HIGH VOLTAGE SWIVEL

ARTICULATION PIVOTANTE HAUTE TENSION

English Abstract

The invention relates to a high voltage swivel, comprising an annular outer
element defining a cylindrical chamber around a longitudinal axis and an inner
cylindrical element coaxial with the outer element and rotatable relative to
said outer
element around said longitudinal axis. The inner and outer elements each
comprise at
least two axially spaced electrical conductors which conductors are rotatable
with the
inner and outer elements, the conductors forming at least two pairs placed
with contact
surfaces in mutual electrical contact. One conductor in each pair is provided
at the inner
element, the other at the outer element and being connected to a respective
voltage line
which extends to an input terminal and to an output terminal respectively, the
conductors being surrounded by an insulating material. The invention is
characterised
in that the electrical conductors of the outer element are provided in a
recess in an
annular solid outer insulating ring, the electrical conductors of the inner
element are
provided in a recess in an annular solid inner insulating ring, coaxial with
the outer
ring, the inner and outer insulating rings each defining a boundary surface
extending in
an axial direction, the boundary surfaces of the rings being placed in close
proximity,
the electrical conductors being placed with their contact surfaces at or near
the
boundary surface.

French Abstract

Cette invention se rapporte à une articulation pivotante haute tension qui comprend un élément annulaire extérieur définissant une chambre cylindrique autour d'un axe longitudinal et un élément cylindrique intérieur coaxial avec l'élément extérieur et pouvant tourner par rapport audit élément extérieur autour dudit axe longitudinal. Les éléments intérieur et extérieur comprennent chacun au moins deux conducteurs électriques parallèles. Ces deux conducteurs peuvent tourner avec les éléments intérieur et extérieur, et ils forment au moins deux paires dont les surfaces de contact assurent le contact électrique mutuel. Un conducteur de chaque paire se trouve à l'élément intérieur, l'autre conducteur, à l'élément extérieur, et ils sont raccordés à une ligne de tension respective qui aboutit à une borne d'entrée et à une borne de sortie, respectivement, les conducteurs étant guipés. La présente invention est caractérisée par le fait que les conducteurs électriques de l'élément extérieur occupent une cavité pratiquée dans une bague isolante extérieure pleine. Les conducteurs électriques de l'élément intérieur se trouvent dans une cavité de bague isolante intérieure pleine, coaxiale avec la bague extérieure. Les bagues isolantes intérieure et extérieure définissent une surface limite dans le sens axial, les surfaces limites des bagues étant rapprochées et les conducteurs électriques étant placés avec leurs surfaces de contact à la surface limite ou près de cette surface.

Claims

6
WE CLAIM:
1. High voltage swivel (1), comprising an annular outer element (2)
defining a cylindrical chamber around a longitudinal axis (27) and
an inner cylindrical element (3) coaxial with the outer element (2)
and rotatable relative to said outer element around said
longitudinal axis (27), the inner and outer elements each
comprising at least two axially spaced electrical conductors
(15,16,17,18;28,29,30,31) which conductors are rotatable with
the inner and outer elements (2,3), the conductors forming at
least two pairs (15,28;16,29;17,30;18,31) placed with contact
surfaces in mutual electrical contact, one conductor in each pair
(15,16,17,18) being provided at the inner element (3), the other
(28, 29, 30, 31) at the outer element (2)and being connected to
a respective voltage line (32,33)) which extends to an input
terminal (6) and to an output terminal (7) respectively, the
conductors (15-18,28-31) being surrounded by an insulating
material, characterised in that,
- the electrical conductors (28-31) of the outer element (2)
are provided in a recess in an annular solid outer insulating ring
(8,9,10,11,12),
- the electrical conductors (15-18) of the inner element (3)
are provided in a recess in an annular solid inner insulating ring
(21,22,23,24), coaxial with the outer ring, the inner and outer
insulating rings (8-12,21-24) each defining a boundary surface
(20, 20') extending in an axial direction, the boundary surfaces
of the rings being placed in close proximity, the electrical
conductors being placed with their contact surfaces at or near the
boundary surface (20,20').
2. High voltage swivel (1) according to claim 1, wherein the
conductors (15-18,28-31) at the outer and at the inner element
(2,3) comprise annular contact surfaces.
3. High voltage swivel (1) according to claim 1 or 2, each electrical
conductor being attached to a connector (32,33) extending axially
from the conductor to a connector surface (34), situated in an
enclosure bound by a cover (40) with an opening (50) for fixedly
receiving a power cable (6) and with fastening means (47) for
connecting the cover (40) to the outer element (2), each
connector (32,33) at the connector surface (34) being provided
with a receiving cavity (35,36) for receiving a conducting wire
(38,39) of the power cable (6).

7
4. High voltage swivel (1) according to any one of claims 1, 2, 3, the
insulating ring (8-12;21-24) comprising a solid insulator of a
thermoplastic polymer.
5. High voltage swivel (1) according to claim 4, wherein said
thermoplastic polymer is one or more of PEEK, PES, PTFE and
Teflon®
6. High voltage swivel according to claim 5, the insulating ring
comprising a polyether ether ketone (PEEK) polymer.
7. High voltage swivel (1) according to any one of claims 1 to 5,
wherein the electrical conductors comprise a copper alloy.
8. High voltage swivel (1) according to claim 7 wherein said
electrical conductors comprise MULTILAM® conductor.
9. Offshore construction comprising a first floating structure (60)
anchored to the sea bed in a wheather vaning manner via a turret
(62), the structure (60) being provided with at least one swivel
(67) according to any one of claims 1 to 8, an electrical lead (68)
extending from a power supply (66) on the vessel to a sub sea
power cable (69) via the swivel.
10. Offshore construction according to claim 9, the power cable (69)
extending to at least a second floating structure (70), at a
distance from the first structure, the second structure connected
to a sub sea hydrocarbon well via a riser (70').
11. Offshore construction according to claim 10, the first floating
structure (60) being connected to a sub sea gas field via a riser
(65), the power cable (69) extending to an on shore power grid
(71), the power supply (66) at the first floating structure (60)
comprising a gas turbine.
12. Offshore construction according to claim 9, the power cable (69)
being connected to a sub sea hydrocarbon transport duct (74)
provided with heating elements (75, 76) for temperature control
of the transported hydrocarbon.

Description

CA 02531309 2011-11-02
originele EP tekst
1
High voltage swivel
The invention relates to a high voltage swivel, comprising an annular outer
element defining a cylindrical chamber around a longitudinal axis and an inner
cylindrical element coaxial with the outer element and rotatable relative to
said outer
element around said longitudinal axis, the inner and outer elements each
comprising
two axially spaced electrical conductors which conductors are rotatable with
the inner
and outer elements, the conductors forming two pairs placed with contact
surfaces in
mutual electrical contact, one conductor in each pair being provided at the
inner
element, the other at the outer element and being connected to a respective
voltage line
which extends to an input terminal and to an output terminal respectively, the
conductors being surrounded by an insulating material.
Such a swivel is known from US patent nr. 4,252,388 describing a slip ring
mounted in a buoy for power transmission from a generating vessel to an
offshore
installation. The vessel can weathervane around the buoy in response to wind
en
current conditions, the slip ring transmitting high voltage three phase power.
The
conductors of the inner element -rotor- are annular plates mounted on a
central frame
of dielectric support brackets, alternately with washer-like dielectric
barriers. The
conductors of the outer element -stator- are provided by carbon brushes
mounted in
brush holders 69 and contact the conductive copper rings of the contacts of
the rotor.
The open ring stack allows high dielectric insulating oil to circulate through
the stack,
allowing smaller dimensions compared to using air as a dielectric.
The known swivel has as a disadvantage that the dielectric oil may be
contaminated by the particles originating from the carbon brushes upon wear.
Hereby
the maximum voltage which can be transmitted by the swivel is limited.
Furthermore, use of a circulating liquid dielectric insulator in the known
swivel is
relatively complex and requires the need for additional pumps and liquid tight
design of
bearings, while at the same time posing limitations to the maximum voltage to
be
transmitted by the swivel.
It therefore is an object of the present invention to provide a high voltage
swivel
of compact and reliable design which can be operated a relatively high
voltages.

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2
Hereto the high voltage swivel according to the present invention is
characterised
in that the electrical contacts of the outer element are provided in a recess
in an annular
solid outer insulating ring,
- the electrical contacts of the inner element are provided in a recess in an
annular
solid inner insulating ring, coaxial with the outer ring,
the inner and outer insulating rings each defining a boundary surface
extending in
an axial direction, the boundary surfaces of each rings being placed in close
proximity,
the electrical conductors being placed with their contact surfaces at or near
the
boundary surface.
By the use of solid insulating material in the form of insulating rings, a
high
dielectric strength can be achieved such that high voltages on the electrical
contacts are
possible, such as voltages up to 33 kV at for instance a nominal current of
395 A.
Furthermore, the use of the solid insulating material allows the size and
weight of the
swivel to be reduced, and hence helps to limit bending moments on the turret
swivel
stack. Reduced contamination of the insulating material by particles resulting
from
wear of the electrical contacts occurs, such that the insulating properties
are maintained
during the lifetime of the swivel.
In one embodiment, the conductors at the outer and at the inner element
comprise
annular contact surfaces. By the use of ring-shaped contact surfaces, instead
of known
carbon brushes, contamination of dielectric oil in the swivel, which can be
used inside
for instance 11kV can be avoided.
In the swivel, each electrical contact comprises a connector extending axially
from the conductor to a connector surface, situated in an enclosure bound by a
cover
with a an opening for fixedly receiving a power cable and with fastening means
for
connecting the cover to the outer element, each connector at the connector
surface
being provided with a receiving cavity for receiving a conducting wire of the
power
cable. By integration of the power cable in terminal boxes that are integrated
in the
body of the swivel, certification of the complete swivel can be carried out
without a
lower voltage limit being imposed by the connectors, which would be the case
when
connectors of an Exe protected type would be applied.
A suitable material for use as the solid insulating material comprises a
polymer
solid electric insulator of polyether ether ketone commercially available
under the
tradename PEEK from Entegri's Inc.

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3
A suitable copper alloy for the electrical contacts is commercially available
under
the tradename MULTILAM copper alloy. Multilam is a nickel plated copper alloy
strip that uses multiple leaf spring louvers and allows contact to be made via
a large
number of defined contact points. Each louver forms an independent current
bridge, so
that the many parallel louvers substantially reduce the overall contact
resistance.
Because of the high power transmitted by the electrical swivel of the present
invention, it can be used in an offshore construction comprising a first
floating structure
provided with a vessel anchored to the sea bed in a weathervaning manner via a
turret,
the vessel being provided with at least one swivel according to the invention,
an
electrical lead extending from a power supply on the vessel to a sub sea power
cable
via the swivel, the sub sea power cable.
The electrical lead can extend to one or more unmanned satellite platforms to
export for instance 22.5 MVA of power, whereas the electrical generation plant
is
situated on an FPSO due to economy of scale benefits and presence of the
operation
and maintenance crews. On the platforms the main drives (e.g. gas compression,
water
injection, gas lift) are electrical, high reliability and low maintenance
allowing the
platforms to be unmanned.
Another suitable application of the high power swivel according to the present
invention is to export electricity to an onshore location from an offshore
FPSO. Instead
of reinjection into the well or transport of gas to shore, gas turbines can be
used on the
FPSO to produce electricity which is transported, via the swivel according to
the
present invention and a submarine power cable to an onshore power grid.
Again another application of the present swivel is to supply power from an
FPSO
to a sub sea pipeline for heating of the pipeline to counteract hydrate
formation due to
low sea water temperatures.
An embodiment of a high voltage swivel according to the present invention will
be described in detail, by way of non-limiting example, in the appended
drawing. In the
drawing:
Fig. 1 shows a longitudinal cross-sectional view of a high voltage swivel
according to the present invention,
Fig. 2 is a schematic cross-sectional view through a conductor pair of Fig. 1;
Fig. 3 shows an embodiment of a cross-sectional view through the high voltage
swivel of Fig. 1;

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4
Fig. 4 shows a detail of the rings of the swivel of Fig. 3;
Fig. 5 shows an alternative embodiment of a swivel of Fig. 1; and
Fig. 6a-6c show an offshore system comprising a high voltage swivel according
to the present invention.
Fig. 1 shows a high voltage swivel 1, comprising a stationary outer annular
wall 2
and an inner cylindrical support 3. The outer annular wall 2 is connected to
top and
bottom connector boxes 4,5 for connection to three phase power cables 6, 7.
Within the
annular wall 2, five insulating rings 8,9,10,11 and 12 are provided which are
fixed to
the outer wall 2. In the insulating rings 8-13 a recess is provided in which
an annular
conductor 15,16,17,18 is situated. A boundary surface 20 of the outer
insulating rings
8-11 is contacting the boundary surface of five inner annular insulators 21-24
which are
fixed to the inner cylindrical support 3. The inner annular insulators 21-24
and the
cylindrical element 3 are rotatable around longitudinal axis 27. Conductors 28-
31 are
provided in recesses of the insulating rings 21-24. The conductors 28-31 are
preferably
formed by ring-shaped conductors, but may be comprised of other shapes, such
as
cylindrical or spherical shapes. The insulators 8-12 and 21-24, even as the
conductors
15-18 and 28-31 comprise contact surfaces in mutual contact at the boundary
surface
20, for transmission of current from a rotatable power lead 6, to a stationary
power lead
7.
The inner electrical conductors 15-18 are connected to electrical connectors
32,33
which extend axially to a connector surface 34 of the upper connector box 5.
The
connectors 32, 33 comprise a cavity 35,36 for receiving a cable 38,39 of three
phase
power lead 6. A cover 40 of the connector box is rotatably connected to the
outer wall 2
via bearings 41,42 seals 43,44,45 and bolts 47. The lower connector box 4
comprises
the same layout as upper connector box 5, and is with a cover 46 fixedly
connected to
the outer wall 2. The power leads 6,7 are clampingly attached to each cover
40,46 via a
clamping device 50.
Dielectric oil is protected from overpressure, over temperature and leakage
via a
Buchholz Relay unit 51 comprising a compensation bladder for accommodating
thermally induced expansion and contraction of the dielectric oil. The present
swivel is
suitable for high voltages, such as 33kV at currents of 395 A or more.
The conductor 15 shown in Fig. 2 is made of bronze and has rounded corners for
ease of assembly. The opposite bronze conductor 18 is provided with recesses
in which

CA 02531309 2011-11-02
a multi-contact ring, such as a Multilam ring, is provided for a resilient
conductive
contact in a number of contact points, hence reducing contact friction. The
gap 83
between the conductors 15, 18 is filled with dielectric oil.
As can be seen from Fig. 3, the inner cylindrical support 3, which may be the
5 rotating part, the outer wall 2 being stationary, is comprised of a first
split ring and an
inner ring 3'of closed circumference, to which the power cables 38, 39 are
connected.
To avoid wear of the conductors 15-18 and 21-24 due to constant small-motion
relative
movements of the rings 2 and 3, the split ring of the cylindrical support 3
can slightly
deform and remain stationary against outer wall 2, upon small excursions of
inner ring
3'. Upon larger rotations, e.g larger than 50 , of the inner ring 3', the
split ring of
support 3 will follow the outer ring's movements. As can be seen from Fig. 4,
the inner
and outer rings 3,3' are coupled via biasing spring 14.
In the embodiment of Fig. 4, the inner ring 3' is attached to the outer
cylindrical
support 3 of closed circumference via radial projection 19, which is situated
between
two springs 14, 14'on the cylindrical support 3. This allows small motions of
the inner
ring 3'with respect to the support 3, which upon such small motions can remain
stationary against outer wall 2 to avoid small motion wear.
Fig. 6a-6c show an offshore system comprising a Floating Production Storage
and Offloading vessel (FPSO) 60 which is anchored to the sea bed 61 via a
turret 62, at
the bottom of which anchor lines 63 and 64 are attached. The vessel 60 can
weathervane around the turret 62, which is geostationary. A product riser 65
extends
from a sub sea hydrocarbon well to a product swivel (not shown) on the FPSO 60
and
from the product swivel via duct 65'to production and/or processing equipment
on the
FPSO. In a power generation unit 66, gas produced from the well may be
converted
into electricity which is supplied to a swivel 67 according to the present
invention. The
power lead 68 extending from the power generation unit 66 is attached to
conductors
on the inner cylindrical support of the swivel 67 which is stationary relative
to vessel
60. The power lead 69, extending to the sea bed is connected to the electrical
conductors of the outer annular wall of the swivel 67 which is fixedly
attached to the
turret 62. The power lead 69 may extend to an unmanned platform 70 attached to
the
sea bed via product riser 70', such as a gas riser, or may extend to an on-
shore power
grid 71, or may be connected to heating elements 75, 76 of a substantially
horizontal
hydrocarbon transfer duct 77 between two floating structures 72,73.

Representative Drawing