220V to 380V Step Up Transformer: When and How | Wilmall
220V to 380V Step Up Transformer: When and How
If your machine, motor, or industrial equipment is rated for 380V but your local supply is only 220V, a 220V to 380V step up transformer is usually the most economical and reliable way to make it run correctly. At Wilmall Transformers, a low-voltage transformer factory in Yueqing, Zhejiang, China, we have exported step up transformers to the Middle East, Southeast Asia, Africa, South America, and Central Asia for over 15 years. This guide explains when you need one, how it works, and how to size it correctly.
When Do You Need a 220V to 380V Step Up Transformer?
Voltage mismatch between supply and equipment is a common problem in export projects. A 220V to 380V step up transformer is required in four typical situations:
- Three-phase equipment rated 380V connected to a 220V three-phase grid. In several countries and industrial zones the phase-to-phase voltage is 220V, yet imported machinery such as pumps, compressors, and machine tools is rated 380–400V. Feeding 380V equipment from 220V simply does not work: motors will not start, contactors will drop out, and heaters will produce roughly one third of their rated output.
- Single-phase 380V loads. Some commercial ovens, dryers, and special industrial heaters are designed for single-phase 380V. If only 220V single-phase is available, a single-phase step up transformer delivers the correct 380V.
- Voltage drop compensation. In long distribution runs the voltage may fall well below nominal. A step up transformer with additional taps can restore 380V at the load end.
- Upgrading a facility to receive 380V equipment. When a company imports a production line rated 380V but the building is only wired for 220V, a bank of step up transformers is often cheaper than re-cabling or replacing the equipment.
Before ordering, confirm the phase count on both sides. A transformer changes voltage, but it does not create phases: to obtain three-phase 380V output you must feed it three-phase 220V input. If you only have single-phase 220V and need three-phase 380V, you also need a phase converter or a VFD.
How a 220V to 380V Step Up Transformer Works
A transformer raises voltage through the turns ratio of its windings. The primary winding is connected to the 220V supply, and the secondary winding is wound with roughly 1.73 times more turns to deliver 380V. Because power is conserved, if the output voltage rises by a factor of about 1.73, the available output current falls by the same factor. A 10kVA unit, for example, delivers about 45A at 220V on the primary side but only about 26A at 380V on the secondary side.
Auto versus isolated design
- ST series (auto transformer). The input and output share a common winding. Auto transformers are lighter, smaller, cheaper, and more efficient for the same rating, which is why they dominate step up and step down applications. The trade-off is that there is no galvanic isolation between input and output.
- STU series (isolated transformer). A separate primary and secondary winding with full galvanic isolation. Use an isolated type when the equipment needs a separated neutral, when you want to eliminate DC offset, or when local codes require isolation.
- DT series (three-phase). Built with three limbs and a delta or star configuration for three-phase 220V to three-phase 380V conversion. These are the standard choice for three-phase motors and industrial loads.
The frequency is never changed by a transformer. If your grid is 50Hz, the output remains 50Hz. Equipment that is strictly frequency-sensitive will need a frequency converter.
How to Size a 220V to 380V Step Up Transformer
Sizing is where most installation problems start. A transformer that is too small overheats, sags under load, and fails early. Follow these steps:
Step 1: Add up the connected load in watts
List every device connected to the transformer and add their nameplate power in watts. For a single three-phase motor, use the motor nameplate kW rating rather than the frame size.
Step 2: Convert watts to VA
Because transformers are rated in VA, divide the wattage by the power factor. For motors and other inductive loads, use a power factor of 0.8. For pure resistive loads such as heaters and incandescent lighting, watts and VA are equal.
Step 3: Apply a safety and starting factor
| Load type | Recommended multiplier on rated VA |
|---|---|
| Resistive loads (heaters, ovens, lighting) | 1.2 – 1.5 |
| General inductive loads (fans, pumps, small motors) | 2.0 – 3.0 |
| Motors with high starting current (compressors, saws, hoists) | 3.0 – 4.0 |
| Electronic loads with inrush (SMPS, converters) | 1.5 – 2.0 |
A transformer can tolerate a short inrush current, but if it is repeatedly forced to supply starting current far above its rating, the voltage sags and the winding temperature rises. Oversizing by one standard step is cheap insurance against early failure or a machine that cannot start.
Step 4: Round up to a standard capacity
Wilmall offers step up transformers from 500VA up to 30kVA in both single-phase and three-phase versions. For a motor-driven application, choose the next standard rating above your calculated VA.
Wilmall ST and DT Series Specifications
| Series | Phase | Input | Output | Capacity range | Winding type |
|---|---|---|---|---|---|
| ST | Single-phase | 220V | 380V | 500VA – 30kVA | Auto |
| STU | Single-phase | 220V | 380V | 500VA – 15kVA | Isolated |
| DT | Three-phase | 220V (phase-to-phase) | 380V | 1kVA – 30kVA | Auto or isolated |
All Wilmall units use high-grade silicon steel laminations, are tested at full load before shipment, and are available with extra taps such as 380V/400V/415V output so you can fine-tune the voltage for your equipment.
Wiring and Installation Notes
- Confirm the phase configuration. For a single-phase unit connect L and N on the 220V side; for a three-phase DT unit connect L1, L2, and L3 on the input and the matching terminals on the output. Do not parallel the phases.
- Earth the enclosure and the neutral point. A missing earth is one of the most common causes of electric shock on workshop floors.
- Fit an input overcurrent protective device. The primary-side breaker should be rated at or slightly above the transformer’s full-load input current so that the winding is protected against overload.
- Keep the transformer ventilated. Mount it in a dry location with free air circulation. Derate by roughly 10% if the ambient temperature exceeds 40°C.
- Check output voltage under load. Measure the output with the equipment running. If it is below 370V at the terminals, use a higher tap or a larger unit.
- Never exceed the continuous rating. Continuous overload shortens insulation life and can cause winding failure.
Common Applications
- Three-phase motors, pumps, and compressors rated 380V fed from 220V three-phase grids
- 380V heating systems and drying ovens in workshops and factories
- Machine tools and production lines imported from 380V markets
- Voltage restoration for long cable runs in industrial facilities
- Test benches and R&D labs that need a stable 380V supply
Frequently Asked Questions
Can a single-phase 220V to 380V transformer run a three-phase 380V motor?
No. A transformer changes voltage but not phase count. To run a three-phase motor you need a three-phase input, then a DT three-phase step up transformer. From single-phase supply alone, you would additionally need a phase converter or a VFD with a three-phase output.
What size transformer do I need for a 5.5kW motor?
Roughly: 5.5kW divided by a power factor of 0.8 gives about 6.9kVA at full load. With a starting factor of 1.5 to 2, a 10kVA to 15kVA three-phase unit is a realistic recommendation. Send us the motor nameplate and we will confirm the exact rating.
Does a 220V to 380V step up transformer convert frequency?
No. The output frequency is identical to the input frequency. If your load is frequency-sensitive, add a frequency converter.
Is an auto transformer safe for industrial use?
Yes. Auto transformers are widely used in industry; the only functional difference is that there is no galvanic isolation. Choose the STU isolated series when you need a separated neutral or isolation from the supply.
Why does my equipment still underperform after adding a transformer?
Check three things first: that the transformer VA rating covers the starting current, that the output tap is set correctly (380V, not 400V), and that the wiring to the load is not undersized, causing voltage drop before the equipment.
Connecting a 220V to 380V Step Up Transformer Safely
Wiring a 220V to 380V step up transformer requires care, because the output voltage is high enough to be dangerous and the three-phase connection must be correct. Confirm the input is single-phase or three-phase as your unit is built for, then connect the input to the marked terminals, the output to the marked high-voltage terminals, and the earth terminal to a proper ground. Before energizing, check with a multimeter that the output reads near 380V between phases, and 220V between each phase and neutral if your star connection provides a neutral. Never touch the output terminals while the unit is live, and use the correct fuse or MCB on the input side. If the wiring diagram is unclear, ask us before connecting, because a wrong three-phase connection can damage the equipment or create a shock hazard.
Request a Quote from Wilmall
Wilmall Transformers is a low-voltage transformer manufacturer in Yueqing, Zhejiang, China, exporting step up, step down, control, and variable transformers for over 15 years. Our 220V to 380V step up transformers are built to CE and RoHS standards, carry a 12-month warranty, and ship with a lead time of 15 to 25 days and a minimum order quantity of just 10 pieces. OEM and ODM customization, including custom voltage taps, terminals, enclosure styles, and packaging, is our standard service.
Request a quote today by sending your load details and photos of the equipment nameplate. Contact Wilmall on WhatsApp, email info@wilmall.com, or use the website inquiry form, and our engineers will confirm the correct capacity and configuration for your project.
