Hot racks and cool customers: Colocating in the capital
Where diesel, data and dark fibre meet
“The electronic equipment in the colocation racks here is always fed from synthetic mains, it never sees the conventional mains power supply. So the synthetic mains powers the equipment and the "real" mains is only used to charge the batteries up. So if the real mains stops, all that happens is the synthetic mains carries on working but it takes its power from the batteries. The batteries start to discharge and when you put the diesel generator in, it begins to charge the batteries up again.”
UPS room with banks of Yuasa lead acid batteries and four Reillo AROS power conversion units at the back
Similar to 12V DC batteries found in cars, banks of Yuasa SWL2500EFR lead-acid cells are configured to deliver an output of around 480V. Rectifiers and other circuitry is utilised to convert the DC to AC which is distributed around the data centre to the server room equipment, the air conditioning and alarm systems too. Needless to say, these batteries stack up to a considerable weight, as Keenan remarks, “You don’t put them in the middle or top floor, you put it all on the ground floor.”
The UPS room fizzed with the sound of electrical activity as if teeming with android insects rising above the noise of the low frequency boom of the air conditioning that was the backdrop to all of the equipment rooms in the building.
There are several UPS rooms in the building but on show was an area recently fitted out with four Reillo AROS UPS units capable of delivering 120kVA apiece. Two UPS systems form a 2N pair to support the customer load and the other two handle the chillers. On the wall at the back was a curious arrangement of Dent Instruments ElitePro XC power meter, coupled with a DataProbe iBoot Hub.
Dent Instruments and Dataprobe monitoring kit
Used for monitoring the power loads from the various sources – mains, generator and battery – it allows Keenan to see how all this is shaping up from an app on his iPhone. From the graphs on the screen he refers to the bottom-centre one first. “That was the generator which was generating no current and then went up and started showing that change. Over on the left, that’s the switchover, as the two mains feeds were failed intentionally. It’s all completely automated. We all get alerts, so we know what’s happening.”
New power generation
Around the back of City Lifeline is where the generators are kept in a separate outhouse. Although it’s quite cramped inside, with each generator having its own separate room, the building itself is quite imposing. Silencers keep the outside noise to a purr – I've heard noisier ice-cream vans – with chrome exhaust pipes snaking out of the generator room and climbing the wall of the main building.
Inside, one of the generators is on load, proving its worth for the next hour. The noise inside is deafening, but you can nose around with ear defenders on. The MTU diesel engine hails from Friedrichshafen, and was built in the old Zeppelin motor factory. These days, MTU is owned by Rolls Royce Power Systems AG. The engine itself is capable of delivering one megaWatt on the shaft. It turns a 1150kVA Stamford alternator which is oversized in order to suppress all the harmonics that the UPSes generate from the rectifiers.
MTU 30-litre V16 diesel generator with Stamford alternator in the foreground
After a quick gander, Keenan points out the safety features from inside the quieter spare generator room. “We’ve various fire suppression devices acting on three levels. One is the engine itself, which says: 'I’ve got a fault, shut down'. The second level behind that is a rate of rise smoke detector, which says: 'this is getting awfully hot very quickly' and sends a signal into the main building fire system.”
The third system is a curious set-up of taut wire suspended above the generator that features a tiny piece of metal that melts at 100˚C. With a touch of sarcasm, Keenan remarks, “It has a wonderful, sophisticated, totally mechanical system that consists of two weights. If the metal melts and the weight drops, it closes that big valve. That’s the connection between the ‘day tank’ and the engine, so it drops and stops the fuel going to the engine. The other weight acts to stop any more fuel coming into the day tank container.”
A day tank is a reservoir of fuel that’s pumped out at the correct pressure to the diesel engine injectors. And talking of fuel, City Lifeline keeps 14,500 litres on site, which is expected to last around three to four days in the event of an outage. Pour that into your family saloon and at 47mpg it’ll get you 150,000 miles – about 400 miles a day for a year. Or if you reckon you could siphon it away, you’d not be far off 20 grand’s worth of fuel.
Having that amount of diesel hanging around involves some maintenance of its own. The fuel needs ‘polishing’ and City Lifeline calls in contractors for this particular job. It’s a process that removes traces of water, bacteria and other particulates that can accumulate in the tanks, ensuring that the generator gets a clean and healthy fuel supply every time its drawn upon.
Load shedding between power sources is managed automatically in the Switch Room
As the tests come to a close, we’re taken to the switch room which manages the handover of power to the UPS array from the mains to the generators and vice versa. One of the team is monitoring the current draw as a clatter of switching is heard.
There’s a sequence to how the switch gear operates, as the power isn’t flipped over in one go. A load-shedder co-ordinates a gradual return to normal. The amp readings on the generator meter he’s checking steadily drop as the load shedder returns the power to a full building load and the generator has less work to do.
Back in generator room it’s quieter now as the diesel engine is in its wind down phase for cooling, eventually switching off automatically. You hear the engine whine a descending portamento for a few seconds as it comes to rest.
Even though these tests are performed regularly each month customers are kept informed, as some of them might choose to have engineers on standby during that window. The test routine gives customers some reassurance that there are no problems and they receive notification of the next monthly test window.
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