Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Explain the operating principles of a transformer.
• Calculate voltage, current, and turns ratio using the transformer equation.
• Describe different types of transformer losses and their effect on efficiency.
• Explain power distribution in the South African context.
• Describe different types of power distribution systems.

Lesson summary

This week, we delve deeper into transformers and power distribution, building upon the foundational knowledge acquired in Week

1. Understanding how transformers function and how power is distributed is critical for a functioning modern society, especially in South Africa where reliable electricity supply remains a significant challenge. From ensuring lights stay on in our homes to powering industries that drive our economy, transformers and efficient power distribution networks play a pivotal role.

Furthermore, with the increasing focus on renewable energy sources and smart grids, a solid understanding of these concepts is essential for future Electrical Technologists.

Lesson notes

2.1 Transformer Principles of Operation A transformer is a static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. It works on the principle of mutual inductance. It consists of two or more coils electrically isolated but magnetically linked.

Primary Winding: The winding connected to the input voltage source (e.g., 230V from the grid).

Secondary Winding: The winding connected to the load (e.g., 12V for a low-voltage appliance).

Core: Usually made of laminated silicon steel to reduce eddy current losses (discussed later). The core provides a low reluctance path for the magnetic flux.

Mutual Inductance: The phenomenon where a changing current in one coil (primary) induces a voltage in another coil (secondary) due to the shared magnetic field (flux). When an alternating current flows through the primary winding, it creates a changing magnetic flux in the core. This changing flux links with the secondary winding and induces an electromotive force (EMF) or voltage in the secondary winding. The magnitude of the induced voltage depends on the number of turns in the secondary winding and the rate of change of flux. 2.2 Transformer Equation The transformer equation relates the voltage, current, and number of turns in the primary and secondary windings: ``` Vp / Vs = Np / Ns = Is / Ip ``` Where: Vp = Primary voltage Vs = Secondary voltage Np = Number of turns in the primary winding Ns = Number of turns in the secondary winding Ip = Primary current Is = Secondary current This equation is crucial for understanding how transformers step up or step down voltage. If Ns > Np, the transformer is a step-up transformer (Vs > Vp). If Ns < Np, the transformer is a step-down transformer (Vs < Vp).