Presented by:
SHAHBAZ HUSSAIN

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Transformer
 A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors
 A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors.
 A changing current in the first circuit (the primary) creates a changing magnetic field.
 This changing magnetic field induces a changing voltage in the second circuit (the secondary). This effect is called mutual induction.
 If a load is connected to the secondary circuit, electric charge will flow in the secondary winding of the transformer and transfer energy from the primary circuit to the load connected in the secondary circuit
 The secondary induced voltage VS, of an ideal transformer, is scaled from the primary VP by a factor equal to the ratio of the number of turns of wire in their respective windings:
 By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to be stepped up — by making NS more than NP — or stepped down, by making it less.
 Transformers are some of the most efficient electrical 'machines', with some large units able to transfer 99.75% of their input power to their output.
 Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids.
Construction
Laminated steel cores
 Transformers for use at power or audio frequencies typically have cores made of high permeability silicon steel.
 The steel has a permeability many times that of free space, and the core thus serves to greatly reduce the magnetising current, and confine the flux to a path which closely couples the windings.
 Early transformer developers soon realized that cores constructed from solid iron resulted in prohibitive eddy-current losses, and their designs mitigated this effect with cores consisting of bundles of insulated iron wires.
 Later designs constructed the core by stacking layers of thin steel laminations, a principle that has remained in use.
 Each lamination is insulated from its neighbors by a thin non-conducting layer of insulation.
 The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux, and so reduce their magnitude.
 Thinner laminations reduce losses, but are more laborious and expensive to construct.
 Thin laminations are generally used on high frequency transformers, with some types of very thin steel laminations able to operate up to 10 kHz.
Solid cores
 Powdered iron cores are used in circuits (such as switch-mode power supplies) that operate above main frequencies and up to a few tens of kilohertz. These materials combine high magnetic permeability with high bulk electrical resistivity.
 For frequencies extending beyond the VHF band, cores made from non-conductive magnetic ceramic materials called ferrites are common. Some radio-frequency transformers also have movable cores (sometimes called 'slugs') which allow adjustment of the coupling coefficient (and bandwidth) of tuned radio-frequency circuits.
Windings
 Cut view through transformer windings. White: insulator. Green spiral: Grain oriented silicon steel.
 Black: Primary winding made of oxygen-free copper. Red: Secondary winding. Top left: Toroidal transformer. Right: C-core, but E-core would be similar. The black windings are made of film. Top: Equally low capacitance between all ends of both windings. Since most cores are at least moderately conductive they also need insulation. Bottom: Lowest capacitance for one end of the secondary winding needed for low-power high-voltage transformers.
Terminals
 Very small transformers will have wire leads connected directly to the ends of the coils, and brought out to the base of the unit for circuitconnections.
 Larger transformers may have heavy bolted terminals, bus bars or high-voltage insulated bushings made of polymers or porcelain.
 A large bushing can be a complex structure since it must provide careful control of the electric field gradient without letting the transformer leak oil.
Transformer
 A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors
Types of Transformers:
 A wide variety of transformer designs are used for different applications.
 Some important types are given as:
 Auto-transformer
 Poly-phase transormer
 Leakage transformer
 Resonant transformer
 Instrument transformers
AUTO-TRANSFORMERS
 An autotransformer with a sliding brush contact
 An autotransformer has only a single winding with two end terminals, plus a third at an intermediate tap point.
POLY-PHASE TRANSFORMER
 For three-phase supplies,a bank of three individual single-phase transformers can be used,or all three phases can be incorporated as a single three-phase transformer.
LEAKAGE TRANSFORMERS
 A leakage transformer,also called a stray-field transformer, has a significantly higher leakage inductance than other transformers.
RESONANT TRANSFORMERS
 A resonant transformer is a kind of the leakage transformer. It uses the leakage inductance of its secondary windings in combination with external capacitors, to create one or more resonant circuits.
INSTRUMENT TRANSFORMERS
 Current transformers, designed to be looped around conductor.
 A current transformer is a measurement device designed to provide a current in its secondary coil proportional to the current flowing in its primary.
Basic principle of Transformer:
TRANSFORMERS
 A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors.
TRANSFORMERS RULES
 Transformer is based on two principles:
 Firstly,that an electric current can produce a magnetic.
 Secondly, electromegnetic induction
TRANSFORMERS
 By changing the current in the primary coil, it changes the strength of its magnetic field
 The changing magnetic field extends into the secondary coil, a voltage is induced across the secondary.
PRACTICAL CONSIDERATION
 An ideal step-down transformer showing magnetic flux in the core.
 The primary and secondary coils are wrapped around a core of very high magnetic permeability,such as iron.
Induction law
 Faraday’s law states that:
Vs=Ns.dΦ/dt
 where VS is the instantaneous voltage.
 NS is the number of turns in the secondary coil.
 Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer,the instantaneous voltage across the primary coil
Vp=Np.dΦ/dt
 If Ns>Np, Vs>Vp
 Such transformer voltage across secondary is greater than primary voltage called step up transformer.
 Voltage cross secondary less than primary voltage called step down transformer.
Ideal power equation
Power input=power output
VpIp=VsIs
Vs/Vp=Ip/Is
Where current is inversaly proportional to respective voltage.
 Step up Vs Voltage increase then secondary current reduced.
 When current passes through resistance then power loss due to heating effect.