The complete guide to online (double-conversion) UPS in India: how it works, IGBT and isolation transformer, key specs, sizing, applications, and buying.
Technology Explainers
If you are responsible for power in a data center, hospital, factory, bank, or government office in India, the online UPS is the single most important piece of equipment standing between your operations and the grid. It is also one of the most misunderstood — buried under spec-sheet jargon, inflated marketing numbers, and the persistent confusion between an "inverter," a "UPS," and an "online UPS." This guide cuts through all of it. It explains what an online UPS really is, how double conversion actually works, which specifications matter (and which are marketing noise), how to size one correctly, and what to demand when buying in India.
What Is an Online UPS?
An online UPS — formally a double-conversion UPS — is a power backup system in which the connected load always runs off the UPS inverter, never directly off the mains. Incoming AC is converted to DC, then converted back to clean AC by the inverter, continuously. Because the load is permanently fed by the inverter, there is no "switchover" when the grid fails — the batteries simply continue supplying the same DC bus, and the output never even flickers.
This is fundamentally different from other topologies. In an offline (standby) UPS, the load runs off raw mains and only transfers to the inverter when power fails — with a brief gap. In a line-interactive UPS, the load runs off mains through an automatic voltage regulator (AVR), transferring to battery only on failure. Only the online UPS delivers zero transfer time and complete isolation from input disturbances. We compare all three in detail in online vs line-interactive vs offline UPS, and the fundamentals in what is an online UPS.
How Online Double Conversion Works
Understanding the signal path makes everything else clear. A double-conversion UPS has four core stages:
Rectifier / charger — converts incoming AC to DC. In a modern UPS this is an IGBT-based rectifier that also draws clean current from the grid and keeps the battery charged.
DC bus — the internal DC link that feeds the inverter. The battery connects here, so when mains fails the inverter keeps drawing from the same bus without interruption.
Inverter — converts DC back to a precise, regulated AC sine wave for the load. This is what your equipment actually runs on, at all times.
Static bypass — a safety path that can route raw mains to the load if the UPS is overloaded or faulted, protecting availability.
Because the input is fully rebuilt into a new waveform, sags, surges, spikes, frequency drift, and noise on the input never reach the load. That is the entire value proposition of online double conversion, explained further in what is double conversion UPS.
The Role of IGBT Technology
Not all double-conversion UPS are built the same. Older designs used thyristor (SCR) based rectifiers; modern systems — including Paradyne's — use IGBT (insulated-gate bipolar transistor) based rectification and high-frequency PWM inverters. The practical advantages of IGBT are real, not cosmetic: cleaner input current (lower input harmonic distortion), better efficiency, a smaller and lighter footprint, and a more stable output. For sites billed on power quality, the cleaner input current also matters. The full technical case is in IGBT-based UPS explained.
Why the Isolation Transformer Matters
Paradyne's online UPS includes an inbuilt isolation transformer, and this is a genuine differentiator for sensitive and critical loads. Galvanic isolation between input and output breaks ground loops and blocks common-mode noise, provides a clean, locally derived neutral-earth reference, and adds a layer of protection for medical, laboratory, and signalling electronics. It is one of the main reasons isolation-transformer online UPS is specified for hospitals, labs, and railway signalling. The benefits and use cases are covered in online UPS with isolation transformer.
Key Specifications to Demand
This is where buyers get misled. Here are the specifications that actually matter, with Paradyne's real figures as a reference point:
Input voltage window — a wide window means the UPS stays on mains through sags and swells instead of cycling the battery. Paradyne single-phase online accepts 160-260V; the three-phase range accepts 300-450V.
Output voltage regulation — Paradyne holds 230V ±1% (single phase) / 400V ±1% (three phase).
Output frequency — 50 Hz ±0.05 Hz, crystal controlled.
Waveform and THD — a true sine wave with total harmonic distortion under 3%. Output THD tells you how clean the power your load receives really is; more on this in UPS harmonics and THD.
Transfer time — NIL / zero, by definition of double conversion.
Power factor — Paradyne online is rated at a 0.8 power factor (lagging to unity). This sets how much real power (kW) you get per kVA — critical for sizing, as explained in kW vs kVA and power factor.
Crest factor — above 4:1, so the UPS handles peaky non-linear loads.
Overload capacity — 110% for 10 minutes.
Operating environment — 0-50°C, up to 85% non-condensing humidity; generator-compatible input frequency tolerance (50 Hz ±10%).
A word of caution: be sceptical of headline efficiency claims. Insist on the efficiency curve at the partial-load band you will actually run at (typically 30-50%), not a single full-load number — and confirm the rated power factor so you read the real kW capacity, not just the kVA.
How to Size an Online UPS
Sizing is where most installations go wrong, almost always by under-buying. The method, in brief:
Total your real load in watts (kW), not VA. Measure where you can.
Convert to a kVA rating using the UPS rated power factor: kVA = kW ÷ power factor. At a 0.8 rating, a 10 kVA UPS delivers about 8 kW.
Add 20-30% headroom for startup inrush, future growth, and to avoid running continuously near 100%.
Size the battery separately for your required backup time.
The full worked method is in how to calculate UPS capacity, and the battery side in how to calculate UPS battery backup time. For specific ratings, see the dedicated guides for 5 kVA, 10 kVA, and 20 kVA systems.
Where an Online UPS Is Essential
Line-interactive UPS is fine for many offices and lighter loads. But there are environments where only an online UPS will do — anywhere the load cannot tolerate even a few milliseconds of disturbance, or where input power quality is poor:
Hospitals and healthcare — ICU, OT, and diagnostics (UPS for hospitals).
Data centers and server rooms — zero-downtime IT loads (UPS for data centers).
Banking and ATMs — transaction integrity (UPS for banks and ATMs).
Industrial and manufacturing — PLCs, CNC, process control (industrial UPS).
Telecom, railways, defence, and labs — mission-critical, continuous-duty loads.
Buying and Compliance in India
In India, an online UPS purchase — especially for institutional or government use — is also a compliance exercise. The essentials to demand:
BIS certification under IS-16242 — the Indian standard for UPS, aligned with the IEC 62040 framework. See BIS certification and IS-16242.
NABL-accredited test reports — independent verification that the datasheet is real; how to read one is in NABL test reports explained.
GeM OEM authorization — for government procurement (buying UPS on GeM).
Warranty, AMC, and service SLA — what actually determines uptime over the life of the system.
Maintenance and Lifecycle
An online UPS is a long-term asset. Plan for correct installation and earthing, a suitable room environment, a preventive maintenance schedule, and battery replacement over its life — all covered in the installation checklist and preventive maintenance schedule. Factoring energy efficiency and battery replacement into a total cost of ownership view almost always favours well-built, well-supported equipment over the lowest initial quote.
The Bottom Line
An online double-conversion UPS is the gold standard of power protection because it isolates your load completely and delivers clean, continuous power with zero transfer time. When you specify one, read past the headline kVA and marketing numbers: confirm the input window, the rated power factor, output THD, the isolation transformer, and the certification that backs it. Get those right and you have a system that quietly does its job for a decade.
Paradyne builds its IGBT-based online UPS range — with inbuilt isolation transformer, true sinewave output, and BIS certification under IS-16242 — specifically for Indian grid conditions. Explore the online UPS specifications, or tell us your load and we will size the right system for you.
