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Three Phase Transformers
9 Series · 120 Models
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Three Phase Transformers Overview
Three-phase dry-type transformers step down, isolate, or adapt three-phase supply for industrial systems and imported equipment without insulating oil, making them fire-safe for indoor installation. QDTB units range from 150 VA to 600 kVA with input voltages up to 1000 V at 50/60 Hz. Product lines SG, SSG, SG10, ZSG, QZB, SGK, and USG span isolation transformers, rectifier transformers, and three-phase auto-transformers, built with high-grade silicon steel cores and pure copper windings for reduced losses and higher efficiency.
Available Series
SG Series
The SG series three-phase dry-type transformers are designed for industrial power distribution applications. Cast resin or open-type construction for indoor use.
SSG Series
The SSG series three-phase servo isolation transformers provide galvanic isolation and voltage matching for servo drive systems and sensitive electronic equipment.
SG10 Series
The SG10 series non-encapsulated dry-type transformers use Nomex insulation system, offering excellent fire resistance and environmental performance.
ZSG Series
The ZSG series three-phase rectifier transformers are designed for rectifier power supply systems, electroplating, and DC power applications.
QZB Series
The QZB series self-coupling voltage reducing starters provide soft-start capability for large three-phase induction motors, reducing inrush current.
SGK Series
SGK three-phase isolation transformers provide galvanic isolation for industrial equipment, 5-50 kVA with custom secondary voltages.
USG Series
USG three-phase transformers step down 380 V to 220 V for machinery and distribution. 3.5-180 kVA, balanced three-phase output.
Three Phase Autotransformers Series
General-purpose three-phase autotransformers step voltage up or down with a single winding that serves as both primary and secondary, offering higher efficiency and smaller size than equivalent isolating transformers. Rated 1–500 kVA for 380V/220V/110V systems, used for voltage conversion, interconnection and step-up applications.
Oil-Immersed Isolation Transformers Series
Oil-immersed three-phase isolation and rectifier transformers provide galvanic isolation between the supply and load with oil-immersed cooling for higher ratings and outdoor duty. Rated 10–2500 kVA, 6/10/35 kV primary, for rectifier, isolation and power-conversion applications requiring robust oil-immersed construction.
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The values below are computed from what you selected above. Anything that cannot be computed yet is shown as an em dash — never as zero.
Iₙ = S / (√3·U) · I_sc = 100·Iₙ / uₖ · S_sc = √3·U·I_sc · I_p = k·Iₖ
Still required to complete the calculation: rated capacity S, impedance voltage uₖ, short-time or peak withstand current.
Per-model values (P0 / Pk / uₖ declared by the factory, losses, noise, temperature rise, dimensions, weight) are not in the product library: those rows stay at an em dash until the factory parameter sheet is supplied. An em dash means the value is unavailable — it is never rendered as zero.
Read-only: no price factor, not part of the sum — the loss-grade cost is already carried by the efficiency (subtype) base price, so charging here would double-bill. Values come from the product library type-test data, interpolated between published capacities; grades the library does not cover show an em dash, never zero.
Reference prices are for estimation only and do not constitute a formal offer.
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Application Scenarios
Imported Equipment
Adapts imported machines to local three-phase voltages, avoiding costly rewinding or replacement.
Power Isolation
Three-phase isolation to suppress harmonics, transients and noise for sensitive industrial loads.
Rectifier Systems
Feeds rectifier bridges and DC drives with dedicated three-phase secondary windings.
Industrial Machinery
Steps down or isolates supply for production lines, injection moulding and packaging equipment.
Elevators & Cranes
Handles high starting currents of hoists and elevators with robust winding construction.
Testing & Laboratories
Adjustable three-phase output for product testing, motor run-in and R&D benches.
Technical Advantages
Dry-Type Safety
No insulating oil, fire-safe and suitable for indoor installation near people and equipment.
Pure Copper Windings
Full copper windings reduce losses and improve thermal performance over aluminium.
Multiple Configurations
Isolation, auto-transformer and rectifier variants from a single product family.
Low-Loss Core
High-grade silicon steel keeps no-load loss low and efficiency high.
FAQ - Three Phase Transformers
What is the difference between an isolation transformer and an auto-transformer?
What does delta-star (Dyn11) connection mean?
How do I choose the kVA rating?
What is the difference between single-phase and three-phase transformers?
What is the minimum order quantity (MOQ) for Three Phase Transformers?
What is the delivery time for Three Phase Transformers?
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Isolation vs Auto-Transformer vs Rectifier Transformer: How to Choose
| Three-Phase Isolation (SG) | Auto-Transformer (QZB) | Rectifier Transformer (ZSG) | |
|---|---|---|---|
| Winding | Separate primary and secondary windings | One tapped winding, part of it shared | Valve-side winding sized for harmonic current |
| Galvanic isolation | Full isolation between supply and load | None, so a supply fault passes through | Isolation to the rectifier, plus a DC barrier |
| Size & cost | Largest for a given rating | Smaller and cheaper for the same throughput | Larger, because the winding carries harmonics |
| Voltage adaptation | Fixed ratio, with taps on request | Continuous matching through the tapped winding | Designed around the DC output required |
| Losses | Baseline for the comparison | Lower, since less copper carries the load | Higher harmonic loss, so a derating is applied |
| Typical duty | Imported equipment and general isolation | Reduced-voltage motor starting and voltage matching | Drive and electrolysis DC supplies |
| Typical application | Machine tools, elevators and test benches | Motor starting on weak supplies | Rectifier and DC process plants |
Where QDTB® Three-Phase Transformers Are Specified
Three-phase dry-type transformers are specified where imported machinery arrives with a supply voltage that does not match the plant, or where the machine's electronics need galvanic isolation from the factory earth. Because the unit is oil-free, it can stand inside the production hall next to the machine it feeds instead of in a separate oil room.
Rectifier transformers feed drive and DC process loads, and their valve windings are sized for the harmonic current the rectifier draws rather than for the DC output alone. That is why the same kVA rating does not transfer directly from an isolation unit to a rectifier unit.
Elevators, cranes and testing laboratories specify the SG and QZB lines for isolation and reduced-voltage starting, where the supply cannot take a direct-on-line start. Test benches add multi-tap primaries so the same bench can be set up for different equipment voltages.
The range covers 150 VA to 600 kVA with input voltages up to 1000 V at 50/60 Hz. Units are built to IEC 60076 / GB1094.1 with high-grade silicon steel cores and copper windings, and custom voltages are quoted against the equipment they will feed.
Frequently Asked Questions
What is the difference between an isolation transformer and an auto-transformer?
An isolation transformer has separate primary and secondary windings for full galvanic isolation. An auto-transformer shares one winding, is smaller and cheaper, but provides no isolation.
What does delta-star (Dyn11) connection mean?
It describes the winding configuration: primary in delta, secondary in star with neutral. Dyn11 is the most common industrial connection, providing a neutral for unbalanced loads.
How do I choose the kVA rating?
Match the transformer to the continuous load plus starting surge. For motor loads, allow for 3-5x starting current or use a soft starter.
What is the difference between single-phase and three-phase transformers?
A three-phase unit transforms balanced three-phase power in one core, using less material and space than three separate single-phase units of the same total kVA, and delivers smoother power for motors. Single-phase is for lighter, distributed loads.
What is the minimum order quantity (MOQ) for Three Phase Transformers?
One unit for standard products. Custom-designed equipment is quoted on specifications — send your parameters or drawings and our sales team will confirm the MOQ for your configuration.
What is the delivery time for Three Phase Transformers?
Standard units are delivered in 30-45 days. Custom or large-capacity units follow a project-specific schedule confirmed at quotation. Rush orders can be accommodated for urgent projects.