Critical power for R&D

Power quality and reliability are as critical to research and development facilities as they are for production, manufacturing, and data centers. A power event in the lab can result in lost data, specimen destruction, equipment failure, and lost preparation time—unacceptable in today's costly R&D programs.

Before proper solutions can be developed, the nature of the electrical load and use of the building must be understood. Can a cryogenic freezer be offline for 10 seconds without damaging specimens? Will a 70% voltage sag trip test equipment or produce erroneous results? Each concern has several solutions with a variety of costs.

Electric Power Research Institute (EPRI) studies have shown that roughly 83% of outages last less than 10 seconds, many occurring during summer thunderstorms, when lightning strikes on or near electrical equipment cause voltage fluctuations. In the case of a direct strike, a short interruption occurs while a breaker is automatically opened and closed through a recloser to clear the faulted line. Trees falling into overhead lines, or high winds slapping them together, may also cause the breaker/recloser operation. Consequently, the first line of defense for any R&D facility is underground feeders from the utility to prevent weather-related power events.

Another source of concern with the utility systems is that they can transmit power-quality problems from one facility to another. For example, an industrial plant with large motors could be the source of transients and disturbances that cause voltage sags, swells, electrical noise, and other disturbances in a nearby R&D facility. Solutions would include installing surge protective devices, obtaining a dedicated utility feeder, or modifying the industrial facility's equipment.

Many problems that affect test equipment can be mitigated by a carefully designed electrical distribution system within the R&D facility. Electrical noise can be caused by motor starters and adjustable-speed drives (ASDs) in a facility's mechanical systems. Separation of load types can be an effective means of mitigating the transmission of electrical noise to critical equipment.

A design that feeds sensitive loads from separate transformers or feeders will attenuate the impedance caused by mechanical equipment in cables and transformers. Maintaining this separation is not difficult, but it does take planning and diligence throughout the facility's life. In addition, panelboards serving critical loads should be located near the load, in an electrical room next to the lab or in the lab itself—in other words, far from loads that generate the electrical noise.

Harmonics can be a particular source of concern in R&D facilities. Harmonics are generated by the non-linear loads of testing equipment and computers—the type of equipment that R&D facilities are full of. Possible solutions include filters, K-rated transformers, and panelboards with 200% neutrals.

To protect equipment that is susceptible to power disturbances from the utility, other facilities or the R&D facility itself, an uninterruptible power supply (UPS) may be necessary. There are basically two types of UPS: static (electronic) and rotary. Both types provide power-conditioning functions that boost the voltage to normal levels when there is a sag, and provide reduction if there is a swell.

Static UPS units have electronic components that take the incoming alternating current AC power, convert it to DC and then invert it back to AC to serve the load. When the power is in a DC state, a bank of batteries provides the energy needed during the voltage sags to keep a steady 60-Hz voltage at the load. In case of a power outage, the batteries are also able to provide backup power for a limited duration, normally 5 to 15 min.

Rotary UPS units use flywheel inertia rather than batteries to provide energy. The rotary takes the “noisy” voltage and spins a generator that produces a clean voltage at 60 Hz. No upstream electrical noise passes to the load, because the motor and generator are mechanically connected.

The generator's flywheel inertia also provides additional power to the load when voltage sags are present. Most systems can provide power to the load for 15 to 30 seconds, long enough for an engine generator to start and power the load.

Load type—and the disturbances that can be tolerated—dictate the UPS application.

It may be cost-effective, for example, to size the UPS for the test