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Views: 1 Author: Site Editor Publish Time: 2024-09-27 Origin: Site
Transformers can also be categorized by their shape and geometry. The shape of a transformer depends on the type of inductor used in its construction and the shape of its core. Any transformer is essentially a pair of inductors wound on the same core. The classifications are as follows:
Utility Transformers: Utility transformers are power transformers that use laminated iron as a core material. These core transformers have various core shapes such as E, L, U, I etc. and are large and bulky. The most common core shape used in these transformers is the E-core or EI-core because the laminated core is shaped like the letter “E” and a bar is placed at the open end of the “E” to complete the structure. The coils are wound onto the core by either the shell method or the core method. In the shell method, both coils are wound on top of each other on the center bar of the “E”. This ensures maximum magnetic coupling between the coils, but at the expense of high coil-to-coil capacitance. The shell method also limits the current carrying capacity of the transformer. In the core method, one coil is wound on the top strip of the “E” and the other coil is wound on the bottom. Magnetic coupling between the coils occurs only due to the magnetic flux through the core. The core method largely reduces the coil-to-coil capacitance and makes it possible to handle high voltages. Utility transformers with EI cores and shell or core windings are most commonly used as 60 Hz transformers and other audio transformers.
Solenoid Transformers: Solenoid transformers are commonly used as loop antennas for RF circuits. These transformers have primary and secondary windings on a cylindrical core (ferrite or powdered iron). The windings are wound around each other or separately. In such a transformer, the primary winding captures the radio signal while the secondary winding provides impedance matching for the first amplifier stage of the radio circuit. Such transformers have become very common in portable radio communication equipment.
Toroidal Core Transformer: The primary and secondary windings of a toroidal core transformer are wound on a toroidal core, and the coils may be wound around each other or separately. Toroidal cores are a better alternative to solenoid cores in RF circuits. They contain the magnetic flux within the core, so as long as the coils are insulated, these transformers can be mounted directly without any other shielding. In addition to the lack of electromagnetic interference, toroidal cores offer higher inductance per coil turn. Since the magnetic flux is still contained within the core, toroidal core transformers offer better magnetic coupling between the coils.
Pot Core Transformers: The main and secondary windings of a pot core transformer are stacked on top of each other or next to each other. Pot cores provide the highest inductance and have the distinct advantage of being self-shielding. One of the main disadvantages of pot core transformers is the coil-to-coil capacitance. Because of the unusually high coil-to-coil capacitance as well as the inductance of both coils, pot core transformers are only suitable for low frequencies. At high frequencies, the required inductance is very low and the capacitive reactance must be largely reduced.
