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Altra connects for the nuclear age

11 April 2011

There seems to have been a turnaround in government attitudes towards nuclear power generation as global warming and energy insecurity become agenda-leading issues. Extensive new nuclear build is apparently inevitable and a lot of companies are gearing up for the supply bonanza that must surely come as a result. We turn our attention to the power transmission end of things and, in particular, to the offerings of a major supplier to this sector

The International Energy Agency has stated that the World must invest $26 trillion (£16.7 trillion) over the next two-decades to avert a global energy shock. Much of this investment, due to the requirement for cleaner ‘green’ energy, will be directed at nuclear power. Many new stations will be built and the infrastructure of these, and existing nuclear installations will come under pressure to perform as never before. This, in turn, will mean unprecedented levels of support from companies that supply specialist products and services to the industry.

Altra Industrial Motion, which includes some well known names from the power transmission world, including Warner, Wichita, Stieber, Twiflex, Bibby, Nuttall and Formsprag, has been preparing for this development. And with the help of group subsidiaries, it has produced a package of electromechanical power transmission products designed for use in critical, safety-related nuclear power applications.

At the core of Altra’s Group offering are high speed gear increaser and reducer drives from Nuttall Gear (formerly Westinghouse Gearing Division). The Nuttall SU high speed gear design offers the key advantage to nuclear operators of proven operation over millions of hours in around half of all nuclear power plants built by Westinghouse. The SU gear drives in these existing facilities continue to be supported through new units, replacement gearing and parts, and Nuttall Gear also offers a full rebuild service to original OEM specifications.

For new applications, Nuttall can supply high-speed drives, designed to American Gear Manufacturers’ Association standards, for custom compressor, fan and pump sets, as well as turbines. These drives have proven reliability in service, and come with features such as rigid cast iron or welded steel housings; dynamically balanced, precision double helical gearing for uniform load distribution and quiet running; oversized split sleeve bearings for smooth, efficient running; split labyrinth non- contact oil seals for longer life, and self-contained forced oil lubricated gears and bearings.

Specifically equipped for nuclear facilities, Nuttall’s units can be supplied with options such as monitoring systems to measure temperature, pressure, and vibration, remote mounted lubrication consoles, and multi-speed shifters.

Fit-and-forget couplings
Other in-service proven products that are designed to deliver ‘infinite’ life in critical applications are Altra’s Bibby and Ameridrives ranges of high performance disc and diaphragm couplings. Designed and manufactured in compliance with API-671, and with torque handling capacities up to 677,400Nm, these non-lube, maintenance-free couplings are currently deployed on a range of demanding duties such as boiler feed pumps, generator sets and gas compressors.

Bibby’s HS series disc couplings, for example, are manufactured from alloy steel, which is fully traceable. The novel design, which effectively drives in friction, rather than shear, to the disc assembly joint, removes the potential for fretting during normal operation, and prolongs the life of the coupling.

HS couplings are also ‘plug-in’ devices, which means they can be installed - and the flexible elements (disc packs) changed - without disturbing adjacent machinery. Moreover, by nature of their design, disc couplings are torsionally stiff and backlash free, and will accept significant levels of angular, radial and axial misalignment without any deterioration of performance.

The Ameriflex range of diaphragm couplings offers features such as: shot-peened 15-5 PH stainless steel diaphragms, for improved fatigue strength and stress corrosion resistance; multiple separated diaphragms to provide power transmission redundancy and design flexibility, and field replaceable flex elements. The ‘fitness for purpose’ of Ameridrives diaphragm couplings for nuclear applications is adequately demonstrated by the company’s 203cm coupling (believed to be the largest multiple diaphragm coupling ever built), which forms part of the power transmission train of a nuclear submarine propulsion system. This coupling, too, is designed to deliver infinite life.

Anti-rotation devices
The third key element in Altra’s nuclear power generation armoury is the centrifugally disengaged, vertical backstop anti-rotation device (ARD) from Formsprag/Stieber. These Altra group subsidiaries were instrumental in the development of a long-life ARD for coolant pumps feeding pressurised water reactors, and they provide continued support for the installed base of these devices by offering field inspections, factory rebuilding and new ARDs with improved bearing performance.

In addition to coolant pumps, Formsprag/Stieber ARDs are also used in other nuclear applications, as backstops for various pumping systems, cooling tower fan backstops, and overrunning clutches in rotating gear drives. Their novel design ensures virtually unlimited speed capability and a high torque holding facility (to 56,450Nm).

These ARDs feature lift-off sprags for no-contact running with no heat generation; moreover, they offer in excess of ten years maintenance-free operation between recommended inspections. They have balanced torque arms to prevent reverse rotation, and use dynamically balanced hydrodynamic babbitted bearings and races for minimal wear and heat generation. Importantly, for nuclear use, the ARDs - like Nuttall’s drives - also offer facilities for monitoring temperature, pressure, and vibration.

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