Uninterruptible power supply [/ənɪnərˈəptəbəl ˈpaʊər səˈplaɪ/] n - A UPS spans the interval between the instant utility power fails and the moment the The Standby Engine takes up the building. The grid may be gone for a few cycles before servers crash; a generator requires 10–30 seconds to start and stabilize. The UPS, backed by Battery energy storage, covers that interval without seam.

Of Its Topologies

• Double-conversion (online). [/ˈdæʊblɛkɒnvɛrsɪɒn ˈɒnlɪnɛ/] n Incoming AC is rectified to DC and inverted back to AC without pause, so the load is always fed from the inverter. There is no transfer time at all; this is the standard for data centers.
• Line-interactive. [/ˈlɪnɛɪntɛræktɪvɛ/] n The load runs on (conditioned) utility power and the inverter engages upon failure. Cheaper, with a brief transfer, and common in wiring closets rather than data halls.

Beyond riding through outages, an online UPS also conditions power, absorbing sags, surges, and noise so the Power distribution unit downstream sees a clean The Current That Comes in Threes waveform.

A single UPS remains a single point of failure, so units are deployed in Redundancy topologies such as N+1 or 2N, and dual-corded loads choose between two UPS outputs by way of a Static transfer switch. When utility returns, an Automatic transfer switch hands the building back from generator to grid.

Part of The Engines of the Hall.