Transformers operate using the principles of electromagnetic induction, which rely on the changing magnetic field induced by alternating current (AC). This alternating magnetic field is essential for inducing a voltage in the secondary winding of the transformer. When AC flows through the primary winding, it continuously changes direction, causing the magnetic field around the winding to alternately expand and collapse. This changing magnetic field induces a voltage in the secondary winding through mutual induction, allowing the transfer of electrical energy from one circuit to another at a different voltage level.
Transformers are designed to work specifically with AC because the alternating current is what generates the changing magnetic flux required for induction. In contrast, direct current (DC) produces a constant magnetic field that does not change direction or magnitude over time. As a result, when DC flows through the primary winding of a transformer, it creates a steady magnetic field that does not induce a voltage in the secondary winding. Without the alternating magnetic field, there is no mechanism for electromagnetic induction to occur in a transformer, making it ineffective for transferring energy between circuits using DC input.
The requirement for AC in transformers is rooted in the fundamental principles of electromagnetism and the behavior of magnetic fields around conductors carrying alternating currents. Therefore, transformers are inherently designed and optimized to operate with AC voltages and currents. They play a crucial role in AC power transmission, distribution, and voltage transformation, enabling efficient electrical energy transfer across different voltage levels in power grids and various electrical systems.