A transformer is a static device that transfers electrical energy from one circuit to another through inductively coupled conductors - the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "Voltage" in the secondary winding. This effect is called mutual induction.
If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (Vs) is in proportion to the primary voltage (Vp), and is given by the ratio of the number of turns in the secondary (Ns) to the number of turns in the primary (Np) as follows:
By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be "Stepped Up" by making Ns greater than Np, or "stepped down" by making Ns less than Np.
In the vast majority of transformers, the windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception.
Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate with the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("Mains") voltage. Transformers are essential for high-voltage electric power transmission, which makes long-distance transmission economically practical.
Difference between Power Transformer and Distribution Transformer:
Different Types Of Power Transformers And Their Uses: Autotransformers:
Smaller, lighter and cheaper than standard dual-winding transformers, autotransformers do not provide electrical isolation. These transformers have a part of their winding included in both input and output circuits – voltage is applied across a portion of the winding, and a higher or lower voltage is produced across another portion of the same winding. Thus, these transformers can step up or down between voltages in the 110-117-120 and 220-230-240 volt ranges. The equivalent power rating of an autotransformer is lower than the actual load. Large three-phase autotransformers are used in electric power distribution systems.
Polyphase transformers:
Power distribution systems require three-phase transformers to be able to step up or down voltages. However, single-phase transformers can be joined together to transform power between two three-phase systems too. However, there are special three-phase transformers manufactured for such tasks which require lesser material, and are smaller in size and weight than their modular counterparts. These transformers are made of three sets of primary and secondary windings, where the three primary windings are connected together, and the three secondary windings are connected together. The main purpose of a polyphase transformer is for grounding and suppression of harmonic currents.
Leakage transformers:
Also known as stray-field transformers, leakage transformers have a significantly higher leakage inductance than other transformers, which can be increased by a magnetic bypass or shunt in the core between primary and secondary windings. It can also be adjusted with a set screw. Due to the loose coupling between the windings, these transformers have a current limitation. The input and output currents of these transformers are low enough to prevent thermal overload in any situation. Leakage transformers can act as both voltage transformers and magnetic ballast, and are used for arc welding, high voltage discharge lamps, doorbells and short-circuit-proof extra-low voltage transformers for toys.
Resonant transformers:
A resonant transformer is one that has one winding with a capacitor, which acts as a tank/tuned circuit. They are driven by pulse or square wave and can function as high Q-factor bandpass filters. These transformers utilize the leakage inductance of the secondary winding combined with external capacitors to form one or more resonant circuits. They are widely used in radio circuits and switching power supplies. The Tesla coil is one such example that is used to generate very high voltages, and is able to provide much higher current as compared to high voltage electrostatic machines.
