Transformer Formula
The transformer is an electrical device that allows to increase or decrease the voltage in an alternating current electrical circuit, maintaining the power. The power that enters the equipment, in the case of an ideal transformer, is equal to that obtained at the output. Real machines have a small percentage of losses. It is a device that converts the alternating electrical energy of a certain voltage level into alternating energy of another voltage level, based on the phenomenon of electromagnetic induction. It is made up of two coils of conductive material, wound on a closed nucleus of ferromagnetic material, but electrically isolated from each other. The only connection between the coils is the common magnetic flux established in the core. The coils are called primary and secondary according to the input or output of the system in question, respectively.
The value of the power for an electric circuit is the value of the voltage by the value of the current intensity. As in the case of a transformer, the value of the power in the primary is the same value for the power in the secondary we have:
input voltage on the primary coil * input current on the primary coil = output voltage on the secondary coil * output current on the secondary coil.
The equation is written
We can also work out the transformer output voltage if we know the input voltage and the number of turns (coils) on the primary and secondary coils, using the equation below;
input voltage on the primary coil / output voltage on the secondary coil = number of turns of wire on the primary coil / number of turns of wire on the secondary coil
The equation is written
we have:
Vp = input voltage on the primary coil.
Vs = input voltage on the secondary coil.
Ip = input current on the primary coil.
Is = input current on the secondary coil.
np = number of turns of wire on the primary coil.
ns = number of turns of wire on the secondaryad coil.
Trasnformer Questions:
1)We have a transformer with a current in the primary coil of 10 A and input voltage in the primary coil of 120 V, if the voltage in the output of the secondary coil is 50 V, calculate the current in the output of the secondary coil.
Answer: As we want to determine the output current in the secondary coil, we use the first equation
, → 
,
= 2.4 * 10 A = 24 A.
Is = 24 A.
2) We have a transformer with an output current on the secondary coil of 30 A and an input current on the primary coil of 2000 turns of 6 A, determine the number of turns on the secondary coil.
Answer: We will use the two equations, the first equation to determine the output voltage on the secondary coil and the second equation to determine the number of turns on the secondary coil.
, → 
,
, → 
,
Substituting,
ns = 400
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