Design of PLC system for nuclear dockyard in Plymouth, England

Undertaking our first large defence sector contract, the Altrad Sparrows team recently began working with a large engineering services company at a nuclear dockyard in the south of England. Working on this nuclear site required an even higher level of scrutiny, with various industry-specific regulations and directives coming into play.

With a highly detailed specification from our customer, the team was tasked with following the requirements closely while making suggestions for improvement where appropriate.

The cranes at the dockyard are halfway through their design life. Like any system, as the crane ages, reliability issues begin to occur, leading to increased breakdowns and problems. The customer was also acutely aware of the risk of obsolescence where spare parts could become difficult, if not impossible, to acquire down the line. Therefore, the customer's primary goal was ensuring that whatever system was installed, it needed to support the cranes for the remainder of their life cycle.

With Altrad Sparrows engineers already advising on crane operations and maintenance at the dockyard, our customer saw an opportunity with this project to streamline its contractor support team, bringing a more joined-up approach and allowing us to work on a broader scope of work than we have previously.

Our team got to work designing a new electric drive and control system for seven dock cranes, involving replacement of the existing programmable logic controllers (PLC), variable speed drives (VSD) and the addition of extra functionality. The engineering team began with the 'scheme design' phase, formulating the initial designs for the system and submitting documents to the customer throughout. This phase then culminates in a presentation of the proposed design to the customer.

As a relatively new sector for Altrad Sparrows, the project brought several challenges that have allowed the team to build on their already extensive knowledge.

Given the nature of the site, working on the cranes and their associated systems is subject to regulations set out by the Office for Nuclear Regulation (ONR) as well as Electromagnetic Compatibility (EMC) requirements to Defence Standards (Def Stan), and Functional Safety. By adopting an iterative approach to the system's design and communicating with the customer throughout, the team can follow all regulations to the letter while developing a deeper understanding of the defence sector's nuances.

The system also needed to be tested in a much more specialist way. Engaging with TÜV SÜD, we developed an outline plan for EMC testing in their anechoic chamber within their facility in Fareham, England. Testing for emissions and susceptibility, the chamber absorbs electromagnetic waves and blocks incoming signals to allow accurate and safe testing.

The complexity of the system itself brings its own challenges. For example, in building a like-for-like system, we initially received over 900 documents from the customer for the engineering and business development teams to work through. Additionally, though our team was only tasked with working on the PLC and the drives, these elements interfaced with other parts. Therefore, the team needed to have a thorough understanding of the entire system so that changes to the PLC and drives would not cause subsequent issues in other areas.

The current system also had many more levels of safety protection than standard models and ensuring these levels were kept intact meant working from precise customer requirements and options. We were also given the scope to suggest and implement other enhancements that would improve the system while still adhering to all necessary regulations. Options and enhancements accepted by the customer include a laser anti-collision system, a variable speed drive on the Long Travel motion to replace their current two-speed system, and anti-crabbing functionality to ensure smooth movement along the runway.

As principal designer and contractor, we will be responsible for safety in the crane area, with the customer overseeing safety on the site as a whole. Construction (Design and Management) Regulations dictate what contractors must do to ensure safety on-site, which will be supplemented by our own project-specific plans and risk assessments as well as toolbox talks and clear communication between all members of the team throughout.

The project's next stage will involve completing a scheme design survey, informing the next phase - the detail design. And beyond the design of the PLC and replacement of the drives, a Altrad Sparrows project engineer continues to liaise with an external supplier to replace the cabs on three of the customer’s cranes.

Working in the defence sector does bring a much higher level of scrutiny and the need to consider many more rules and regulations. However, we bring our high safety and quality standards to defence sector customers to ensure their critical equipment remains safe and continues to perform.

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