Polymer composition and a power cable comprising the polymer composition
An alternating current (AC) power cable includes a conductor surrounded by at least an inner semiconductive layer including a first semiconductive composition, an insulation layer including a polymer composition, an outer semiconductive layer including a second semiconductive composition, and optionally a jacketing layer including a jacketing composition, in that order. The polymer composition of the insulation layer includes an unsaturated low density polyethylene (LDPE) copolymer of ethylene with one or more polyunsaturated comonomers and a crosslinking agent. The polymer composition of the insulation layer has a dielectric loss expressed as tan δ (50 Hz) of 12.0×10 −4 or less, when measured at 25 kV/mm and 130° C. according to “Test for Tan δ measurements on 10 kV cables”.
1. An alternating current (AC) power cable, comprising a conductor surrounded by at least an inner semiconductive layer comprising a first semiconductive composition, an insulation layer comprising a polymer composition, an outer semiconductive layer comprising a second semiconductive composition in that order, wherein the polymer composition of the insulation layer comprises a polyolefin and a crosslinking agent, wherein the polymer composition contains vinyl groups in an amount of at least 0.3/1000 carbon atoms and wherein the polymer composition of the insulation layer has a dielectric loss expressed as tan δ (50 Hz) of 12.0×10 −4 or less, when measured at 25 kV/mm and 130° C. according to “Test for Tan δ measurements on 10 kV cables” as described in the description part under “Determination methods”.
2. The cable according to claim 1 , wherein the polymer composition of the insulation layer has a dielectric loss expressed as tan δ (50 Hz) of 11.0×10 −4 or less, when measured at 25 kV/mm and 130° C. according to “Test for Tan δ measurements on 10 kV cables” as described in the description part under “Determination methods”.
3. The cable according to claim 1 , wherein the polymer composition of the insulation layer has a dielectric loss expressed as tan δ (50 Hz) of 0.01 10.0×10 −4 , when measured at 25 kV/mm and 130° C. according to “Test for Tan δ measurements on 10 kV cables” as described in the description part under “Determination methods”.
4. The cable according to claim 1 , wherein the polyolefin is obtainable by a high pressure process comprising:
(a) compressing one or more monomer(s) under pressure in a compressor, using a compressor lubricant for lubrication,
(b) polymerising a monomer optionally together with one or more comonomer(s) in a polymerisation zone,
(c) separating the obtained polyolefin from the unreacted products and recovering the separated polyolefin in a recovery zone,
wherein in step a) the compressor lubricant comprises a mineral oil.
5. The cable according to claim 4 , wherein the mineral oil is a white mineral oil which meets the requirements given for white mineral oil in European Directive 2002/72/EC of 6 Aug. 2002, Annex V, for plastics used in food contact.
6. The cable according to claim 4 , wherein the compressor lubricant comprises white oil as the mineral oil and is suitable for production of polymers for food or medical industry.
7. The cable according to claim 1 , wherein the crosslinking agent is peroxide.
8. The cable according to claim 1 , wherein the polyolefin is a saturated LDPE homopolymer or a saturated LDPE copolymer of ethylene with one or more comonomer(s) or an unsaturated LDPE polymer, which is selected from an unsaturated LDPE homopolymer or an unsaturated LDPE copolymer of ethylene with one or more comonomer(s).
9. The cable according to claim 1 , wherein the polyolefin is an unsaturated LDPE homopolymer or an unsaturated LDPE copolymer of ethylene with at least one polyunsaturated comonomer and optionally with one or more other comonomer(s).
10. The cable according to claim 1 , wherein each of the inner and outer semiconductive composition comprises independently a conductive filler.
11. The cable according to claim 1 , wherein the cable further comprises a jacketing layer comprising a jacketing composition.
12. The cable according to claim 1 , wherein at least the polymer composition of the insulation layer is crosslinked in the presence of said crosslinking agent.
13. The cable according to claim 1 , wherein at least the first semiconductive composition of the inner semiconductive layer and the polymer composition of the insulation layer are crosslinked.
14. The cable according to claim 1 , which is a MV, HV or EHV AC power cable.
15. The cable according to claim 11 , wherein the jacketing composition is over the outer semiconductive layer.
16. A process for producing an alternating current (AC) power cable according to claim 1 , comprising:
applying on a conductor an inner semiconductive layer comprising a first semiconductive composition, an insulation layer comprising a polymer composition, an outer semiconductive layer comprising a second semiconductive composition, and optionally a jacketing layer comprising a jacketing composition.