JPH06333430A - Polyethylene for power cable insulating layer and bridged polyethylene insulated power cable using it - Google Patents

Abstract

PURPOSE:To obtain a polyethylene for power cable insulating layer, of which tandelta is never raised under the high temperature and high electric field, and to obtain a bridged polyethylene insulated power cable, which has a large dielectric breakdown value under the high temperature and which can feed a large capacity of electricity, by using this polyethylene. CONSTITUTION:The low density polyethylene synthesized by the high pressure radical polymerization of ethylene is used and this polyethylene has the following characteristic: MFR 0.1-10g/10min.; D 0.915-0.935g/cm<3>; absorbancy of ketone type carbonyl group, which has a peak at 1725+ or -4cm<-1> of wave number, at 0.03-1.0, absorbancy of ester type carbonyl group, which has a peak at 1743+ or -4cm<-1> of wave number, at 1.0 or less, absorbancy on the basis of other carbonyl group less than 0.03 in the infrared absorption spectrum. Or/And the component to be fused at a fusing temperature T ( deg.C) or more, which is obtained with a formula T=687XD-547 is included at 3weight% or less at the time of measuring CFC when density of the low density polyethylene is expressed with D (g/cm<3>).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to polyethylene which has excellent electrical characteristics even under high temperature and high electric field and is suitable as a material for an insulating layer of a power cable, and a crosslinked polyethylene insulated power cable using the same. .

[0002]

2. Description of the Related Art As an electric power cable, an OF cable having an insulating layer made of kraft paper or semi-synthetic paper impregnated with insulating oil and a crosslinked polyethylene insulated power cable having an insulating layer made of crosslinked polyethylene are used. ing. Among these power cables, cross-linked polyethylene insulated power cables are widely used because they are easy to maintain and have a small dielectric loss. With the expansion of the field of use, the use environment is becoming higher in pressure.

By the way, in the case of the above-mentioned cross-linked polyethylene insulated power cable, the average operating electric field shifts to a higher level and the operating temperature rises to a higher temperature in response to the progress of higher voltage. Go. For example, 275
The average operating electric field of a kV class cross-linked polyethylene insulated power cable is about 6 kV / mm, and the operating temperature is about 9
Raises to 0 ° C.

When the operating electric field rises in this manner, the electric field concentration on the defective portion existing in the insulator layer becomes larger, and in some cases, several tens of kV /
reach up to mm. When the cross-linked polyethylene insulator layer is placed under a high temperature and a high electric field, the dielectric loss tangent (tan) is increased.
δ) rises, the insulator layer heats up, and the dielectric breakdown value thereof drops significantly. In addition, the dielectric loss increases as tan δ increases, and as a result, the power transmission capacity of the power cable decreases.

Further, in order to maintain high insulation performance for a long period of time, it is necessary to keep tan δ at a low level even when an electric field about twice the average operating electric field is applied.
Therefore, in order to manufacture a cross-linked polyethylene power cable with stable insulation performance and a large transmission capacity, it is necessary to configure the insulator layer with cross-linked polyethylene whose tan δ is maintained at a low level even at a high average operating electric field. You will need it.

[0006]

The present invention meets the above-mentioned demands for crosslinked polyethylene power cables and has an average operating electric field of 10 kV / mm or more at high temperature.
Even when a double electric field is applied, tan δ has high insulation performance without increasing, and polyethylene useful as a material for an insulator layer of a power cable capable of large-capacity power transmission,
An object is to provide a crosslinked polyethylene power cable manufactured using the polyethylene.

[0007]

Means for Solving the Problems In the course of intensive studies to achieve the above-mentioned object, the inventors of the present invention have selected an uncrosslinked polyethylene which is a starting material of the crosslinked polyethylene constituting the insulating layer, The relationship between the properties and tan δ was investigated. As a result, as will be described later, it was found that a specific high-pressure low-density polyethylene is useful for achieving the above-mentioned object, and the polyethylene of the present invention and a cross-linked polyethylene insulated power cable produced using the same are developed. Came to.

That is, the polyethylene for the power cable insulating layer of the present invention is a low density polyethylene synthesized by radical polymerization of ethylene and has the following properties: a, MFR of 0.1 to 10 g / 10 min; b, density is 0.915 to 0.935 g / cm ³ ; c, in infrared absorption spectrum, wave number is 1725 ± 4 cm
The absorbance of the ketone type carbonyl group having a peak at the position of ^-1 is 0.03 to 1.0, the absorbance of the ester type carbonyl group having a peak at the position of the wave number of 1743 ± 4 cm ^-1 is 1.0 or less, and , The absorbance based on other carbonyl groups
Is less than 0.03; and a low density polyethylene synthesized by radical polymerization of ethylene, having the following properties: a, MFR of 0.1 to 0.1 10 g / 10 min; b, density 0.951 to 0.935 g / cm ³ ; d, measurement using a cross fractionation apparatus combining temperature rising elution fractionation and gel permeation chromatograph When the density is D (g / cm ³ ), the following formula: T = 687 × D−547 (1) The elution temperature T (° C.) calculated based on % Or less; a low density polyethylene having
It is a low-density polyethylene characterized by having all the properties of b, c, and d.

The crosslinked polyethylene insulated power cable of the present invention is characterized in that the insulator layer is formed of any of the above-mentioned polyethylene crosslinked bodies. The polyethylene of the present invention is a low-density polyethylene synthesized by radical polymerization of ethylene under a high pressure method. These low density polyethylenes have an MFR (melting flow rate) of 0.1 to 10 g / 10 minutes. Preferably 0.7 to 5 g / 10 minutes, particularly preferably 0.8 to 3 g
/ 10 minutes.

When polyethylene having an MFR that is too high is used, it is difficult to form an insulating layer during the production of a power cable because the melt tension is lowered, and polyethylene having an MFR that is too low is used. If used, the melt extrusion coating of the insulating layer on the conductor becomes difficult and the productivity is reduced. The MFR referred to here is a value measured according to JIS K7210.

The low density polyethylene has a density of
It is from 0.915 to 0.935 g / cm ³ . Preferably,
0.917 to 0.928 g / cm ³ , particularly preferably 0.918
It is about 0.924 g / cm ³ . If the density of the polyethylene is too high, the flexibility of the insulating layer formed will be reduced, causing a difficulty in handling the power cable during practical use. This is because it is difficult to actually use it because there are too many essential components.

The density referred to here is JISK7112.
The value measured according to Furthermore, low-density polyethylene of the present invention, in the infrared absorption spectrum measurement resolution of wavenumber is 4 cm ^-1 or more, the absorbance of the ketone type carbonyl group having peaks at wavenumber 1725 ± 4 cm ^-1 is
0.03-1.0, preferably 0.03-0.5, wave number 1743
The absorbance of the ester type carbonyl group having a peak at ± 4 cm ⁻¹ is 1.0 or less, preferably 0.5 or less,
A peak at a wave number of 1743 ± 4 cm ^-1 does not have to exist, and has a property c that the absorbance based on other carbonyl groups is smaller than 0.03, and preferably the peak does not exist. Is. The property c is almost unchanged even when polyethylene is crosslinked.

The absorbance referred to here is the measurement sample of 1 mm.
It is a value when converted into hits, and the unit is-/ mm. An insulator layer formed by using polyethylene that does not satisfy the above property c is affected by a carbonyl group, and tan δ is increased particularly at high temperature and high electric field, and accordingly, dielectric loss of the insulator layer is increased and power consumption is increased. The transmission capacity of the cable will decrease. Further, in such a power cable, heat generation due to an increase in tan δ causes a large decrease in the dielectric breakdown value at high temperature.

The property d of the low-density polyethylene of the present invention was measured by using a cross fractionation device (hereinafter referred to as CFC) which is a combination of temperature rising elution fractionation and gel permeation chromatograph. At times, in the relationship between the elution temperature T calculated by the formula (1) and the density D of the low-density polyethylene, the component eluted at a temperature equal to or higher than the elution temperature T is 3% by weight or less based on the total elution amount, It is preferably 1.5% by weight or less.

The measurement using CFC in the present invention is carried out as follows using a commercially available device. That is, based on the principle described in J. Appl. Polym. Sci., 26, 4217 (1981), first, the target polyethylene is completely melted at 140 ° C, and then 140 ° C to 0 ° C at 1 ° C.
After cooling at 0 / min and holding at 0 ° C. for 30 minutes, measurement is performed under the conditions described below. By this measurement, the compositional distribution of polyethylene is measured by detecting the concentration of the component eluted at each temperature by gradually increasing the temperature and plotting the relationship between the amount eluted and the elution temperature.

The insulator layer made of polyethylene which does not satisfy the above property d is ta at high temperature and high electric field.
As nδ increases, the dielectric loss of the insulating layer increases accordingly, and the transmission capacity of the power cable decreases. Further, the heat generation due to the increase of tan δ causes the dielectric breakdown value at a high temperature to be significantly reduced. Therefore, in the ultra-high voltage power cable operated under high temperature and high electric field, it is preferable to use polyethylene having both the above-mentioned properties c and d as the insulating layer resin.

The polyethylene for the power cable insulating layer of the present invention has a peak of 1 of the differential elution curve showing the relationship between the elution temperature and the elution amount in the measurement using the above CFC.
/ 2 of the height hot side of the area of the portion surrounded by the tangent and the differential elution curve in (S _H) and the ratio of the total area of the peaks _{(S A) [S = (} S H / S A) X100: unit%] is 8% or less, preferably 7% or less, particularly preferably 6% or less.

The polyethylene of the present invention is, for example, Chem.
It can be produced by a known method described in documents such as Eng., 113 Dec (19), 1966. Specifically, first,
The ethylene gas refined in the ethylene plant and the unreacted ethylene gas circulated from the reactor as described later were sent to the primary compressor, where they were compressed to about 200 kg / cm ² and then Send to the secondary compressor.

In this secondary compressor, 1500-35 together with unreacted ethylene gas circulated from the reactor described later.
After being compressed to about 00 kg / cm ² , it is pressed into a reactor together with a radical initiator and the like, and the radical polymerization reaction proceeds at a maximum reaction temperature of 150 to 350 ° C. in this reactor. At this time, only about 18 to 20% by weight of the fed gas is polymerized, so the polymerized polymer and unreacted ethylene gas are separated by a high pressure separator of about 200 kg / cm ² , and then about Separate with a low pressure separator of about 0.3 kg / cm ² .

The unreacted ethylene gas separated by the high pressure separator is returned to the secondary compressor, and the unreacted ethylene gas separated by the low pressure separator is transferred to the surge tank,
A part of it is returned to the ethylene refining system of the ethylene plant via the compressor, and the rest is returned to the primary compressor described above together with the refined ethylene gas. The polymerized polymer separated with the low pressure separator is pelletized with a pelletizer, and this is used as the polyethylene of the present invention.

The power cable of the present invention is based on the high-pressure low-density polyethylene synthesized as described above and having the above-mentioned properties a, b, c or / and d, to which, for example, benzoyl peroxide is added. , T-
Butyl peroxybenzoate, dicumyl peroxide, t-butyl cumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butyl peroxyhexene, 2,4-dichloro- After blending an organic peroxide such as benzoyl peroxide as a cross-linking agent and coating the outer periphery of the conductor with the obtained mixture to form an uncross-linked insulator layer, the above-mentioned high pressure method low It can be produced by converting density polyethylene into a crosslinked body.

[0022]

Examples of the invention

Example 1 Based on the method described in Chem. Eng., 113 Dec (19), 1966, the following conditions: reactor, tubular reactor; reaction pressure, 2800 kg
/ cm ² ; maximum reaction temperature, 280 ° C; ethylene supply rate, 35 kg / hr
Polymerization initiator, t-butyl peroxybenzoate; Polyethylene was synthesized at a polymerization initiator supply rate of 1.45 g / hr.

With respect to the obtained polyethylene, as described below, measurement using CFC, MFR measurement, density measurement, IR
Analysis was carried out. CFC measurement: model, CFCT-150A (manufactured by Mitsubishi Petrochemical Co., Ltd.) solvent, o-dichlorobenzene flow rate, 1 ml / min. Concentration, 4 mg / ml injection amount, 0.4 ml column, AD80M / S, 3 tubes (manufactured by Showa Denko KK) Elution temperature, 0 ° C, 5 ° C, 10 ° C, 20 ° C, 30 ° C, 40
℃, 45 ℃, 49 ℃, 52 ℃, 55 ℃, 58 ℃, 61
℃, 64 ℃, 67 ℃, 70 ℃, 73 ℃, 76 ℃, 79
℃, 82 ℃, 85 ℃, 88 ℃, 91 ℃, 94 ℃, 97
℃, 100 ℃, 120 ℃, 140 ℃ Elution time, 39 minutes Detector, infrared spectrophotometer Detection wavelength, 3.42μm MFR: JIS K7210 conforming Density: JIS K7112 IR analysis (carbonyl groups in polyethylene (Identification): Using a 1600 series FT-IR manufactured by Perkin Elmer, wave number resolution 4 cm ^-1 , integration number 64 times, sample thickness about 1
The measurement was performed under the condition of mm, and the presence or absence of peaks and the absorbance at each wave number shown in Table 1 were measured. The above results are shown in Table 1.

With respect to 100 parts by weight of this polyethylene, 2 parts by weight of dicumyl peroxide (crosslinking agent), 4,4'-
Thiobis- (6-t-butyl-3-methylphenol)
(Antioxidant) 0.3 part by weight was added, and this mixture was added to 15 parts.
A 0 mm ² conductor was extrusion-coated with an inner semiconductive layer and an outer semiconductive layer as an insulating layer, and then subjected to a crosslinking treatment to produce a power cable.

The average electric field of this power cable at room temperature and temperature of 90 ° C. is 5 kV / mm and 10 kV / m.
The tan δ was measured at m, 15 kV / mm, 20 kV / mm and 25 kV / mm. As a measuring device,
Soken Electric Co., Ltd.'s automatic suring bridge (model:
DAU-PSC-UA), the measurement frequency is 50Hz
And

The results are shown in Table 1. Example 2 The radical polymerization reaction conditions were as follows: reactor, autoclave reactor; reaction pressure, 2000
kg / cm ² ; maximum reaction temperature, 235 ° C .; ethylene supply, 45 kg / hr
A polymerization initiator, t-butyl peroxyisobutyrate and t
-Butyl peroxypropyl carbonate; supply of polymerization initiator, 1.28 g / hr;
Polyethylene was synthesized in the same manner as in Example 1.

Using this polyethylene, a power cable was manufactured under the same conditions as in Example 1. The CFC measurement, MFR, density, IR analysis and tan δ measurement of the power cable of this polyethylene were performed in the same manner as in Example 1. The results are shown in Table 1. Examples 3 to 5 and Comparative Examples 1 to 4 A power cable was manufactured and evaluated in the same manner as in Example 1 except that polyethylene having the properties shown in Table 1 was used. The results are shown in Table 1.

[0028]

[Table 1]

As is clear from the results shown in Table 1, the power cable manufactured using the polyethylene of the present invention has an average electric field of 20 kV / mm at a high temperature of 25 kV.
There is almost no increase in tan δ even at / mm. Therefore, the electric power cable of the present invention can secure the long-term stability of the insulation performance even in an ultrahigh voltage transmission application in which the average operating electric field is 10 kV / mm or more.

[0030]

As is apparent from the above description, the power cable of the present invention in which the insulating layer made of polyethylene as a base resin is formed is tan even under high temperature and high electric field.
Almost no increase in δ. Therefore, it can function as a power cable having a large dielectric breakdown value at high temperature and a large transmission capacity. This is an effect based on the fact that the polyethylene of the present invention has the above-mentioned properties a, b, c or / and d.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Yamamoto 1 Tohocho, Yokkaichi, Mie Prefecture Yokkaichi Research Institute, Mitsubishi Petrochemical Co., Ltd. (72) Inventor, Mitsugu Ishioka 1 Tohocho, Yokkaichi, Mie Incorporated company Yokkaichi Research Institute (72) Inventor Setsuo Goto 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Petrochemical Co., Ltd. Inside Yokkaichi Research Institute

Claims (5)

[Claims] 1. A low density polyethylene synthesized by radical polymerization of ethylene, having the following properties: a, MFR of 0.1 to 10 g / 10 min; b, density of 0.915 to 0.935 g / cm. ³ ; c, In the infrared absorption spectrum, wave number 1725 ± 4 cm
The absorbance of the ketone type carbonyl group having a peak at the position of ^-1 is 0.03 to 1.0, the absorbance of the ester type carbonyl group having a peak at the position of the wave number of 1743 ± 4 cm ^-1 is 1.0 or less, and , The absorbance based on other carbonyl groups
A polyethylene for a power cable insulation layer, characterized in that it is a low density polyethylene having: less than 0.03. 2. A low-density polyethylene synthesized by radical polymerization of ethylene, having the following properties: a, MFR of 0.1 to 10 g / 10 min; b, density of 0.915 to 0.935 g / cm. ³ ; d, in the measurement using a cross fractionation apparatus combining a temperature rise elution fractionation and a gel permeation chromatograph, when the density of the low density polyethylene is D (g / cm ³ ), the following equation: T = A low-density polyethylene having a content of 3% by weight or less, which is eluted at a temperature equal to or higher than the elution temperature T (° C.) calculated based on 687 × D-547, which is a power cable insulation layer. For polyethylene. 3. A low-density polyethylene synthesized by radical polymerization of ethylene, having the following properties: a, MFR of 0.1 to 10 g / 10 min; b, density of 0.915 to 0.935 g / cm. ³ ; c, In the infrared absorption spectrum, wave number 1725 ± 4 cm
The absorbance of the ketone type carbonyl group having a peak at the position of ^-1 is 0.03 to 1.0, the absorbance of the ester type carbonyl group having a peak at the position of the wave number of 1743 ± 4 cm ^-1 is 1.0 or less, and , The absorbance based on other carbonyl groups
D is smaller than 0.03; d, in a measurement using a cross fractionation apparatus combining a temperature rise elution fractionation and a gel permeation chromatograph, the following when the density of the low density polyethylene is D (g / cm ³ ): Electric power characterized by being a low-density polyethylene having a component eluted at a temperature equal to or higher than the elution temperature T (° C.) calculated based on the formula: T = 687 × D-547 at 3% by weight or less; Polyethylene for cable insulation layers. 4. A cross-linked polyethylene insulated power cable, wherein an insulation layer is formed of the cross-linked polyethylene according to claim 1, claim 2, or claim 3. 5. The crosslinked polyethylene insulated power cable according to claim 4, wherein the average operating electric field is 10 kV / mm or more.