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A voltage stabilizer takes a supply that wanders and holds the output inside a narrow band, so motors, controls, and electronics see the voltage they were built for. It does not store energy and it does not cover an outage. This sheet explains the three designs PSS installs, from 0.5 kVA to 3,000 kVA, and where a stabilizer belongs next to a UPS or a generator.
What to measure before choosing a type
- How far the mains moves. A logger on the incoming supply for a few days shows the low and high points, not a single reading at noon.
- Single-phase or three-phase, and whether the three phases drift apart. Unbalance needs a three-phase unit that corrects each phase.
- How fast the swings are. A slow sag over minutes and a flicker every few seconds are different machines.
- The load. Motors have a starting current well above their running current. The stabilizer has to pass that, not only the steady load.
Servo, relay, and static
| Relay | Servo | Static | |
|---|---|---|---|
| How it corrects | Taps on a transformer, switched by relays | A motor moves a brush along a variable transformer | Electronic switches, no moving parts |
| Speed | A step at a time | Smooth, but limited by the motor | The fastest of the three |
| Output | Steps, so the voltage jumps between taps | A continuous correction | Tight and continuous |
| Fits | Small, tolerant loads | Most plant and building loads | Sensitive electronics and loads that cannot wait |
All three are built for a wide incoming range and can include an automatic bypass, so the load stays fed if the stabilizer itself is taken out for service. Ratings run from a small single-phase unit at 0.5 kVA up to 3,000 kVA three-phase sets for a whole incoming supply.
Where it sits in the power chain
On an unstable grid the stabilizer is the first thing the supply meets, ahead of the distribution board that feeds sensitive equipment. A UPS downstream then spends its time as a UPS, not as a daily voltage corrector that empties the batteries. On a generator, the stabilizer can also hold the set’s output while the load steps on and off, which is the usual “generator protection” use.
It is the wrong tool for a complete power cut. Nothing in a stabilizer stores energy. Pair it with a UPS for no-break loads and with a generator for long outages.
Practical specification and commissioning notes
- Log before you buy. Capture line-to-line and line-to-neutral voltage, frequency, phase imbalance, and the time of each event. A multimeter snapshot cannot show a ten-second sag.
- Separate capacity from correction. kVA is the load the unit can carry. Input range, response time, output accuracy, overload, and short-circuit behaviour are separate requirements.
- Check the neutral and bypass. Three-phase loads, nonlinear power supplies, and a bypass path can put current in the neutral. The protection and cable sizes must be checked with the actual load.
Commission the stabilizer at low, normal, and high input conditions where they can be safely simulated. Record output voltage under steady load and while the largest motor starts. The handover should include the input window, output tolerance, bypass procedure, protection settings, and the next inspection date.
Common problems and how to fix them
The output is still low at certain times of day
The incoming voltage has fallen below the range the unit can lift. A logger will show it. The remedy is a unit with a wider input window, or a supply change, not a larger kVA rating of the same window. kVA is capacity. The correction range is a separate specification.
Motors trip on start even though the stabilizer is “big enough”
The running load fitted, and the starting current did not. Size for the highest current the stabilizer must pass, and check that the bypass can carry the same current.
A servo unit chatters all day
The mains is flickering inside a band narrower than the servo’s dead band should ignore, or the sensing circuit is set too tight. A static unit is the better match when the supply jitters rather than drifts.
Frequently asked questions
Is a stabilizer the same as a UPS?
No. A stabilizer corrects voltage while the mains is present. A UPS stores energy and carries the load when the mains is gone. Many sites need both, in that order: stabilizer, then UPS.
Do I stabilize the whole incoming supply or only one board?
Only the circuits that suffer. Stabilizing a welder and a lighting feeder wastes capacity. A dedicated unit on the sensitive board is usually the clearer design.
What does the bypass do?
It connects the load straight to the incoming supply so the stabilizer can be isolated. Use it for maintenance, not as the normal path. On bypass, the load sees the raw mains again.
Talk to PSS about voltage
PSS supplies and installs servo, relay, and static stabilizers sized to the supply you actually have. Contact the PSS team to book a first site survey and a voltage log.
