Construction Of Automatic Phase Changer

Fig 2; wiring up of a dual primary coil ,ains transformer in {a} series and {b} parallel.
A main transeormer is specified by:
{1} its secondary {output} voltages vs.
{2} its maximum power pmax which the transformer can pass quoted in VA {volt - amp}. This determines the maximum output {secondary} current, Imax.
    Where VS is the secondary voltage. If there are two give the maximum for each coil.
{3} its construction – it may be PCB – mounting, chassis mounting {with solder tag construction} or to roidalcal high quality design}
Imax /    VS= Pmax
    STEP DOWN TRANSFORMER.
If the first coil has more turns than the second coil, the secondary voltage is smaller than the primary voltage!
This is called a step –down trasformer. If the secondary coil has half as many turns as the first coil, the secondary voltage will be half the size of the primary voltage.
If thew second coil has one tenth . as many  turns, it has one tenth the voltage. In general
Secondary current- primary current = number of turns in primary – number of turns in secondary
In the primary – number of turns
    So a step – down transformer with 100 coil in the primary and 10 coils in the secondary will reduce the voltage by by a fractor of 10 but multiply the current by the factor of 10at the same time. The power in an electric is equal to the current times voltage
Cwatts= volt xamps is one way to remember this} so you can see the power in secondary coil is theoretically the same as the power in the primary coil (in reality there is some loss of power between the primary and the secondary because some of the magnetic flux teaks out the core; some energy is lost because the core heat up, and so on)