Leakage flux that escapes from the core and passes through one winding only resulting in primary and secondary reactive impedance.Joule losses due to resistance in the primary and secondary windings.(b) Unlike the ideal model, the windings in a real transformer have non-zero resistances and inductances associated with: Eddy current losses due to joule heating in the core that are proportional to the square of the transformer's applied voltage.Hysteresis losses due to nonlinear magnetic effects in the transformer core, and.(a) Core losses, collectively called magnetizing current losses, consisting of The ideal transformer model neglects the following basic linear aspects of real transformers: Leakage flux of a transformer Deviations from ideal transformer The load impedance referred to the primary circuit is equal to the turns ratio squared times the secondary circuit load impedance. The ideal transformer identity shown in eq. 5 is a reasonable approximation for the typical commercial transformer, with voltage ratio and winding turns ratio both being inversely proportional to the corresponding current ratio. The transformer winding voltage ratio is directly proportional to the winding turns ratio. With a voltage source connected to the primary winding and a load connected to the secondary winding, the transformer currents flow in the indicated directions and the core magnetomotive force cancels to zero.Īccording to Faraday's law, since the same magnetic flux passes through both the primary and secondary windings in an ideal transformer, a voltage is induced in each winding proportional to its number of windings. The windings are wound around a core of infinitely high magnetic permeability so that all of the magnetic flux passes through both the primary and secondary windings. This varying flux at the secondary winding induces a varying electromotive force (EMF, voltage) in the secondary winding due to electromagnetic induction and the secondary current so produced creates a flux equal and opposite to that produced by the primary winding, in accordance with Lenz's law. Ī varying current in the transformer's primary winding attempts to create a varying magnetic flux in the transformer core, which is also encircled by the secondary winding. Perfect coupling implies infinitely high core magnetic permeability and winding inductance and zero net magnetomotive force (i.e. V P = − N P d Φ d t denoting referred to the primary.Īn ideal transformer is a theoretical linear transformer that is lossless and perfectly coupled. Transformers range in size from RF transformers less than a cubic centimeter in volume, to units weighing hundreds of tons used to interconnect the power grid. A wide range of transformer designs is encountered in electronic and electric power applications. Since the invention of the first constant-potential transformer in 1885, transformers have become essential for the transmission, distribution, and utilization of alternating current electric power. Transformers can also be used for isolation, where the voltage in equals the voltage out, with separate coils not electrically bonded to one another. Transformers are most commonly used for increasing low AC voltages at high current (a step-up transformer) or decreasing high AC voltages at low current (a step-down transformer) in electric power applications, and for coupling the stages of signal-processing circuits. Faraday's law of induction, discovered in 1831, describes the induced voltage effect in any coil due to a changing magnetic flux encircled by the coil. Electrical energy can be transferred between separate coils without a metallic (conductive) connection between the two circuits.
A varying current in any one coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force across any other coils wound around the same core. Ī transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. Pole-mounted distribution transformer with center-tapped secondary winding used to provide " split-phase" power for residential and light commercial service, which in North America is typically rated 120/240 V.