Transformer (electrical)
An electrical transformer is a static electromagnetic device that transfers electrical energy between two or more circuits through electromagnetic induction, typically changing the voltage and current levels while keeping frequency and power (ideally) constant. It consists of a primary coil and one or more secondary coils wound around a shared iron core. Transformers are indispensable in power transmission, allowing high-voltage transmission over long distances to reduce resistive losses.
Key Formula
Vs/Vp = Ns/Np = Ip/Is
LaTeX: \dfrac{V_s}{V_p} = \dfrac{N_s}{N_p} = \dfrac{I_p}{I_s}
| Symbol | Meaning | Unit |
|---|---|---|
| Vₚ | Primary voltage | Volt (V) |
| Vₛ | Secondary voltage | Volt (V) |
| Nₚ | Number of turns in primary coil | Dimensionless |
| Nₛ | Number of turns in secondary coil | Dimensionless |
| Iₚ | Primary current | Ampere (A) |
| Iₛ | Secondary current | Ampere (A) |
Worked Example
Problem
A step-down transformer has 2000 turns in the primary coil and 200 turns in the secondary coil. The primary voltage is 11,000 V. Find the secondary voltage and secondary current if the primary current is 5 A.
Solution
Step 1: Turns ratio: Nₛ/Nₚ = 200/2000 = 0.1. Step 2: Secondary voltage: Vₛ = Vₚ × (Nₛ/Nₚ) = 11000 × 0.1 = 1100 V. Step 3: Secondary current: Iₛ = Iₚ × (Nₚ/Nₛ) = 5 × (2000/200) = 5 × 10 = 50 A. Check (ideal transformer): Vₚ × Iₚ = Vₛ × Iₛ → 11000 × 5 = 1100 × 50 = 55000 W ✓
Answer
Vₛ = 1100 V; Iₛ = 50 A
Step-Up vs Step-Down Transformer Comparison
| Property | Step-Up Transformer | Step-Down Transformer |
|---|---|---|
| Turns ratio Nₛ/Nₚ | Greater than 1 | Less than 1 |
| Voltage change | Vₛ > Vₚ (increased) | Vₛ < Vₚ (decreased) |
| Current change | Iₛ < Iₚ (decreased) | Iₛ > Iₚ (increased) |
| Primary use | Power station output | Distribution to homes |
| Example | 11 kV → 132 kV (grid) | 11 kV → 230 V (home) |
Interactive Tools
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Related Terms
Inductor
An inductor is a passive electrical component, typically a coil of wire, that stores energy in a magnetic field when current flows through it and opposes changes in current through electromagnetic induction. Its inductance (measured in henries) quantifies the ratio of the magnetic flux linkage to the current. Inductors are essential in filters, oscillators, transformers, and switching power supplies.
Magnetic Field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials, exerting a force on them perpendicular to their velocity. It is represented by the magnetic flux density B (measured in tesla) and arises from electric currents, changing electric fields, and intrinsic magnetic moments of elementary particles. Magnetic fields are central to the operation of motors, generators, MRI machines, and data storage devices.
Electrical Power
Electrical power is the rate at which electrical energy is transferred or consumed by a device, equal to the product of the voltage across it and the current through it. It determines how quickly a device does work or dissipates energy as heat, light, or motion. Power is critical in the design of electrical systems, from household appliances rated in watts to large industrial generators rated in megawatts.
From Latin "transformare" meaning "to change the shape of", from "trans-" (across) + "formare" (to form). The electrical transformer was invented independently by several engineers around 1885, including Ottó Bláthy, Miksa Déri, Károly Zipernowsky (ZBD group) and Lucien Gaulard.