AEDC space chambers' power supply upgrade project to improve safety, result in significant savings Published May 9, 2012 By Philip Lorenz III AEDC/PA ARNOLD AIR FORCE BASE, Tenn. -- People coming and going to work at AEDC, including test customers, have a lot invested in the facilities and buildings that make up the world's largest ground testing complex. When they flip a switch to turn on an office light or to set conditions for a space chamber test on a multi-million dollar weapons system test project, they expect safe and reliable power will be available. Customers like the Missile Defense Agency are literally counting on it. An aging infrastructure, even though well maintained, has limitations, said Elijah Minter, Investment Program Manager, AEDC Space and Missiles Systems Projects Section. Minter is AEDC's Air Force project manager for a two-phase power system upgrade project impacting the Space System Test Facility (SSTF) and space chambers 7V and 10V. "This is all about preserving our high-value national [test] capabilities that cannot be found anywhere else in the world," he said. Minter said he expects the project to be completed no later than October. "With our current diesel generators no longer able to ensure a controlled warm-up of the chambers during a loss of electrical power, this project provides a dual source of safe and reliable power to protect personnel and test assets valued at more than $150 million." He added, "Responding to lessons learned from the past, the project team performed upfront planning that showed the original concept was not optimal for lifecycle cost savings. This will save $2 million in lifecycle cost versus the 'traditional' diesel generator approach, and it will result in a dramatic reduction in the arc flash hazard." Space chamber conditions, which simulate the environment of space and near-space, require controlling and maintaining very cold conditions for long periods of time. "You can only cool metal down and heat metal up so fast without damaging it, so once you're on conditions at 20 degrees Kelvin, you've got to be very careful to stay there or warm up under controlled conditions," Minter said. The need for stable power for the heating and refrigeration systems for 7V and 10V is just part of the challenge driving the need for the upgrade. "Even a short power outage can shut down the computers that control the system and collect test data" he said. "That's where the uninterrupted battery backup system comes in. Since the battery backup system has a really fast transfer rate, the computers don't even blink." Minter said the battery backup system addresses one problem, but the power upgrade will provide additional power to keep the refrigeration compressors operational, lowering the risk of component damage and the loss of data due to a longer outage. "The refrigeration compressors do not require a fast transfer rate," he said. "But they do require a lot more power, so that's the second half of the job. Currently, small diesel generators are used to provide power in an emergency like most other facilities." He said diesel generators are maintenance intensive, expensive and must be replaced approximately every 20 years. "You've got low voltage and medium voltage that you've got to support," Minter said. "At the completion of this project, there will be two power sources fed from two interconnected unit substations. That's not been done anywhere on the base before." However, the customer will still have the option of bringing in a diesel generator as additional backup during a test. "We have the ability to hook up a temporary generator if we needed to," Minter said. "We can set two 1 megawatt generators out on the grass and plug them in, literally plug and play to these systems." The current phase of the project has involved installing the medium and low voltage unit substations without impacting ongoing test operations. Minter said the new consolidated substations have many advantages over the older units. "These two substations are located inside what is called an e-house, where a technician who needs to work on them will be in an enclosed, dry climate-controlled building," he said. "They've got adequate lighting, they're out of the weather conditions and they can safely operate all of the equipment inside the e-house without environmental concerns, plus it makes the equipment last significantly longer." Describing the substations, Minter said, "They are a beefed up version of the breaker panel in your house. It's a large bank of giant breakers that distribute power to the various parts of the building. The unit substation consists of a transformer and the switchgear - it's stepping down the voltage each time." Minter said the new equipment is safer to operate and maintain. "We're also getting gas insulated switchgear (GIS)," he said. "It's a new design of switchgear that virtually eliminates the ability for an arc flash to occur from that piece of equipment." Kirk Rutland, AEDC's maintenance division deputy, said testing conducted in the space chambers requires reliable power for long periods of time. "Most of the 10V tests run 24-hours-a-day for several weeks at a time," he said. "While we rely on back-up generators in other areas, 10V can take a day or two to safely come off test conditions and return the test article to ambient conditions. Relying on an emergency generator for that timeframe presents a higher risk. "The major risk of power interruption or failure is to the test article and some of the sensitive test instrumentation within the chamber environment. Both can sustain damage if the environment rapidly changes. Most of this test equipment includes unique items costing several millions, taking a long time to replace." Capt. Tim Calver, a space chamber test project manager with AEDC's Space and Missile Ground Test Complex, put the current upgrade project into context. "The power project will increase the reliability of the 7V and 10V chambers and supporting systems by providing redundant power that will seamlessly transition to an alternate source should the primary source be interrupted," Calver said. "As a result, the 10V and 7V chambers will have increased robustness against unscheduled power outages that might occur during testing. The greatest benefit will be to our 10V and 7V customers as the upgrade decreases the potential for lost test time, reduces the possibility of damage or contamination to their test articles and increases the reliability of the test chamber operation. Consequently, customer test programs will be better protected from unexpected costs related to power loss or disruption." Calver also commented on the consequences of a prolonged loss of power to the space chambers at AEDC. "A power failure or interruption while the chambers and test articles are at test conditions could result in shutdown of the support systems needed to sustain cryogenic and vacuum environmental test conditions, possibly allowing cryogenic deposition of ices that degrade chamber performance," he said. "As a result, an outage could necessitate a warm-up cycle to clean and decontaminate the chamber and test article. Safeguard procedures are in place to protect test articles from temperature and pressure rises that could occur if a power outage occurs, but cryogenic vacuum conditions can only be held for a limited time during a prolonged outage." Calver added, "It takes a significant amount of time to pump a chamber down to the proper temperature and pressure ranges and any unexpected rise in these conditions could add costly time to a test. Without a doubt, the installation of redundant, reliable power is a boon to our test customers, the Space and Missile Ground Test Complex, and AEDC."