Transformer paper and other non-conductive transformer components
View Patent ↗A transformer paper comprising polyetherimide fibers is disclosed, along with a method of making the transformer paper and articles.
1. A transformer paper comprising a consolidated product of a fiber composition, the fiber composition comprising, based on the total weight of fibers in the fiber composition:
35 to 70 weight % of polyetherimide homopolymer fiber, polyetherimide copolymer fiber, or a combination of the foregoing;
at least 5 weight % of binder fibers comprising aromatic polyamide fibrids, aromatic polyamide fibers, or a combination comprising at least one of the foregoing; and
5 to 30 weight % of liquid crystal polymer fiber,
wherein the binder fibers comprise less than 10 weight % of a polycarbonate.
2. The transformer paper of claim 1 , wherein the polyimide retains at least 90% of its molecular weight upon exposure to silicone, vegetable or mineral oil at a temperature of 150 to 200° C.
3. The transformer paper of claim 1 , wherein the polyimide retains at least 90% of its molecular weight upon exposure to silicone, vegetable, or mineral oil at a temperature of 180° C.
4. The transformer paper of claim 1 , wherein the consolidated product has
a resistivity of at least 1000 MOhm-cm;
an electrical breakdown strength of at least 600 Volt/mil;
a thermal capability exceeding the standards for NEMA Class F (155° C.) and NEMA Class H (180° C.);
a tear strength, measured as Elmendorf tear strength of at least 85 mN; and
a thickness of more than 0 to less than 100 millimeters.
5. The transformer paper of claim 1 , wherein the consolidated product has a porosity sufficient to allow transformer oil to circulate through and conduct gases out of the consolidated product.
6. The transformer paper of claim 5 , wherein the porosity is 10 to 90% by volume.
7. The transformer paper of claim 1 , wherein the polyetherimide comprises structural units of the formula
wherein in the foregoing formulas,
n is greater than 1,
R is an aromatic hydrocarbon group having 6 to 20 carbon atoms, a halogenated derivative thereof, a straight or branched chain alkylene group having 2 to 10 carbon atoms, a cycloalkylene group having 3 to 20 carbon atoms, or a divalent group of the formula
wherein Q 1 is a bond, —O—, —S—, —C(O)—, —SO2-, —SO—, and —C y H 2y — and a halogenated derivative thereof wherein y is 1 to 5; and
Z 1 is each independently an aromatic C 6-24 monocyclic or polycyclic moiety optionally substituted with 1 to 6 C 1-8 alkyl groups, 1 to 8 halogen atoms, or a combination comprising at least one of the foregoing.
8. The transformer paper of claim 7 , wherein Z 1 is a divalent group of formula
wherein Q a is each independently a single bond, —O—, —S—, —C(O)—, —SO 2 —, —SO—, and —C y H 2y — and a halogenated derivative thereof wherein y is an integer from 1 to 5, and
R is a divalent group of the formula
and a combination comprising at least one of the foregoing, wherein Q 1 is a single bond, —O—, —S—, —C(O)—, —SO 2 —, —SO—, —C y H 2y — or a halogenated derivative thereof wherein y is an integer from 1 to 5.
9. The transformer paper of claim 7 , wherein Z is 2,2-(4-phenylene)isopropylidene and R is m-phenylene, p-phenylene diarylsulfone, or a combination comprising at least one of the foregoing.
10. The transformer paper of claim 1 , wherein the aromatic polyamide is poly(p-phenylene terephthalamide), poly(p-phenylene terephthalimide-co-3′4′-oxydiphenylene terephthalimide), or a combination comprising at least one of the foregoing aromatic polyamides.
11. The transformer paper of claim 1 , wherein the liquid crystal polymer is poly(4-hydroxybenzoic acid-co-6-hydroxy-2-napthoic acid).
12. A method of forming the transformer paper of claim 1 , comprising
forming a layer from a slurry comprising
a suspension solvent; and
a fiber composition comprising a combination of
35 to 70 wt. % of polyetherimide fibers;
at least 5 wt. % of aromatic polyamide fibers; and
5 to 30 wt. % of liquid crystal polymer fibers,
wherein the wt. % of the fibers is based on the total weight of the fibers in the fiber composition;
dewatering the layer; and
consolidating the layer to form the fibrous substrate.
13. The method of claim 12 , wherein the consolidating is conducted on a static press.
14. The method of claim 12 , wherein the layer is exposed to subatmospheric pressure during at least a portion of the process.
15. The method of claim 12 , wherein the consolidating is conducted in a continuous roll press.
16. A transformer component comprising the transformer paper of claim 1 .
17. The transformer component of claim 16 , wherein the component is a porous paper, nonporous paper, creped paper, stick paper, spacer, pressboard, or a rigid structure.
18. The transformer component of claim 16 having a porosity of greater than 0 to less than 120 s·in 2 /dl.