EP-4739990-A1 - APPARATUS FOR TESTING CABLES

EP4739990A1EP 4739990 A1EP4739990 A1EP 4739990A1EP-4739990-A1

Abstract

An apparatus (20) for testing cables comprises housing assembly (22), an elongate member support assembly (24) and at least one tensioning means (26) configured to apply tension to a cable in use (not shown). Tensioning means (26) is mounted to the elongate member support assembly (24) such that applying tension to the cable causes a reaction compression in the elongate member support assembly (24). The elongate member support assembly (24) is moveable relative to the housing assembly (22). Elongate member support assembly (24) comprises three pivotally interconnected arms (24a, 24b and 24c). At the end of arms (24a and 24c), tensioning means (26) to apply tension to a cable in use are located.

Inventors

KIMPTON, Angus Owain
MACGREGOR, David James
JOLLIFFE, Martin Stuart

Assignees

Osbit Limited

Dates

Publication Date: 20260513
Application Date: 20240627

Claims (11)

1 . An apparatus for testing elongate members , the apparatus comprising : an elongate member support assembly disposed substantially adj acent to and extending the length of an elongate member in use , wherein said elongate member support assembly is moveable relative to a housing assembly in which the apparatus is disposed; at least one tensioning means configured to apply tension to said elongate member, wherein said at least one tensioning means is mounted to said elongate member support assembly such that applying tension to said elongate member causes a reaction compression in said elongate member support assembly; and at least one drive assembly configured to continually move said elongate member support assembly relative to said housing assembly to enable said elongate member in use to have its bend radius continually changed under tension . .
2 . An apparatus according to claim 1 , wherein said elongate member support assembly comprises a plurality of pivotally interconnected support arms .
3 . An apparatus according to claims 2 , further comprising first and second pluralities of pivotally interconnected support arms disposed in parallel .
4 . An apparatus according to claim 2 or 3 , wherein an end of at least one of said plurality of pivotally interconnected support arms is moveable relative to said housing assembly .
5 . An apparatus according to any one of the preceding claims , the apparatus configured to move a centre portion of an elongate member being tested reciprocably along a first axis , wherein portions towards the ends of said elongate member being tested are restricted to only move along a plane lying perpendicular to said first axis .
6 . An apparatus according to any one of the preceding claims , further comprising first and second tensioning means disposed at opposite ends of said elongate member support assembly .
7 . An apparatus according to any one of the preceding claims , wherein the elongate member support assembly further comprises at least one guide member shaped to define the extent of curvature of an elongate member in use .
8 . An apparatus according to any one of the preceding claims , further comprising a bend sti f fener surrounding an elongate member in use .
9 . An apparatus according to any one of the preceding claims , wherein said at least one drive assembly comprises a motor driven crank configured to reciprocate at least a part of said elongate member support assembly .
10 . An apparatus according to any one of the preceding claims , further comprising a housing assembly .
11 . A method of testing an elongate member, the method comprising : mounting an elongate member in an apparatus according to any one of the preceding claims ; and operating the apparatus to continually change the bend radius of the elongate member under tension .

Description

Apparatus for Testing Cables The present disclosure relates to an apparatus for testing elongate members , such as cables and pipes . Subsea Power Cables are used to trans fer power from of fshore wind turbines to sub-stations and from of fshore sub-stations to land . Cables are a signi ficant part of the cost of installing a windfarm . Such cables can be unreliable i f not constructed and installed correctly and the cost of subsea cable repair is very high . It is therefore desirable to test the durability of elongate members such as subsea power cables and pipes . Until recently, of fshore wind turbine generators have been fixed to the seabed in shallow water using a monopile foundation and in deeper water, a j acket . As the adoption of of fshore wind power becomes more widespread, there is a need to construct wind farms in deeper water or where the seabed is otherwise unsuitable for foundation installation . Here , floating wind turbine generators are used . The floating foundation is anchored to the seabed using an array of chains or cables . Because it is floating the wind turbine generator moves up and down with the tide , moves laterally to allow its tethers to react loads from current and wind and pitches and rolls with the waves . The cable that connects the wind turbine generator with the sub-station has to compensate for this relative motion between seabed and the floating foundation . Power cables are designed to be flexible , they need to bend to be transported and during installation . Once installed further bending is usually minimal on fixed bottom applications. Motions between the seabed and a floating foundation are consistently frequent and often accommodated by creating an S-shape in the cable. The S-shape is supported by a mid-water arch to control the bend radius. To compensate for the motion the S-shape in the cable is continuously changing, bending the cable continuously throughout its life. If subjected to a large number of bend cycles, a power cable can fail through fatigue. Fatigue failure can be in the metal of the armour wire, causing reduction in tensile strength and prevention of even bending, in the metal of the conductors, causing increased electrical resistance or by fretting of the insulation causing a short. To qualify a cable for a floating wind farm, a power cable must be fatigue tested. During the fatigue test, physical and electrical integrity of the cable is continuously monitored. In January 2022, The International Council on Large Electric Systems (CIGRE) published a new document Ref: 862 "Recommendations for mechanical testing of submarine cables for dynamic applications" . The document describes tests that are required to qualify a cable. There are two principals that can be applied when testing a cable, the bend can be controlled by using a rigid former set at the cable bend test radius, or by using a flexible bend stiffener. The bend former method is best used to characterise the power cable and the bend stiffener is best used when there is a power cable termination system to be tested. CIGRE 862 also recommends that the cable is tested under representative tension. During a test the tension is applied to the cable using an end termination. This would typically consist of a conical collar placed around the cable armour and potted onto the cable using an epoxy resin . Figure 1 is a schematic of a known apparatus for testing a cable 2 . A cable 2 100 units long is mounted between two tensioning springs 4 and 6 . The tensioning springs 4 and 6 are connected to anchor points 8 and 10 which are supported by the housing of the apparatus and are moveable up and down in a direction parallel to axis X to flex the cable as shown . Alternatively, anchor points 8 and 10 may remain stationary whilst cable 2 is flexed at its centre up and down to deform springs 4 and 6 . This provides the same relative movement . In order to flex the cable by the required amount , each spring 4 and 6 must extend from an initial 10 units of extension at the straight configuration to an extension of 13 . 2 units at the upper and lowermost extents of the flex . This configuration suf fers from several disadvantages . Firstly, the spring must provide a constant tension to the cable to replicate conditions in the field and provide a valid test . The spring constant is defined as the force applied per unit extension . Where extension is large , the spring must have a very flat spring constant , i . e . a small change in tension that applies over a long extension . This can be di f ficult to provide and requires low friction in the spring system . Secondly, the tension in the cable is reacted by the anchor points 8 and 10 at each end which requires a very strong frame to carry this load, particularly when bending away from the centre line of the cable . Such test rigs are therefore large and the apparatus requires a very strong structure anchored to the ground . This is costly to provide and