GB2154783A - Electric cables - Google Patents

Electric cables Download PDF

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Publication number
GB2154783A
GB2154783A GB08504380A GB8504380A GB2154783A GB 2154783 A GB2154783 A GB 2154783A GB 08504380 A GB08504380 A GB 08504380A GB 8504380 A GB8504380 A GB 8504380A GB 2154783 A GB2154783 A GB 2154783A
Authority
GB
United Kingdom
Prior art keywords
mineral
methyl hydrogen
powder
hydrogen polysiloxane
magnesia
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.)
Granted
Application number
GB08504380A
Other versions
GB2154783B (en
GB8504380D0 (en
Inventor
Ian Oswald Wilson
John Thomas Roberts
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Balfour Beatty PLC
Original Assignee
BICC PLC
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by BICC PLC filed Critical BICC PLC
Publication of GB8504380D0 publication Critical patent/GB8504380D0/en
Publication of GB2154783A publication Critical patent/GB2154783A/en
Application granted granted Critical
Publication of GB2154783B publication Critical patent/GB2154783B/en
Expired legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
    • H01B7/28—Protection against damage caused by moisture, corrosion, chemical attack or weather
    • H01B7/282—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable
    • H01B7/285—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable by completely or partially filling interstices in the cable
    • H01B7/288—Preventing penetration of fluid, e.g. water or humidity, into conductor or cable by completely or partially filling interstices in the cable using hygroscopic material or material swelling in the presence of liquid
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
    • H01B3/10—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances metallic oxides
    • H01B3/105—Wires with oxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
    • H01B3/46—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes silicones
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A30/00—Adapting or protecting infrastructure or their operation
    • Y02A30/14—Extreme weather resilient electric power supply systems, e.g. strengthening power lines or underground power cables

Landscapes

  • Chemical & Material Sciences (AREA)
  • Polymers & Plastics (AREA)
  • Health & Medical Sciences (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Organic Insulating Materials (AREA)
  • Insulated Conductors (AREA)

Abstract

A mineral insulated cable comprises a mineral insulating powder impregnated with a methyl hydrogen polysiloxane, preferably in liquid form. The methyl hydrogen polysiloxane assists to render the powder hydrophobic, by limiting the ingress of moisture, and preventing reduction in insulation resistance on exposure to atmospheric humidity. A preferred form of mineral insulating powder is magnesia. The percentage, by weight, of the methyl hydrogen polysiloxane is preferably in the range 0.005% to 5% of the mineral insulating powder. The polysiloxane withstands higher annealing temperatures than the prior art siloxanes.

Description

SPECIFICATION Electric cables This invention reiates to electric cables of the kind comprising at least one electric conductor and an outer metallic sheath, separated from one another by a compacted mineral, electrically insulating, powder. For convenience, this type of cable will hereinafter be referred to as mineral insulated cable.
In accordance with the invention, a mineral insulated cable comprises a mineral insulating powder impregnated with a methyl hydrogen polysiloxane. The methyl hydrogen polysiloxane assists to render the powder hydrophobic, by limiting the ingress of moisture, and preventing reduction in insulation resistance on exposure to atmospheric humidity.
This additive has the advantage over known additives (for example, those disclosed in UK Patent Application No. 2106307A) of being capable of withstanding higher annealing temperatures which may be required during the manufacture of the cable.
Preferably the methyl hydrogen polysiloxane is in liquid form.
The mineral insulating powder may be a quartz-silica sand or limestone. Preferably, however, the powder is magnesia.
The percentage, by weight, of the methyl hydrogen polysiloxane is preferably in the range 0.005% to 5% of the mineral insulating powder. This percentage is that at the start of manufacture of the cable, before any drawing or annealing. In the case where the magnesia is caustic (lightly burnt) magnesia, the percentage range is preferably 0.5% to 5%. It has been found that additions below 0.5% are less effective in preventing moisture ingress and loss of insulation resistance. In the case where the magnesia is dead-burnt or fused magnesia (which has a smaller particle surface area than caustic magnesia), the percentage range is preferably 0.005% to 1%. It has been found that above 1% the methyl hydrogen polysiloxane adversely affects the fiow of powder during manufacture of the cable.
The cable may be manufactured by any of the known techniques for manufacturing mineral insulated cable. The methyl hydrogen polysiloxane may be added to the powder as the powder is added during manufacture of the cable. Alternatively, the methyl hydrogen polysiloxane may be pre-mixed with the powder before the powder is added during manufacture of the cable.
In accordance with another aspect of the invention, a mineral insulated cable comprises a mineral insulating powder of dead-burnt or fused magnesia, wherein the magnesia is impregnated with a hydrophobic material. The hydrophobic material is preferably a siloxane, preferably methyl hydrogen polysiloxane, and preferably in liquid form. The hydrophobic material is preferably in the percentage range, by weight, of 0.005% to 1 % of powder.
EXAMPLE 2% by weight of Dow Corning 1107 (methyl hydrogen polysiloxane) was pre-mixed with caustic magnesia. Similarly 2% by weight of MS 200/20 cS (dimethylpolysiloxane manufactured by Dow Corning Limited) was pre-mixed with caustic magnesia. Both samples were used to manufacture mineral insulated cable under identical conditions.
Lengths of each cable were annealed in a tube furnace for 1+ hours at temperatures of 500"C to 650"C in increments of 50"C. Each length of cable was then subjected to a water repellency test by immersing an end in water for one minute. Surplus water was wiped off and the insulation resistance of each length was measured. The criteria adopted for the evaluation of the deterioration temperature of each silicone was that the initial insulation resistance of 10,000 megohms should be retained, or should recover to this value within 10 minutes. The deterioration temperature of the methyl hydrogen polysiloxane was found to be 650"C, whereas the deterioration temperature of the dimethylpolysiloxane was found to be only 500"C.
1. A mineral insulated cable comprising a mineral insulating powder impregnated with a methyl hydrogen polysiloxane.
2. A mineral insulated cable according to Claim 1, wherein the methyl hydrogen polysiloxane is in liquid form.
3. A mineral insulated cable according to Claim 1 or Claim 2, wherein the percentage, by weight, of the methyl hydrogen polysiloxane is 0.005% to 5% of the mineral insulating powder.
4. A mineral insulated cable according to any of Claims 1 to 3, wherein the mineral insulating powder is magnesia.
5. A mineral insulated cable according to Claim 4 wherein the mineral insulating powder is caustic magnesia.
6. A mineral insulated cable according to Claim 5, wherein the percentage, by weight, of the methyl hydrogen polysiloxane is 0.5% to 5% of the mineral insulating powder.
7. A mineral insulated cable according to Claim 4, wherein the mineral insulating powder is dead-burnt magnesia.
8. A mineral insulated cable according to Claim 7, wherein the percentage, by weight, of the methyl hydrogen polysiloxane is 0.005% to 1% of the mineral insulating powder.
9. A mineral insulated cable substantially as hereinbefore described.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electric cables This invention reiates to electric cables of the kind comprising at least one electric conductor and an outer metallic sheath, separated from one another by a compacted mineral, electrically insulating, powder. For convenience, this type of cable will hereinafter be referred to as mineral insulated cable. In accordance with the invention, a mineral insulated cable comprises a mineral insulating powder impregnated with a methyl hydrogen polysiloxane. The methyl hydrogen polysiloxane assists to render the powder hydrophobic, by limiting the ingress of moisture, and preventing reduction in insulation resistance on exposure to atmospheric humidity. This additive has the advantage over known additives (for example, those disclosed in UK Patent Application No. 2106307A) of being capable of withstanding higher annealing temperatures which may be required during the manufacture of the cable. Preferably the methyl hydrogen polysiloxane is in liquid form. The mineral insulating powder may be a quartz-silica sand or limestone. Preferably, however, the powder is magnesia. The percentage, by weight, of the methyl hydrogen polysiloxane is preferably in the range 0.005% to 5% of the mineral insulating powder. This percentage is that at the start of manufacture of the cable, before any drawing or annealing. In the case where the magnesia is caustic (lightly burnt) magnesia, the percentage range is preferably 0.5% to 5%. It has been found that additions below 0.5% are less effective in preventing moisture ingress and loss of insulation resistance. In the case where the magnesia is dead-burnt or fused magnesia (which has a smaller particle surface area than caustic magnesia), the percentage range is preferably 0.005% to 1%. It has been found that above 1% the methyl hydrogen polysiloxane adversely affects the fiow of powder during manufacture of the cable. The cable may be manufactured by any of the known techniques for manufacturing mineral insulated cable. The methyl hydrogen polysiloxane may be added to the powder as the powder is added during manufacture of the cable. Alternatively, the methyl hydrogen polysiloxane may be pre-mixed with the powder before the powder is added during manufacture of the cable. In accordance with another aspect of the invention, a mineral insulated cable comprises a mineral insulating powder of dead-burnt or fused magnesia, wherein the magnesia is impregnated with a hydrophobic material. The hydrophobic material is preferably a siloxane, preferably methyl hydrogen polysiloxane, and preferably in liquid form. The hydrophobic material is preferably in the percentage range, by weight, of 0.005% to 1 % of powder. EXAMPLE 2% by weight of Dow Corning 1107 (methyl hydrogen polysiloxane) was pre-mixed with caustic magnesia. Similarly 2% by weight of MS 200/20 cS (dimethylpolysiloxane manufactured by Dow Corning Limited) was pre-mixed with caustic magnesia. Both samples were used to manufacture mineral insulated cable under identical conditions. Lengths of each cable were annealed in a tube furnace for 1+ hours at temperatures of 500"C to 650"C in increments of 50"C. Each length of cable was then subjected to a water repellency test by immersing an end in water for one minute. Surplus water was wiped off and the insulation resistance of each length was measured. The criteria adopted for the evaluation of the deterioration temperature of each silicone was that the initial insulation resistance of 10,000 megohms should be retained, or should recover to this value within 10 minutes. The deterioration temperature of the methyl hydrogen polysiloxane was found to be 650"C, whereas the deterioration temperature of the dimethylpolysiloxane was found to be only 500"C. CLAIMS
1. A mineral insulated cable comprising a mineral insulating powder impregnated with a methyl hydrogen polysiloxane.
2. A mineral insulated cable according to Claim 1, wherein the methyl hydrogen polysiloxane is in liquid form.
3. A mineral insulated cable according to Claim 1 or Claim 2, wherein the percentage, by weight, of the methyl hydrogen polysiloxane is 0.005% to 5% of the mineral insulating powder.
4. A mineral insulated cable according to any of Claims 1 to 3, wherein the mineral insulating powder is magnesia.
5. A mineral insulated cable according to Claim 4 wherein the mineral insulating powder is caustic magnesia.
6. A mineral insulated cable according to Claim 5, wherein the percentage, by weight, of the methyl hydrogen polysiloxane is 0.5% to 5% of the mineral insulating powder.
7. A mineral insulated cable according to Claim 4, wherein the mineral insulating powder is dead-burnt magnesia.
8. A mineral insulated cable according to Claim 7, wherein the percentage, by weight, of the methyl hydrogen polysiloxane is 0.005% to 1% of the mineral insulating powder.
9. A mineral insulated cable substantially as hereinbefore described.
GB08504380A 1984-02-20 1985-02-20 Electric cables Expired GB2154783B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB848404407A GB8404407D0 (en) 1984-02-20 1984-02-20 Electric cables

Publications (3)

Publication Number Publication Date
GB8504380D0 GB8504380D0 (en) 1985-03-20
GB2154783A true GB2154783A (en) 1985-09-11
GB2154783B GB2154783B (en) 1987-08-19

Family

ID=10556883

Family Applications (2)

Application Number Title Priority Date Filing Date
GB848404407A Pending GB8404407D0 (en) 1984-02-20 1984-02-20 Electric cables
GB08504380A Expired GB2154783B (en) 1984-02-20 1985-02-20 Electric cables

Family Applications Before (1)

Application Number Title Priority Date Filing Date
GB848404407A Pending GB8404407D0 (en) 1984-02-20 1984-02-20 Electric cables

Country Status (1)

Country Link
GB (2) GB8404407D0 (en)

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2056158A (en) * 1979-07-27 1981-03-11 Okazaki Mfg Co Ltd Mineral insulated cable assembly and method of making the same

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2056158A (en) * 1979-07-27 1981-03-11 Okazaki Mfg Co Ltd Mineral insulated cable assembly and method of making the same

Also Published As

Publication number Publication date
GB2154783B (en) 1987-08-19
GB8504380D0 (en) 1985-03-20
GB8404407D0 (en) 1984-03-28

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Legal Events

Date Code Title Description
732E Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977)
PCNP Patent ceased through non-payment of renewal fee

Effective date: 20010220