CA1057043A - Power cable - Google Patents
Power cableInfo
- Publication number
- CA1057043A CA1057043A CA233,938A CA233938A CA1057043A CA 1057043 A CA1057043 A CA 1057043A CA 233938 A CA233938 A CA 233938A CA 1057043 A CA1057043 A CA 1057043A
- Authority
- CA
- Canada
- Prior art keywords
- insulation
- power cable
- water
- plastic
- electrolyte
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Compositions Of Macromolecular Compounds (AREA)
Abstract
ABSTRACT
A power cable having a plastic electrical insula-tion which is partially or wholly composed of a plastic material is disclosed, the plastic material containing an inorganic or organic electrolyte which ionizes when dissolved in water. This prevents deterioration of the insulation called "water tree" which has been a great disadvantage to the plastic insulation such as cross-linked polyethylene of conventional insulated cables.
A power cable having a plastic electrical insula-tion which is partially or wholly composed of a plastic material is disclosed, the plastic material containing an inorganic or organic electrolyte which ionizes when dissolved in water. This prevents deterioration of the insulation called "water tree" which has been a great disadvantage to the plastic insulation such as cross-linked polyethylene of conventional insulated cables.
Description
This invention relates to a power cable wherein the deterioration of plastic insulation caused by a phenomenon called "water tree" is effectively prevented and to the acces-sories of the cable. More particularly it relates to a method of preventing such deterioration of plastic electrical insula-tion used for power cables and accessories, the method being suitable for application to power cables for relatively low voltage of the class 3 to 22 KV, through to high voltage power cable of the class 66 to 154 KV.
It is well known that power cables insulated with plastic typified by cross-linked polyethylene, polyethylene, ethylene-propylene rubber and butyl rubber possess many advan-tages. On account of these advantages, plastic insulated power cables are widely used. When they have been in service for a long period of time, however, a phenomenon called "water tree" occurs wherein exterior water enters the insulation and diffuses and condenses therein. The insulation material of the cable thus deteriorates and dielectric breakdown may result. In order to prevent this, a metal sheath of lead, aluminum or the like is generally provided over the insulation layer.
"Water tree" can be prevented in a cable that is provided with a metal sheath. However, the cable is then not only very expensive but also is difficult to handle due to the increased weight by the addition of the metal layer.
-1- ~
B`
..
.. . . . ..
. . . ` ~ ..
.. . . - . . . ` ` ~.` ~.:
-. ` , - . . . -... . . . ~ .
.
These are the drawbacks of the conventional cables.
Generally, this invention provides a power cable in which such drawbacks are alleviated and a method is pro-vided for prevention of "water tree" in the insulation layer of the cable.
The mechanism of the initiation and development of the "water tree" phenomenon has not been previously known.
The present inventors, however, have successfully clarified the mechanism and then arrived at the method of this inven-tion preventing the occurrence of "water tree".
"Water tree" takes place where the electric fieldis strong and a mass of minute voids filled with water is formed. The voids are formed when the chemical potential~w of the water contained in the minute voids is decreased by an electric field. This can be expressed in the following formula:
~w = ~o ~ 2 o(7p)TEl _____--- (1) In Formula (1) above,~O represents the chemical potential of water in the minute voids when there is no electric field; ~ the specific inductive capacity of water;
~O the dielectric constant of vacuum; p the density of water;
El the electric field in a mass of minute voids filled with water; and T the temperature.
In Formula (1), (~ap)T ~ 0 ..
.
Therefore, ~w~ and the water where there is no electric field, namely external water, enters and diffuses into the minute voids. As a result of this, the minute voids increase to form the "water tree".
Assuming that the minute voids are of spherical shape and that the electric field in the insulation of the cable is Eo, the value of El can be obtained from the following formula:
E = 3~ Eo _______- (2) ~2 + 2~1 wherein 2 = C_ j-~/w~o (complex specific inductive capacity) -------- (3) a: conductivity of water w: angular frequency As apparent from Formula (1), the smaller the value of El, the lower the growth rate of the "water tree"
will be. Accordingly, "water tree" can be prevented by making the value of El smaller.
In accordance with this invention, an electrolyte which dissolves in water and increases the electric conduc-tivity of the water is added to the insulation material duringpreparation of the insulator to provide a small value of El 80 that "water tree" can be prevented. In other words, the principle that El in Formula (2) becomes smaller as ~ in Formula (3) becomes greater is utilized in the invention.
: .
. . : . .. : . -- : - : - .
- - : ' - '' ~ - : .
~057043 The invention will become more apparent from the following description:
Any inorganic or organic matter that dissolves in water to increase the electric conductivity of the water may be employed as the electrolyte. The preferred electro-lytes for use accoxding to the invention include strong elec-trolytes as for example sodium chlorlde, sodium sulfate, potassium chloride, potassium sulfate, other alkali metal salts, alkali earth metal salts, ammonium chloride and other ammonium salts, cupric sulfate and other metal salts, sodium acetate, other salts of other carboylic acid, salts of organic sulfonic acids, etc., of which sodium sulfate is most effec-tive in preventing the "water tree". These electrolytes neither move in the insulation, nor enter into the insulation.
The quantity of the electrolyte to be added is at least 10 7% by weight of the insulation material. Addi-tion of the electrolyte in excessive quantities would produce an adverse effect in terms of the insulation characteristics and the infiltration of water due to osmotic pressure. To avoid this, the amount added should be less than 1% by weight of the insulation material.
To ensure an effective prevention of "water tree", it is also preferable to disperse the electrolyte as evenly as possible, in the form of micro-particles of less than several~m in the plastic material which is used to form the insulation. The best results can be obtained by the use of - 10~7043 plastic insulation formed with plastic material prepared with the micro-particles of the electrolyte evenly dispersed therein.
The process for achieving even dispersion of the minute particles of an electrolyte measuring less than severalJ~m may be selected from the following:
(1) Mixing of micro-particles of electrolyte and the insulation material in a mixer extruder called "Brabender Plastograph" (Trade Mark) or by rolls or the like;
It is well known that power cables insulated with plastic typified by cross-linked polyethylene, polyethylene, ethylene-propylene rubber and butyl rubber possess many advan-tages. On account of these advantages, plastic insulated power cables are widely used. When they have been in service for a long period of time, however, a phenomenon called "water tree" occurs wherein exterior water enters the insulation and diffuses and condenses therein. The insulation material of the cable thus deteriorates and dielectric breakdown may result. In order to prevent this, a metal sheath of lead, aluminum or the like is generally provided over the insulation layer.
"Water tree" can be prevented in a cable that is provided with a metal sheath. However, the cable is then not only very expensive but also is difficult to handle due to the increased weight by the addition of the metal layer.
-1- ~
B`
..
.. . . . ..
. . . ` ~ ..
.. . . - . . . ` ` ~.` ~.:
-. ` , - . . . -... . . . ~ .
.
These are the drawbacks of the conventional cables.
Generally, this invention provides a power cable in which such drawbacks are alleviated and a method is pro-vided for prevention of "water tree" in the insulation layer of the cable.
The mechanism of the initiation and development of the "water tree" phenomenon has not been previously known.
The present inventors, however, have successfully clarified the mechanism and then arrived at the method of this inven-tion preventing the occurrence of "water tree".
"Water tree" takes place where the electric fieldis strong and a mass of minute voids filled with water is formed. The voids are formed when the chemical potential~w of the water contained in the minute voids is decreased by an electric field. This can be expressed in the following formula:
~w = ~o ~ 2 o(7p)TEl _____--- (1) In Formula (1) above,~O represents the chemical potential of water in the minute voids when there is no electric field; ~ the specific inductive capacity of water;
~O the dielectric constant of vacuum; p the density of water;
El the electric field in a mass of minute voids filled with water; and T the temperature.
In Formula (1), (~ap)T ~ 0 ..
.
Therefore, ~w~ and the water where there is no electric field, namely external water, enters and diffuses into the minute voids. As a result of this, the minute voids increase to form the "water tree".
Assuming that the minute voids are of spherical shape and that the electric field in the insulation of the cable is Eo, the value of El can be obtained from the following formula:
E = 3~ Eo _______- (2) ~2 + 2~1 wherein 2 = C_ j-~/w~o (complex specific inductive capacity) -------- (3) a: conductivity of water w: angular frequency As apparent from Formula (1), the smaller the value of El, the lower the growth rate of the "water tree"
will be. Accordingly, "water tree" can be prevented by making the value of El smaller.
In accordance with this invention, an electrolyte which dissolves in water and increases the electric conduc-tivity of the water is added to the insulation material duringpreparation of the insulator to provide a small value of El 80 that "water tree" can be prevented. In other words, the principle that El in Formula (2) becomes smaller as ~ in Formula (3) becomes greater is utilized in the invention.
: .
. . : . .. : . -- : - : - .
- - : ' - '' ~ - : .
~057043 The invention will become more apparent from the following description:
Any inorganic or organic matter that dissolves in water to increase the electric conductivity of the water may be employed as the electrolyte. The preferred electro-lytes for use accoxding to the invention include strong elec-trolytes as for example sodium chlorlde, sodium sulfate, potassium chloride, potassium sulfate, other alkali metal salts, alkali earth metal salts, ammonium chloride and other ammonium salts, cupric sulfate and other metal salts, sodium acetate, other salts of other carboylic acid, salts of organic sulfonic acids, etc., of which sodium sulfate is most effec-tive in preventing the "water tree". These electrolytes neither move in the insulation, nor enter into the insulation.
The quantity of the electrolyte to be added is at least 10 7% by weight of the insulation material. Addi-tion of the electrolyte in excessive quantities would produce an adverse effect in terms of the insulation characteristics and the infiltration of water due to osmotic pressure. To avoid this, the amount added should be less than 1% by weight of the insulation material.
To ensure an effective prevention of "water tree", it is also preferable to disperse the electrolyte as evenly as possible, in the form of micro-particles of less than several~m in the plastic material which is used to form the insulation. The best results can be obtained by the use of - 10~7043 plastic insulation formed with plastic material prepared with the micro-particles of the electrolyte evenly dispersed therein.
The process for achieving even dispersion of the minute particles of an electrolyte measuring less than severalJ~m may be selected from the following:
(1) Mixing of micro-particles of electrolyte and the insulation material in a mixer extruder called "Brabender Plastograph" (Trade Mark) or by rolls or the like;
(2) Dissolving the particles of electrolyte in, for example, water or alcohol, and mixing the solution with the insulation material by suitable means as for example rolls or the mixer extruder called "Brabender Plastograph"
(Trade Mark);
~ 3) Immersing pelletized insulation material into the aforementioned solution. Then, after the micro-particles have been made to stick to the surfaces of the pellets by evaporation of the solvent, molding the insulation by a conventional process using an extruder or the like;
(4) Adding the aforementioned particles of electrolyte to additives usually used with the insulation materials. The mixture is then used in molding the insulation.
The electrolyte material can be added by any of the foregoing processes. Furthermore, in the case of insu-lations that are molded by a method other than extrusion _5_ B-' l~D57043 molding, as for example mold joints, the electrolyte material may be added beforeh~nd to the plastic tape which is a mold material, or the micro-particles of the electrolyte may be allowed to stick to the tape surface beforehand. With this arrangement the "water tree" resulting from any flaws in the adhesive surfaces can be effectively prevented.
The features and advantages of this invention will more fully appear from the following detailed descrip-tion taken in connection with the accompanying drawing which is a cross-sectional view illustrating a plastic insulated power cable.
In the drawing, the reference numeral 1 indicates a core conductor and 3 a plastic insulation layer. Normally a semiconductive layer 2 is provided between the core conduc-tor 1 and the plastic insulation layer 3. Outwardly of the insulation layer 3, there is provided a plastic sheath 6, made for example of polyvinyl chloride, there being another semiconductive layer 4 and a screening layer 5 of copper tape therebetween.
When the present invention is applied to the plastic insulated power cable illustrated in the drawing, however, the screening layer 5 is no longer required and can be omitted. Then, the structure of the cable can be simplified with the electrolyte mixed in the plastic insulation layer 3 and with the insulation arranged round the conductor 1.
The particular advantages to the plastic insulated --`` 10~7043 power cable prepared in accor~ance with this invention include:
(1) The use of a metal sheath for preventing the infiltration of water is no longer required.
(2) "Water tree" can be prevented even if there are foreign matter and voids in the insulation layer or flaws on the surface of the insulation layer and the semiconductive layer such as protrusionsor the like.
(Trade Mark);
~ 3) Immersing pelletized insulation material into the aforementioned solution. Then, after the micro-particles have been made to stick to the surfaces of the pellets by evaporation of the solvent, molding the insulation by a conventional process using an extruder or the like;
(4) Adding the aforementioned particles of electrolyte to additives usually used with the insulation materials. The mixture is then used in molding the insulation.
The electrolyte material can be added by any of the foregoing processes. Furthermore, in the case of insu-lations that are molded by a method other than extrusion _5_ B-' l~D57043 molding, as for example mold joints, the electrolyte material may be added beforeh~nd to the plastic tape which is a mold material, or the micro-particles of the electrolyte may be allowed to stick to the tape surface beforehand. With this arrangement the "water tree" resulting from any flaws in the adhesive surfaces can be effectively prevented.
The features and advantages of this invention will more fully appear from the following detailed descrip-tion taken in connection with the accompanying drawing which is a cross-sectional view illustrating a plastic insulated power cable.
In the drawing, the reference numeral 1 indicates a core conductor and 3 a plastic insulation layer. Normally a semiconductive layer 2 is provided between the core conduc-tor 1 and the plastic insulation layer 3. Outwardly of the insulation layer 3, there is provided a plastic sheath 6, made for example of polyvinyl chloride, there being another semiconductive layer 4 and a screening layer 5 of copper tape therebetween.
When the present invention is applied to the plastic insulated power cable illustrated in the drawing, however, the screening layer 5 is no longer required and can be omitted. Then, the structure of the cable can be simplified with the electrolyte mixed in the plastic insulation layer 3 and with the insulation arranged round the conductor 1.
The particular advantages to the plastic insulated --`` 10~7043 power cable prepared in accor~ance with this invention include:
(1) The use of a metal sheath for preventing the infiltration of water is no longer required.
(2) "Water tree" can be prevented even if there are foreign matter and voids in the insulation layer or flaws on the surface of the insulation layer and the semiconductive layer such as protrusionsor the like.
(3) Since the electrolyte to be added for the purpose of preventing "water tree" is available at a low cost, the use of it causes negligible increase in the cost of material. Such increase in the cost of material is only about 1% of, for example, the cost of a cros~-linked poly-ethylene insulated power cable, while the metal sheath which is employed conventionally to prevent "water tree" causes an increase in cost of 100%.
(4) The addition of the electrolyte does not cause any increase in weight and any difficulty in the work with the cable.
(5) The electric characteristics of the power cable are unaffected by the addition of the electrolyte.
The following description covers some of the preferred embodiments of this invention by way of examples:
Micro-particles (grain size not exceeding l~ m) of sodium chloride, sodium sulfate, ammonium chloride, copper sulfate or sodium acetate were added in the proportions shown ' ' '' . :. ' - ' - :
in Table 1 and mixed with DCP (di-cumyl peroxide) which is employed as a cross-linking agent for polyethylenP. Using each mixture, a cross-linked polyethylene insulated power cable of the class of 6 KV was prepared by a conventional method. Each of the power cable samples prepared in this man-ner was subjected to a test carried out by immersing it in water and applying high voltage of 8 KV thereto for a period of 180 days. After the test, the samples were checked for "water tree". However, no samples showed occurrence of 'Iwater tree", while a sample of power cable which had been prepared without addition of electrolyte showed the occur-rence of "water tree" as shown in Table 1 as a comparison example.
Electrolyte added Amount added to DCP (wt %) "Watbr Tree"
NaCl 0.01 None " O.1 "
" 1 1' a2S4 0 05 " 0.1 "
NH4C1 0.1 CuSO4 0.2 ,.
Sodium acetate 0.5 "
Not added -- Occurred , .
1~D57043 Micro-particles of sodium sulfate of grain size not exceeding l~m were mixed with polyethylene in a propor-tion of 0.01% using a "Brabender Plastograph". Using this mixture, a cross-linked polyethylene cable of the class of
The following description covers some of the preferred embodiments of this invention by way of examples:
Micro-particles (grain size not exceeding l~ m) of sodium chloride, sodium sulfate, ammonium chloride, copper sulfate or sodium acetate were added in the proportions shown ' ' '' . :. ' - ' - :
in Table 1 and mixed with DCP (di-cumyl peroxide) which is employed as a cross-linking agent for polyethylenP. Using each mixture, a cross-linked polyethylene insulated power cable of the class of 6 KV was prepared by a conventional method. Each of the power cable samples prepared in this man-ner was subjected to a test carried out by immersing it in water and applying high voltage of 8 KV thereto for a period of 180 days. After the test, the samples were checked for "water tree". However, no samples showed occurrence of 'Iwater tree", while a sample of power cable which had been prepared without addition of electrolyte showed the occur-rence of "water tree" as shown in Table 1 as a comparison example.
Electrolyte added Amount added to DCP (wt %) "Watbr Tree"
NaCl 0.01 None " O.1 "
" 1 1' a2S4 0 05 " 0.1 "
NH4C1 0.1 CuSO4 0.2 ,.
Sodium acetate 0.5 "
Not added -- Occurred , .
1~D57043 Micro-particles of sodium sulfate of grain size not exceeding l~m were mixed with polyethylene in a propor-tion of 0.01% using a "Brabender Plastograph". Using this mixture, a cross-linked polyethylene cable of the class of
6 KV similar to those described in Example 1 was prepared.
The cable was subjected to water immersion and high voltage of 8 KV for 180 days in the same manner as in Example 1.
However, no "water tree" occurred.
An aqueous solution of sodium sulfate was prepared and polyethylene pellets immersed therein and then removed.
The aqueous solution adhering to the surfaces of the pellets was quickly dried with hot air. The proportion of sodium sulfate deposited and adhering to the pellet surfaces to that of the polyethylene was 0.02~ by weight. A power cable similar to those of Example 1 was prepared using the poly-ethylene pellets. The power cable did not show any "water tree" after it had undergone the same test as in Example 1.
An aqueous solution of sodium sulfate was prepared and the solution added while polyethylene was subjected to a roll mixing process. The solution was evaporated during the process and the sodium sulfate mixed with the polyethylene.
The polyethylene composition thus obtained was used for the , . ' ' - . - ~
.
~05~043 preparation of a power cable, which was subjected to the test in the same manner as in Example 1. However, no "water tree"
was formed.
Sodium chloride or sodium sulfate were adhered to the surfaces of polyethylene pellets by the same method as in Example 3. Then, using the pellets, cross-linkable poly-ethylene tapes for mold joints were prepared. Following this, cross-linked polyethylene mold joints of the class of 20 XV
were prepared from the tapes. Each joint sample thus obtained was subjected to a test carried out for a period of 12 months by placing the joint in water and applying high voltage of 8 KV
thereto. Table 2 shows the test results for those samples in comparison with a sample which was prepared without such additives. Table 2 also shows a sample which was prepared by adhering sodium sulfate to the tape surface only.
AdditivesRatio to polyethylene, wt % "Water tree"
NaCl 0.05 None " 0.1 "
Na2S4 0 05 ~ O.1 "
No additive --- Occurred Na2SO4 only to 0.01 None tape surface ~ 1~)57043 As shown in Examples 1 through 5, "water tree" of the plastic insulations of power cables and accessories can be effectively prevented in accordance with this invention. With the conventionally employed water screening layer such as a metal sheath thus no longer required for preventing "water tree", the invented method gives a great advantage in terms of costs.
E ~ ~LES 6 - 9 AND COMPARISON EXAMPLES 1 AND 2 Cross-linkable polyethylene tapes were prepared from compositions which were obtained by blending 0.002 part by weight (Example 6), 0.02 part by weight (Example 7), 0.2 part by weight (Example 8) and 0.5 part by weight (Example 9) respectively of sodium sulfate with 100 parts by weight of polyethylene. Using each of the non-bridged polyethylene tapes, a mold joint part of 20 KV cross-linked polyethylene insulated power cable was prepared.
In addition to those joint part samples, joint parts were also prepared, for comparison, one from a cross-linkable polyethylene tape (Comparison Example 1) and another from another cross-linkable polyethylene tape made of poly-ethylene containing a cross-linking agent with 0.5 part by weight of talc blended in 100 parts of the polyethylene (Comparison Example 2). These comparison samples of mold joint parts of 20 KV cross-linked polyethylene insulated power cables were prepared in the same manner as the other samples.
The six different mold joint parts of 20 RV
~ .
, .' ' ' : ' .
,~ . .
.
. ', ' ~
: . :
: .
cross-linked polyethylene insulated power cables prepared as described were subjected to tests in water with high voltage of 8 KV applied for a period of 18 months. After the test, each mold joint sample was examined for the presence or absence of "water tree" and also for dielectric strength.
The test results are shown in Table 3.
TA~3LE 3 Kinds of "Water tree" in Dielectric strength mold_~ints insulator layer Before test Aftertest Sample of Example 6 None More than AC180KV AC190 KV
Sample of Example 7 " " " " AC200 KV
Sample of Example 8 " " " " AC180 KV
Sample of Example 9 " " " " AC200 KV
Comparison Example 1 Occurred " " " AC 80 KV
Comparison Example 2 " " " " AC 70 KV
B
- -
The cable was subjected to water immersion and high voltage of 8 KV for 180 days in the same manner as in Example 1.
However, no "water tree" occurred.
An aqueous solution of sodium sulfate was prepared and polyethylene pellets immersed therein and then removed.
The aqueous solution adhering to the surfaces of the pellets was quickly dried with hot air. The proportion of sodium sulfate deposited and adhering to the pellet surfaces to that of the polyethylene was 0.02~ by weight. A power cable similar to those of Example 1 was prepared using the poly-ethylene pellets. The power cable did not show any "water tree" after it had undergone the same test as in Example 1.
An aqueous solution of sodium sulfate was prepared and the solution added while polyethylene was subjected to a roll mixing process. The solution was evaporated during the process and the sodium sulfate mixed with the polyethylene.
The polyethylene composition thus obtained was used for the , . ' ' - . - ~
.
~05~043 preparation of a power cable, which was subjected to the test in the same manner as in Example 1. However, no "water tree"
was formed.
Sodium chloride or sodium sulfate were adhered to the surfaces of polyethylene pellets by the same method as in Example 3. Then, using the pellets, cross-linkable poly-ethylene tapes for mold joints were prepared. Following this, cross-linked polyethylene mold joints of the class of 20 XV
were prepared from the tapes. Each joint sample thus obtained was subjected to a test carried out for a period of 12 months by placing the joint in water and applying high voltage of 8 KV
thereto. Table 2 shows the test results for those samples in comparison with a sample which was prepared without such additives. Table 2 also shows a sample which was prepared by adhering sodium sulfate to the tape surface only.
AdditivesRatio to polyethylene, wt % "Water tree"
NaCl 0.05 None " 0.1 "
Na2S4 0 05 ~ O.1 "
No additive --- Occurred Na2SO4 only to 0.01 None tape surface ~ 1~)57043 As shown in Examples 1 through 5, "water tree" of the plastic insulations of power cables and accessories can be effectively prevented in accordance with this invention. With the conventionally employed water screening layer such as a metal sheath thus no longer required for preventing "water tree", the invented method gives a great advantage in terms of costs.
E ~ ~LES 6 - 9 AND COMPARISON EXAMPLES 1 AND 2 Cross-linkable polyethylene tapes were prepared from compositions which were obtained by blending 0.002 part by weight (Example 6), 0.02 part by weight (Example 7), 0.2 part by weight (Example 8) and 0.5 part by weight (Example 9) respectively of sodium sulfate with 100 parts by weight of polyethylene. Using each of the non-bridged polyethylene tapes, a mold joint part of 20 KV cross-linked polyethylene insulated power cable was prepared.
In addition to those joint part samples, joint parts were also prepared, for comparison, one from a cross-linkable polyethylene tape (Comparison Example 1) and another from another cross-linkable polyethylene tape made of poly-ethylene containing a cross-linking agent with 0.5 part by weight of talc blended in 100 parts of the polyethylene (Comparison Example 2). These comparison samples of mold joint parts of 20 KV cross-linked polyethylene insulated power cables were prepared in the same manner as the other samples.
The six different mold joint parts of 20 RV
~ .
, .' ' ' : ' .
,~ . .
.
. ', ' ~
: . :
: .
cross-linked polyethylene insulated power cables prepared as described were subjected to tests in water with high voltage of 8 KV applied for a period of 18 months. After the test, each mold joint sample was examined for the presence or absence of "water tree" and also for dielectric strength.
The test results are shown in Table 3.
TA~3LE 3 Kinds of "Water tree" in Dielectric strength mold_~ints insulator layer Before test Aftertest Sample of Example 6 None More than AC180KV AC190 KV
Sample of Example 7 " " " " AC200 KV
Sample of Example 8 " " " " AC180 KV
Sample of Example 9 " " " " AC200 KV
Comparison Example 1 Occurred " " " AC 80 KV
Comparison Example 2 " " " " AC 70 KV
B
- -
Claims (13)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A "water tree" free electric power cable or accessory thereof comprising a conductor enclosed in a sheath of plastic insulation wherein the plastic insulation has dispersed therein or adhered thereto a water soluble strong electrolyte capable of increasing the conductivity of water, in an amount of 10 7 to 1 percent by weight.
2. The insulated power cable or accessory of claim 1 wherein the plastic insulation is selected from the group of polyethylene, cross-linked polyethylene, ethylene-propylene rubber and butyl rubber.
3. The insulated power cable or accessory of claim 1 wherein the electrolyte is selected from the group of sodium chloride, sodium sulfate or mixtures thereof.
4. The insulated power cable or accessory of claim 1 wherein the electrolyte is selected from salts of the alkali metals, alkaline earth metals, copper, ammonia, carboxylic acids and organic sulfonic acids.
5. The insulated power cable or accessory of claim 4 wherein the electrolyte is selected from the group of sodium chloride, sodium sulfate, potassium chloride, potassium sulfate, ammonium chloride, cupric sulfate and sodium acetate.
6. The insulated power cable or accessory thereof according to claim 1 wherein the insulation or a portion thereof is a thin layer of tape having the strong electro-lyte adhered to the surface thereof.
7. A method for preventing the deterioration of plastic insulation called "water tree" in-electric power cable or accessories thereof which comprises adding to the plastic insulators material in an amount of 10-7 to 1% by weight of the insulation material, micro-particles of a strong electro-lyte which dissolves in water to increase the electric con-ductivity of the water.
8. The method of claim 7 wherein the insulation material is selected from the group of polyethylene, cross-linked polyethylene, ethylene-propylene rubber and butyl rubber.
9. The method of claim 7 wherein the strong electro-lyte is sodium chloride or sodium sulfate or mixtures thereof.
10. An improved method for the manufacture of plastic insulated power cable or an accessory thereof to prevent the deterioration of the insulation called "water tree", the improvement comprising adding to the plastic insulation material before forming of the insulation, a strong electrolyte capable of increasing the electrical conductivity of water, in an amount of 10-7 to 1% by weight of the plastic insulation.
11. The improved method according to claim 10 wherein the strong electrolyte is caused to adhere to the surfaces of pelletized plastic insulation material in the form of micro-particles and the pellets are then molded into insulating material about a conductive member to form a power cable.
12. The improved method according to claim 10 wherein the strong electrolyte is added to an additive for the plastic insulation material before forming of the insulation.
13. The improved process of claim 10 wherein the strong electrolyte is dissolved in a solvent, the solution so obtained is added to plastic insulation material, the solvent is then evaporated to leave the electrolyte in the form of micro-particles dispersed in the insulation material, and the insulation is then formed from the mixture.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA233,938A CA1057043A (en) | 1975-08-22 | 1975-08-22 | Power cable |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA233,938A CA1057043A (en) | 1975-08-22 | 1975-08-22 | Power cable |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1057043A true CA1057043A (en) | 1979-06-26 |
Family
ID=4103870
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA233,938A Expired CA1057043A (en) | 1975-08-22 | 1975-08-22 | Power cable |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1057043A (en) |
-
1975
- 1975-08-22 CA CA233,938A patent/CA1057043A/en not_active Expired
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