Have we ever wondered how we get just 220V AC electricity at our homes when it comes from a Power station that could be as high 155,000 to 765,000 volts? Or if we want to give a supply to a circuit from an AC supply, how are we going to give just the required 12V? We use a component known as Transformer which does this simple operation
Brief Introduction to an Electrical Transformer
A Transformer is an electrical device that takes electricity of one voltage and changes it into another voltage. In AC circuits, AC voltage, current and waveform can be transformed with the help of Transformers. Transformer plays an important role in electronic equipment. AC and DC voltage in Power supply equipment are almost achieved by transformer’s transformation and commutation. Figure 1 shows the Transformer.
Basically, a Transformer changes electricity from high to low voltage or low to high voltage using two properties of electricity. In an electric circuit, there is magnetism around it. Second, whenever a magnetic field changes (by moving or by changing strength) a voltage is made.
A Transformer takes in electricity at a higher voltage and lets it run through lots of coils wound around an iron core. “. A single-phase Transformer can operate to either increase or decrease the voltage applied to the primary winding. Because the current is alternating, the magnetism in the core is also alternating. Also around the core is an output wire with fewer coils. The magnetism changing back and forth makes a current in the wire. Having fewer coils means less voltage. When it is used to “decrease” the voltage on the secondary winding with respect to the primary it is called a Step-down Transformer. When a Transformer is used to “increase” the voltage on its secondary winding with respect to the primary, it is called a Step-up Transformer.
However, a third condition exists in which a transformer produces the same voltage on its secondary as is applied to its primary winding. In other words, its output is identical with respect to input. This type of Transformer is called an “Impedance Transformer” and is mainly used for impedance matching or the isolation of adjoining electrical circuits.
Working of a Transformer
The working principle of Transformer is very simple. It depends upon Faraday’s law of electromagnetic induction. Actually, mutual induction between two or more winding is responsible for transformation action in an Electrical Transformer.
According to Faraday’s laws of electromagnetic induction,
“Rate of change of flux linkage with respect to time is directly proportional to the induced EMF in a conductor or coil“.
When one winding which is supplied by an alternating electrical source as shown in figure 2. The alternating current through the winding produces a continually changing flux or alternating flux that surrounds the winding. If any other winding is brought nearer to the previous one, obviously some portion of this flux will link with the second. As this flux is continually changing in its amplitude and direction, there must be a change in flux linkage in the second winding or coil.
According to Faraday’s law, there must be an EMF induced in the second. If the circuit of the later winding is closed, there must be an electric current flowing through it.
Now let us see the working of a Transformer in detail. The winding which takes electrical power from the source, is generally known as Primary winding of Transformer as shown in figure 2. The winding which gives the desired output voltage due to mutual induction in the transformer, is commonly known as Secondary winding of Transformer.
The difference in voltage between the Primary and the Secondary windings is achieved by changing the number of coil turns in the Primary winding compared to the number of coil turns on the Secondary winding.
As the Transformer is a linear device, a ratio is done between the number of turns of the primary coil divided by the number of turns of the secondary coil. This ratio, called the ratio of transformation, more commonly known as a Transformers “turns ratio”. This turn’s ratio value dictates the operation of the Transformer and the corresponding voltage available on the secondary winding.
If the Transformer’s ratio is 10:1, then if there are 2200 volts on the Primary winding there will be 220 volts on the Secondary winding. Then we can see that if the ratio between the number of turns changes the resulting voltages must also change by the same ratio.
Given below is an example of a Transformer which is set to 10:1 ratio. As seen in figure 3 from the Proteus tool, we can see that 24V AC is being given to the primary winding of the Transformer. The graph of the input is also shown in figure 4.
In figure 5 and figure 6, we can see that only 2.4V and -2.4V is given respectively as can be read from the DC voltmeter coming from the secondary winding of the Transformer. In other words, out of 24V from the AC supply, only 2.4V is being supplied after reducing it to 10:1.
The graph below shows that only 2.4V and -2.4V is received from the Positive Half cycle and Negative Half cycle
Transformers works only with AC supply
Transformers require an alternating magnetic flux to operate correctly. Transformers cannot be used to transform or supply DC voltages or currents, since the magnetic field must be changing to induce a voltage in the secondary winding. Therefore, Transformers do not Operate on DC Voltages, and works only with AC.
Features of a Transformers 12-0-12 500mA
Transformers are rated in Volt-amperes (VA), or in larger units of Kilo Volt Amperes (kVA). 12-0-12 means that the voltage or the potential difference between each of the end terminal of the secondary winding and the mid-point of the secondary winding of the Transformer is 12V. And, between the two ends of the secondary winding, we will get 12 + 12 = 24V. 500mA means the current delivery capability of the secondary winding of the Transformer. Normally it is said in VA. It would be 25 x 0.5 = 12VA. The ratings are based on the requirements of the loads that are to be connected to the Transformer.
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