For a 50 kVA factory, choose a three-phase stabilizer rated at least 25% above your real running load in kVA, with an input range that covers the lowest and highest voltage on every phase at your site. Work it out in five steps: add up the load, convert kW to kVA, allow for motor starting, add margin, and check the voltage. Example: 32 kW of running motors ÷ 0.8 = 40 kVA, plus 25% = 50 kVA.
Step 1: What is my real load?
List every machine the stabilizer will feed and read the kW on each nameplate. Then ask: how many run at the same time? A workshop with ten machines rarely runs all ten at full load together. Add up the machines that really run together on a busy day. If you have a load sheet or an electricity bill showing maximum demand, use that.
Step 2: How do I convert kW to kVA?
Stabilizers are rated in kVA, machines usually in kW. For a typical factory with motors, divide kW by about 0.8. So 32 kW ÷ 0.8 = 40 kVA. If your nameplates already show kVA or amps, use those directly.
Step 3: Do I need to allow for motor starting?
Yes. A motor started direct-on-line can pull several times its running current for a few seconds. Compressors behave the same way. If your largest motor is big compared with the total load, or several motors start together, you need more room. Soft starters, star-delta starters and VFDs reduce this.
Step 4: How much margin should I add?
Add 25% to the running load. 40 kVA × 1.25 = 50 kVA. If your answer falls between two sizes, or you plan to add machines soon, go up a size. Do not oversize by a lot — a much bigger stabilizer costs more without helping.
Step 5: What voltage range do I need?
This is the step most buyers skip. Measure each phase at your worst time — often the evening peak, or the morning start in industrial areas. Write down the lowest and highest. The stabilizer's input range must cover both, on every phase, because in Pakistan the three phases are often unbalanced.
What does a 50 kVA three-phase stabilizer look like?
The Voltec SJW 50 kVA is an imported three-phase servo stabilizer. Its data:
| Spec | SJW 50 kVA |
|---|---|
| Input, per phase | 150–260V |
| Output, per phase | 220V ±2.5% |
| Input, 3-phase | 260–450V |
| Output, 3-phase | 385V ±3% |
| Frequency | 50–60 Hz |
| Protection | Over/under-voltage, phase failure, time delay |
| Display and control | Digital volt/amp meter, bypass switch |
| Warranty | 1 year on the coil |
Phase-failure protection matters most: if one phase is lost, a three-phase motor can burn in minutes. The bypass switch keeps the factory running while the stabilizer is serviced.
What about 30 kVA or 100 kVA?
The same five steps apply. Under about 30 kVA on a single-phase supply, a single-phase servo is often enough — the 30 kVA single-phase servo works from 60V for very weak lines (it is not three-phase). From 100 kVA up, Voltec supplies three-phase industrial units built to order with tender documentation: see industrial stabilizers.
Servo or solid-state for a factory?
For a whole three-phase factory feed, servo is still the practical choice. Solid-state SCR (up to 10 kVA) and IGBT (up to 20 kVA) suit single sensitive machines inside the factory, such as a CNC or laser. More in servo vs SCR vs IGBT for factory low voltage.