As of my last update in September 2021, transformers are not typically used in direct current (DC) power transmission systems. Transformers are primarily designed for alternating current (AC) systems due to the way they function and the fundamental principles of electromagnetism.
Transformers work based on the principle of electromagnetic induction, which relies on the varying magnetic fields created by alternating current. When AC flows through the primary winding of a transformer, it creates a changing magnetic field, which induces a voltage in the secondary winding, allowing for voltage transformation and power transfer between different voltage levels.
In DC systems, there is no changing magnetic field as there is in AC systems, so the traditional electromagnetic induction principle does not apply. As a result, standard transformers cannot be used for direct current transmission.
DC power transmission systems usually rely on high-voltage direct current (HVDC) technology for long-distance power transmission. HVDC systems use power electronic devices such as thyristors or insulated gate bipolar transistors (IGBTs) to convert AC to DC and vice versa. Power can then be transmitted at high voltage in the form of direct current, which reduces transmission losses over long distances compared to AC transmission.
So, while transformers are not directly used in DC power transmission systems, converters and power electronic devices play a crucial role in facilitating efficient HVDC transmission. It's essential to keep in mind that technology is continuously evolving, and there might be developments beyond my last update. Always refer to the latest information from reliable sources to stay updated on the latest advancements in power transmission technologies.