The Fundamentals of Electricity

What is Electricity?

Electricity is a vague term to many, and a familiar one to some. One thing we all have in common is this: we understand that electricity allows the modern world to work. Without electricity, we couldn’t have computers, power grids, sustainable air conditioning, modern vehicles. Agriculture would be far behind, as would space exploration, defense systems, communications, quality of life, the most basic of appliances, and more. Virtually all of our modern technology relies on electricity to function. So, what is it?

Electricity is a form of energy resulting from the movement of charged particles, namely electrons. Humans harnessed the power of electricity by engineering ingenious ways to move charges along conductors. Electrical power generation tends to require 3 primary components:

  1. Magnet
  2. Conductor
  3. Relative motion between the two

The valence-shell electrons (inhabiting the outermost electron shell) flow freely in atoms of electrically-conductive material, such as copper and iron. This is also the same property which allows such materials to conduct heat well, as the electrons are provided a greater area to “bounce” around in. The electrons can conduct and reject heat (a certain amount of randomized kinetic energy), but electric current cannot be produced without the use of a magnet.

When a magnetic field is moved across a wire, the valence electrons in the wire are “budged”. This is known as Faraday’s law of induction. The movement of these electrons in the same direction in unison induces a surrounding electromagnetic field, which can in-turn “budge” other conductors. This feat allows us to engineer ways to control the flow of electricity, and use it to move bodies. A field of study was developed to discover more useful ways to utilize electricity, called Electrical Engineering. There are a number of terms in Electrical Engineering which are necessary to understand before fully comprehending electrical systems. Below we will review these terms, their definitions, and how they apply to our job.

 

Voltage ( V )

Voltage is the difference in electrical potential energy between two points in a circuit. To understand this mathematically, consider that voltage is equal to the amount of energy in joules contained within each coulomb of electrons.

V = J/C

A voltage drop occurs in a circuit when a resistor is added, which demands a certain amount of energy for it to be powered (lightbulb, fan, etc.). The measurement of the voltage of a resistor (aka voltage drop) is the difference in electrical potential energy between point A – before the resistor, and point B – after the resistor. To measure the relative voltage of a power supply, or of any particular point in a circuit, one measurement is taken at that point and another is taken from ground.

 

Current ( I )

Current describes the flow of electrons along a conductor in a circuit. To understand this mathematically, consider that current is equal to the number of coulombs of electrons passing a single point per second of time.

I = C/sec

Current, measured in amps (A), is “pushed” by the voltage (energy) through a circuit to deliver power to resistors along that circuit.

 

Resistance ( R )

Resistance, measured in ohms, is the measurement of “push-back” a circuit component provides against an electrical current. This can be thought of as similar to a ball valve restricting the flow of water through a pipe. The more open the valve, the lesser the resistance. The more closed the valve, the greater the resistance.

V = IR

The formula above is known as Ohm’s Law, which describes the relationship between voltage, current, and resistance. If the resistance of a circuit increases, either the amperage will decrease or the voltage will have to increase to maintain amperage. A resistor is any component in a circuit which provides resistance, consuming energy, whether or not that energy is used for useful work.

 

Charge ( Q )

“Charge” is measured in Coulombs (C). One coulomb is equal to 6.24 x 1018 electrons. This can be thought of as a “basket of electrons” for the sake of mental imagery.

 

Energy

Energy is the measurement of the ability of work to be performed. Work is defined as force applied over a distance. So, the greater the energy, the more potential force is available to be applied over a distance. Energy is measured in Joules (J).

 

Power

Power (P) is the measurement of the rate at which work is performed. This can be measured as “power equals (x) number of joules of energy transferring to perform useful work per second of time”. Power is measured in watts (W). The basic formula for power is W = J/sec. The formula below applies specifically to electrical circuits.

P = VI

Power equals voltage multiplied by current. This is, that the product of the voltage (energy) and the current in a circuit indicate to us the amount of work that is being performed. This is the amount of energy being transferred to perform useful work every second. In your home, this energy could be turning a fan, lighting a bulb, or heating an oven.

 

kWH

The measurement of “kilowatt hours” (kWH) represents how many kW of power will be consumed if the present rate of power consumption were to continue at its current value for 1 hour. This is the measurement which determines what homeowners will be charged for power consumption.

 

AC vs DC

AC” is an abbreviation for Alternating Current, and “DC” is an abbreviation for Direct Current. AC is an electrical current which switches “polarity”, or direction, at the rate of 60Hz in the USA (60x per second) and 50Hz in other countries (50x per second). This is represented graphically as a sine wave (see below). The “y” axis represents voltage, while the “x” axis represents time.

ac dc

AC tends to be used for power transmission, power systems, and higher-voltage equipment.

In DC, electrical current travels in a single direction. DC is used more for small electronic components, such as control systems.

 

Applications:

Applying the definitions above, we know that a 12V battery has 12 Joules of electrical potential energy per coulomb of electrons difference between the anode and the cathode. We also know that a reading of 120V on our home electrical circuits indicates that we have 120 Joules of electrical potential energy per coulomb of electrons relative to ground.

Circuit Types

When designing circuits, electrical engineers utilize two different circuit variations; series and parallel. In a series circuit, all resistors are in a single line. In a parallel circuit, two or more resistors are on different lines from one another, fed from the same power source. As seen in the image below, R1 and R2 are in series, while R3 and R4 are in parallel.

series parallel

If one resistor were to fail in a series circuit and open the circuit, all other resistors in the circuit would be left with no power. For example, let’s say R2 is a lightbulb. After some time, R2 burns out, the circuit is left broken, and resistors R1, R3, and R4 have no power.

If one resistor in a parallel circuit were to fail, the other resistors will still have power. For example, if R3 were to fail, the electrical energy still has a complete circuit of flow if it were to travel through R1, R2, and R4.

 

Basic Wiring

In electrical engineering, there are 3 basic types of wires everybody should know:

  • Hot (source of energy)
  • Neutral (return, or common line)
  • Ground (often “Earth ground”)

 

Home Electricity

The electricity in a home is fed from an outdoor step-down transformer, bringing voltage from high voltage 3-phase AC down to 120V single phase AC. This power runs into your home on 3 lines; hot line 1, hot line 2, and neutral.

home elec 1

The current travels down line 1 (black wire), through the meter, and into the panel where it is distributed to individual “branch circuits” feeding resistors in the home, and returns from those resistors to the panel using neutral lines (white), and returns to the transformer using the main neutral line (white wires in the home and panel, bare copper on the main line). When polarity alternates, current travels down line 2 (red) to repeat the same process through branch circuits which are fed from that line. It is a best practice to balance the load between line 1 and line 2.

home elec 2

Home Electrical Panel

A home electrical panel will include the following items:

  • Incoming Line 1 (large black wire) connected to buss bar.
  • Incoming Line 2 (large red wire) connected to buss bar.
  • Outgoing neutral line (large white wire) connected to neutral bar.
  • Bare copper wires feeding into a ground bar (main ground wire denoted with “green” tape in image).
  • Circuit breakers protecting branch circuits fed from Line 1.
  • Circuit breakers protecting branch circuits fed from Line 2.
  • Main circuit breaker.

panel

 

Branch Circuits and Receptacles

Above, we discussed that resistors in the home are located on “branch circuits”, as seen in the image below. Most appliances in the home are fed from basic 120V receptacles.

branch.gif

In a basic American 120V household electrical receptacle, you will see 3 holes which look like a surprised face. The image below features a dual 120V receptacle, capable of feeding power to 2 appliances. In the image, the short straight hole is the “hot” portion of the receptacle. This is the part of the receptacle which connects to the power source. The long straight hole is the “neutral” portion of the receptacle, which carries power back to the source to complete the circuit. The round hole is the “ground” portion of the receptacle.

rec

The hot connection is fed downstream of either line 1 or line 2. The netural connection provides a path back to the panel, to connect to the neutral bar. The ground connection provides a path to the ground bar in the panel.

 

What is a “Ground”?

            A “ground” in an electrical circuit is a metal rod placed in the ground, providing a path which brings current to the Earth if the voltage traveling through the circuit becomes too high, such as in the case of a lightning strike or ground-fault. When voltage reaches a certain level, the current overcomes the resistance of the Earth at the point of the metal rod. This protects the circuit components from conducting too much energy. The ground bar in an electrical panel is fed from the ground wires of various equipment, and even the panel being grounded itself, and is connected to the metal ground rod going into the Earth.

 

Types of Circuit Issues

There are 3 primary types of circuit issues.

  • Ground Fault – In a ground fault, a hot source has unintentionally come into contact with a ground wire, or the frame of the piece of equipment grounded. When this occurs, current travels on the ground wire to the Earth, redirecting stray electricity.
  • Short Circuit – A short circuit occurs when a hot source comes into contact with a neutral path, bypassing resistors. This increases the current and voltage on the neutral line, which travels back to the transformer, down to the panel and may trip a breaker or blow a fuse. This often occurs when wire insulation becomes deteriorated or damaged.
  • Open Circuit – An open circuit is any circuit which isn’t closed and therefore cannot be used as a path for electric current. Turning off an appliance using a switch is creating an open circuit. Open circuits become an issue when a resistor on the circuit fails, not allowing electricity to travel through.

How a Transformer Works

Transformers are electrical devices that can be used to increase or decrease voltage in a circuit. They achieve this by using the principle of electromagnetic induction. Transformers are composed of an iron core, “primary” windings from the power source, and “secondary” windings to the load. As voltage increases in the primary windings of the transformer, an electromagnetic field is induced, which is carried by the core. This field induces a current and accompanying electromagnetic field in the secondary windings.

xfmr

The above image is of a step-down transformer. In order to step down (decrease) the voltage, there must be more primary windings than secondary windings on the transformer. In order to step up (increase) the voltage, there must be more secondary windings than primary windings.

 

From the Power Station to the Customer

The following image represents the electricity flow from the power generating station to the customer.

transmission

A couple things to note:

  • The power generating station could consist of a solar farm, coal plant, nuclear plant, hydroelectric dam, or wind turbine farm.
  • Electricity is transported long distance at a high voltage to minimize energy losses.
  • “Transmission Customers” include large industrial customers.
  • The step-down transformer located at the local substation is necessary to bring the electrical energy down to a manageable level.
  • Amazon’s JIT sites are considered “Subtransmission Customers”, as we bring in 34.5kV.
  • Stores, shops, and other relatively low energy buildings are examples of “Primary Customers”.
  • Homes make up most “Secondary Customers”.

 

Now, you have a better idea of how the modern world operates. Cheers to learning!

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