What is a three-phase transformer?
A three-phase transformer is a piece of “static” or “passive” electronic equipment that passes electrical energy between electronic circuits. They can vary in size from those operating small domestic appliances to large industrial installations.
Importance in Power Distribution
A three-phase transformer is much more efficient than a single-phase transformer. It can also deliver more power. The secondary circuit contains a magnetic flux. that induces an electromotive force and can step up (increase) or step down (decrease) voltages yet doesn’t change the frequency.
Key components of a three-phase transformer
Core Structure
The core serves as a “magnetic bus bar” (this efficiently ‘focuses’ the electric power into one single location) connecting the magnetic “source” to a magnetic “load”. It functions like a conductor.
Windings
Very simply put, a transformer is just two windings on an iron core. The source voltage winding is termed the primary winding, while the one connected to the load is termed the secondary winding. Using magnetic induction (electromagnetic force), energy is transferred from the primary winding to the secondary winding.
Insulation and cooling
External: this is required to reduce the heat on the outside main body of the transformer and it’s associated in/out parts
Internal: this is required to remove heat from the core and coils/windings inside the transformer.
How three-phase transformers operate
Voltage transformation
Transformers follow a well-established scientific relationship – Faraday’s Law of Induction. They feature a pair of windings where mains AC passes through the primary winding. This creates a varying magnetic flux. This magnetic flux then reaches the secondary winding and generates another AC voltage through electromagnetic induction.
Phases and phase relationships
In very simple terms, three-phase power supplies are much more efficient than single-phase power supplies, able to send three times as much power yet needing only three wires rather than two.
Types of three-phase transformers
Core type vs. shell type: With their excellent mechanical stability, core-type transformers are used for high-frequency application. Shell type transformers tend to be smaller and thus much simpler to install.
Delta and Wye configurations
Delta configuration: this is used for electric current loads up to 277VAC. It is a circuit where three loads are connected in triangular fashion where each load represents one side of the triangle.
A Wye configuration: this is used for electric current loads above 277VAC. Here the circuit’s three loads are connected in a Y formation, each ‘leg’ of the Y for each load.
Autotransformers
These use just a single coil to adjust voltage, and there isn’t any isolation between the primary and secondary circuits. They change the voltage when electrical energy is transferred from one circuit to another. The windings are separate, but unlike those of an isolation transformer, the primary and secondary wirings are electrically connected.
Advantages of three-phase transformers
Efficiency: three-phase, ready-wired transformers are much easier to install, making them more efficient to work with.
Balanced load: wiring size and costs are kept lower because for the same amperage, a three-phase circuit provides higher power density than that of a one-phase circuit. It is also far easier to balance three-phase power, which results in lower harmonic currents and reduces the need for large neutral wires.
Reduced losses: there are much lower energy and transmission and distribution losses.
Efficiency: when it comes to handling higher loads three-phase transformers are more efficient and therefore more suitable. They not only reduce the loss of energy and enhance energy conservation but improve overall performance and present lower operating costs.
Enhanced power quality: with three-phase transformers, voltage fluctuations, harmonic distortion and phase imbalances are all reduced, providing for better power quality. This brings with it a smoother operation, fewer disruptions and fewer power inequalities which offers a general increase in productivity for commercial and industrial installations.
Compact design: in relation to the power they handle, three-phase transformers are more compact in design and so need a smaller space for installation and thus lower costs.
Scalability: three-phase transformers allow modifications to the electrical infrastructure and can even be added or incorporated into existing power systems without the need for major power downtimes.
Applications of three-phase transformers
Three-phase power transformers are used in various industries for their very versatile and flexible operational options – driving motors, mining, power rectifications, the petrochemical industry, shopping centers, schools, offices, textiles, printing, packaging, testing industries and more.
Utility distribution: used for the cost-effective power transmission and distribution in power grids over long distances as well as for in industrial low-voltage applications.
Installation and Maintenance
For safety, reliability and efficiency, is important that any transformer, not only three-phase ones, are correctly installed by trained and accredited engineers. Consider the area they are to be installed in, mount and adjust them as per manufacturers’ recommendations and ensure taps and re-routing of wiring is correct. The transformer should also be correctly grounded, energized and connected, in that order, before performing a final inspection.
There are three primary methods for determining the suitable condition of a transformer:
- Open-circuit test
- Short-circuit test
- Winding resistance measurement
Routine maintenance
Three checks should be made on a daily basis:
- Check levels of the magnetic oil gauge for the main tank and conservator tank and keep filled to the correct level
- Replace the silica gel if its color changes to pink
- Seal any discovered leakage
Safety
You will be dealing with high-voltage equipment, so always:
- use appropriate personal safety equipment
- use a well-grounded safety cable or chain
- be cautious near high-voltage power lines
- keep a safe distance
- follow company and HSE safety guidelines
To avoid overheating: have effective cooling methods in place to prevent damage and to maintain efficiency, performance, and transformer lifespan.
Regulatory compliance
Transformers must meet industry safety standards
In order to guarantee customer safety, product reliability, and the business brand reputation, transformers must adhere to safety standards as well as to regulatory compliance. As well as being of best design, they must regularly be tested and maintained. The practices recommended by the International Electrotechnical Commission (IEC), the Institute of Electrical and Electronics Engineers (IEEE) and local regulatory bodies should be always followed.
In conclusion
Three-phase current transformers have become vital to precisely measure and protect three-phase power. They are available in a range of sizes suitable for various applications and current ratings.
Further information and reading
From the UK Government
Notices of publication and a consolidated list for designated standards for power transformers in relation to ecodesign and energy labeling – https://www.gov.uk/government/publications/designated-standards-conformity-assessment-and-management
Using the power transformer regulatory relief tool – https://www.gov.uk/government/publications/ecodesign-requirements-for-power-transformers-find-out-whether-your-installation-is-eligible-for-regulatory-relief/how-to-use-the-power-transformer-regulatory-relief-tool
Keeping up with transformer regulation following on from when the UK left the EU – https://www.legislation.gov.uk/eur/2019/1783/introduction
