Power & capacity
- kVA — apparent power; the unit UPS are rated in.
- kW — real power your load actually consumes.
- Power factor (pf) — kW ÷ kVA. Unity pf (pf 1) means kVA = kW.
- Inrush — the brief, high startup current drawn by motors, compressors and power supplies (often 2–10× running current).
- Crest factor — the ratio of peak to RMS current, important for how well a UPS handles non-linear loads.
Topology
- Offline (standby) — feeds mains to the load, switches to battery only on failure.
- Line-interactive — adds voltage regulation (AVR) without going to battery.
- Online double-conversion — converts AC→DC→AC continuously, zero transfer time, cleanest output.
- VFI / VI / VFD — IEC classes: Voltage & Frequency Independent (online), Voltage Independent, Voltage & Frequency Dependent (offline).
- Transformerless — modern UPS design without a bulky output transformer — lighter, smaller, more efficient.
- ECO mode — runs on bypass for efficiency, transfers to inverter only on a fault.
Battery, redundancy & architecture
- Autonomy (runtime) — how long the UPS powers the load on battery alone.
- VRLA — valve-regulated lead-acid, the standard UPS battery (3–5 year life).
- Lithium-ion — longer-life, lighter, faster-charging battery (8–10 years).
- N+1 — one spare module/unit so a single failure does not drop the load.
- 2N — two fully independent systems for the highest availability.
- Hot-swap — a module or battery that can be replaced without powering down.
- Bypass / EMBS — an alternative mains path (static automatic, or external maintenance bypass switch) for service and faults.
Monitoring & power quality
- SNMP — the standard IT protocol for monitoring UPS status and alarms.
- Modbus / BACnet — protocols for building management and industrial SCADA.
- NetMan — Riello's network communication card family.
- Volt-free contacts — simple relay signals for alarms and EPO where networking is unavailable.
- Sag / swell / transient — a brief voltage dip, rise or spike.
- Harmonic distortion (THD) — waveform pollution from non-linear loads; online UPS isolate the load from it.
- EN 50160 — the European standard describing mains voltage characteristics.
Frequently asked questions
What does VFI mean on a UPS?
VFI (Voltage and Frequency Independent) is the IEC classification for online double-conversion UPS, where the output is completely independent of the input voltage and frequency.
What is the difference between kVA and kW?
kVA is apparent power (the UPS rating); kW is real power (what your load uses). They are linked by power factor — at unity pf, kVA equals kW.
What does N+1 mean?
N+1 means installing one more module or unit than the load requires, so any single unit can fail or be maintained without dropping the load.
What is a maintenance bypass (EMBS)?
An external switch that feeds the load directly from mains so the UPS can be isolated and serviced while the equipment stays running.