In major applications like major computer installations, process control in chemical plants, safety monitors, IC units of hospitals etc., even a temporary power failure may lead to large economic losses.
Description of High-availability power systems Redundancy options
For such critical loads, it is of paramount importance to use UPS systems.But all UPS equipments should be completely de-energized for preventive maintenance at least once per year. This limits the availability of the power system. Now there are new UPS systems in the market to permit concurrent maintenance.
High-Availability Power Systems
The computing industry talks in terms of "Nines" of availability. This refers to the percentage of time in a year that a system is functional and available to do productive work. A system with four "Nines" is 99.99 percent available, meaning that downtime is less than 53 minutes in a standard 365-day year. Five "Nines" (99.999 percent available) equates to less than 5.3 minutes of downtime per year.
Six "Nines" (99.9999 percent available) equates to just 32 seconds of downtime per year. These same numbers apply when we speak of availability of conditioned power. The goal is to maximize the availability of conditioned power and minimize exposure to unconditioned utility power. The concept of continuous availability of conditioned power, takes this concept one step further. After all, 100 percent is greater than 99.99999 percent.