Improving Switchgear Inspections At London Stansted

Time really is money for most businesses. That includes airports, where diverse 24/7/365 operations put increasing pressure on maintenance teams charged with the performance of a wide range of critical tasks.

This article is based on one that ran in the UK publication Engineering Maintenance Solutions.

Like many other major airports around the world, London Stansted Airport is open for business 24/7. The continuous operation of its passenger terminal is crucial. As London’s third busiest airport, Stanstead also needs to be at the ready for every eventuality, be it bad weather or a security alert. These facts of airport life have typically put maintenance teams responsible for the reliability of the facility’s low-voltage equipment under huge time pressure.

At best, Stansted’s engineers had four hours per night in which to conduct predictive maintenance inspections. By the time they had made the system safe, this window of opportunity was reduced even more. This meant the entire inspection cycle was significantly protracted and no system could be checked under load.

With the installation of IRISS CAP Series infrared inspection windows, the savings in terms of inspection time and associated costs have been massive. Payback was instant. But the benefits extend way beyond that.

An initial thermal survey of the fully energized low-voltage systems that serve the main terminal block took only five hours, showing just two minor cable faults. For the first time, the airport had a benchmark for trending future performance and the complete assurance that everything was working optimally.

“Quite simply, this was not possible before we installed IRISS CAP Series infrared inspection windows,” says Stansted’s Engineering Compliance Manager, David Potter. “We were able to check individual circuits when they were switched off, but busbars continued to be a particular concern. They contain a huge amount of copper that absorbs a lot of heat over time before they go into fault status. You can’t see this if the system isn’t live.”

Mission impossible
London Stansted Airport has permission to handle 35 million passengers annually. Its throughput peaked at 23 million in 2007, but now some 17.5 million people pass through the terminal building each year. Night operations largely involve Ryanair and easyJet aircraft and cargo flights. Although early-morning hours offer a relatively quiet period for planned maintenance, passenger processing normally starts around 3.30 a.m.—by which time all electrical systems must be up and running. 

Potter, an engineer with 24 years experience at Stansted, is responsible for strategic planning and maintenance of electrical distribution at the facility—both high- and low-voltage. Unfortunately, while parts of the high-voltage network can be selectively shut down without compromising the operation, the low-voltage equipment does not have
similar capacity.

“Our high-voltage network is owned and managed by UKPNS, but maintenance of low-voltage equipment is down to our own engineering teams,” Potter explains.
“We confirm the maintenance schedule with the Airline Operators Committee three months in advance, and our Maximo planning system flags up what needs to be inspected each night, but in every case it’s a race against time.”

The airport’s electrical infrastructure is enormous. Power is brought onto the site at 33kV and transformed down to 11V. The low-voltage network feeds all manner of systems in the main terminal building—typically related to IT and baggage handling. Therefore, any unexpected interruption in the power supply could have serious consequences. The potential cost of failure is also enormous: The airport’s Service Quality Rebate scheme (SQR) is a program whereby the airport has to compensate its customers, the airlines and  the handling agents if it fails to meet an agreed level of expectation.

Although efficient maintenance had previously prevented serious low-voltage system failures, Potter wanted greater assurance. He had considered installing infrared windows to complement outsourced thermal imaging surveys and to allow live inspection, but products available in the marketplace were deemed unsuitable.

As he puts it, “A small crystal window may have been fine for small switchgear, but the size of our equipment meant that we would end up with so many windows, our substation would look like a submarine. Even if it had been viable from a practical standpoint, the cost would be huge. And, crucially, an individual window would be too small to allow the all-important inspection of an entire busbar.”

Eureka
Potter’s “Eureka” moment came when he read an article on IRISS Custom Application Product (CAP) Series infrared windows made from transmissive polymer. This type of fully impact-resistant material allows the window to be any size—an ideal solution for applications involving large switchgear. He quickly contacted IRISS for assistance.

Although IRISS initially considered the work to be a two-phase project, the low cost of its product allowed all substations serving the terminal block to be fitted with the new CAP windows at one time. The potential savings in inspection time and the ability to inspect live systems, including the busbars, easily justified the investment.

The specification was approved on Nov. 6, 2012, a comprehensive installation plan was then drawn up by IRISS and the entire job completed by Christmas.

Getting it all done
According to Potter, the IRISS team was quite flexible in working to complete the job within the time constraints imposed by 24-hour operation. Having installed an isolation sheet on each cabinet, the thick door panel was removed to the access road where the required hole was cut with a jigsaw and the appropriate IRISS CAP Series window fitted.

This work continued until a total of 72 windows had been installed, comprising a combination 6”, 12” and 24” products—all of them available in the standard range. The largest window is, of course, ideal for thermal inspection of busbars and multiple components.

Given the fact that IRISS CAP Series windows can be fully customized to suit the application, they offer users a wide range of benefits. For example, a window no longer needs to be round, nor is its size restricted. (A crystal window, by comparison, becomes too fragile beyond a 4” diameter.) Moreover, the IRISS technology reduces the number of windows required, their installation time and associated costs.

The payback
Once they were in place, the new IRISS windows at London Stansted had an immediate impact on switchgear inspection time.

“It took just five hours to complete the job in daylight hours, including walking from one substation to the next and coffee breaks,” David Potter recalls. “Previously it would take us two nights to inspect just one panel. Now there’s no need for isolations or back feed and our engineers’ safety is completely assured. A single thermographer with a thermal imaging camera and without PPE can do everything.”

IRISS performed the first thermal imaging survey following the installation of its windows on Jan. 8, 2012. It’s a testament to the skill of the London Stansted Airport maintenance team that only two minor faults were discovered. (Considering the scale of the airport operation, that’s a significant achievement.) The thermal inspection report provided a comprehensive snapshot of the health of the entire low-voltage network at London Stansted.

Potter is quite pleased with the report. “I now have the thermal performance of each system printed out,” he notes, “and for the first time, a benchmark on which to base future thermal inspections. Previously, it would take us a couple of years to inspect the complete network and even then we had no idea what was happening under load.”

These days, with the knowledge that his switchgear systems have been thoroughly inspected, Potter is able to rest much easier. “Now, we can see the live circuits and cables and the temperature rise on busbars,” he explains. “This means we are able to apply trends to every system. In short, I now know the terminal is truly safe and that’s a big tick against my list. I’m really sold on this technology.” MT

Coincidentally, the IRISS CAP Series window technology referenced in this article has been named a Runner Up in the “2012 Maintenance & Reliability Innovator of the Year Award Program.” Congratulations!