Transformers are essential electrical systems devices, enabling alternating current (AC) transfer between circuits at a stable frequency. This is achieved through electromagnetic induction, where voltage levels are adjusted to meet specific requirements. Central to the operation of transformers are their windings, which play a pivotal role in the device’s functionality. This blog explores the different types of transformer winding, their materials, and their applications.
What is Transformer Winding?
Transformer windings comprise numerous turns of copper or aluminium coils, which are bundled together to form a winding. These windings can be classified into two main types: primary winding and secondary winding. The primary winding receives electrical energy from the source, while the secondary winding transmits electrical power to the load.
The materials used in transformer windings are primarily aluminium and copper. Copper is favoured for its high mechanical strength and conductivity, making it suitable for large transformers. Aluminium, being less expensive and lighter, is often used in smaller and medium-sized transformers.
Types of Transformer Winding
Transformer windings come in various types, each suited for different applications:
1. Multilayer Helical Windings
Multi-layer helical windings are primarily used in high-voltage transformers rated at 110 kV and above. These windings consist of several cylindrical layers wound concentrically and connected in series. The outer layers are shorter than the inner layers to ensure uniform capacitance distribution, enhancing the transformer’s surge performance.
2. Helical Windings or Spiral Windings
Helical windings, also known as spiral windings, are used in low-voltage, high-capacity transformers where the current is high, and the winding turns are fewer. These windings come in three types: single helical, double helical, and disc-helical.
- Single Helical Winding: Features a single layer of turns in each winding, arranged axially along a screw line.
- Double Helical Winding: Reduces eddy current losses in conductors due to fewer parallel conductors in the radial direction.
- Disc-Helical Winding: Consists of parallel strips placed side by side in a radial direction to cover the entire radial depth of the winding.
3. Disc Windings
Disc windings are a type of transformer winding that is constructed by connecting several conductor discs in series. Each disc is made up of multiple insulated conductor turns that are wound around spacers to provide electrical isolation and structural support. These windings are known for their robustness and are typically utilised in transformers with a rating above 25 kV due to their high voltage handling capabilities.
4. Foil Windings
Foil windings are made from thin sheets of aluminium or copper, wound into multilayer spiral windings. These are used in high-capacity transformers where the current ranges from 12 to 600 A. Foil windings can be constructed with single or multiple sheets wound in parallel, providing a compact and efficient design.
5. Cylindrical Windings
Cylindrical windings use low voltage up to 6.6 kV and current ratings from 10 to 600 A. These windings are often used in a multilayer form with circular conductors wound on vertical strips to improve cooling. They are suitable for high-voltage applications up to 33 kV, 800 kVA, and current ratings up to 80 A.
6. Crossover Windings
Crossover windings are used in high-voltage windings of small transformers. These windings are divided into several coils to reduce the voltage between adjacent layers. The coils are axially separated by 0.5 to 1 mm, with the voltage between adjacent coils kept within 800 to 1000 V. Crossover windings offer higher strength than cylindrical windings under normal conditions but have higher labour costs.
7. Disc & Continuous Disc Winding
Disc windings and continuous disc windings are both commonly employed in high-capacity transformers. These winding types feature multiple flat coils or discs that are arranged either in series or parallel. This design provides the windings with robust construction, high mechanical axial strength, and cost efficiency, making them an ideal choice for such applications.
8. Aluminum Windings
Aluminum windings are commonly used in transformers in North America, especially in dry-type and low-voltage transformers. While copper windings are more prevalent worldwide, aluminium windings are preferred for their lower initial cost and flexibility. They offer similar performance and efficiency as copper windings but with inherently lower eddy losses due to aluminium’s higher resistivity.
Special Instruments for Transformer Windings
For transformer maintenance and diagnostics, special instruments play a crucial role in ensuring the optimal performance and longevity of these essential devices. These instruments help in monitoring and assessing the condition of transformer windings, providing valuable insights into their integrity and operational health. By regularly employing these diagnostic tools, we can preemptively address potential issues, thereby maintaining the reliability and efficiency of transformers in various applications.
Transformer Winding Resistance Meter
The transformer winding resistance meter is an essential diagnostic tool used to measure the resistance of windings in transformers, generators, motor windings, and other inductive components. This measurement ensures proper connections and tightness, indicating issues like loose connections or shorted turns.
Transformer Winding Temperature Indicator
Advantages and Disadvantages of Transformer Windings
Transformer windings come with a range of advantages that make them essential for efficient transformer operation. A few advantages are:
| Advantages | Disadvantages |
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Minimises flux leakage and iron loss. |
Difficult to twist the windings.
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High mechanical strength.
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Lower accuracy in coil positioning.
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Efficient at high frequencies.
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High manual labour costs.
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Low failure rate.
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Cost-effective production.
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Applications of Transformer Windings
Transformer windings are crucial in various applications, including:
- Stepping up or stepping down voltage levels in AC circuits.
- Modifying capacitor values, resistance, or inductance.
- Adjusting voltage or current levels for specific requirements.
Final Thoughts
By understanding the different types of transformer windings and their applications, organisations can make informed decisions when selecting transformers, thus ensuring optimal performance and reliability.
Utilising solutions such as UPT (Universal Power Transformer) for selecting the ideal transformer, and implementing advanced tools like transformer winding resistance meters and temperature indicators, can significantly reduce the risk of operational failures. Proper maintenance and precise winding selection contribute to efficient power distribution and voltage management, thereby enhancing overall system efficiency. This strategic approach not only lowers maintenance costs and prevents equipment downtime but also fosters a more sustainable and cost-effective energy infrastructure.
