Principles of Electricity Generation and Transmission

Chapter 7: Generating Electricity

DC motors convert electrical energy into kinetic energy. Magnetic flux is the amount of magnetic field flowing through a given area, determined by the density of field lines and the surface area. Two factors affect magnetic flux: 1. Area and 2. Magnetic field strength.

Faraday's law states that a changing magnetic flux in a conducting loop or coil induces an electromotive force (EMF) with a magnitude proportional to the rate of change of magnetic flux. Electromagnetic induction occurs when the magnetic flux through a loop changes over time, creating a potential difference. This induces a current in the loop.

The EMF graph is negative when the magnetic flux graph has a positive gradient, and vice versa. Lenz's Law states that when a conductor experiences a change in magnetic flux, an induced current creates a magnetic field that opposes the initial change. This can be determined by the right-hand coil rule.

Factors Affecting Induced Current

• Direction of magnetic flux passing through the loop.
• Whether the flux is increasing or decreasing.

The magnetic flux changes based on the area of the loop within the magnetic field and the strength of the magnetic field itself.

Generators and Current Types

An alternator transforms kinetic energy into AC electricity via electromagnetic induction, while a generator can produce either AC or DC. AC (Alternating Current) features periodically alternating direction and voltage, whereas DC (Direct Current) maintains a constant direction.

• Slip rings: Used in AC generators to allow the coil to rotate while maintaining electrical contact.
• DC Generator: Uses a split-ring commutator to switch connections every half-rotation, ensuring a constant output voltage direction.

Chapter 8: Transmitting Electricity

Electric charge is the fundamental quantity of electricity. Electric current measures the rate of flow of charge, voltage measures the difference in stored energy per unit of charge, and resistance opposes the flow of current.

Ohm's Law defines the relationship between voltage, current, and resistance. Power is the rate at which energy is delivered or dissipated in electrical components.

AC Theory and Measurements

AC electricity varies sinusoidally over time. Key magnitude descriptors include:

• Peak value: The amplitude of voltage or current.
• Peak-to-Peak: The difference between maximum and minimum values.
• RMS (Root Mean Square): A value used to compare AC power delivery to DC power, representing the equivalent constant magnitude that would deliver the same power.

Transformers and Power Transmission

Transformers transfer power between circuits by increasing or decreasing voltage. A step-up transformer increases secondary voltage, while a step-down transformer decreases it. An electrical load consumes power within a circuit.

AC power is preferred for transmission because transformers can reduce current in transmission lines, minimizing voltage drop and power loss. Electricity is transmitted at high voltage and low current for efficiency. In household systems, transformers act as power supplies for sub-circuits where resistance is typically negligible.