A three-phase double-wound autotransformer is a type of electrical transformer that can efficiently adjust voltage levels in a three-phase power system while sharing some common winding turns between the primary and secondary sides. It is a combination of an autotransformer and a three-phase transformer. Here's how it operates:
Basic Structure: The transformer consists of a magnetic core made of laminated steel and three sets of windings: the primary winding, the common winding, and the secondary winding.
Primary Winding: The primary winding is connected to the three-phase power source and is designed to handle the highest voltage and current levels. It's wound around the core, just like in a regular transformer.
Common Winding (Shared Winding): This winding is the key feature of a double-wound autotransformer. It's connected to the primary and secondary circuits and serves as both the primary winding for the secondary circuit and the secondary winding for the primary circuit. This winding has a common set of turns shared between the two circuits.
Secondary Winding: The secondary winding is connected to the load and provides the required voltage transformation. It's also wound around the core.
Voltage Transformation: The voltage transformation in a double-wound autotransformer occurs due to the turns ratio between the common winding and the secondary winding. Since the common winding is shared between the primary and secondary sides, a portion of the voltage from the primary side is directly transferred to the secondary side, without going through the entire primary winding. This feature allows for voltage adjustment with fewer turns and better efficiency compared to a regular transformer.
Advantages:
Compact Design: The shared winding allows for fewer turns and a more compact design.
Lower Copper Losses: The common winding reduces the amount of copper needed for winding, resulting in lower resistive losses.
Improved Voltage Regulation: The autotransformer action helps improve voltage regulation on the secondary side.
Disadvantages:
Lower Isolation: The autotransformer configuration provides less electrical isolation between the primary and secondary sides compared to a regular transformer.
Limited Voltage Ratios: The voltage transformation capabilities are limited by the shared winding configuration.
Applications: Three-phase double-wound autotransformers find application in scenarios where efficient voltage adjustment is needed within a limited space. They are commonly used in power distribution systems, industrial settings, and situations where the trade-off between voltage adjustment and isolation can be managed.
It's important to note that while a double-wound autotransformer offers certain advantages, such as efficiency and compactness, it may not be suitable for all applications, especially those requiring high levels of electrical isolation between primary and secondary circuits.