By Jeffrey D. Phelps, HDR, Inc.

In today’s power intensive and power sensitive world, interruptions - even when few, far between and minor - can be devastating. And although most hospitals and other health care facilities don’t generally consider a rotary uninterruptible power supply (UPS), that option should not be dismissed out of hand.

As with any critical operation, unreliable power - especially in rural areas - can have dire consequences for health care facilities. In a typical health care facility, the electrical system operates on three-phase power. A single-phase outage could not only cause circuit breakers to trip and fuses to blow, it could also damage motors, sensitive medical equipment and HVAC systems. As a result, even brief outages can disrupt critical functions.

Another serious consequence of power outages is downtime that results in lost revenue. Although the financial cost of downtime is difficult to gauge in precise terms, one study, “The 2001 Cost of Downtime Survey” by Contingency Planning Research in conjunction with Contingency Planning & Management magazine, offered estimates based on responses from various industries including energy, manufacturing, financial, banking, information technology and retail. Almost half of the respondents said each hour of downtime would cost their companies up to $50,000. Almost 10 percent said the figure would be more than $1 million. And 40 percent said that without power, they would be out of business in 72 hours.

Rotary UPS Benefits

A rotary UPS provides instantaneous electric power from energy stored in a spinning mechanical device. It is designed to offset the effects of brownouts, sustained over-voltages, outages, surges and spikes. Before a generator kicks on in response to an outage, a momentary power break occurs. Although the amount of ride-through time is load-dependent, rotary UPS provides enough ride-through time to get a generator started and online before power loss occurs. The rotary UPS not only bridges the gap, but also provides line conditioning. Therefore, although it has not been routinely specified for healthcare settings, rotary UPS may be worth a look.

This 1 MW rotary UPS serves a hospital in rural Southwest Ohio. Photo by Brad Deaton, Engineering DynamicsClick here to enlarge image

In particular, rotary UPS closes the gap between the time of the outage and the load transfer to generators. Furthermore, a rotary UPS can sustain overloads up to 104 percent almost indefinitely, 125 percent for 10 minutes and up to 150 percent for two minutes. It also has a high fault current-clearing ability of approximately 10 full load current without going to bypass for one-half cycle. Compared with other uninterruptible power sources, it handles high in-rush loads and currents. In other words, it can start large hospital equipment loads - a chiller for instance - while maintaining voltage stability.

A rotary UPS also isolates hospital loads from the utility. It is less temperature-sensitive compared to a static or battery UPS system. This means it can operate in higher ambient temperatures, reducing the cost that other systems might require to cool the space. Finally, it provides a power factor near unity for the facility.

In some instances, it may make sense to use rotary UPS rather than a second power feed. Instead of routing in a new feed, smaller hospitals in particular may choose to conduct a feasibility study. The cost of a second feed varies widely, depending on issues such as tap proximity, but it could be comparable to that of a rotary UPS. Additionally, a second feed does not solve the problem of multiple power interruptions; for example, one interruption when the outage occurs, another when the generator starts and yet another when the second feed breaks to return to the grid. Even if the whole grid goes down, a rotary UPS with a generator would be able to operate every light fixture, outlet, chiller and motor on full power as if the power failure had never occurred.

Parallel or Overlap Transfer

A transfer switch has typically been a large gray box sitting in the corner of the electrical room. Typically, both emergency and normal sources were wired to this box. When a loss occurred, power was transferred to the available source either manually or automatically. However, the transfer switch doesn’t have to conform to this model. It could consist of two independent electrically operated circuit breakers - ot necessarily in the same location - controlled through a programmable logic controller (PLC). If an outage occurs, the PLC controls the circuit breakers and performs the function required.

For example, with a standard open transition transfer switch, two outages would normally occur during a utility power loss: one from the initial outage and a second from the return to restored utility power. Using parallel or overlap transfer, the second outage would be eliminated by operating the generator in parallel, completing a make-before-break transfer. Before an anticipated interruption (such as a storm approaching the area) the back-up on-site generator and the utility can be placed into parallel operation. Even if the utility were to fail for several seconds, the generator could handle the load with no service interruption. Once the storm passed, power could be overlap-transferred back to the utility, eliminating an outage to the facility.

This solution allowed one healthcare facility - a 50-bed hospital in a remote rural community at the end of the utility line - to ride through a three-day transformer failure outage and continue to do business as usual.

Parallel power could also allow a facility to peak-shave some of the load. In other words, the generated power could be placed in parallel with utility power for a potential cost benefit during peak usage periods. Here, too, it may be in a facility’s best interest to evaluate this option. The health care entity must make certain that the reduction in demand offsets equipment operations costs. Additionally, the facility must have an agreement with the utility. And the facility and electrical system will have to meet the utility requirements and guidelines for parallel operation.

Rotary UPS Downsides

While a rotary UPS has many benefits, it also has a few pitfalls, one of which is its cost of operation. During use, the rotary device constantly spins. It costs money to keep the rotary UPS online. If the rotary UPS were to discharge or spin down, it must be recharged or spun back up to the required RPM. The electrical system, in turn, must be sufficiently sized to recharge the UPS in addition to handling its normal loads. Another concern is that a rotary discharges a lot of heat. This can be overcome by engineering an adequate ventilation system for the space.

Even with these downsides, health care facilities may be wise to consider UPS. For example, during a lengthy medical procedure, a power blip can force a procedure restart. What’s more, single phasing can do irreparable damage to sensitive equipment. Replacing motors, restarting equipment and/or rescheduling procedures can have economic ramifications and potentially affect the facility’s quality of health care. Deploying a rotary UPS system or paralleling strategies can close the gap between short-term power outages and long-term solutions.

Author

Jeffrey D. Phelps, P.E., is an electrical engineer with Omaha-based architectural and engineering firm HDR.