An Overview of Transformers and Coils

The core and windings of the transformer are some of the most important parts, and their assembly will often dictate the classification of a transformer. The core is what is used to structurally support windings, and their materials typically consist of soft iron to minimize eddy current and Hysteresis losses. The windings or coils of the transformer components are what handle currents and voltages, and they are often bundled together and connected to one another to create a complete assembly. While the materials used to produce the coils or windings may differ depending on application, each turn always needs to be individually insulated to ensure that current is forced through turns rather than skipping them. Generally, the windings or coils of transformers are classified as primary or secondary types, meaning the winding serves either input our output voltages.
 
When discussing closed-core transformers in particular, the two primary types are core form and shell form transformers. With core form transformers, the coils are wrapped around the core. With the shell form type, on the other hand, the core itself will surround the coils. As the core form assembly is the most cost-efficient for construction, they are more common for high voltage transformer distribution and power stations on the lower end of voltage and power rating ranges. When the application presents high voltage and power ratings, shell form transformers are the more desirable type due to their better kVA-to-weight ratios on average.
 
To efficiently insulate coils and transformers, materials such as cardboard, paper, and polymer resin may be implemented between windings, cores, terminals, and other electrical equipment components for isolation. While insulation can maintain the path of voltage and protect sensitive components, it is also important to enact cooling methods for both the core and coil assembly. With the use of transformer oil consisting of hydrocarbon mineral oils, the coils and transformer core can be immersed for cooling. With a metallic cylindrical drum known as a conservator, transformer oil is conserved above the assembly. Conservators take advantage of venting and only permit half of the component to be filled, allowing for oil to expand and contract safely during temperature fluctuations.
 
As heat will collect in the oil over time from cooling, cooling tubes are also implemented. Through either natural circulation or with the assistance of a pump, hot and cold oil can be moved through the system for ample cooling. In the case of an emergency such as if there is an internal fault, an explosion vent serves to expel hot oil in order to prevent the chance of an explosion.