Transformer definition-operating principle

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Electrical Transformer Definition

Transformer is an electrical static device which transfers a power from primary circuit to secondary circuit without changing its frequency or phase of the signal. Transformer doesn’t contains any physical contact between primary and secondary where as it works on the Faraday’s “electromagnetic induction” phenomenon.

Electromagnetic induction phenomenon

The phenomenon of electromagnetic induction was discovered independently by Michael and Joseph Henry in 1831. However, Faraday was the first to publish the results of his experiments and thus receive credit for the discovery. This states that the electromotive force (EMF) induces in the coil which is placed in a varying magnetic field. The relationship between electromotive force (EMF) or “voltage” and flux was formalized in an equation now referred to as “Faraday’s law of induction.

E = dΦ/dt

€ Is the magnitude of the EMF in volts?
Φ Is the magnetic flux through the circuit (in Weber’s).
Faraday’s experiments included winding a pair of coils around an iron ring, thus creating the first toroidal closed-core transformer.

History of Transformer

One of the oldest innovations of Electrical Engineering, the Transformer has a long, yet interesting history of developments spanning over a century. Born in 1885, first patented by three Hungarian Engineers working in Ganj, Budapest, Karoly Zipernowsky, has beenserving mankind selflessly, to help harness electricity for everyday purposes. Transformer shall continue to justify its existence, as is the present day knowledge of Science & Technology.

Operating Principle of electrical transformer

In its simplest form a Transformer consists of two windings, the voltage is applied to one set of windings, called the primary, which builds up a magnetic flux through the coupling medium(Air or iron). This flux induces a counter electromotive force in the primary winding thereby limiting the current drawn from the supply. This is called the no load current and consists of two components- one in phase with the voltage which accounts for the iron losses due to eddy currents and hysteresis, and the other 90° behind the voltage which magnetizes the core. This flux induces an electromotive force in the secondary winding too. When load is connected across this winding, current flows in the secondary circuit. This produces a demagnetizing effect, to counter balance this the primary winding draws more current from the supply so that

Vp/Vs = Np/Ns

Where Vp ,Ip and Np are the voltage, current and number of turns in the primary side while Vs, IS and NS are the voltage current and number of turns in the secondary respectively.

The ratio of turns in the primary and secondary windings depends on the ratio of voltages on the Primary and secondary sides.

Basic Functions of a Electrical Transformer

The basic purpose or function of the electrical transformer is to transfer power efficiently and instantaneously from one electrical source to the external load. In doing so, the transformer also provides some important additional functions as follows:

  • The primary to secondary turn’s ratio can be established to efficiently accommodate widely different Input/output voltage levels.
  • Multiple secondaries with different numbers of turns can be used to achieve multiple outputs at different voltage levels.
  • Separate primary and secondary windings facilitate high voltage input/output isolation, especially important for safety in off-line applications.

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