We need transformer because, We know that the electricity we uses, that is developed in power stations. Power station supplies that electricity at very high voltage because electricity losses are very low at high voltage. Therefore, they need a devise to convert electricity into high voltage.
- What is a Transformer
- Who invented Transformer?
- Formation of a Transformer
- Working of Transformer
- Use of Transformer
- Why Transformer don’t works with DC?
What is a Transformer
It is a device which can convert low voltage alternating current(AC) into high voltage AC or high voltage AC into low voltage AC. Transformer is an electrical device which work on the principal of mutual induction and used to raise or lower the current and the voltage.
But, that high voltage alternating current is not needed at our home. Because, our home appliances cannot deal with that high voltage. So we need a devise that converts the high voltage alternating current(AC) into low voltage alternating current.
That required device is transformer.
Who invented Transformer?
The Transformer was invented by Otto blathy, Miska Deri, Karoly Zipernowsky in 1830’s but it comes in practical use in 1886, when William Stanley built the first reliable commercial transformer.
It is one of the important electronic component in the stabilizer we use, our mobile charger, laptop charger, etc. Yes, there is many other component also required in that electronic equipment for converting alternating current to direct current or many other things but, that’s no our topic right now.
Which device converts low voltage AC into high voltage AC that device is known as step-up transformer. And which converts high voltage AC into low voltage AC that device is known as step-down transformer.
Transformer only works with alternating current(AC) it cannot work with direct current(DC). WHY?
Formation of a Transformer
First of all we need a soft iron core. This core is laminated.
As shown in the figure above two current conducting loops are there on two side of the iron core and both loops are individually connected with alternating current(AC) source. However, the coil at the left side of the iron core, is called as primary coil and the coil wound at the right side, is known as the secondary loop.
Also checkout: Rectifier
Just look at the transformer’s diagram, Isn’t that two primary and secondary loop looks like solenoid. so, if we apply voltage to the primary loop it will works like a solenoid and it will create a magnetic field.
The core is made of soft iron and it is a ferromagnetic substance. Ferromagnetic is a type of substance that don’t allow the magnetic field to go outside of it. That means all of the magnetic field generated because of primary loop that will reach to the secondary loop via iron core.
The current is alternating(AC) so the magnetic field will also change with time. So, it is varying magnetic field it is not constant. That means flux will also vary. However, according to Faraday’s law varying flux will develop induced EMF(Electromotive force).
ℰs = electromotive force(EMF)in secondary coil
ℰp = electromotive force(EMF)in primary coil
Ns = number of turns in secondary coil
Np = number of turns in primary coil
Is = current in secondary coil
Ip = current in primary coil
For step-up transformer:
According to the equation above, if number of turns in secondary coil(Np) will more than the number of turns in primary coil(Np). So, the induced EMF of secondary(ℰs) will also more than the induced EMF of primary(ℰp).
ℰs > ℰp
Ns > Np
For step-down transformer:
And if number of turns in secondary coil(Np) is less than the number of turns in primary coil(Np). So, the induced EMF of secondary(ℰs) will also less than the induced EMF of primary(ℰp ).
ℰs < ℰp
Ns < Np
Suppose that primary coils’ each turn has flux = φp
Number of turns in primary and secondary coil is different but cross sectional area in them are same. So,
Secondary coils’ each turn will also have flux = φs [ φp = φs ]
Total flux in primary coil = φp·Np·φ
Use of Transformer
- Changing the voltage or current
The main use of it is to step up(increase) or step down(decrease) the voltage or the current. as mentioned above, power stations uses step up transformer(convert low voltage AC into high voltage AC) and we use step down transformer(convert high voltage AC into low voltage AC) so, home appliances can easily.
- To block direct current(DC)
Transformer has inductive reactance, which can stop the direct current(DC) from passing one circuit to other circuit.
- AC vs. DC power transmission
As you know mostly we transmit the power in AC, and the main reason behind it is transformer. so, If we use it we can increase or decrease the voltage at any stage with minimum loss. You can consider the same example given first use of it(1. Changing the voltage or current ).
- In our chargers of phones / laptops
Normally our home’s plug give 220V output. If we provide that much volts current directly to our mobile devices so, it will damage them. That’s step down transformer are used in chargers(adapter). Step down transformer will decrease the voltage so our mobile devices can safely get charged.
- Galvanic isolation
Imagine you are working on a very expensive and heavy circuit and it burn out because of any other circuit you had connected with it!
If we connect any two circuits with the transformer of ratio 1:1(number of turns in secondary coil = number of turns in primary coil )
So there will be no increase and decrease in the voltage but if one circuit fails so other will not get affected because of it.
NOTE: [ 1:1 (Ns = Np) ] ratio transformers are known as isolation transformer.
Why Transformer don’t works with DC?
Transformer work on the principle of mutual induction.
When we supply the alternating current(AC) to the primary coil(which is wound in shape of solenoid ), a varying magnetic field will be developed around it. As mention above The Soft iron core is a ferromagnetic substance.(it is a type of substance that don’t allow the magnetic field to go outside)That means all of the magnetic field generated because of primary loop that will reach to the secondary loop via iron core.
The magnetic field is varying because of alternating current(AC), that means the developed flux will be also varying. According to Faraday’s Law of Electromagnetic Induction varying flux will develop induced EMF(Electromotive force). This way it will work.
Now, If we apply direct current(DC) to the primary coil there will no magnetic field will be developed because, magnetic fields are only created when the current is varying. But, direct current can’t be vary so, there will no magnetic field created, no flux will be developed and no EMF(Electromotive force)will induced!
So, what is meaning of that type of transformer? That’s why it don’t works with direct current(DC).
The method could possibly used for the transfer of electricity across the country via the power lines. the circuit was not supplying the most efficient or maximum efficiency, due to the core losses not equaling the copper losses. So if you increases the voltage out, then the current out must decreases.
A transformer is built to transfer the energy from one circuit into another circuit by way of magnetic coupling. However, An alternating current creates a magnetic flux in the core on its way through the first winding, inducing the voltage in the others. It can convert high and low voltages, it cannot convert AC to DC.May 1, 2017
Advantages: A transformer will increase or decrease AC voltages, currents, or impedance. The available power cannot change, but will slightly decrease, depending on the efficiency of the transformer. A transformer may also be used to isolate grounds. Transformers are widely used in power transmission.
To avoid the overall losses and increased cost, the best option is to use “stepped–core” (or cruciform core), which utilizes the space, better than other type of cores and the length of mean-turn of the winding is lower compared to the rectangular or square cores.
When a DC voltage is applied to the primary winding of a transformer, due to low resistance, the winding acts as a short circuit across the terminals of the DC source that lead to the flow of heavy current through the winding resulting in overheating of the winding.
DC can shock you as well. It’s just that more current is required in case of DC to feel the shock than that required for ac. This is due to the fact that the current flowing through our body depends on four factors. Above 25-30mA, the current flow through our body is dangerous.
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Done B.tech from Dharmsinh Desai University, Nadiad