Introduction to Electricity & Electrical Systems

• Electrical, Electronics, and Mechanical Systems is also referred to as "Building Utilities 2"
• Module goals:
  • To introduce Electricity and Electrical Systems
  • To identify the important terms in Electrical Systems
  • To identify the different units of measurements in Electrical Systems

Electricity

• A phenomenon and manifestation principally comprising atoms, electrons, protons, and neutrons.

Definition of Electricity

• A form of energy generated by friction, induction, or chemical change that manifests with magnetic, chemical, and radiant effects.
• Electricity involves the motion of free electrons passing through a solid conductor.

Notes on Electricity

• William Gilbert, an English physicist known as the "Father of Electricity"
• The instantaneous nature of electric current means it travels at the speed of light.

General Classes of Electricity

• Dynamic Electricity (electrodynamic): Flows through a substance as electric current.
• Static Electricity (electrostatic)

Electric Current

• An electric current is the flow in an electric circuit and can be either direct (DC) or alternating (AC).

Electric Circuit

• An electric circuit is the path for electric current.

Types of Electric Current

• Direct Current (DC): A current that flows at a consistent rate and in the same direction, typically from negative to positive and is uniform in strength.
• Alternating Current (AC): A current that reverses direction and varies periodically in time rate and direction.

Direct Current Facts:

• Direct current (DC) is used in any electronic device with a battery for a power source.
• Rechargeable devices use an AC adapter to convert AC to DC for charging.
• A complete set of AC changes is referred to as a cycle.
  • Frequency is measured in cycles per second, or Hertz.
  • The frequency for lighting is 60 Hertz.
  • The frequency for motors is 25 Hertz.
  • Phasing can be single-phase or three-phase.

Facts on Alternating Current (AC):

• Most households and offices use AC due to its efficiency in power loss and converting voltages with transformers.
• AC is effective for long distance transport.
• AC powers electric motors in appliances like fridges and dishwashers.
• AC also powers devices from the mains, such as TVs, laptops, tablets, and smartphones

Comparison of Direct Current (DC) vs. Alternating Current (AC)

• Direct Current (DC):
  • Fixed polarity
  • Steady (continuous) but can vary in magnitude (fluctuating)
  • Steady value
  • Easier to measure at 1.5 volts
• Alternating Current (AC):
  • Reverses polarity
  • Varies between reversals
  • Stepped up or down
  • Easier to amplify at 110 V+

Electrical Circuits

• An electrical circuit is a complete conducting path that carries current from an electricity source through an electrical device (load) and back.

Types of Circuits

• Closed Circuit: Complete and continuous path.
• Open Circuit: Broken, incomplete, or disconnected.
• Series Circuit: Current flows through all components along one path.
• Parallel Circuit: Components arranged so current divides; each component is assured charge, and other paths work independently if one breaks.
• Short Circuit: bridging a circuit part with a conductor of low resistance.
  • The bypassed piece may stop working and a large current flow can cause wires to heat up and potentially start a fire.

Circuit Trivia:

• Series circuits: if one bulb fails in Christmas lights, the entire string might not work.
• Houses use parallel circuits, so a single burnt-out bulb won't cut power to the entire house.
• Circuit breakers and fuse boxes disconnect circuits as a safety measure during a short circuit.
• A short circuit is any electrical failure.

Electricity Sources

• Battery: A combination of two or more electric cells that store and supply direct current via electrochemical means.

Battery Facts:

• Primary Batteries: Deliver electricity once assembled and connected in a circuit without being renewable.
• Secondary/Storage Batteries: Require electricity from an external source to deliver electric current and are mainly used for emergency lighting; rechargeable.

Generators

• A machine converting mechanical energy to electrical energy.

Generator Facts:

• Alternating Current Generators (or Alternators): Convert mechanical energy to electrical energy with alternating current.
• Direct Current Generators: Rotating machines supplying electrical output with unidirectional voltage and current.
  • They are generally used for elevators, escalators, telecommunications, signal systems, and clock systems.

Dynamo Electric Machines

• An electrical generator that creates direct current using a commutator.

Types of Machines:

• Motors: Machines converting electrical energy to mechanical energy.
• Transformers: Machines converting voltage levels, either stepping up from lower to higher or stepping down from higher to lower.
• Rotary Converters: Machines changing alternating current to direct current and vice versa.

Machine Trivia:

• Electric motors brought about the advancement of technology and engineering, allowing for modern daily life.
• High-rise condominium buildings are usually designed with a step-up transformer.

Electric Power Generation

• Electric Power Generation is the source of electricity.

Electric Power Generation:

• Transmission Lines: High voltage power lines that run cross country or along major roads.
• Circuits: Lines that run along highways and major roads to communities and businesses.
• Substations: Distribute power to several circuits.
• Tap Lines: Serve smaller groups of customers and neighborhoods along main circuits.
• Individual Transformers: Reduce power to usable voltage levels.

Electrical Terms

• Conductors:
  • Materials allowing electricity to pass easily and have free electrons on the surface, enabling current to pass through easily.
  • Conductors allow the transmission of heat or light.
  • i.e. Copper, Brass, Steel, Gold, and Aluminum are good conductors and used in electric circuits and wires.

Conductor Trivia:

• Humans and animals are conductors; hence, electric shocks occur.
• The human body is a good conductor, providing a resistance-free path for current flow.
• Insulators: Materials that resist or don't allow current flow through them.
  • Insulators do not have free electrons
  • They provide protection against heat and sound.
  • Wood, cloth, glass, mica, quartz, plastic, and rubber are good insulators.

Insulator Trivia:

• Glass is best insulator with highest resistivity
• Coulomb: A unit of electricity compromising approximately 6.25 x 10^18 electrons.
• Ampere (I): The current measures the rate of flow of one coulomb or 6.25 x 10^18 electrons per second, and Ampacity measures the current-carrying capacity of a wire or cable.

Electrical Units:

• Volt (V): Electrical unit of voltage or potential difference between two points in an electric field.
• Watt (W): The electric power is the rate of doing electrical work.
• Watt-hours (Whr): Energy and capacity to do work.
• Ohm: Resistance that allows one ampere of current flow when one volt is impressed upon it.
  • In a DC circuit, Ohm is call resistance (R)
  • In an AC circuit, Ohm is call impedance (Z)

Ohm's Law

• The relationship between current, voltage, and resistance.
  • The current within a DC circuit is directly proportional to the voltage and inversely proportional to the resistance of the circuit.

Ohm's Law Terms:

• I = Current (Amperes)
• V = Voltage (Volts)
• R = Resistance (Ohms)
• W = Electric Power (Watts)

Ohm's Law Formulas:

• I = V/R
• V = IR
• R = V/I

Other Equations associated with Ohm's Law:

• W = I^2R or VI
• Whr = I^2Rt

Ohm's Law Keynote:

• A higher voltage means the higher the current.
• A higher resistance means the lower the current.