Two different problems
Voltage fluctuation and power failure get talked about together and are not the same fault. Voltage in this belt wanders, especially on the same feeder as heavy plant. A servo stabilizer corrects that: it holds the output inside a window while the supply is present. It does nothing when the supply goes away, because it has no stored energy.
An online UPS has stored energy. The load runs off the inverter continuously, so a cut is not an event the load ever sees. That is what protects a PLC, a drive or a line that cannot be stopped halfway.
What goes wrong when you pick the wrong one
The common mistake is a stabilizer in front of equipment whose real problem is short outages. The voltage looks clean on a meter and the line still drops. The opposite mistake is a UPS sized only for the outage, fed by an incomer that swings enough to keep the UPS on battery, which wears the battery out early.
What we stock from Fuji Electric
| Product | Fixes | Typical use |
|---|---|---|
| Servo stabilizer, air-cooled | Voltage variation | Lower ratings, ventilated rooms |
| Servo stabilizer, oil-cooled | Voltage variation | Higher ratings, hot or dusty locations |
| Online UPS, 1 phase | Outage and variation | Instrumentation, IT, small controls |
| Online UPS, 3 phase | Outage and variation | Production lines, drives, plant automation |
These are built to rating rather than held on a shelf, so they carry a lead time. Ask before you plan around a date.
Where we see them going in
Manufacturing plants running automation continuously. Data rooms and server cupboards where a dirty shutdown costs more than the hardware. Anything with a VFD, which is noticeably less tolerant of a sagging supply than the motor it drives.
Figures quoted by any manufacturer for backup time are indicative and assume a load and a battery condition. Confirm against the current datasheet and your own load before you commit to a rating.