What is a UPS system in a data centre?

A UPS (Uninterruptible Power Supply) bridges the gap between a power outage and generator startup — typically 10-30 seconds. Without a UPS, even a momentary grid flicker would crash every server in the facility. Three main types exist: static battery UPS (most common, uses lithium-ion or VRLA batteries, 5-15 minute runtime), rotary UPS (spinning flywheel stores kinetic energy, 15-30 seconds of ride-through), and diesel rotary UPS (DRUPS, combines flywheel and diesel generator in one unit). UPS systems are sized in kVA and typically rated at N+1 or 2N redundancy. A 10 MW data centre requires $3-6M in UPS infrastructure alone, representing 15-20% of total electrical system cost.