Principles of Electricity

What class is a HVAC transformer that converts 120VAC to 24VAC

Class 2 transformer

What is a generator?

• has stator with magnets and rotor with many wires wrapped around it that spins.

Define Matter

• All forms of matter exist in the state we are familiar with is due to the amount of heat and pressure contained.

Define Element

• periodic table lists various known elements.

• Matter with more than 1 element is a compound. Water is a compound, copper is an element.

Define Molecule

• smallest particle that can exist and still exhibit characteristics of the original material.

• Smallest part that can be observed before you are breaking up into atoms.

  • a compound can be broken down into elements or molecules

Define Atoms

• Smallest particles that can exist that can still exhibit characteristics of that element.

• Can actually be broken down into smaller constituents (protons, neutrons, electrons) with its Nucleus and electrons orbiting it like the sun

• Nucleus holds protons and neutrons

  • electrons orbit the nucleus. Due to the magnetic attraction from the charge of the protons.

  • Charge determined by # electrons orbiting nucleus compared to protons

    • negative if more electrons, positive if more protons

    • May have more than 1 shell of electrons orbiting, the further away the electron is, the easier it is for that electron to get knocked out of the shell to share with a different atom - this is what a conductor is.

Define Current

• Defined as electron flow

• 1 ampere = 1 coulomb per second (easier way to measure electron flow) = 6.28 × 10^18 electrons

• Capital letter I represents current (coulomb is hard to abbreviate)

• Electron flow is from negative to positive. Conventional current is from positive to negative.

Define Voltage

• imbalance of electron distribution or a charge difference between 2 points

• Difference in charge

• Measured in volts, abbreviated letter E

• “Electrical Pressure” that must exist in order for current to flow.

• Aka Electromotive Force

• More voltage applied on the same resistance = more current flow (V=IR)

• Electrical fire may happen if components cannot sustain the higher current flow (which may happen it overvoltage). This is due to heat.

6 ways voltage can be produced?

1. Magnetic - alternator or generator

2. Chemical - reaction between 2 substances (battery)

3. Friction - static charge from rubbing 2 materials together

4. Heat - 2 dissimilar metals joined at a junction (thermoplie or thermocouple), when heat detected there is a voltage formed from that junction.

5. Pressure - piezoelectric effect when pressure applied to a crystal (barbecue igniters)

6. Light - light striking photovoltaic or solar cells

Define Resistance

• low resistance = conductor, high = insulator

• Opposition to current flow

• Abbreviation is R

• Messured in ohms

Alternating Current generation

• electrical current generated by power plants is commonly AC

  • usually 3600 rpm

  • To get 60hz, generators use many wires electrically insulated to pass through magnetic field in one second.

  • Usually 3 phase to allow smaller conductors to be used.

• As a rotor spins, north pole wires get a negative charge and south pole gets a positive charge, as the rotor spins, the wires lose their charge and come around to the next magnet pole, alternating the charge.

Direct Current

• always same direction

• Electron flow in a battery is from negative to positive terminal. Continues until there is no charge differences between battery poles

  • when recharging, electron flow is reversed which restores battery poles

Electrolysis

• break down ionic compounds into their elements

• Electrolyte = solution often with water mixed with a compound (results in a mixture of positive or negative charge when mixed).

  • Each part of the compound has ions with a negative or positive charge.

• Electrolysis needs electrical energy to drive the reaction, this is applied to the 2 terminals:

  • In electrolysis, the anode is positive and cathode is negative (anode is oxidized always, cathode is reduced always) [oxidation is losing electrons, reductions is gaining electrons]

• Electroplating is an example, where the product is coated by using the base metal as a cathode

• Electrolysis can be destructive in piping systems, it can cause corrosion. Minimized by using alternate materials or sacrificial anode.

Electromagnetism

• When current flows through conductor, magnetic field is generated. Strength of this field is directly proportional to how much current is flowing.

  • A magnetic compass would point parallel to the magnetic field set up around the wire (not point to the wire). It follows the magnetic lines of flux.

    • Essentially it would make a perpendicular line with the wire if you holding it above the wire with it was live.

    • If held to the right side, it the compass needle would point up and down

  • Electromagnet is several turns of wire wrapped around an iron core.

    • Strength of magnetic field dependent on:

      1. type of core material

      2. amount of current passing

      3. number of turns of wire around core.

    • Great advantage of electromagnets is that you control when they are magnetic, if no current, then there is no magnetic field.

Transformer

• Induced voltage only happens when current is changing (AC circuits)

• mutually induced voltage via iron core between 2 coils. Amount of voltage depends on coil turns. Less coils on secondary means a step down in voltage. Vice versa with more coils.

Series, parallel, series-parallel circuits.

Obj 2 - Series and parallel circuits

-Series circuit is the simplest. Any fault components in that circuit stops flow.

-Parallel allows multiple paths for current flow

-Series-parallel is 2 series circuits wired together sharing a common power source.

Ohm’s law, series vs parallel rules

• E=IR : it takes 1 volt to push 1 amp through 1 ohm.

• Series: add resistors together for total resistance, voltage is ratio’d by resistance, current is the same

• Parallel: 1/RT = 1/R1 + 1/R2 + 1/R3, voltage in parallel is the same but current splits based on ratio.

  • the total resistance ends up being always less than the smallest resistor in the circuit.

Cathodic Protection for underground piping is provided by:

Metallic rod in ground connected to the pipe with a conductor