1. What is a Three-Phase Transformer?
A three-phase transformer is a static electromagnetic device designed to transfer energy or transmit AC electrical signals between electrical circuits through Faraday’s electromagnetic induction phenomenon.
Three-phase transformers play a crucial role in power transmission systems. This device is widely and commonly used for industrial purposes, including power generation, transmission, and distribution.
Three-phase transformers are installed in locations that consume a significant amount of electrical energy, such as high-rise buildings, apartment complexes, hospitals, and substations.
2. Working Principle of a Three-Phase Transformer
The working principle of a three-phase transformer is quite simple. It operates based on two physical phenomena:
Electric current passing through a conductor creates a magnetic field.
The variation of magnetic flux in a conductor coil induces an electromotive force (EMF).
By understanding the working principle of the transformer, you can easily grasp its operation process and the key principles to ensure efficient performance while maintaining the rated power capacity.
3. Structure of a Three-Phase Transformer
To be compatible with large power grid systems, three-phase transformers are designed with relatively complex structures. The main components of a three-phase transformer include the magnetic core, windings, transformer casing, and other auxiliary parts.
Image of structure A three-phase transformer
3.1. Magnetic Core of the Transformer
The magnetic core consists of the Yoke and the Limb. The Limb is where the windings are placed, while the Yoke connects the Limbs to form a closed magnetic circuit.
The transformer’s core is made of multiple thin sheets of electrical steel (silicon steel) insulated from each other. These materials are chosen for their excellent magnetic properties.
3.2. Transformer Windings
The windings are usually made of copper or aluminum and are insulated. They are responsible for receiving and transmitting electrical energy.
The primary coil (N1) receives electrical energy (connected to the AC power supply).
The secondary coil (N2) transmits electrical energy (connected to the load).
The number of turns in the two coils varies depending on the transformer’s function, which determines whether N1 is greater than N2 or vice versa.
3.3. Transformer Casing
The casing material depends on the transformer type and is commonly made of plastic, wood, steel, cast iron, or sheet metal. Its primary function is to protect the internal components of the transformer.
3.4. Auxiliary Components of a Three-Phase Transformer
To complete the structure of a three-phase transformer, several essential auxiliary components are included, such as:
Transformer oil
Transformer bushings
Transformer base
Voltage meter
4. Types of Three-Phase Transformers
Three-phase transformers are typically classified based on voltage levels, core materials, winding configurations, application purposes, and installation locations. Below are the most commonly used three-phase transformers on the market today:
Sealed three-phase transformers
Open three-phase transformers
Dry-type transformers
Amorphous core transformers
4.1. Sealed Three-Phase Transformers
Sealed three-phase transformers are cooled through expansion fins. When the internal temperature rises, these fins expand, allowing air to flow directly over them, helping to dissipate heat.
4.2. Open Three-Phase Transformers
Transformers are electrical devices that change AC voltage from one level to another. Open three-phase transformers are equipped with an auxiliary oil tank and are typically distribution transformers. They operate with input voltages of 35kV, 22kV, or 10kV and output voltages of 0.4kV while being immersed in standard insulating oil.
4.3. Dry-Type Transformers
Dry-type transformers do not use any liquid insulation to immerse their windings or core. Instead, the windings and core are housed in a sealed container and are air-pressurized.
These transformers have no moving parts, are entirely solid-state, and ensure a long lifespan without operational issues under normal conditions. Unlike oil-filled transformers, which rely on flammable dielectric liquids, dry-type transformers use high-grade insulation systems that are environmentally safe.
Dry-type transformers provide a reliable and safe power supply without requiring fire-resistant vaults, oil containment basins, or toxic gas ventilation. These safety features allow them to be installed inside buildings near electrical loads, improving system efficiency and reducing costly secondary distribution losses.
4.4. Amorphous Core Transformers
Amorphous core transformers are energy-efficient transformers installed in power grids. Their magnetic cores are made of amorphous metal. A typical material (Metglas) consists of iron alloyed with boron, silicon, and phosphorus, formed into thin strips (e.g., 25 µm) that are rapidly cooled after melting.
These materials have high magnetic permeability, very low coercivity, and high electrical resistance. Their thin layers and high resistivity minimize eddy current losses in AC magnetic fields. However, amorphous alloys generally have lower saturation flux density and higher magnetostriction compared to conventional silicon-steel electrical steels.