Download Physics Tutorial: Inductance and Transformers

Physics Tutorial: Inductance and Transformers
A transformer is an apparatus for changing a given electrical current into
another current of different voltage. There are two kinds of transformers: step
down and step up. Step up transformers increase the voltage where step down
transformers decrease the voltage.
Explanation: We call this device a transformer because it transforms electrical
energy into magnetic energy, and then back to electrical energy again. A
transformer consists of two coils of wire both wrapped around the same core.
The primary coil is the input coil and the secondary coil is the output coil. The
relationship between the number of turns in the coil, voltage, and current in is V s /
Vp = Ip / Is = Ns / Np. The V represents voltage, I represents current, and N
represents the number of turns of the coil. The s represents secondary and p
represents primary.
A transformer’s basic operating principle is that of mutual inductance. Mutual
inductance occurs when two coils are so close together that the magnetic field
of one coil links with the magnetic field of the other coil. Current is induced in the
second coil when the magnet field produced by the first coil changes. A
transformer only works with alternating current. Direct current would cause a
magnetic field in the core, but not a changing one. This would cause the voltage
induced in the second coil to be equal to zero.
A transformer is used because they cause almost no energy loss.
Application: Power is supplied to houses everywhere in the developed world. In
the power grid, voltage can be as high as 765000V. This power is stepped down
to 72000V at your local substation. From here, the power is stepped down to
about 220V at a transformer on a utility pole. The voltage is so high in the
beginning so it can travel long distances. It is stepped down so often so it can be
used in the home. Certain appliances like air conditioners and stoves use about
220V where smaller appliances use less. If such a high voltage were applied to
these appliances they would need step down transformers installed in them.
More about transformers: AC vs DC generators
Transformers only work on AC, which is one of the great advantages of AC.
Transformers allow 240V to be stepped down to convenient levels for digital electronics
(only a few volts) or for other low power applications (typically 12V). Transformers step
the voltage up for transmission, as mentioned above, and down for safe distribution.
Without transformers, the waste of electric power in distribution networks, already high,
would be enormous. It is possible to convert voltages in DC, but more complicated than
with AC. Further, such conversions are often inefficient and/or expensive. AC has the
further advantage that it can be used on AC motors, which are usually preferable to DC
motors for high power applications.
Step Up Transformer
This type of transformer used for increase the incident voltage. Number of turns
in secondary coil is larger than the number of turns in primary coil.
Step Down Transformer
This type of transformer used for decrease incident voltage. Number of turns in
primary coil is larger than the number of turns in secondary coil.