Transformer Theory and Calculators
Transformers are electrical devices that change AC voltages.

They are used to change voltage by
stepping up the
primary voltage on the secondary side
stepping down the voltage. They are also used to match impedance and as isolating devices that isolate the ground.

A.C. is required to operate transformers
because the voltage induction that occurs between the primary and secondary requires a rapidly expanding and collapsing electromagnetic field that only alternating current provides.

Because electrical power distributed as high voltage has a reduced current, smaller cable sizes can be used.

cost effectiveness of smaller cables is the reason for high voltage distribution but it must be stepped back down for  consumer safety.



Edison "king of DC" tried to keep consumers using his DC electricity it was very inefficient as voltage dropped rapidly over distances
Current wars  elephant in New York    human electrocution

Tesla developed AC polyphase distribution systems and devices and kicked off the
"2nd Industrial Revolution"

AC can be transformed to dangerous but far traveling voltages and then stepped back down to relatively safe voltages for the consumer
Tesla Coil  
Tesla Video Shrine Tesla Roadster     BBC Tesla Documentary

Recall the right hand rule :

grab the conductor with right hand

thumb points in direction of current flow

fingers point towards the North pole of the electromagnetic field

remember in AC a reversal is happening 60 times as second



When a magnetic field cuts through a conductor a voltage is induced
in the conductor.

If the conductor forms a closed circuit, current will and create a magnetic field that opposes the field that induces the voltage

Lenz;s L


the alternating magnetic field of the primary field induces a voltage in the secondary


The lower coil (primary) induces a voltage in
the upper coil (secondary) energizing the lamp
 The batteries of an electric vehicle
are energized  by an
"inductive pluggin puck"
the puck is the primary

Your electric toothbrush...... or the hypodermal battery of a human pacemaker can be recharged by inductive means





what type of transformer is this a step up or step down transformer?


if 100 volts AC are applied at the primary what is the voltage at the secondary of this transformer

if 10 amp are input what current flows from the secondary?

if 250 w are input how much power is output?



Step Up or Step Down ?
the iron core is permeable to electromagnetic fields so it is concentrates
the changing field causes the iron atoms to flip flop generating heat thus wasting some energy






Multi cylinder internal combustion engines use a
coil and distributor to ignite fuel in the combustion chambers

Here, although no voltage change would occur, the load is electrically isolated from the source.
Hence the term isolating transformer

Remember that the power going into a transformer is the same as the power coming out
        Pin = Pout

Step Down
down  Isup 

Step Up      Vsup     Isdown



Center tapped transformer
Can be multi tapped to provide multiple voltages (as in single phase 120/240v systems)
Or to trim final output


Step down pole transformer stepping down
8000V to single phase 120/240V
- note the neutral supported triplex cable
- lines 1 + 2 twist around the bare neutral support cable






Industrial step-down transformer