Powering up the datacentre – a not so simple issue

Disaster recovery backup sites supplied by underground cables may seem more secure than those connected to overhead lines, but that's not the case

If anyone knows how to protect against power outages caused by extreme weather it would be Jeff Biggs. The vice president of operations and engineering for Peak 10, a fast-growing US datacentre operator, Biggs has taken many steps to harden Peak 10’s co-location facilities in Florida against the state’s annual threat of hurricanes.

Those steps include making sure Peak 10’s Jacksonville, Florida datacentre taps into the city’s underground power lines in two places, in case one substation or line goes down. The steps also include buying a massive 1,500 kilowatt backup diesel generator for another Florida datacentre, at Tampa Bay, along with emergency refuelling contracts with two separate suppliers in case of an extended outage.

However, Biggs admits that recent storm-related power outages in Denver, Seattle and St Louis, all of which left parts of those cities dark for a week or longer, would have tested and perhaps overwhelmed Peak 10’s precautions.

“An outage that long, oh my God, it would catch even my fuel suppliers off guard,” he says.

The continued growth of the internet, combined with cheaper PC-based technologies, has led the number of servers worldwide to double since 2000, according to market research company IDC.

Much attention has been paid to how to cut the spiralling costs of powering and cooling these servers. But less thought has been devoted to how to better protect datacentres from power outages now that incidents of turbulent weather caused by global warming appear to be on the rise.

An example can be seen in a major US airline, whose Seattle reservations datacentre went dark on December 15 when its backup generator failed to turn on after windstorm-induced blackouts.

“They had all of the right pieces in place; it just wasn’t well-implemented, so it shut the business down,” says Mark Svenkeson, president of datacentre builder Hypertect.

Experts say datacentre managers must increase both the diligence and the scope of their outage-proofing efforts, especially since few electrical utilities will be investing in upgrading their fragile infrastructure.

Perhaps the most apparently obvious infrastructure upgrade — burying existing above-ground electrical lines, especially in areas where wind, hail, heavy snow or falling trees are perennial threats to electrical poles and towers — still isn’t viable or even desirable in most cases, experts say.

“In terms of safety, reliability and especially cost, underground lines are the least preferred choice of engineers,” says Rick Pieper, a technical director at Henkels & McCoy, an engineering firm that builds both above- and below-ground power lines.

According to Pieper, there are three main components of power lines. The first are the lower-voltage lines serving individual homes or businesses or residential neighbourhoods. They include secondary lines connected to homes that carry between 120 and 480 volts, as well as distribution lines inside newer neighbourhoods that typically carry between 12,000 and 34,000 volts.

There are also distribution lines transmitting electricity from substations along main roads. High-voltage transmission lines carry 69,000 to 765,000 volts of electricity over long distances.

Underground distribution and transmission lines are mainstream in Europe. But the vast majority in the US remain above ground.

High-voltage power lines are only found underground in the US in dense commercial areas such as downtown major metropolitan areas, where above ground lines interfere with traffic and real estate.

While underground wires appear less vulnerable than above-ground power lines, they have several disadvantages. Above-ground lines are typically uninsulated and cooled by air. Underground lines, in contrast, quickly build up heat.

One way to prevent underground cables from melting is to bathe them in oil travelling inside the same steel piping. That oil must be constantly cleaned to maintain its cooling properties and to keep it from breaking down into hydrogen gas, which can be explosive, says Stan Johnson, a manager at the North American Electric Reliability Council (NERC).

An alternative is to cool underground lines by letting a certain amount of electricity “bleed through” to the ground, Potter says. That has the disadvantage of making them less efficient, and the resulting electrified ground can also harm animals or humans.

Underground wires are also more vulnerable to being accidentally dug up, says Peak 10’s Biggs.

Repairing underground wires takes longer, too. And they are not necessarily less prone to storm damage, says NERC’s Johnson, who points out that salt water brought in by hurricanes can cause as much damage to underground lines as winds do to the overhead variety.

In all, experts say that extensive studies by electrical utilities and third parties show that installing underground power lines, especially high-voltage ones, can cost up to US$20 million (NZ$28 million) per mile, about 10-20 times more than stringing them overhead.

Even pro-reliability watchdogs such as NERC don’t advocate underground power.

“We push for a more reliable system, yes, but we do not as a general rule push for utilities to build underground lines rather than aerial transmission poles,” says Johnson.

On the other side of the ledger, a dense underground power grid can benefit datacentre operators by allowing them to tap into lines two or more times for redundancy’s sake.

“That’s the holy grail for datacentres if you can do that,” says Biggs.

But other experts say the high cost of real estate is causing many datacentres to migrate to suburban or rural locations, where underground lines are rare.

“As the electricity arrives from the generating plant, I can tell you it’s all going to be up in the air somewhere,” Henkels’ Pieper says.

Hypertect’s Svenkeson recommends datacentres have two backup generators, or a “backup for their backup”. But he says that because of new US Environmental Protection Agency emission requirements that went into effect at the start of this year, backup generators have both become pricier and harder to find. Peak 10’s Biggs claims that the number of back orders at many manufacturers is so large it would take a year for a generator ordered today to be delivered.

However, underground power may become more practical as the technology to cool and insulate the cables improves.

One plastic insulator, cross-linked polyethylene (XLPE), allows underground transmission lines nowadays to carry up to 345,000 volts, says Pieper. Technologists promise superconductors using liquid nitrogen to cool conductive wires that will allow electricity to travel over long distances with no power loss.

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