Transformers are electrical devices that rely on the principles of electromagnetic induction to transfer energy between two or more coils. The fundamental operation of a transformer involves alternating current (AC). There are a few reasons why transformers don't work well, or at all, with direct current (DC):
Principle of Electromagnetic Induction: Transformers operate on the principle of electromagnetic induction, where a changing magnetic field induces a voltage in a nearby coil. In AC, the current alternates direction, causing a changing magnetic field. However, in DC, the current flows in one direction continuously, resulting in a constant magnetic field. Without a changing magnetic field, there is no voltage induction in the secondary coil, and the transformer does not function as intended.
Magnetic Saturation: Transformers are designed to operate with varying magnetic fields. In the case of DC, the magnetic field can saturate the core of the transformer. When the core saturates, it loses its ability to induce voltage effectively, and the transformer efficiency decreases significantly.
Eddy Currents and Hysteresis Losses: Transformers experience losses due to eddy currents and hysteresis in the core material. These losses are more pronounced in DC than in AC. Eddy currents are circulating currents induced in the core, and hysteresis involves the energy lost as the core magnetization constantly changes direction. These losses make DC operations less efficient and can lead to overheating.
DC Transformer Design Challenges: Designing a transformer specifically for DC operation requires specialized considerations, such as the use of a magnetic bias to prevent saturation. DC transformers tend to be more complex and less practical than their AC counterparts.
While transformers are unsuitable for direct current, there are devices called converters or inverters that can convert DC to AC and vice versa. These devices allow transformers in systems that involve direct current sources. Additionally, modern power systems primarily use AC for long-distance power transmission due to the ease of voltage transformation using transformers and the reduced loss during transmission.