The device used for transferring electrical energy from one circuit to another is known as a transformer. A transformer works on the principle of mutual induction. A transformer is further of 2 types based on the number of turns in the windings or coil of the transformer. These are called step-up transformers and step-down transformers.
Transformers are used for a wide range of purposes, including increasing the voltage from electric generators to enable long-distance transmission of electricity and decreasing the voltage of conventional power circuits to run low-voltage devices like doorbells and toy electric trains. They’re substantially used to help with loss of power due to variations in the resistance of a line. In this article, we shall discuss step-up and step-down transformers.
A transformer mainly comprises two types of windings called primary and secondary windings. These windings are wound on a magnetic iron core with many layers and each layer does not make contact with the other layer. They are separated from each other using lamination. An alternating current flowing through the primary coil of a transformer induces a changing magnetic field in the primary coil. Due to mutual induction, the current is induced in the secondary coil. A transformer is rated in kVA, which is the product of the voltage and current in the transformer. The voltage generated by the secondary coil is proportional to the number of turns in the coil. The structure of a transformer coil is shown below:
Structure of a Transformer
Types of Transformer
There are two types of transformer:
- Step-Up Transformer
- Step-Down Transformer
Step-Up Transformer
We have learnt that a transformer consists of a core and windings. In case of a step up transformer, the number of secondary windings is more than the primary windings. The step-up transformer gives the higher voltage as a output because the voltage is directly proportional to the number of turns in the windings. Hence, in a step up transformer with N1 turns in primary winding, N2 turns in secondary winding and I1 and I2 current in primary and secondary windings:
Thus, a step up transformer increases the voltage and decreases the current on the secondary windings side. A diagram of step up transformer is shown below:
Step-Up Transformer
Step Down Transformer
In a step-down transformer, the number of turns in primary winding is larger than the turns in secondary winding . Ohm’s law states that current and voltages are directly proportional to each other, which means a low voltage in the secondary coil means a high current in secondary windings. Thus we can say that, in a step down transformer with N1 turns in primary winding, N2 turns in secondary winding and I1 and I2 current in primary and secondary windings:
Thus, a step down transformer decreases the voltage and increases the current on the secondary windings side. A diagram of step down transformer is shown below:
Step-Down Transformer
Step-up and step-down transformers have a similar construction and components used.. The only difference is that the number of turns of the primary winding of a step-up transformer is less than the number of turns of the secondary winding, while in a step-down transformer the number of turns of the primary winding is greater than the number of turns of the primary winding. Number of turns of the secondary coil. The main components of a transformer are:
- Transformer core: The transformer core is generally made of steel or iron sheets insulated from each other by rollers. The core therefore consists of laminated steel cores.
- Transformer Windings: The primary and secondary windings of a transformer are made of thick, insulated copper wires.
There are two types of transformer construction
- Shell-Type Transformer
- Core-Type Transformer
Shell Type Transformer
Core of a shell type transformer is made using E and L shaped laminations. It has 3 legs to provide mechanical strength to the core. Both primary and secondary windings are wound on the central limb of the E part of the core. To ensure that both windings can be wound on the central limb, the area of cross section of the central limb is kept twice the area of cross section of side limbs.
Shell Type Transformer
Core Type Transformer
Core of a shell type transformer is made using U and L shaped laminations. It has only 2 legs. Both primary and secondary windings are wound on the two limbs of the U part of the core. The main advantage of this type of construction is that it uses less amount of iron to make the core.
Core Type Transformer
We know that any transformer works on the principle of mutual induction according to which a changing current in one coil induces electromotive force or current in another coil. When alternating current flows through primary coil of a transformer, it produces a varying magnetic field which induces a current in the secondary coil. The current induced depends upon the number of turns in windings of the secondary coil. The relation between the number of turns, voltage and current across primary and secondary coil is:
[Tex]\frac{N_1}{N_2} = \frac{V_1}{V_2} = \frac{I_2}{I_1}
[/Tex]
where,
N1 = number of turns in primary winding
N2 = number of turns in secondary winding
V1 = voltage across primary winding
V2 = voltage across secondary winding
I1 = current in primary winding
I2 = current in secondary winding
It must be noted that energy is neither created nor destroyed in either step up or step down transformer. The product of Voltage and current i.e. power across the primary and secondary coils in a transformer remains the same.
There are various terms associated with both step up and step down transformer such as:
- Transformer Formula
- Turn Ratio
- Efficiency of a Transformer
Transformer Formula
According to this formula, the power in primary winding is equal to the secondary winding. As power is equal to product of voltage and current, we can write it as:
Vp x Ip = Vs x Is
where,
Vp = volatge in primary coil
Ip = current in primary coil
Vs = voltage in secondary coil
Is = current in secondary coil
Turn Ratio
The ratio of the Np to Ns is called the turn ratio of the transformer. It is mathematically written as:
[Tex]Turn ratio = \frac{Np}{Ns}
[/Tex]
where,
Np = turns in primary coil
Ns = turns in secondary coil
Efficiency of a Transformer
The ratio of the power input to a transformer and the power output by a transformer is called its efficiency. It is denoted using the symbol [Tex]\eta
[/Tex]. It can be calculated as:
[Tex]\eta = \frac{Po}{Pi}*100
[/Tex]%
[Tex]\eta
[/Tex] = ([Tex]\frac{Po}{Pi} + L
[/Tex]) x 100%
where,
Po = output power
Pi = input power
L = loss of power
Power plants generate power and are generally located far away from the main city. The power from the power plants need to be supplied for consumption. The main challenge faced in transporting this power is prevention of power loss as the power or energy being sent is wasted to a large extent on sending through wires. To prevent this power loss, transformers are used. A step up transformer is used at the power stations to send the energy by increasing the voltage to a great extent. This in turn reduces the current and the loss of power is prevented. At the site where electricity or power is to be used, step down transformer reduces this high voltage to a level that can be used by the consumers. On reducing the voltage, the current increases and this is then used by consumers.
The working of a transformer can be reversed. It means that the step up transformer can work as a step down transformer and vice versa. The only thing we need to do is reverse the connections of input source from the primary winding to the secondary winding. Thus in case of a step up transformer, if we connect input source to secondary winding which has lesser number of turns, then now it acts as a primary winding and the transformer will act as step down transformer. Similarly, we can also make a step down transformer behave like a step up transformer.
Transformer has the following applications:
- They are used to increase the power of the electricity produced in the power plant to transport them to long distance.
- It is used to lower the high voltage received from power plants so that it can be used for household consumption.
- Transformers can reduce or increase the voltage of the sound signals.
- Various electronic devices such as TV, mobile, radio, etc. also make use of transformer.
- They are also used for impedance matching.
Basis of Difference
| Step Up Transformer
| Step Down Transformer
|
|---|
Number of turns
| The number of turns in primary winding is less than that in secondary winding.
| The number of turns in primary winding is more than that in secondary winding.
|
Effect on Voltage
| It increases or steps up the voltage in the output circuit.
| It decreases or steps down voltage in the output circuit.
|
Effect on Current
| Current in output circuit is less than the current in input circuit.
| Current in output circuit is more than the current in input circuit.
|
Maintenance
| It requires less maintenance.
| It requires high maintenance.
|
Mathematical relation between turns
| N1 < N2
| N2 < N1
|
Applications
| It is used in X-rays extraction, microwaves, ovens, etc.
| It is used in CD players, TV, washing machines, etc.
|
Advantages of Step-Up transformer
- It is easy to maintain.
- It has high efficiency.
- It is able to start quickly.
Advantages of Step-Down transformer
- It has high reliability and high durability.
- It is less expensive as compared to step up transformer.
- It can provide different voltages required for household appliances.
Disadvantages of Step-Up transformer
- It requires a mechanism to cool it as it produces a large amount of heat.
- It is very huge in size.
- It can work only with AC current.
Disadvantages of Step-Down transformer
- It requires frequent maintenance.
- It can work only with AC current.
1. What is the number of turns in the secondary coil of a transformer if the number of turns in primary coil are 300 and the current in the primary coil of the transformer is 5A. The current flowing through the secondary coil is 2A.
Given N1 = 300, N2 = ?, I1 = 5A, I2 = 2A
We know that N1 / N2 = I1 / I2
300/N2 = 5/2
N2 = 120
2. What is the number of turns in the secondary coil of a transformer if the number of turns in primary coil are 500 and the current in the primary coil of the transformer is 3A. The current flowing through the secondary coil is 8A.
Given N1 = 500, N2 = ?, I1 = 3A, I2 = 8A
We know that N1 / N2 = I2 / I1
500/N2 = 8/3
N2 = 500 * 3/8 = 187.5 ~ 188 turns
3. What is the number of turns in the primary coil of a transformer if the number of turns in secondary coil are 200 and turn ratio of the transformer is given to be 6.
Given N2 = 200, Turn ratio = 6, N1 = ?
We know that Turn ration = N1/ N2
6 = N1 / 200
N1 = 1200
4. Calculate the efficiency if input power and output power are 200W and 180W respectively. Also calculate the power loss.
Given Pi = 200W, Po = 180W
We know that [Tex]\eta
[/Tex] = (Po/ Pi) x 100%
[Tex]\eta
[/Tex] = (180 / 200) x 100%
[Tex]\eta
[/Tex] = (9 / 10) x 100%
[Tex]\eta
[/Tex] = 90%
Conclusion
In this article, we have studied step-up and step-down transformers. It helps in increasing or reducing the voltage level in an AC circuit to ensure the correct operation of the circuit’s various electrical components. Hence, it is an important device in the field of Electrical Engineering.
1. On what principle does a transformer work? Explain it.
A transformer works on the principle of mutual induction. According to it, a changing current in one coil induces an electromotive force (emf) in the other coil near it.
2. What is the relation between number of turns in primary and secondary coil in step up transformer?
Number of turns in primary coil is lesser than the number of turns in secondary coil in step up transformer.
3. What physical quantity remains unchanged in a transformer?
Power or the product of voltage and current remains unchanged in a transformer.
4. Identify the type of transformer if the primary coil has 100 turns and secondary coil has 50 turns.
As the number of turns in primary coil is 100 which is greater than 50 that is the number of secondary coils, it is a step down transformer.
5. What is the core of a transformer made up of?
The core of a transformer is generally made up laminated soft iron sheets.
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