GB2127612A

GB2127612A - Water-tight wire and submersible motor

Info

Publication number: GB2127612A
Application number: GB08323575A
Authority: GB
Inventors: Minoru Iwata; Kiyohiko Sano
Original assignee: Ebara Corp; Furukawa Electric Co Ltd
Current assignee: Ebara Corp; Furukawa Electric Co Ltd
Priority date: 1982-09-06
Filing date: 1983-09-02
Publication date: 1984-04-11
Also published as: BR8304828A; JPS5944711A; GB8323575D0; GB2127612B; JPS6342803B2; AU556723B2; AU1862383A

Abstract

A water-tight wire comprises, in order, a conductor, a heat-resistant enamel layer, a main insulating layer of a crosslinked polyethylene or a polypropylene and an outer protective layer of a polyvinyl chloride composition using, as a base material, a polyvinyl chloride having a number average polymerization degree of 2,000 or higher. The enamel layer is preferably polyamideimide or epoxy resin. The water-tight wire has an excellent dielectric breakdown characteristic, a high exterior damage resistance and an excellent water treeing proof. A submersible motor using a primary winding constituted by said coated wire has a markedly enhanced life characteristic.

Description

SPECIFICATION Water-tight wire and submersible motor This invention relates to a water-tight wire having an excellent dielectric breakdown characteristic, a high exterior damage resistance and an excellent water-tree-proofness as well as to a submersible motor using a primary winding constituted by said watertight wire and thereby having a markedly enhanced life characteristic.

With respect to submersible motors, most populariy used are those of water-tight type which is filled with water when in service. In water-tight type submersible motors, because they are always used in water, the water resistance of their insulation system, particularly winding, is the most important factor that determines their reliability and life.

Hitherto, many kinds of insulated wires each having a different structure have been used for windings for submersible motors. Recently, for these submersible motor windinds, there have been mainly used wires having three insulating layers having respective functions, namely, an enamel layer (innermost layer), a main insulating layer (middle layer) and an outer protective layer (outermost layer).

For the enamel layer, a polyvinyl formal polymer, a polyester polymer, an epoxy polymer, a polyamideimide polymer or the like is used. The action of this layer has not been fully clarified except that it acts as a copper damage-shielding layer when the conductor is a soft copper wire. However, it is empirically known that the layer prolongs the life of submersible motor windings.

As the main insulating layer, a polyethylene particularly crosslinked polyethylene, polypropylene or the like are widely used because they excel in water resistance, are low in price and good in processability, compared with other kinds of polymers. However, insulated wires with a main insulating layer composed of these polymers, when used in submersion, have the drawback that the main insulating layer is locally deteriorated by water treeing in a short period of time. In order to overcome this drawback, the use as the material of the main insulating layer, of a mixture of a crystalline polypropylene and an ethylene-propyiene rubber or an ethylene-propylene terpolymer is proposed in Japanese Patent Publication No. 33140/1970. However, the combination of the above-mentioned enamel layer and this main insulating layer alone were not able to provide a satisfactory improvement.

In the meantime, a crosslinked polyethylene, a polypropylene and the like are suitable from the point of view of dielectric strength and economy, but are not necessarily superior in resistance to exterior damage. Accordingly, when these polymers are used as an outermost insulating layer, the wire surface gets scratches in winding and other operations causing deterioration of insulation and breaking of wire. In order to prevent these phenomena, it is generally practised that the main insulating layer is covered by an outer protective layer composed of a material having a high resistance to exterior damage. For example, covering by a polyamide polymer is proposed in Japanese Patent Public Disclosure (Laid-Open) No. 37823/1980. Although polyamide polymers are superior in exterior damage resistance, they are inferior in water-sealing properties.Therefore, the polymers can not sufficiently prevent water penetration into the main insulating layer composed of a polyethylene, a polypropylene or the like and accordingly can not effectively prevent the deterioration of the main insulating layer due to a water treeing phenomenon.

Thus, water-tight wires having a conventional outer protective layer composed of a polyamide polymer have had the drawback that, when used in water as, for example, in the case of submersible motor windings, they are deteriorated in the insulation in a short period of time and can not withstand long-time use.

An object of this invention is to provide a superior water-tight wire having a strong waterproof property and a sufficient damage resistance, free from water penetration and therefore water-treeing in the main insulating layer and thereby capable of long-time use.

Another object of this invention is to provide a submersible motor using a primary winding constituted by said water-tight wire and thereby having a markely improved life characteristic.

Still another object of this invention may become apparent to those skilled in the art from the following description and disclosure.

Fig. 1 represents the relationship between water immersion time at 550C and dielectric breakdown voltage, for the coated wire of this invention (Example 1 ) and coated wires of Comparative Examples 2, 3 and 4.

Fig. 2 represents the relationship between water immersion time at 750C and dielectric breakdown voltage, for the coated wire of this invention (Example 1 ) and coated wires of Comparative Examples 2, 3 and 4.

The water-tight wire according to the first aspect of the present invention comprises a conductor, a heat-resistance enamel layer, a main insulating layer and an outer protective layer, said three layers being formed on said conductor in this order, said main insulating layer being composed of a crosslinked polyethylene or a polypropylene and said outer protective layer being composed of a polyvinyl chloride composition using, as a base material, a polyvinyl chloride having a number average polymerization degree of 2000 or higher. The second aspect of the invention is a submersible motor using a primary winding constituted by the water-tight wire according to the first aspect of the present invention.

The essential feature of the water-tight wire of this invention is that the wire uses, as its outer protective layer, a crosslinked or non-crosslinked polyvinyl chloride composition using as a base material a polyvinyl chloride having a number average polymerization degree of at least 2000 and desirably 2000 to 3500. When this polyvinyl chloride having a number average polymerization degree of at least 2000 was used as an outer protective layer, surprisingly it was found that the resulting coated wire is superior in water-sealing property to coated wires using a polyamide resin and can sufficiently suppress the water treeing phenomenon of the main insulating layer composed of, for example, a crosslinked polyethylene.It was also found that a polyvinyl chloride having a number average polymerization degree smaller than 2000 has a waterproof ability equivalent to or lower than that of a polyamide resin. It was further found that the polyvinyl chloride having the above-mentioned polymerization degree provides satisfactory resistance to exterior damage which is required when the winding is inserted into the motor slot as well as satisfactory coatability. As the number average polymerization degree of the polyvinyl chloride increases, its waterproof property increases but the number average polymerization degree exceeding 3500 is not desirable because the polyvinyl chloride then comes to possess worsened processability.

When the polyvinyl chloride is used as an outer protective layer provided on the main insulating layer, it can contain, if necessary from processing requirements, plasticizers, stabilizers, lubricants, fillers and pigments which are all used in ordinary polyvinyl chlorides. Further, a crosslinked polyvinyl chloride can be used which is obtained by adding crosslinking co-agents to a polyvinyl chloride and irradiating the resulting mixture with an ionizing radiation, whereby the mechanical strength of the outer protective layer at high temperatures can be improved.

In the water-tight wire of this invention, as the main insulating layer, there is used a crosslinked polyethylene or a polypropylene. This polymer, in combination with the above-explained outer protective layer, can maintain its original insulation resistance for a long period of time without causing a water treeing phenomenon. The crosslinked polyethylene coating layer can be formed by extrusioncoating a polyethylene on the enamel-coated wire and then adopting either the crosslinking method by exposure to an ionizing radiation or the crosslinking method with a silane compound (Japanese Patent Publication No. 1711/1973). The crosslinked polyethylene layer formed particularly by the crosslinking method by exposure to electron rays scarcely causes void formation and accordingly maintains water resistance for a long period of time.As the polypropylene, a crystalline polypropylene is desirable which enables use of a larger current capacity and has excellent resistance to environmental stress cracking.

The heat-resistant enamel layer can be formed by coating one of the afore-mentioned polymers of conventional use in the form of a varnish. Of those polymers, a polyamideimide and epoxy polymer which are difficult to be hydrolyzed during submersed use and have excellent heat resistance are desirable.

The submersible motor of this invention has the same structure as ordinary water-tight motors, except that it uses as the primary winding the water-tight wire according the aforementioned aspect of this invention.

Hereinunder, this invention will be explained by referring to Examples and Comparative Examples; however, the invention is in no way restricted by these Examples.

EXAMPLES 1 to 4, COMPARATIVE EXAMPLES 1 to 4 In Examples 1 to 4 and Comparative Examples 1 to 4, there was used a polyamideimide enamel wire (Furukawa Al wire manufactured by the Furukawa Electric Company Limited) having an outside diameter of 2.4 mm and whose baked enamel film has a thickness of 0.03 mm. The conductor of the wire was a soft copper wire and the polymer forming the heat-resistant enamel layer was a polyamideimide polymer used in the form of varnish. The polyethylene composition (hereinafter to be referred to as composition A) constituting the main insulating layer as well as polyvinyl chloride compositions (hereinafter to be referred to as compositions B, C, D and E) forming the outer protective layer were as follows.

Composition A Rexion W 2000 100 parts by weight (low density polyethylene manufactured by Nippon petrochemical Co., Ltd.) Antioxidant Nocrac 300 0.3 part by weight (manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) Composition B NIPOLIT CL 100 parts by weight (polyvinyl chloride of 2500 number average polymerization degree manufactured by Chisso Corporation) Stabilizer Sinaka Lead TS G 7 parts by weight (tribasic lead sulfate manufactured by Shinagawa Chemical Industries Co., Ltd.) Plasticizer Adkcizer C-8 40 parts by weight (manufactured by Adeka Argus Chemical Co., Ltd.) Lubricant Sinaka Lead DS-2 1 part by weight (dibasic lead stearate manufactured by Shinagawa Chemical Industries Co., Ltd.) Composition C 101 EP 100 parts by weight (polyvinyl chloride of 1450 number average polymerization degree manufactured by Nippon Zeon Co., Ltd.) Stabilizer . Sinaka Lead TS-G 7 parts by weight Plasticizer Adkcizer C-8 40 parts by weight Lubricant Sinaka Lead DS-2 1 part by weight Composition D NIPOLIT CR 100 parts by weight (polyvinyl chloride of 2100 number average polymerization degree manufactured by Chisso Corporation) Stabilizer Sinaka Lead TS-G 7 parts by weight Plasticizer Adkcizer C-8 40 parts by weight Lubricant Sinaka Lead DS-2 i part by weight Composition E TK-2500 R 100 parts by weight (polyvinyl chloride of 3800 number average polymerization degree manufactured by Shinetsu Chemical Co., Ltd.) Stabilizer Sinaka Lead TS-G 7 parts by weight Plasticizer Adkcizer C-8 40 parts by weigh? Lubricant Sinaka Lead DS-2 1 part by weight Each of compositions A to E was kneaded in a roll mill at a temperature of 1 60C (A) or 1 80C (B to E) and each of the resulting sheets of these compositions was pelletized.

Respective pellets were extrusion-coated on the above-mentioned enamel wire by the use of an extruder of 40 mm OD and 28 L/D. At that time, the main insulating layer and the outer protective layer were combined as shown in the following table.

TABLE

Comp. Comp. Comp. Comp.

Example 1 Example 2 Example 3 Example 4 Example 1 Example 2 Example 3 Example 4 Enamel layer Polyamide- < --------------------------------------------------------------------- Same as left ----------------------------------------------------- > lmide A A A A A A A B Main Crosslinking < --------------------------------------------------------------------- Sane feit ------------------------------------------------------ > insutating by electron layer (30 M rad.) B B E C 6-nyion A Oute Cross Inkling < -----Same as laft -------------------- > Crossllnking protective by eiectron by etectron layer beame beame (30 M rad.) (30 M rad.) Dlalactrlc No dielectric < --------------------- Same as left ------------------------------------- > Caused < --------- Same as left ---------------- > treakdown breakdown dielectrin voltage at 10.000 breakdown (test lor volts at 10,000 coll) volts Motor life. hr. > 20,000 > 20,000 > 20,000 15,000 5,000 5,000 3,00 3,000 As shown in the table, in Example 1 and Comparative Examples 1 and 3, the polyethylene composition A was applied on the enamel wire and the resulting wire was exposed to electron beams of 1 MeV to cause crosslinking to the polyethylene. Then, as the outer protective layer, the composition B was applied in Example 1, the composition C in Comparative Example 1 and 6-nyion in Comparative Example 3. In Examples 2, 3 and 4, the composition A was applied and then, as the outer protective layer, the compositions B, E and D were applied, respectively. In Comparative Example 4, the composition B was applied and then the composition A was applied thereon.Thereafter, in Examples 2, 3 and 4 and Comparative Example 4, irradiation of electron beams of 1 MeV was applied to both the main insulating layer and the outer protective layer. Each of the insulated wires of Examples 1 to 4 and Comparative Examples 1, 3 and 4 thus obtained had a polyethylene layer of 0.3 mm thickness and a polyvinyl chloride layer of 0.2 mm thickness. The insulated wire of Comparative Example 2 obtained had only the composition A layer of 0.5 mm thickness irradiated by electron beams of 1 MeV.

The coated wires produced in Example 1 and Comparative Examples 2, 3 and 4 were tested for dielectric breakdown voltage by the following method.

The middle part (50 cm long) of a sample coated wire (1 m long) was immersed in water under the following two conditions. The test piece was subjected to a dielectric strength test (6 kv, 5 min, AC) in the same water and then the dielectric breakdown voltage (BVD) of the test piece was measured by the use of a method of linear rise voltage in which the electric voltage was increased at a rate of 0.5 kv/sec.

Immersion conditions 550C 0.5 to 1 hour, 4 hr, 24 hr, 48 hr 750C 0.5 to 1 hr, 4 hr, 24 hr, 48 hr The results were as shown in Fig. 1 (when immersed in water of 550C) and Fig. 2 (when immersed in water of 750C).

As is obvious from Figs. 1 and 2, the coated wire of Example 1 showed the highest dielectric breakdown voltage at each measurement point. Thus, this wire is very excellent in water resistance.

Each of the coated wires produced in Examples 1 to 4 and Comparative Examples 2 to 4 was wound into a test coil having the same structure as actual coils for motor assembling. The test coil was immersed in a 50% aqueous propylene glycol solution for 2 months. Then, the coil was subjected to a dielectric strength test by applying sine wave AC voltages of 2,000, 3,000, 4,000, 5,000, 6,000 and 10,000 volts. The results were shown in the table.

As is seen in the table, the coated wires of Examples 1 to 4 caused no dielectric breakdown even at 10,000 volts, while the coated wires of Comparative Examples 2 to 4 did cause dielectric breakdown at 10,000 volts.

All coated wires produced in Examples 1 to 4 and Comparative Examples 1 to 4 were formed into respective coils and each coil was incorporated into a water-tight type submersible motor of 37 kw for use in deep wells, using an aromatic polyamide paper as a slot liner, whereby respective submersible motors were produced.

These submersible motors were subjected to long period operation under conditions of 9O0C coil temperature, 400 v and 50 cycles to measure the life of each motor. The life of the motor is expressed in the number of hours up to the time when the insulation resistance of a coil system was reduced to 50%. The results are shown in the table.

As is shown in the table, in the submersible motors using the coated wires of Examples 1 to 3, insulation resistance hardly dropped even after 20,000 hr of operation. However, in the submersible motor using the coated wire of Example 4, insulation resistance dropped at 15,000 hr. On the other hand, in the submersible motor using the coated wire of Comparative Example 1, insulation resistance dropped markedly at 5,000 hr. This indicates that the number average polymerization degree of the polyvinyl chloride of the outer protective layer placed on the crosslinked polyethylene layer in the coated wire according to the first aspect of this invention has an effective action on the waterproof propery of the coil winding. Comparative Examples 2 and 3 are examples of submersible motors using conventional coated wires.In both of these motors, insulation resistance dropped at 5,000 hr or less.

This indicates that the water-tight wire (as primary winding for motors) according to the first aspect of this invention is far superior to conventional coated wires. In the submersible motor using the coated wire of Comparative Example 4 in which the materials of the main insulating layer and the outer protective layer used in the coated wire of Example 2 were used as materials of the outer protective layer and the main insulating layer, respectively, insulation resistance dropped at 3,000 hr. This indicates that the meritorious effect of this invention is brought about not by the mere combination of two coating layers (the crosslinked polyethylene layer and the polyvinyl chloride layer) of the coated wire used as a primary winding but by the order in which these two layers are placed.

EXAMPLE 5 A coated wire was produced in the same manner as in Example 1, except that the polyethylene composition A used in Example 1 was replaced by a composition using a crystalline polypropylene as a base material (hereinafter the composition is referred to as composition F and has the following formulation) and crosslinking by irradiation of electron beams was omitted.

Composition F Noblen BC8B 100 parts by weight (polypropylene manufactured by Mitsubishi Petrochemical Co., Ltd.) Antioxidant Nocrac 300 0.3 part by weight (manufactured by Ouchi Shinko Chemical Industriai Co., Ltd.) Copper damage inhibitor Mark CDA-1 0.3 part by weight (manufactured by Adeka Argus Chemical Co., Ltd.) In the same manner as in Example 1, this coated wire was incorporated into a submersible motor and the life of the resulting motor was measured. Insulation resistance hardly dropped even after 20,000 hr.

As will be appreciated from the above explanation, the coated wire having three coating layers according to this invention is excellent in dielectric breakdown characteristic and resistance to exterior damage and further can sufficiently suppress occurrence of water treeing during submerged use.

Accordingly, it is very suitable as a water-tight wire. Also, the submersible motor of water-tight type using the above-mentioned coated wire as its primary winding has an at least several times longer life than conventional motors for use for the same purpose and thus its practical value is very high.

Claims

1. A water-tight wire comprising a conductor, a heat-resistance enamel layer, a main insulating layer and an outer protective layer, said three layers being formed on said conductor in this order, said main insulating layer being composed of a crosslinked polyethylene or a polypropylene and said outer protective layer being composed of a polyvinyl chloride composition using, as a base material, a polyvinyl chloride having a number average polymerization degree of 2,000 or higher.

2. The water-tight wire according to Claim 1 , wherein the outer protective layer is composed of the polyvinyl chloride has a number average polymerization degree of 2,000 to 3,500.

3. The water-tight wire according to Claim 1, wherein the outer protective layer is composed of a crosslinked polyvinyl chloride composition using, as a base material, a polyvinyl chloride having a number average polymerization degree of 2,000 to 3,500.

4. The water-tight wire according to Claim 1, wherein the conductor comprises a soft copper wire.

5. The water-tight wire according to Claim 1, wherein the heat-resistant enamel layer comprises a polymer selected from the group consisting of a polyamideimide polymer and an epoxy polymer.

6. The water-tight wire according to Claim 1, wherein the main insulating layer comprises a crosslinked polyethylene.

7. A submersible motor using a primary winding constituted by a water-tight wire according to Claims 1 to 6.

8. A water-tight wire substantially as described herein with reference to and as illustrated in the accompanying drawings.

9. A submersible motor using a primary winding constituted by a water-tight wire according to Claim 8.