Uninterruptible Power Supplies: Specification Strategies
The first step to minimizing disruptions in power sources takes place during the power system’s design. Identifying the facility’s needs, understanding the business model and predicting user needs are paramount when specifying a system that balances reliability and cost.
UPS solutions range from large, centralized units to small, rack-mounted units that handle only the most critical information-technology loads. A reliable power system depends on quality equipment and reliable design. A facility’s UPS system should be able to protect critical and high-tech equipment in an outage and to facilitate planned power outages so technicians can conduct routine maintenance.
Among the considerations that can help system designers and managers determine the right UPS solution are these:
• Facility-distribution type. The two configurations of UPS distribution systems are centralized and distributed.
In a centralized configuration, the units are in a common location for more efficient maintenance, security, cooling and, in many cases, fire rating of the room. This configuration provides efficiencies that make it very appealing to managers. On the downside, the backup-power source can be farther from the protected load, requiring more distribution equipment and creating more potential failure points.
A distributed configuration puts the units closer to the loads they protect, minimizing potential failure points but increasing construction costs because many of the items listed above are repeated throughout the facility.
• Duration. An organization’s business model determines the length of time a UPS must provide power. Does the application call for a quick-ride-through UPS, or does it require 15 minutes of backup capacity to systematically shut down sensitive electronics in the event of a longer power outage?
Normally, a risk assessment will prompt designers to weigh the capacity of the UPS against the system’s cost. Companies that rely on uptime for life safety and revenue usually are willing to spend more to achieve longer-term backup.
• Reliability. Determining an organization’s reliability needs is essential for providing value to occupants. Some organizations can tolerate short periods of downtime, while others definitely cannot. The amount of reliability a system provides is a function of the engineering design and the specific equipment specified.
A preventive maintenance program also plays a critical role in reliability over the system’s life.
• Flexibility. If the UPS system does not have the flexibility to bypass equipment for maintenance purposes, the facility still will need to provide downtime to maintain or repair the system, even if designers and managers implement a highly reliable system. This situation is acceptable for some organizations, but it absolutely cannot happen for others.
Managers have two bypass options. A static bypass switch provides a means to internally bypass the UPS in the event of a failure. Technicians also can use this switch to internally bypass the UPS to perform maintenance. A static bypass switch is engineered to provide uninterrupted power to a load during normal-to-bypass and bypass-to-normal transitions.
By comparison, a maintenance bypass is an external bypass, or wraparound, configuration with a make-before-break configuration so technicians can service, maintain, or replace the UPS without interrupting the equipment’s power supply.