Transformer Structure
Basic function: A transformer is a special electrical device that uses a process called electromagnetic induction to change the voltage of alternating current (AC). It can either increase the voltage (this is called a step-up transformer) or decrease the voltage (a step-down transformer), depending on what is needed.
Main components: The transformer is made of two main coils of wire: the primary coil and the secondary coil. These coils are wrapped around a soft iron core that is laminated. Laminating the core helps improve performance by reducing energy losses.
Coil connections: The primary coil is connected to the AC power supply where the electricity first enters. The secondary coil is connected to the output circuit where the changed voltage exits the transformer and is sent to the rest of the system.
Laminated core: The iron core inside the transformer is made up of thin layers, or laminations, rather than one solid piece. This special design helps reduce unwanted currents, called eddy currents, which would otherwise waste energy as heat.
Transformer Working Principle
Electromagnetic induction: The way a transformer works is based on two important ideas in physics—electromagnetic induction and mutual induction. These principles explain how electricity and magnetism interact.
Changing field: When alternating current flows through the primary coil, it creates a magnetic field that keeps changing direction. This changing magnetic field moves through the iron core.
Induced voltage: As the magnetic field passes through the secondary coil, it creates (or induces) a new voltage in the secondary coil. This is how energy is passed from one coil to the other without any direct connection.
Voltage magnitude: The strength or size of the voltage that appears in the secondary coil depends on how many turns of wire are in each coil. More turns usually mean more voltage.
Types of Transformers
Step-up transformer: This kind of transformer increases the voltage from the primary coil to the secondary coil. It does this because the secondary coil has more loops or turns of wire than the primary coil (Nₛ > Nₚ).
Step-up use: Step-up transformers are commonly used in power lines to raise the voltage before electricity travels long distances. Higher voltage means less current, which helps reduce energy loss.
Step-down transformer: This type of transformer decreases the voltage. The secondary coil has fewer turns of wire than the primary coil (Nₛ < Nₚ).
Step-down use: Step-down transformers are used in electrical appliances to lower the voltage to a safe level that won’t damage the device.
Relationship Between Turns and Voltage
Turns-voltage formula: The relationship between the number of turns in a transformer coil and the voltage is explained by the formula Nₚ / Nₛ = Vₚ / Vₛ. In this formula, Nₚ is the number of turns in the primary coil, Nₛ is the number of turns in the secondary coil, Vₚ is the voltage across the primary coil, and Vₛ is the voltage across the secondary coil. This formula means that the voltage changes depending on how many turns each coil has. If one coil has more turns, it will get more voltage, and if it has fewer turns, it will get less voltage.
Direct proportion: This relationship is a direct proportion, which means that if the number of turns goes up, the voltage also goes up. So, if a coil has more turns, it will produce a higher voltage. On the other hand, if the coil has fewer turns, the voltage will be lower. This helps engineers design transformers to get the right voltage for different uses.
Ideal Transformer
Theoretical model: An ideal transformer is a simplified model that we imagine in theory. It is considered perfect, meaning no energy is lost at all during the process. In this perfect situation, all the electrical power that goes into the primary coil comes out from the secondary coil without any energy being wasted.
Power equation: For an ideal transformer, we say that the input power and output power are equal. This is shown by the formula VₚIₚ = VₛIₛ, where V stands for voltage and I stands for current. This formula shows that if the voltage increases, the current must decrease, and if the voltage decreases, the current increases—so the total power stays the same.
Energy Losses in a Transformer
Real transformers: In the real world, transformers are not ideal. That means they do lose some energy. When a transformer changes voltage, some of the electrical energy gets turned into heat or other forms that are not useful.
Coil resistance loss: The wires in the transformer coils are not perfect. They have resistance, which causes them to get hot when current flows through them. This is called I²R loss, where I is current and R is resistance. To reduce this kind of energy loss, engineers use thicker wires, which have lower resistance.
Eddy currents: Inside the iron core of the transformer, little swirling electric currents called eddy currents can form. These currents waste energy by turning it into heat. To reduce this, the core is built from thin layers of iron, called laminations, which are separated by insulation. This reduces the size of eddy currents.
Hysteresis loss: The iron core gets magnetized and demagnetized again and again as the current changes direction. Each time this happens, a bit of energy is lost as heat. This is called hysteresis loss. To reduce this loss, engineers use soft iron, which can be magnetized and demagnetized easily.
Flux leakage: Ideally, all the magnetic field lines from the primary coil should pass through the secondary coil. But in reality, some of the magnetic field escapes—this is called flux leakage. It reduces the transformer’s efficiency. To reduce this problem, engineers wind the coils close together so more of the magnetic field reaches the secondary coil.
Transformer Efficiency
Efficiency definition: The efficiency of a transformer shows how good it is at changing electrical power from one voltage to another without losing much energy. A high-efficiency transformer gives out nearly all the power it takes in, with only a little bit lost.
Efficiency formula: To calculate efficiency, we use the formula: η = (VₛIₛ / VₚIₚ) × 100%. In this formula, η (the Greek letter eta) means efficiency, VₛIₛ is the power output, and VₚIₚ is the power input. The answer is given as a percentage.
Ideal vs real: In an ideal transformer, the efficiency would be 100%, meaning no energy is lost at all. But in real transformers, the efficiency is usually a bit less than 100% because of the energy losses like resistance, eddy currents, and hysteresis. Even so, good transformers can still be more than 95% efficient.
Uses of Transformers in Daily Life
Household appliances: Many devices we use at home—like phone chargers, laptops, and televisions—use step-down transformers. These transformers reduce the high voltage from the wall socket to a lower voltage that the device can safely use.
Power transmission: When electricity is sent over long distances through power lines, step-up transformers are used to raise the voltage. This helps the electricity travel more efficiently. Before the electricity enters our homes or factories, step-down transformers lower the voltage again so it’s safe to use.
Other applications: Transformers are also used in special machines like medical equipment, welding tools, and induction heaters. In each case, the transformer helps the equipment work safely and efficiently by making sure it gets the right voltage.