Transformers Explained - How transformers work

Introduction to Transformers00:00:00

Transformers are ubiquitous and essential for modern electrical systems, bridging power stations and homes. They convert voltage and current but only work with alternating current (AC). They are rated in VA or kVA, not watts, a topic explained later. Transformers vary in size from small doorbell units to massive power station equipment.

Transformer Construction and Operation00:01:27

A transformer consists of two separated coils, primary and secondary, wrapped around an iron core. The primary coil connects to the power supply, and the secondary coil connects to the load. Transferring power between coils efficiently changes voltage: step-up transformers increase voltage while decreasing current, and step-down transformers decrease voltage while increasing current. This is crucial for efficient power transmission over long distances.

AC and DC Current in Transformers00:05:26

An electrical current creates a magnetic field around a wire. In AC, the current and magnetic field constantly reverse, creating a sine wave pattern. This changing magnetic field is key for transformers; it induces a voltage in the secondary coil. DC current, however, creates a constant magnetic field, which doesn't induce a continuous voltage, making transformers incompatible with DC.

Efficiency and Losses in Transformers00:08:47

To improve efficiency, a ferromagnetic iron core concentrates the magnetic field. However, eddy currents in the core cause heating and energy loss, which are mitigated by using laminated sheets. Other losses include magnetic leakage flux, disturbances at joints, and copper losses in the wires due to resistance, generating heat. The humming sound often heard from transformers is caused by the alternating current expanding and contracting the core laminations.

Understanding Volt-Amperes (VA) and Kilowatt (kW)00:10:09

Transformers are rated in VA or kVA because they transfer apparent power, which is the product of voltage and current. The actual power (kilowatts) delivered depends on the load's power factor, which accounts for reactive power (energy wasted as heat). The video uses a beer analogy where liquid is 'true power' (kW) and foam is 'reactive power' (VAR), explaining why manufacturers rate transformers by total 'glass' size (VA).

Transformer Calculations00:13:23

The video demonstrates how to calculate voltages, currents, and turns ratios for both step-up and step-down transformers, assuming ideal conditions without losses. It provides formulas for finding unknown values when other parameters are given, emphasizing that power remains constant on both sides of a perfect transformer.