Turntables are key to power cable production

Kvaerner Markham has completed an order for the design, build and installation of a series of storage and degassing turntables for Europe's biggest manufacturer of power cables, Pirelli.

Kvaerner Markham has completed an order for the design, build and installation of a series of storage and degassing turntables for Europe's biggest manufacturer of power cables, Pirelli.

Forming part of the cable production process and measuring up to 12m in diameter with a 1000t capacity, the turntables are dedicated to the manufacture of submarine cables used for power transmission and distribution.

The contract is valued in excess of GBP 1 million.

Following Kvaerner Markham's earlier involvement in the supply of a vertical cable laying-up machine, the new contract covers a 10m-diameter, 200t-capacity storage turntable, three 300t degassing units of the same diameter, which act as ovens for heat soaking the finished cable, and a massive 12m, 1000t final storage table, all of which embody a common design philosophy.

The job was undertaken on a turnkey project basis, with Kvaerner Markham carrying out the engineering design, including computerised finite element analysis, fabricating the equipment at the division's Prince of Wales Road works, installing the turntables at Erith and commissioning the plant and associated control system.

Submarine cables are used for the electrical feeding of islands, the transfer of cheap power generated on natural or artificial islands, the crossing of sea inlets and rivers, and for connections to offshore energy facilities.

The five new units, termed interprocess turntables, are designed to store these large diameter cables, after all the elements such as conductors, insulation, armouring and polyethylene jacket are brought together by means of a vertical laying-up process.

The three degassing units additionally function as ovens, raising the temperature of the cable to 85C for a period of two to three weeks, which allows trapped noxious and flammable gases to dissipate safely.

Each horizontal turntable features a slew bearing-mounted, central hub providing axial support and location, to which are connected a series of spokes, varying in size and number according to the specified load, and which are daisychained together at the outer edge.

There are two sets of support wheels fitted to these radial spokes, which run on concentric inner and outer rails fixed directly to the foundations.

The turntable is powered by peripherally mounted epicyclic geared DC motors, driving a gear ring running around the edge of the table.

On top of the radial spokes there is a continuous flat surface, decked with steel sheeting and polyester coated, which provides a base for the cable to coil onto smoothly.

The spokes incorporate self-contained wheel boxes, each with a steel wheel running on taper roller bearings and a steel spindle.

The circumference of the outer track allows twice as many wheels as the inner, offsetting the natural outward bias of weight distribution, whilst the precise track positions themselves were verified by FE analysis to ensure equal loads.

The rails themselves are fabricated from high tensile steel and greased to protect them from friction, wear and erosion.

The three degassing tables are each housed within a steel-faced oven enclosure, insulated with rockwool on all sides and incorporating built-in 120kW heating elements.

There is also a removable top section or lid, built in sections to facilitate lifting and incorporating ventilation louvers to allow the escape of released gases.

Heat transfer is by condensation and, given the closely packed nature of the cable inside, ample time is allowed for it to soak up to the required temperature.

The 15kW epicyclic drive units, three per turntable, are mounted on fabricated subassemblies, which enable adjustment of the pinion gears to optimise mesh and backlash; each of the drive motors runs in load sharing mode and reduced operation is provided in the event of failure of a single unit.

The outer gear rings themselves were made in segments, and then adjusted on assembly to ensure continuous and accurate PCD (pitch circle diameter).

Any unbalanced radial loads are contained by the slew bearing in the central hub, which maintains accurate location of the table and hence correct meshing of the gears.

For each turntable, Kvaerner Markham additionally built and supplied a switchgear panel, containing DC convertors, heat regulators and associated controls.

Floor mounted and protected to IP45 environmental requirements, these panels provide for local manual operation, with forward, reverse, stop and emergency pushbuttons, or remote automatic control, the mode being selected by switch.

Front LED indicators provide an instant display of status and table speed, while there is also a powerful diagnostics tool included.

The company also provided continuous guards and safety fencing, as well as service trenches for maintenance purposes.

Back to top