According to the principle of electromagnetic induction, Michael Faraday and James Clerk Maxwell’s theory of electromagnetic induction states that a changing magnetic field causes a voltage generation (electromotive force) to produce current.
A varying current can induce an EMF in a coil. By the principle of mutual induction, when another coil is brought next to such coil, the flux induces emf in the other coil.
The coil which has a different flux is called the primary coil and the coil in which the emf is induced is called the secondary coil, while the two coils together form a unit called a transformer.
Transformers are electrical devices consisting of two or more coils of wire that are used to transfer electrical energy through a changing magnetic field.
A transformer consists of a primary coil to which input is given and a secondary coil to which output is collected. Both these coils are wound on a core material. Typically, an insulator forms the core of the transformer.
- Np = Number of turns in the primary winding.
- Ns = Number of turns in the secondary winding.
- Ip = Current flowing in the primary of the transformer.
- Is = Current flowing in the secondary of the transformer.
- Vp = Voltage across the primary of the transformer.
- Vp = Voltage across the secondary of the transformer.
- Φ = Magnetic flux is present around the core of the transformer.
One of the main reasons that we use alternating AC voltages and currents in our homes and workplaces is that AC supplies can easily be generated at a convenient voltage, which is converted to a much higher voltage And then distributed across the country. A national grid of pylons and cables over very long distances.
A transformer is represented in a circuit. The primary winding, secondary winding, and core of the transformer are also shown in the following figure.
Therefore, when a transformer is connected to a circuit, the input supply is given to the primary coil so that it produces a magnetic flux varying with this power supply and that flux is induced in the secondary coil of the transformer, which is separately Different emf produces different current. Since the flux must be varied, to transfer the emf from the primary to the secondary, a transformer always operates on alternating current.
A single-phase transformer can serve to increase or decrease the voltage applied to the primary winding. When a transformer is used to “step up” the voltage on the primary winding, it is called a step-up transformer. When it is used to “reduce” the voltage on the secondary winding with respect to the primary, it is called a step-down transformer.
However, a third situation exists in which a transformer produces the same voltage on its secondary as applied to its primary winding. In other words, its output is the same with respect to voltage, current, and power transfer. This type of transformer is called an “impedance transformer” and is mainly used for impedance matching or isolation of nearby electrical circuits.
The difference in voltage between the primary and secondary windings is achieved by changing the number of coils turns in the primary winding (NP), while changing the number of coils on the secondary winding (NS).
Step-up and Step-down Transformers
Depending on the number of turns in the secondary winding, the transformer may be called a step up or step down transformer.
There will be no difference between the primary and secondary power of the transformer. Accordingly, if the voltage on the secondary is high, a low current is drawn to stabilize the power. Also, if the voltage across the secondary is low, a high current is drawn, so the power must be the same as on the primary side.
Step Up Transformers
When the secondary winding has more turns than the primary winding, the transformer is called a step-up transformer. Here the induced emf is greater than the input signal.
Step Down Transformer
When the secondary winding has fewer turns than the primary winding, the transformer is called a step-down transformer. Here the induced emf is less than the input signal.
Since the transformer is basically a linear device, there now exists a ratio between the number of turns of the primary coil divided by the number of turns of the secondary coil. This ratio is called the ratio of change, commonly known as the transformer “turn ratio” or “the ratio of transformation” (TR).
The number of turns of the primary and secondary winding affects the voltage rating, it is important to maintain a ratio between the turns so as to have an idea about the induced voltage.
This turn ratio value determines the operation of the transformer and the respective voltage available on the secondary winding.
It is necessary to know the ratio of the number of turns on the primary winding to that of the secondary winding. The turn ratio, which has no units, compares two turns in sequence and is written with a colon, such as 3:1 (3-to-1).
If there are 3 volts on the primary winding, then 1 volt on the secondary winding will be 3 volts-to-1 volts. Then we can see that if the ratio between the number of turns changes then the resulting voltage must also change by the same ratio, and this is true.
Transformers are all about “ratio”. The ratio of primary to secondary, ratio of input to output, and turn ratio of a given transformer will be equal to its voltage ratio. In other words for a transformer: “turns ratio = voltage ratio”. The actual number of turns of the wire on any given winding is generally not important, only the winding ratio, and this relationship is given by:
The ratio of primary to secondary, the ratio of input to output, and the turn ratio of a given transformer will be proportional to its voltage ratio. Hence it can be written as
Assuming an ideal transformer and phase angles: ΦP ≡ ΦS
The sequence of numbers ratio values is very important when expressing transformers because the turn ratio of 3:1 expresses a very different transformer relationship and output voltage in which the turn ratio is given as 1:3.