Science F3 C8-PPT-Part II Transformer

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GENERATION OF ELECTRICITYScience Form 3 Chapter 8

Last update: 4/8/2010


Part II Function and Structure of a Transformer

F3 C8 GENERATION OF ELECTRICITY


Function and Structure of a Transformer

• A transformer is a device used for stepping up or stepping down the voltage of an alternating current



• It consists of laminated soft iron plates with two coils of insulated wire wound round them



• The coil of wire which carries the input alternating current is called the primary coil



• The coil of wire which carries the output alternating current is called the secondary coil



• When an alternating current flows into the primary coil, a magnetic field is set up around the iron core. This induces an alternating current in the secondary coil



• Laminated soft iron plates are used to form the core in order to reduce the loss of energy in the form of heat in the core


Step-Up Transformer


Step-Up Transformer

• Has more turns of wire in the second coil than in the primary coil

• The input voltage is stepped up so that the output voltage is greater than the input voltage

• The output alternating current is smaller than the input current


Step-Down Transformer


Step-down Transformer

• Has more turns of wire in the primary coil than in the secondary coil

• The input voltage is stepped down so that the output voltage is smaller than the input voltage

• The output alternating current is greater than the input current


A Comparison Of V And I Between Step-up And Step-down Transformers

Types of transformer

Input OutputVoltage Current Voltage Current

Step-up Lower Higher Higher Lower

Step-down Higher Lower Lower Higher


Efficiency of Transformer

• A transformer is never 100% efficient. This is because of– Resistance in the coils– Energy lost in the form of heat in the iron core

• The efficiency of a transformer is raised by:– Using copper wires for the coil (copper has a low

resistance)– Using laminated soft iron plates to form the core


CalculatonPrimary input voltage (Vp)

=Number of turns in primary (Np)

Secondary output voltage (Vs) Number of turns in secondary coil (Ns)

Vp=

Np

Vs Ns


Worked example

• A transformer has 100 turns of wire in the primary coil and 200 turns in the secondary coil. What is the output voltage if the voltage supplied to the primary coil is 10V?

• Ratio Method

Science F3 C8-PPT-Part II Transformer

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