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Need for UPS and on-line UPS

Short answer

UPS provides no-break clean power to critical loads during supply disturbances and bridges the gap until the DG starts. On-line UPS always supplies the load from the inverter via rectifier and battery, giving zero transfer time and full isolation; it has lower efficiency and higher cost.

Why UPS is required for industrial electrification? Explain about On-line UPS.

Why UPS is required in industrial electrification

A UPS (Uninterruptible Power Supply) gives continuous, clean AC power to critical loads during supply failure and disturbances.

  • PLCs, DCS/SCADA, computers and instruments lose data or trip on even a few milliseconds' interruption.
  • It protects equipment from voltage sags, spikes, surges, harmonics and frequency variation.
  • It bridges the 10–15 s gap until the DG set starts and takes load.
  • It enables safe, orderly shutdown of processes and avoids loss of production.
  • It supplies emergency lighting, communication, alarm and security systems.

On-line UPS

In an on-line (double-conversion) UPS, the load is always supplied by the inverter.

  1. Rectifier/charger converts mains AC to DC, feeds the inverter and keeps the battery charged (float).
  2. Battery is connected to the DC bus permanently.
  3. Inverter converts DC to regulated sine-wave AC for the load.
  4. Static bypass switch transfers the load to mains if the inverter fails or is overloaded.

When mains fails, the battery continues feeding the inverter, so there is zero transfer time.

        ┌────── static bypass ──────┐
 AC ─►[Rectifier]─►DC─►[Inverter]───┴─► Load
                    │
                [Battery]

Advantages: no break, complete isolation from mains disturbances, stable voltage and frequency. Disadvantages: higher cost and losses (efficiency ≈ 90–94%).

✓ Answer checked by Claude Opus 5.5 (high effort)

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