Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Describe the construction of a basic transformer.
• Apply the transformer equation to calculate voltage and current.
• Explain the different types of energy losses in a transformer.
• Understand eddy currents and hysteresis losses.

Lesson summary

This week, we delve into the heart of electrical power distribution systems: transformers. Transformers are essential devices that allow us to efficiently transmit electrical energy over long distances and then safely distribute it to our homes, schools, and businesses. Without transformers, our modern electrical grid, so critical to daily life in South Africa, simply wouldn't be possible. Imagine life without lights, computers, or appliances – that's the reality without efficient power distribution enabled by transformers.

Lesson notes

2.1 Transformer Construction A transformer is a static (stationary) electrical device that transfers electrical energy from one circuit to another through electromagnetic induction. It works on the principle of mutual inductance.

The key components of a transformer are: Core: The core is made of laminated silicon steel. Laminations are used to reduce eddy current losses (more on this later). The core provides a low-reluctance path for the magnetic flux. Silicon steel is chosen for its high permeability and low hysteresis losses. Common core types include core-type and shell-type.

Primary Winding (Np): This winding is connected to the input voltage source (AC). When AC voltage is applied, it produces a changing magnetic flux in the core. The number of turns in the primary winding is denoted as Np.

Secondary Winding (Ns): This winding is connected to the load. The changing magnetic flux produced by the primary winding induces a voltage in the secondary winding. The number of turns in the secondary winding is denoted as Ns. 2.2 The Transformer Equation (Ideal Transformer) The relationship between the primary and secondary voltages and currents in an ideal transformer (no losses) is defined by the transformer equation: 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 Turns Ratio (a): The ratio Np/Ns is called the turns ratio (a). If a > 1, the transformer is a step-down transformer (Vs Vp). Used to increase voltage.