Picking the Right UPS for Your Critical Applications: A White Paper on Availability

Overview

The guide contrasts three topologies: passive standby, line-interactive and online double conversion. Among them only online double conversion provides zero transfer time, frequency regulation, power factor correction and harmonic correction. Passive standby is considered unsuitable for three-phase applications and limited to single-phase workstation loads. Common power-quality problems are catalogued by disturbance type, showing which topology removes which. This is why the guide frames selection as matching topology to the disturbances a site must tolerate.

Design choices layered on double conversion form the second part. Double-conversion systems can exceed 96% efficiency without availability compromise. Transformer-free designs are increasingly used between 200 kW and 5 MW, with about 300 kW cited as the threshold below which their space, weight and cost advantages dominate. Capacity-on-demand modularity comes in two forms: software-keyed capacity steps (40-80 kVA, 80-120 kVA or 160-200 kVA) and row-based modular units that grow in 15 kW power cores up to 45 or 90 kW per cabinet.

Finally the eco-mode variant is covered: keeping the inverter energised costs under 1% of rated power, yields 4-4.5% savings against typical double conversion and efficiencies above 98%, and makes transfers nearly seamless. The paper dates from 2018 and its figures are vendor claims, but it works as a compact introduction that compares topology, transformer and modularity choices in one frame.

Key points

1. Of the three topologies, only online double conversion provides zero transfer time, frequency regulation, power factor correction and harmonic correction.
2. Passive standby is considered unsuitable for three-phase applications and limited to single-phase workstation loads.
3. Double-conversion systems can exceed 96% efficiency without availability compromise.
4. Transformer-free designs are increasingly used for 200 kW-5 MW; about 300 kW is cited as the threshold below which their space, weight and cost advantages dominate.
5. Software-keyed capacity steps such as 40-80, 80-120 or 160-200 kVA; row-based modular units grow in 15 kW power cores up to 45 or 90 kW per cabinet.
6. Keeping the inverter active in eco mode costs under 1% of rated power, yielding 4-4.5% savings and efficiencies above 98%.

Using it in design

• Give UPS catalogue entries a topology enum, transformer-based vs transformer-free, modular increment (kW) and maximum frame, and eco-mode type (passive bypass vs active inverter).
• Require double conversion for three-phase critical loads.
• When eco mode is used, display its transfer behaviour.
• Suggest right-sizing via capacity-on-demand when the initial load is well below design load.

Who should read it

Designers and decision makers choosing UPS topology and modularity for the first time.

Related standards

• IEC 62040-3

Publication details

Authors

Vertiv

Publisher

Vertiv

Year

2018

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation