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Power Transformer


Power transformer is a device, which transfer electrical energy from circuit to another, through its coils, which are essentially, a set of conductors with inductive couplings. A Power transformer share several common features, although the designs for each type vary according to their applications.

Power Transformers can be classified according to their power capacities, by frequency ranges, by voltage class, by cooling type, by applications, by their end purposes and by their winding turns ratio. However, the most common types are as follows:

  • Auto Power transformer: These have a sliding brush contact. There are two end terminals with a single winding, whereas the third one stays at an intermediate tap point. They are often adjustable (variac) and feature an exposed part on the winding coils. The secondary connection is established through the sliding brush.


  • Poly-phase Power transformer: These are 3-phase step-down transformers (converting higher voltage to lower ones), with the Zigzag transformer being the most popular. It is used for grounding and to suppress harmonic currents.
  • Leakage Power transformer:Also known as the stray-field transformers, these have significantly higher leakage inductances than the rest. The leakage inductance can be increased with the help of a magnetic bypass (shunt) in its core, between the primary and the secondary terminals. The most popular usage of this kind of transformers is in the arc welding industry and where extra-low voltage is required to prevent short-circuiting. The resonant transformer also comes under this category and the Tesla coil is a good example of it. They are used to generate very high voltages, resulting in higher current flows than achieved through any electrostatic, high-voltage generating machine. The CCFL inverter makes use of the resonant transformer.


  • Audio power transformer:Specifically designed to be used in audio circuits, they are used for blocking either the radio frequency interference or an audio signal’s DC component. They also combine or split audio signals, matches the impedance between high and low impedance circuits (e.g. matching amplifier output to loudspeakers; matching instrument output to a mixer’s input etc.)
Instrument transformers: These are for measuring the voltage and the current in an electrical power system and to protect and control it from damages resulting from sudden electrical spikes.
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