What is a Three-Phase Dry-Type Transformer?
Time：2025-08-8 Auther：ZTelec-www.ztelectransformer.com
A three-phase dry-type transformer is a power device composed of three independent single-phase dry-type transformers integrated into one unit. Each single-phase transformer includes two sealed high-voltage windings and one low-voltage winding. All windings are fully enclosed in a housing isolated from the atmosphere, achieving oil-free operation and eliminating the risks associated with transformer oil.
Its main advantage lies in its dedicated design for three-phase AC power systems (each phase shifted by 120°). Compared with single-phase transformers, it features significant differences in magnetic circuit structure, winding configuration, and electrical performance, making it ideal for various industrial, commercial, and residential power supply applications.
The Necessity of a Three-Phase System
Three-phase AC power consists of three voltages (phases A, B, and C) with equal amplitude and frequency, offset by 120°. This design offers clear benefits:
Efficient Power Transmission: Three-phase systems deliver constant instantaneous power, ensuring smoother motor operation and reducing mechanical wear.
Lower Material Costs: They require around 25% less conductor material than single-phase systems for the same power, reducing network construction costs.
Industrial Compatibility: Most industrial equipment—motors, inverters, and high-power machinery—runs on three-phase power, making three-phase transformers essential.
Three-Phase Iron Core Structure
1. Three-Column Core (Mainstream Design)
Each of the three core legs carries the windings for one phase (A, B, C), connected by a common yoke to form a complete magnetic circuit. Magnetic flux in each phase is coupled with the other two phases, enabling natural compensation for minor load imbalances. This design is compact, cost-effective, and widely used in standard power distribution applications such as 10kV/400V systems.
2. Five-Legged Core (For High Harmonics or Large Capacity)
This design adds two side yoke legs to the standard three-legged core, creating a five-legged structure. It diverts third harmonic flux, lowering parasitic core losses and noise, making it ideal for data centers, frequency converter systems, and harmonic-rich environments where stability is critical.
Special Design Features of Three-Phase Dry-Type Transformers
1. Optimized Winding Arrangement
Overlapped Winding: Alternating high-voltage and low-voltage windings enhance electromagnetic coupling, reduce leakage reactance, and improve energy efficiency.
Axially Split Winding: Dividing each phase winding into two parallel sections increases short-circuit withstand strength and enhances operational safety.
2. Upgraded Cooling System
Dedicated ventilation ducts between windings, combined with AN (natural air) or AF (forced air) cooling, ensure effective heat dissipation under high load. Embedded temperature sensors in each phase winding monitor heat rise in real time, supporting precise overheating protection.
Winding Connection Methods
Dyn11 Connection: Delta high-voltage winding and star low-voltage winding with neutral conductor, ideal for industrial power and residential lighting with harmonic suppression.
Yyn0 Connection: Star connection on both sides with a neutral point, suitable for low-voltage residential distribution with simplified grounding design.
Dd0 Connection: Delta on both sides, providing strong short-circuit resistance for harsh environments like ships and mining sites.
With their specialized magnetic circuit structure, advanced winding arrangements, efficient cooling, and flexible connection options, three-phase dry-type transformers are essential for connecting high-voltage grids to low-voltage loads. They provide efficient, stable, and safe power conversion solutions for industrial production, commercial facilities, and residential areas—solidifying their role as a critical component in modern power distribution systems.
