Lesson Notes By Weeks and Term v4 - SHS 3
ELECTRICAL SYSTEMS DESIGN
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ELECTRICAL SYSTEMS DESIGN
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Subject: Applied Technology
Class: SHS 3
Term: 2nd Term
Week: 10
Grade code: 2.4.1.LI.5
Strand code: 4
Sub-strand code: 1
Content standard code: 2.4.1.CS.1
Indicator code: 2.4.1.LI.5
Theme: ELECTRICAL AND ELECTRONIC TECHNOLOGY
Subtheme: ELECTRICAL SYSTEMS DESIGN
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Transformers are one of the most important devices in our electrical world. From the giant ones you see at ECG and GRIDCo substations to the small black box that charges your phone, transformers are everywhere. They make it possible to transport electricity efficiently from the Akosombo Dam over long distances and then safely use it in our homes and schools. Without them, our modern electrical grid would not be possible. This lesson will demystify this essential component, explaining how it is built and the scientific principles that make it work.
A. What is a Transformer? A transformer is a static (it has no moving parts) electrical device that transfers electrical energy from one alternating current (AC) circuit to another, either at a higher voltage (step-up) or a lower voltage (step-down).
Crucial Point: Transformers work only with Alternating Current (AC), not Direct Current (DC). This is because their operation depends on a *changing* magnetic field, which only AC can produce. B. The Laws of Electromagnetic Induction The operation of a transformer is based on the principle of mutual electromagnetic induction. This principle is governed by two fundamental laws: Faraday's Law of Electromagnetic Induction: This law states that whenever the magnetic flux (the amount of magnetic field lines) linked with a coil of wire changes, an electromotive force (e.m.f.), or voltage, is induced in the coil. In simple terms: If you have a coil of wire and you bring a magnet closer to it or move it away, a voltage will be created in the wire. The key is *change* or *movement*. An AC supply naturally creates this continuously changing magnetic field. Magnitude: The law also states that the size of the induced voltage is directly proportional to the rate at which the magnetic flux changes and the number of turns in the coil. Faster change = more voltage. More turns of wire = more voltage. Lenz's Law: This law gives the direction of the induced current. It states that the direction of the induced current is always such that it opposes the change in magnetic flux that produced it. In simple terms: Nature doesn't like change. If you try to increase the magnetic field in a coil, the coil will create its own magnetic field in the opposite direction to fight your change. This principle is a consequence of the law of conservation of energy. C. Construction of a Transformer A simple transformer has two main components: The Core: This provides a path for the magnetic flux. The Windings: These are the coils of wire where the electrical energy is transferred. The Core: Material: It is made of a ferromagnetic material, usually soft iron or silicon steel. These materials allow magnetic flux to pass through them very easily (they have high magnetic permeability). Lamination: The core is not a solid block of iron. Instead, it is made of thin, insulated sheets (laminations) of steel pressed together. Reason for Lamination: To reduce energy loss due to eddy currents. A changing magnetic field in a solid metal block would induce large, swirling currents within the block itself. These currents (eddy currents) just produce heat and waste energy. By slicing the core into thin, insulated sheets, the path for these currents is broken, significantly reducing the energy loss. The Windings: There are two windings, electrically insulated from each other but magnetically linked by the core. Primary Winding: The coil connected to the AC power source (the input). Secondary Winding: The coil connected to the load (the output, e.g., your appliance). Material: The windings are made of high-conductivity copper wire, coated with a thin layer of enamel for insulation. D. Principle of Operation Here is a step-by-step explanation of how a transformer works: Input: An alternating voltage (AC) is applied to the primary winding. Creating a Magnetic Field: Because the voltage is alternating, it drives an alternating current through the primary winding. This current produces a continuously changing and reversing magnetic field (or magnetic flux) in the soft iron core. Linking the Flux: The soft iron core is highly permeable, so it concentrates almost all of this magnetic flux and guides it through to the secondary winding. This process is called mutual induction. Inducing Output Voltage: As this changing magnetic flux passes through (or "cuts") the coils of the secondary winding, it induces an alternating voltage across it, according to Faraday's Law of Induction. Output: If the secondary winding is connected to a load, this induced voltage will drive an alternating current through the load.
Energy is transferred from the primary circuit to the secondary circuit through the magnetic field, without any direct electrical connection. E. The Transformer Equation and Turns Ratio For an ideal transformer (one with no energy losses), the ratio of the secondary voltage (Vs) to the primary voltage (Vp) is equal to the ratio of the number of turns in the secondary winding (Ns) to the number of turns in the primary winding (Np).
Voltage and Turns Ratio Formula: $$ \frac{V_s}{V_p} = \frac{N_s}{N_p} $$