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Over the first half of 2010, City Lifeline, a leading colocation data centre in central London, became more and more aware of these issues and of the need both to be able to offer Tier 3 facilities to its customers and of customers becoming more demanding about Tier levels. At the same time, it became clear that the existing single generator was becoming old and needing more and more maintenance effort. City Lifeline has always had an on-going investment programme, continuously working to keep one of the longest established colocation data centres in London up to the most modern facility standard and offering its customers high levels of resilience and redundancy.

Discussions led to the consideration of replacing the existing single and rather elderly generator with a new and modern N+1 pair of generators with automatic failover detection, so that if one set failed to operate correctly, the other would automatically detect the failure, start up and change over to replace it. The essential issue is “concurrent maintainability” – the ability to ensure full service delivery under any circumstance, including, for example, a mains power failure when a generator is undergoing an oil change. 

Some significant restrictions immediately became apparent. Whilst the old generator had been there a long time, any new equipment would have to meet 2011 planning, pollution and noise regulations. Being in central London, only 100 yards or so from the boundaries of the City of London, space was highly constrained. Not only that, but the only possible site was on the existing concrete plinth where the existing generator stood, and no outage or “at-risk” time was acceptable to City Lifeline’s customers. And the site is in a residential area and in a conservation area. Not the easiest of design or negotiation tasks.

A task team led by Roger Keenan, City Lifeline’s managing director (himself an engineer by background) was established in July 2010. The team talked to suppliers, brought in specialists such as fire consultants, talked to the local authority planners, and prepared a Feasibility Study. The project was feasible, but would require a great deal of specialist engineering, some luck with the planning consent, around £600,000 in cost and 12 months to design, build, install and commission. City Lifeline’s Board gave the go-ahead as part of the continuing long-term upgrade and renewal of the facilities and as in line with the policy decision to offer Tier 3 standards to the central London marketplace.

The project team made the decision to split the contracts and manage them internally. Many design discussions were undertaken with the selected preferred contractors over October and November. The contract for the generator sets was awarded to Musgrave Generators of Leicester, for the acoustic enclosures (the most complex, difficult and sensitive part) to AC Manufacturing of Colchester and for the flues to Midtherm Engineering of Birmingham. The two engines and the two alternators were delivered to the Musgrave factory in Leicester a few days before Christmas 2010. Metal and insulation were delivered to ACM at the same time. All went into storage over the Christmas break.

In parallel with the design of the new generator system, negotiations with the local authority planners took place. Since no records of the planning applications for the existing generator could be found, it was necessary to first apply for a “Certificate of Lawfulness” to clarify the legal right to have a generator on site in the place where the new system was to go. This proceeded smoothly through the local authority’s legal department. A full planning application was then made through a professional planning consultant, including a large amount of supporting documentation concerning physical size, visual impact, a full acoustic survey of the site and an impact statement concerning the likely effects of the operation of the generators on local residents and businesses. Somewhat to everyone’s surprise, no objections at all were received during the public consultation and planning permission was granted for the design as originally submitted, quickly and efficiently once the consultation was over. Some conditions were imposed by the Environmental Health department, but nothing that the design did not already achieve. 

The engine selection was a 30-litre V-16 from MTU in Germany, because it met the most modern European pollution requirements and was small enough to fit in the space available. Electronically-controlled, it produces as much power from a 30-litre engine as the old generator did from 50 litres.

The engines are permanently heated to keep them ready to start at any time and come to full power quickly. To conserve energy, motorised louvres on the enclosure inlets shut down when the engines are not running.

The alternators are permanent magnet excited units from Stamford in Lincolnshire. Stamford made a well-engineered product available in the timeframe required, and it could be oversized within the frame size selected. The lowered output impedance translates into a lower sub-transient reactance, helping the generator to overcome the harmonic distortions introduced by a non-linear load.

To fit within the space, the radiators had to be mounted above and outside the engine acoustic enclosures, and the space restrictions meant they had to lie flat, with air intakes at the bottom and the outlets at the top, with a cover that could be removed to allow maintenance access.

Fire shutdown is from electronic rate-of-temperature-rise detectors. Backup is a simple, independent, thermal link, melting at 100 deg C and causing two drop-valves to operate. One cuts the fuel supply to the enclosure, the other cuts the fuel to the engine.

The acoustically-supressed enclosures had to meet requirements at the limits of what is practically possible to meet - a noise level of 65dBA at 1 metre. They also had to fit on the only space available – the existing concrete plinth sized for a 40ft cargo container which carried the old generator. And the height could be no higher than the existing wall to retain the sightlines of residents on the other side of it.

Construction took place in Leicester and Colchester over the spring of 2011, with first running in April. After acceptance tests in May, the complete systems were shipped to site in London in June. Cutover and service entry was in early August and the two generators have been fully supporting the building electrical load since then.

All in all, a very successful project. Two generator sets, specially designed, consented, built, installed, commissioned and entered into service in less than a year from initial conception to completion at a relatively modest cost. In central London, in a residential area, in a conservation area. No mean feat.

Technical Specification

Configuration	N+1 diesel generator pair with automatic failover detection and changeover
Engines	MTU 16V-2000-G65TD. 800KW Prime Power each set
Engine Configuration	30-litre V16, 90 degrees, electronic controls
First Load Step	505KW
Alternators	Stamford HC1634K, 1110KVA, 4-pole, 50Hz, 415V, permanent magnet exciter
Controls	Deepsea 7310
Fuel Consumption	205 litres/hour at 100% load
Daytank	1,000 litres each set, automatic refill from external pumpsets
Fuel Bunding	110% of daytank capacity as part of enclosure construction
Cooling	Horizontal roof-mounted dry coolers, variable-speed fans
Cooling Capacity	Engine 435KW, Intercooler 248KW
Standby Heating	Heated to 40 deg C permanently, 2.5KW standby heater
Fire Prevention	Dual rate-of-rise detectors per set, dual thermal link drop-valves per set
Acoustic	65dBA at 1 metre, hemispherical method
Output failure	Automatic detection and switching to reserve set
Monitoring	VFC contacts to remote displays and BMS

 

By Roger Keenan, MD, City-Lifeline

• Posted on: 16th January 2012 at 12:00am
• Topics: Power & Cooling; Hosting;