the hole bottom of each of the holes. The water tree generation test method is formed so as to maintain a test piece manufacturing step for manufacturing the test piece, a dipping step for immersing the test piece in the water tank after the test piece manufacturing step, After the dipping process, And an electric field action step of generating a water tree between the electrode portion and the bottom of the hole by applying an electric field to the electrode portion, and the test piece manufacturing step is a metal flat plate, The first mold member formed with a plurality of protrusions formed so that the cross-section becomes smaller as it goes perpendicular to the surface and toward the tip, and the inside of the box-shaped second mold member in which the inflow space is formed A mold member installation step to be installed, a polymer material inflow step for allowing the polymer material heated to a predetermined temperature to flow into the inflow space after the mold member installation step, and the polymer material inflow step. A first polymer material layer forming step of forming a first polymer material layer by allowing the polymer material in the inflow space to cure by being allowed to stand for a predetermined time while maintaining the predetermined temperature; After the first polymer material layer forming step, the first polymer material From the layer, and the first mold member and the second mold member to remove mold release step, after the releasing step, opposite to the first surface of the first mold part of the polymeric material layer is present An electrode portion forming step for forming the electrode portion so as to maintain a predetermined gap from the tip of the protrusion on the surface; and a second polymer material layer made of a polymer material after the electrode portion forming step. And an electrode covering step of sandwiching the electrode part together with the first polymer material layer.

The test piece manufacturing method according to the present invention is a method of manufacturing a test piece used in a water tree generation test for generating a water tree on a test basis. The test piece is a flat plate in which an electrode portion is embedded in a polymer material. A plurality of holes formed so that the cross-section becomes smaller from one flat surface to the bottom and perpendicular to the surface, and the electrode portion is formed with a hole bottom of each hole. The test method of the water tree generation test is formed so as to maintain a predetermined distance in the hole depth direction, and includes a water tank part in which a test piece can be immersed and an electric field applied to the electrode part arranged outside the water tank part. An electric field generator capable of acting, and a test using a water tree generator having a dipping step in which the test piece is immersed in the water tank unit, and an electric field is applied to the electrode unit after the dipping step. , The electrode part and the hole And a field action step of generating a water tree between the first and second test pieces. The test piece manufacturing method is a metal flat plate that is perpendicular to one surface and has a smaller cross section toward the tip. After the mold member installation step, the mold member installation step of installing the first mold member formed with a plurality of protrusions formed in the inside of the box-shaped second mold member in which the inflow space is formed, and after the mold member installation step A polymer material inflow step for allowing the polymer material heated to a predetermined temperature to flow into the inflow space; and the polymer material in the inflow space after the polymer material inflow step. A first polymer material layer forming step of forming a first polymer material layer by allowing it to stand for a predetermined time while maintaining the temperature to form a first polymer material layer; and after the first polymer material layer forming step, the first polymer material layer Remove the first mold member and the second mold member from the layer. And to release step, after the releasing step, on the surface opposite to the first surface of the first mold part of the polymeric material layer is present, the distal end with a predetermined gap between the projection In order to maintain, after the electrode part forming step of forming the electrode part and the electrode part forming step, the second polymer material layer made of a polymer material sandwiches the electrode part together with the first polymer material layer. An electrode coating step.

  According to the present invention, it is possible to reproduce a water tree in a state closer to a water tree actually generated in an insulated cable used in a liquid.

It is a block diagram which shows the structure of the water tree generation | occurrence | production test apparatus of 1st Embodiment which concerns on this invention. It is a schematic front view which shows the test piece of FIG. It is the III-III arrow side view of FIG. It is the elements on larger scale of the IV section of FIG. It is a schematic front view which shows the state which assembled the 1st-3rd type | mold member for manufacturing the 1st resin layer of FIG. It is a schematic perspective view which shows the adjustment board of FIG. It is a schematic front view which shows the state which formed the electrode part in the electrode side surface of the 1st resin layer obtained by filling the inflow space of FIG. 5 with XLPE. It is a block diagram which shows a part of structure of the water tree generation | occurrence | production test apparatus of 2nd Embodiment which concerns on this invention.

  Hereinafter, an embodiment of a water tree generation test method according to the present invention will be described.

[First Embodiment]
A first embodiment will be described with reference to FIGS. FIG. 1 is a block diagram showing the configuration of the water tree generation test apparatus of the present embodiment. FIG. 2 is a schematic front view showing the test piece 10 of FIG. 3 is a side view taken along the line III-III in FIG. FIG. 4 is a partially enlarged front view of a portion IV in FIG.

  FIG. 5 is a schematic front view showing a state in which the first to third mold members 41 to 43 and the like for manufacturing the first resin layer 21 of FIG. 1 are assembled. FIG. 6 is a schematic perspective view showing the adjustment plate 49 of FIG. FIG. 7 is a schematic front view showing a state in which the electrode portion 30 is formed on the electrode-side surface 21c of the first resin layer 21 obtained by filling the inflow space 45 of FIG. 5 with XLPE.

  First, the configuration of the water tree test apparatus used in the water tree generation test method of the present embodiment will be described. This water tree generation test apparatus has a water tank section 6 fixed on a gantry 9a, a water temperature adjustment section 7, and an electric field generation apparatus 1. This apparatus is for immersing a test piece 10 in a water tank section 6 to generate a water tree on the test piece 10.

  The water tank 6 is a substantially rectangular parallelepiped container into which, for example, an NaCl aqueous solution is injected, and the upper part is open. Moreover, it has the grounding part 9 in the bottom part.

  The water temperature adjusting unit 7 is disposed at the bottom of the water tank unit 6 and can heat or cool the NaCl aqueous solution in the water tank unit 6.

  The electric field generator 1 is disposed outside the water tank unit 6 and generates an electric field between the electrode unit 30 inside the test piece 10 and an electrode side surface 21c (described later) formed on the first resin layer 21. It has a function generator 3 and an amplifier 2. The electrical connection between the electric field generator 1 and the test piece 10 will be described later.

  The test piece 10 has the resin part 20 and the electrode part 30, and the high voltage | pressure side lead wire 5a is attached. The resin part 20 includes two resin layers, that is, a first resin layer 21 and a second resin layer 22. These first and second resin layers 21 and 22 are each formed of a thermosetting polymer material, in this example, cross-linked polyethylene (XLPE).

  Each of the first and second resin layers 21 and 22 is a rectangular plate having an outer dimension of about 150 mm × 100 mm and has a predetermined thickness (FIGS. 1 and 2). In this example, the first and second resin layers 21 and 22 have substantially the same shape.

  Five electrode holes 21 b are formed on one surface (opening-side surface 21 a) of the first resin layer 21. Each of these electrode holes 21b opens to the opening-side surface 21a of the first resin layer 21, and is formed so as to extend from the opened portion to the inside perpendicularly to the opening-side surface 21a. As shown in FIG. 3, these electrode holes 21 b are formed in a square area of about 50 mm × 50 mm on the opening-side surface 21 a, with one predetermined centering on the predetermined electrode hole 21 b and further at four places on the front, back, left and right. A total of five are formed, one for each. In this example, the distance between adjacent electrode holes 21b is about 9 mm.

  The inner surface of each of these electrode holes 21b has a cylindrical shape near the opening-side surface 21a, and has a substantially conical shape with the electrode hole 21b bottom substantially pointed near the bottom of the electrode hole 21b (FIG. 4). In this example, the tip is hemispherical and has a radius of curvature of about 20 μm.

  The distances in the depth direction of the electrode hole 21b at the bottom of the electrode side surface 21c and the electrode hole 21b (left and right direction in FIGS. 1 and 2) are adjusted to be a predetermined value. The adjustment method will be described later.

  The electrode part 30 is formed by applying a conductive paint containing, for example, Ag or the like to one surface (electrode-side surface 21 c) of the first resin layer 21. Although not shown in detail, the electrode part 30 is covered and protected by an aluminum tape or the like.

  The high-voltage side lead wire 5 a is attached in a state of being sandwiched between the electrode part 30 and the aluminum tape, and can be conducted to the electrode part 30. The high voltage side lead wire 5 a is electrically and mechanically connected to the high voltage portion of the amplifier 2. Further, the low-voltage side lead wire 5b electrically connects the grounding portion 9 and the amplifier 2.

  The second resin layer 22 is bonded to the first resin layer 21 so as to sandwich the electrode portion 30, the high-voltage side lead wire 5 a and the aluminum tape together with the first resin layer 21.

  Here, a procedure for manufacturing the test piece 10 will be described. First, a part of an apparatus for manufacturing the test piece 10 will be described.

  The apparatus for manufacturing the test piece 10 has three mold members, that is, a first mold member 41, a second mold member 42, and a third mold member 43.

  The first mold member 41 has, for example, a substantially rectangular flat plate portion 41a made of metal such as stainless steel, and five protrusions 41b attached to one surface of the flat plate portion 41a. Each protrusion 41b is made of metal such as stainless steel and extends perpendicularly to the surface. These protrusions 41b correspond to the electrode holes 21b. That is, the arrangement of the five protrusions 41b is the same as that of the five electrode holes 21b.

  The outer peripheral surface of each of these protrusions 41b has a cylindrical shape on the side close to the surface, and has a substantially conical shape with a substantially sharp tip on the tip side from this cylindrical shape. Each tip has a hemispherical shape with a radius of curvature of about 20 μm. The first mold member 41 is installed inside the second mold member 42 such that each protrusion 41b is vertical.

  The 2nd type | mold member 42 is a substantially rectangular parallelepiped box shape, and the upper surface is opening. The edge of the opening is formed flat. The inside of the second mold member 42 becomes an inflow space 45 into which resin can flow.

  The third mold member 43 has a substantially rectangular plate shape made of metal such as stainless steel, and has a through hole 43a at least at one location. In the through hole 43a, the heated and melted XLPE can be distributed. The through hole 43a allows the internal XLPE to flow out due to an increase in internal pressure.

  The third mold member 43 is an adjustment plate, which will be described later, on the edge of the opening of the second mold member 42 so as to block a part (most part) of the inflow space 45 in the third mold member 43 from above. 49 to be fixed. The state in which XLPE flows through the through hole 43a will be described later. The third mold member 43 is fixed in a state parallel to the flat plate portion 41 a of the first mold member 41.

  A plurality of adjustment plates 49 are stacked vertically on the edge of the opening of the first mold member 41. As shown in FIG. 6, the adjustment plate 49 has a rectangular hole 49a formed in the center of the rectangular plate. The shape of the rectangular hole 49 a is the same as the shape of the opening of the second mold member 42.

  The third mold member 43 is fixed on the adjustment plate 49 stacked on the edge of the opening of the second mold member 42. At this time, each rectangular hole 49a of each adjustment plate 49 and the opening of the second mold member 42 are fixed in a penetrating state. By adjusting the number of adjustment plates 49, the distance between the surface (lower surface) of the third mold member 43 facing the first mold member 41 and the tip of each protrusion 41b can be adjusted.

  By adjusting this distance, the distance in the depth direction of the electrode hole 21b between the electrode-side surface 21c and the bottom of the electrode hole 21b can be adjusted.

  Below, the procedure which produces the test piece 10 using these 1st-3rd type | mold members 41-43 grade | etc., Is demonstrated.

  First, the first mold member 41 is accommodated in the second mold member 42. At this time, the first and second mold members 41 and 42 are installed so that each protrusion 41b of the first mold member 41 extends vertically. Next, a plurality of adjustment plates 49 are stacked on the edge of the opening of the second mold member 42. Thereby, the distance between the lower surface of the third mold member 43 and the tip of each protrusion 41b is adjusted.

  Thereafter, the third mold member 43 is attached on the adjustment plate 49. At this time, the distance between the tip of each protrusion 41b of the first mold member 41 and the surface of the third mold member 43 facing the first mold member 41 is a predetermined distance. Thus, the assembly of the first to third mold members 41 to 43 is completed (FIG. 5).

  Next, a pipe or the like (not shown) is attached to the through hole 43a of the third mold member 43, and XLPE is poured into the inflow space 45 as indicated by a broken line arrow A shown in FIG. At this time, XLPE is a fluid that is heated to a predetermined temperature, for example, about 150 ° C. and has a predetermined viscosity, and is not crosslinked.

  The XLPE is filled in the inflow space 45 in a state where it is not cross-linked. The XLPE filled in the inflow space 45 is held at a pressure larger than the atmospheric pressure. In this state, the first to third mold members 41 to 43 are held for a predetermined time, for example, several hours in a state where XLPE is introduced. At this time, XLPE is solidified by promoting the crosslinking reaction. The solidified XLPE becomes the first resin layer 21 described above.

  Then, the 1st-3rd type | mold members 41-43 are removed from the 1st resin layer 21, ie, release. After releasing the first to third mold members 41 to 43, a conductive paint is applied to the electrode-side surface 21c of the released first resin layer 21. Thereafter, the high-voltage side lead wire 5a is brought into contact with the applied conductive paint. In this state, an aluminum tape (not shown) is applied to the electrode-side surface 21c so as to cover the entire area where the conductive paint is applied and the high-voltage-side lead wire 5a that is in contact with the conductive paint. To do. Thereby, the electrode part 30 is formed (FIG. 7).

  Thereafter, the second resin layer 22 is attached to the electrode side surface 21 c of the first resin layer 21. As a result, the electrode portion 30 including the portion where the conductive paint is applied and a part of the high-voltage side lead wire 5a is sandwiched between the first and second resin layers 21 and 22. The manufacture of the test piece 10 shown in FIG.

  Next, a procedure for generating a water tree on the test piece 10 using the test piece 10 manufactured in the above procedure will be described.

  First, the high-voltage side lead wire 5a of the test piece 10 manufactured by the above-described procedure is electrically and mechanically connected to the amplifier 2 (FIG. 1).

  Next, the test piece 10 is immersed in the water tank 6 containing the NaCl aqueous solution. In this state, the function generator 3 applies a voltage having a predetermined frequency to the electrode unit 30. This voltage is adjusted by the amplifier 2. Thereby, a predetermined voltage is applied to the electrode unit 30.

  Moreover, the temperature in the water tank part 6 is adjusted with the water temperature adjustment part 7 grade | etc., So that it may become the underwater temperature in which an insulated cable is actually arrange | positioned. At this time, the temperature of the NaCl aqueous solution is measured with a thermometer 8 or the like.

  By applying a voltage to the electrode part 30 for several days, a water tree is generated between the hole bottom of the electrode hole 21 b of the test piece 10 and the electrode part 30.

  The test piece 10 of the present embodiment has an inner surface shape of the electrode hole 21b as compared with the case where the electrode hole 21b is formed by pressing the protrusion 41b of the first mold member 41 with a predetermined force on the surface of the plate material of XLPE. The outer peripheral shape of the protrusion 41b is more accurately transferred. This is because, after the XLPE is heated and melted, it flows into the periphery of the protrusion 41b, and then the internal crosslinking reaction proceeds to solidify.

  In addition, as described above, when the electrode hole 21b is formed by pushing the protrusion 41b of the first mold member 41 into the plate material, the molecular structure of XLPE around the electrode hole 21b and the molecular structure of other parts To be different. This is because the protrusion 41b of the first mold member 41 is pushed into the plate material to form the electrode hole 21b while destroying the molecular structure of XLPE.

  On the other hand, since the test piece 10 of the present embodiment is formed as described above, the molecular structures of the periphery of the electrode hole 21b and other parts are the same. For this reason, the state where the water tree is generated, that is, the state of XLPE around the electrode hole 21b is kept substantially the same as the state of XLPE of an insulated cable used in water, for example.

  As a result, the water tree generated in the test is more similar to the water tree generated in an XLPE cable or the like actually placed in water.

  As can be seen from the above description, according to the present embodiment, it is possible to reproduce a water tree in a state close to a water tree generated in an insulated cable actually used in the liquid. For this reason, the water tree can be evaluated with higher accuracy.

[Second Embodiment]
A second embodiment will be described with reference to FIG. FIG. 8 is a block diagram showing a part of the configuration of the water tree generation test apparatus of the present embodiment. In addition, this embodiment is a modification of 1st Embodiment (FIGS. 1-7), Comprising: The same code | symbol is attached | subjected to the same part or similar part as 1st Embodiment, and duplication description is carried out. Omitted.

  In the test apparatus used in the water tree generation test method of the present embodiment, the side water tank 51 is attached so as to cover a part of the opening-side surface 21a of the first resin layer 21 and all the five electrode holes 21b. ing. As for this side surface water tank part 51, the surface facing the 1st resin layer 21 is opened. Further, a spout 51a is formed on the upper surface for pouring a liquid, in this example, an aqueous NaCl solution. Liquid leakage is suppressed between the edge of the opening of the side water tank 51 and the opening-side surface 21a by a sealing material.

  Further, in this test apparatus, a side water tank portion 51 is also attached to the second resin layer 22 side. That is, the test apparatus is configured such that the test piece 10 is sandwiched between the two side water tank parts 51.

  As described in the example of FIG. 1, when the entire test piece 10 is immersed in the NaCl aqueous solution in the water tank unit 6, the sealability between the first and second resin layers 21 and 22 is not maintained, that is, predetermined. In the case where the adhesive force is not maintained, or when the test period is long, there is a possibility that the liquid enters from the interface between the first and second resin layers 21 and 22. If liquid flows from the interface, the water tree generation test cannot be performed.

  On the other hand, in the test apparatus of the present embodiment, the same effect as that of the first embodiment can be obtained, and the inflow of liquid from the interface between the first and second resin layers 21 and 22 can be suppressed.

[Other Embodiments]
The description of the above embodiment is an example for explaining the present invention, and does not limit the invention described in the claims. Moreover, each part structure of this invention is not restricted to the said embodiment, A various deformation | transformation is possible within the technical scope as described in a claim.

  In the above embodiment, five electrode holes 21b are formed in the test piece 10, but the present invention is not limited to this. At least one may be formed.

  Moreover, although the electrode part 30 of the test piece 10 is formed by apply | coating a conductive paint to the electrode side surface 21c of the 1st resin layer 21, it is not restricted to this. A thin plate coated with a conductive paint may be attached to the electrode side surface 21c.

  In this embodiment, XLPE, which is one of thermosetting resins, is used as the polymer material, but the present invention is not limited to this. Other thermosetting polymer materials may be used. It is also possible to use a thermoplastic polymer material.

DESCRIPTION OF SYMBOLS 1 ... Electric field generator, 2 ... Amplifier, 3 ... Function generator, 5a ... High voltage | pressure side lead wire, 5b ... Low voltage | pressure side lead wire, 6 ... Water tank part, 7 ... Water temperature adjustment part, 8 ... Thermometer, 9 ... Grounding part, 9a ... frame, 10 ... test piece, 20 ... resin part, 21 ... first resin layer, 21a ... opening side surface, 21b ... electrode hole, 21c ... electrode side surface, 22 ... second resin layer, 30 ... electrode part, 41 ... first mold member, 41a ... flat plate part, 41b ... projection, 42 ... second mold member, 43 ... third mold member, 43a ... through hole, 45 ... inflow space, 49 ... adjusting plate, 49a ... rectangular hole , 51 ... Side water tank part, 51a ... Spout

Claims (7)

A water tree having a water tank part in which a flat test piece in which an electrode part is embedded in a polymer material can be immersed, and an electric field generator arranged outside the water tank part and capable of applying an electric field to the electrode part In a water tree generation test method for generating a water tree on the test piece using a generator,
The test piece is formed with a plurality of holes formed so that the cross-section becomes smaller from one flat surface to the bottom and perpendicular to the surface, and the electrode portion is a hole of each hole. It is formed so as to maintain a predetermined hole depth direction distance from the bottom,
The water tree generation test method is as follows:
A test piece manufacturing process for manufacturing the test piece;
After the test piece manufacturing step, an immersion step of immersing the test piece in the water tank part;
After the dipping step, an electric field is applied to the electrode part to generate a water tree between the electrode part and the hole bottom; and
Have
The test piece manufacturing process includes:
A box made of a metal flat plate that has a plurality of protrusions formed so that the cross-section becomes smaller toward one end and perpendicular to one side, and an inflow space is formed inside A mold member installation step of installing in the shape of the second mold member;
After the mold member installation step, the polymer material inflow step for allowing the polymer material heated to a predetermined temperature to flow into the inflow space;
After the polymer material inflow step, the first polymer material forming the first polymer material layer is formed by allowing the polymer material in the inflow space to stand and cure for a predetermined time while maintaining the predetermined temperature. A layer forming step;
A mold release step of removing the first mold member and the second mold member from the first polymer material layer after the first polymer material layer forming step;
After the mold release step, the electrode is disposed on the surface of the first polymer material layer opposite to the surface on which the first mold member is present so as to maintain a predetermined gap from the tip of the protrusion. Forming an electrode part, and
An electrode covering step of sandwiching the electrode portion together with the first polymer material layer in a second polymer material layer made of a polymer material after the electrode portion forming step;
A water tree generation test method characterized by comprising: Before the polymer material inflow step, a plate-shaped third mold member having a through hole formed in at least one place is attached to the second mold member, and a third mold member installation step for closing the inflow space is performed. Have
The polymer material inflow step includes a step of flowing the polymer material from the through hole;
The water tree generation test method according to claim 1. 3. The third mold member installation step includes an adjustment step of adjusting a distance between the tip of the protrusion and the electrode portion to a predetermined range necessary for water tree evaluation. The water tree generation test method described.   4. The water tree generation according to claim 1, wherein the electrode forming step includes a step of applying a conductive paint to a surface of the first polymer material layer. 5. Test method.   The water tree generation test method according to any one of claims 1 to 4, wherein the polymer material is a thermosetting polymer material.   The water tree generation test method according to any one of claims 1 to 5, wherein the polymer material is cross-linked polyethylene. In a method for producing a test piece used in a water tree generation test for generating a water tree on a trial basis,
The test piece is
A flat plate in which an electrode portion is embedded in a polymer material, and a plurality of holes are formed so that a cross section becomes smaller from one flat surface to the surface and toward the bottom, and The electrode part is formed to maintain a predetermined hole depth direction distance from the hole bottom of each of the holes,
The test method of the water tree generation test is as follows:
It is a test using a water tree generator having a water tank part in which a test piece can be immersed, and an electric field generator arranged outside the water tank part and capable of acting on an electric field on the electrode part,
An immersion step of immersing the test piece in the water tank part;
After the dipping step, an electric field is applied to the electrode part to generate a water tree between the electrode part and the hole bottom; and
Have
The method of manufacturing the test piece is as follows:
A box made of a metal flat plate that has a plurality of protrusions formed so that the cross-section becomes smaller toward one end and perpendicular to one side, and an inflow space is formed inside A mold member installation step of installing in the shape of the second mold member;
After the mold member installation step, the polymer material inflow step for allowing the polymer material heated to a predetermined temperature to flow into the inflow space;
After the polymer material inflow step, the first polymer material forming the first polymer material layer is formed by allowing the polymer material in the inflow space to stand and cure for a predetermined time while maintaining the predetermined temperature. A layer forming step;
A mold release step of removing the first mold member and the second mold member from the first polymer material layer after the first polymer material layer forming step;
After the mold release step, the electrode is disposed on the surface of the first polymer material layer opposite to the surface on which the first mold member is present so as to maintain a predetermined gap from the tip of the protrusion. Forming an electrode part, and
An electrode covering step of sandwiching the electrode portion together with the first polymer material layer in a second polymer material layer made of a polymer material after the electrode portion forming step;
A test piece manufacturing method characterized by comprising:

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