Single Phase Transformer
Principle of operation.
Transformer is a static device (and doesn’t contain on rotating parts, hence no friction
losses), which convert electrical power from one circuit to another without changing its
frequency. it Step up (or Step down) the level of AC Voltage and Current.
Transformer works on the principle of mutual induction of two coils or Faraday Law’s Of
Electromagnetic induction. When current in the primary coil is changed the flux linked to
the secondary coil also changes. Consequently an EMF is induced in the secondary coil due
to Faraday law’s of electromagnetic induction.
The transformer is based on two principles: first, that an electric current can produce a
magnetic field (electromagnetism), and, second that a changing magnetic field within a coil
of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing
the current in the primary coil changes the magnetic flux that is developed. The changing
magnetic flux induces a voltage in the secondary coil.
A simple transformer has a soft iron or silicon steel core and windings placed on it(iron
core). Both the core and the windings are insulated from each other. The winding connected
to the main supply is called the primary and the winding connected to the load circuit is
called the secondary.
Winding (coil) connected to higher voltage is known as high voltage winding while the
winding connected to low voltage is known as low voltage winding. In case of a step up
transformer, the primary coil (winding) is the low voltage winding, the number of turns of
the windings of the secondary is more than that of the primary vice versa for step down
transformer.
As explained earlier, EMF is induced only by variation of the magnitude of the flux.
When the primary winding is connected to ac mains supply, a current flows through it. Since
the winding links with the core, current flowing through the winding will produce an
alternating flux in the core. EMF is induced in the secondary coil since the alternating flux
links the two windings. The frequency of the induced EMF is the same as that of the flux or
the supplied voltage.
By so doing (variation of flux) energy is transferred from the primary coil to the secondary
coil by means of electromagnetic induction without the change in the frequency of the
voltage supplied to the transformer. During the process, a self induced EMF is produced in
the primary coil which opposes the applied voltage. The self induced EMF is known as back
EMF.
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