Transformers: An Introduction

Introduction to Transformers

  • Transformers are essential electrical devices used in various applications including:

    • Electricity distribution

    • Construction work

    • Electronic equipment

  • The primary purpose of a transformer is to transform voltage:

    • Voltage can enter the transformer at one value and exit at another.

Types of Transformers

Step-up Transformer

  • A step-up transformer increases the output voltage relative to the input voltage.

  • Characteristics:

    • Has more 'turns' or 'windings' on the secondary side compared to the primary side.

Step-down Transformer

  • A step-down transformer decreases the output voltage relative to the input voltage.

  • Characteristics:

    • Has fewer 'turns' or 'windings' on the secondary side compared to the primary side.

Overview of Transformer Operation

  • In the course of this unit, the following topics will be covered:

    • Principles of mutual induction

    • Types of transformers

    • Step-up and step-down transformers

    • Calculating values in transformers

    • Educational videos concerning transformer operation processes

Working Principle of Transformers

Mutual Inductance

  • Definition: Mutual inductance is the phenomenon where a changing magnetic field produced by one coil induces a voltage in an adjacent coil.

  • Transformer design includes:

    • Two or more coils placed in close proximity to foster mutual inductance.

Steps of Transformer Operation (1-8)

  1. A circuit is supplied with alternating current (AC), which fluctuates between positive and negative polarity through its 360° cycle.

  2. The AC flows into the primary coil.

  3. This flow generates a magnetic field in the primary coil, illustrated by blue lines representing the lines of magnetic flux.

  4. When electric current is passed through a conductor (i.e., the primary coil), a magnetic field is formed around the conductor.

  5. As the current alternates, the resulting magnetic field also alternates, expanding and collapsing in response to the changes in current.

  6. The changing magnetic field from the primary winding encroaches upon the secondary winding.

  7. The varying magnetic field induces an electromotive force (emf) in the secondary coil, creating a voltage.

  8. This induced emf generates sufficient voltage to facilitate current flow to a connected load when enclosed in a closed circuit.

Importance of AC in Transformers

  • Key Points:

    • An alternating current is necessary to produce an alternating magnetic field (expanding and collapsing), which is vital for mutual inductance.

    • The operation relies on the 'changing magnetic flux' to induce voltage in the secondary coil.

Efficiency Enhancements in Transformers

  • One method to improve mutual inductance is by winding coils around an iron core, yielding benefits such as:

    • Increased magnetic flux levels

    • Greater mutual inductance

  • Reason for Iron Core Usage:

    • Iron is a ferrous material with magnetic properties, containing magnetic flux and reducing energy loss.

Losses in Transformers

  • Overview: All transformers experience power losses, leading to efficiency reduction. Output power is always slightly less than input power.

Types of Power Losses

1. Copper Losses

  • Definition: Copper loss refers to power loss in the transformer due to the resistance of the copper wire in the windings.

  • Characteristics:

    • Generates heat due to resistance; unavoidable due to conductor properties.

    • Varies with current in windings.

Calculating Copper Losses

  • The equation to calculate copper loss (heat loss) is: (P_{c} = I^{2} R)

    • Where:

    • $P_{c}$ = Power (Copper loss)

    • $I$ = Current flowing in the windings

    • $R$ = Resistance of the windings

  • Example Calculation:

    • For a transformer with copper windings with resistance of 5ohms and a current of 12A

    • Copper/heat loss = 720W

    • This indicates that the power lost due to heat in the copper windings is 720 Watts, which is significant in understanding the efficiency of the transformer.

Reducing Copper Losses

  • Methods include:

    • Increasing the cross-sectional area of conductors (may increase machine size).

    • Lowering winding temperature to reduce resistivity.

    • Using materials with lower resistivity than copper or aluminum.

2. Iron Losses

  • Definition: Iron losses occur in the transformer core due to alternating flux and are also called core losses.

  • Types:

    • Eddy Current Losses:

    • Induced currents in the core produce heat that can cause damage if not managed.

    • Hysteresis Losses:

    • These result from the residual magnetism in the core material when the magnetic field is removed.

Reducing Iron Losses

  • A laminated iron core constructed from thin sheets of iron:

    • Shortens the current path to minimize eddy currents.

    • Each sheet is insulated to restrict current flow to individual laminations only.

    • The materials used may include silicon-iron or nickel-iron alloys which are more easily magnetized compared to pure iron.

Conclusion

  • An understanding of transformer operation, including mutual inductance, types of transformers, losses, and enhancements for efficiency is crucial in electrical engineering.

  • Visual aids such as videos further contextualize these concepts, especially in regards to energy loss in transformers.