POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 1
Unit 1 Energy and Power
Topic 1.3 Electrical Distribution System and Circuits
Lesson 1.3.A: Electrical Distribution System
Purpose
A variety of energy sources were explored in Topic 1.2, along with the infrastructures that make these
energy sources useful and the emerging technologies related to their improved use in the future. Scientific
and engineering advancements that made the efficient transmission and distribution of energy possible
were extremely important catalysts for the industrial revolution and modern society. To date, electrical
energy has been the most widely utilized in this regard. Power Plants perform large-scale energy
conversion from available energy sources to electrical energy, which is subsequently transmitted and
distributed through the power grid to a variety of industrial, public, and private customers. Many renewable
energy sources incorporate a more direct conversion from the energy source to electrical energy at a much
smaller scale than power plants, making them suitable for inclusion in the power grid.
This activity is focused on the electrical energy distribution system. Emphasis will center on three areas:
 Why alternating current (AC) is utilized over direct current (DC)
 The electrical power transmission and distribution system (a.k.a. the Power Grid)
 Electrical energy and power calculations
Subsequent activities will address the energy conversion from the original form to electrical energy and
additional electrical system calculations.
Procedure
During this activity, you will:
 Familiarize yourself with an image that illustrates the components of a residential power grid
 Read an about the “War of Currents” and answer a set of questions pertaining to the article.
 Perform a case-study for an electrical energy distribution system, with emphasis on electrical
power availability and energy losses throughout the system
 Residential Power Grid: The image below was found online at the address indicated below the
image. In the space provided around the image, identify where in Bow you have seen an example
of each type of component identified:
http://www.abovetopsecret.com/forum/thread358031/pg1
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 2
 The War of Currents
Dominant Source: http://maps.thefullwiki.org/War_of_Currents
Introduction
During the initial years of electricity distribution, Thomas
Edison's (http://thomasedisonfacts.com/)
direct current was the standard for the United States and
Edison was not inclined to lose all his patent royalties. Direct
current worked well with incandescent lamps that were the
principal load of the day, and with motors. Direct current
systems could be directly used with storage batteries, providing
valuable load-leveling and backup power during interruptions of
generator operation. Direct current generators could be easily
paralleled, allowing economical operation by using smaller
machines during periods of light load and improving reliability.
At the introduction of Edison's system, no practical AC motor
was available. Edison had invented a meter to allow customers to be billed for energy
proportional to consumption, but this meter only worked with direct current. As of 1882
these were all significant technical advantages of direct current.
From his work with rotary magnetic field, Nikola Tesla
(http://twmtec.com/tesla.htm) devised a system for
generation, transmission, and use of AC power. He
partnered with George Westinghouse to commercialize
this system.
Several undercurrents lay beneath this rivalry. AC cannot
be properly understood without a substantial
understanding of mathematics and mathematical physics,
which Tesla possessed. Edison was a brute-force
experimenter, but was no mathematician. Tesla had
worked for Edison but was undervalued. Bad feelings were exacerbated because Tesla had
been cheated by Edison of promised compensation for his work.
Electric power transmission
The competing systems
Edison's DC distribution system consisted of generating plants feeding heavy distribution
conductors, with customer loads (lighting and motors) tapped off them. The system operated
at the same voltage level throughout; for example, 100 volt lamps at the customer's location
would be connected to a generator supplying 110 volts, to allow for some voltage drop in the
wires between the generator and load. The voltage level was chosen for convenience in lamp
manufacture; high-resistance carbon filament lamps could be constructed to withstand 100
volts, and to provide lighting performance economically competitive with gas lighting. At the
time it was felt that 100 volts was not likely to present a severe hazard of electrocution.
In the alternating current system, a transformer was used between the (relatively) high
voltage distribution system and the customer loads. Lamps and small motors could still be
operated at some convenient low voltage. However, the transformer would allow power to be
transmitted at much higher voltages. This had the practical significance that fewer, larger,
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 3
generating plants could serve the load in a given area. Large loads, such as industrial motors
or converters for electric railway power, could be served by the same distribution network
that fed lighting, by using a transformer with a suitable secondary voltage.
Transmission loss
The advantage of AC for distributing power over a distance is due to the ease of changing
voltages with a transformer. Power is the product current × voltage (P = IV). For a given
amount of power, a low voltage requires a higher current and a higher voltage requires a
lower current. Since metal conducting wires have a certain resistance, some power will be
wasted as heat in the wires. This power loss is given by P = I²R. Thus, if the overall
transmitted power is the same, and given the constraints of practical conductor sizes, lowvoltage, high-current transmissions will suffer a much greater power loss than high-voltage,
low-current ones. This holds whether DC or AC is used.
Transforming DC power from one voltage to another was difficult and expensive due to the
need for a large spinning rotary converter or motor-generator set, whereas with AC the
voltage changes can be done with simple and efficient transformer coils that have no moving
parts and require no maintenance.
Current wars
Edison's publicity campaign
Edison carried out a campaign to discourage the use of alternating current, including
spreading disinformation on fatal AC accidents, publicly killing animals, and lobbying against
the use of AC in state legislatures. He also tried to popularize the term for being electrocuted
as being "Westinghoused". Years after DC had lost the "war of the currents," in 1902,
Edison’s film crew made a movie of the electrocution of Topsy, a Coney Island circus
elephant who had recently killed a man, with high voltage AC. Edison opposed capital
punishment, but his desire to disparage the system of alternating current led to the invention
of the electric chair. Harold P. Brown, who was at this time being secretly paid by Edison,
constructed the first electric chair for the state of New York in order to promote the idea that
alternating current was deadlier than DC.
Niagara Falls
Experts announced proposals to harness Niagara Falls for
generating electricity, even briefly considering compressed air as
a power transmission medium. Against General Electric and
Edison's proposal, George Westinghouse
(http://inventors.about.com/library/inventors/blwestinghouse.htm) won the
international Niagara Falls Commission contract, using Tesla’s AC
system. The commission was led by Lord Kelvin and backed by
entrepreneurs such as J. P. Morgan, Lord Rothschild, and John
Jacob Astor IV. Work began in 1893 on the Niagara Falls
generation project and electric power at the Falls was generated
and transmitted as alternating current.
On November 16, 1896, electrical power was sent from Niagara
Falls to industries in Buffalo from the hydroelectric generator at the Edward Dean Adams
Station. The hydroelectric generators were built by Westinghouse Electric Corporation
using Tesla's AC system patent. The nameplates on the generators bore Tesla's name. To
appease the interests of General Electric, the contract to construct the transmission lines to
Buffalo using the Tesla patents were given to them.
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Competition outcome
The successful Niagara Falls system was a turning point in the acceptance of alternating
current. AC replaced DC for central station power generation and power distribution,
enormously extending the range and improving the safety and efficiency of power
distribution. Centralized power generation became possible when it was recognized that
alternating current electric power lines can transport electricity at low costs across great
distances by taking advantage of the ability to change voltage across the distribution path
using power transformers. The voltage is raised at the point of generation (a representative
number is a generator voltage in the low kilovolt range) to a much higher voltage (tens of
thousands to several hundred thousand volts) for primary transmission, followed by several
downward transformations, to as low as that used in residential domestic use, such as, e.g.,
120 / 240 VAC at 60 Hertz in North America and 230 / 400 VAC at 50 Hertz in Europe.
Remnant and existent DC systems
Some cities continued their DC networks well into the 20th century. Portions of Boston,
Massachusetts along Beacon Street and Commonwealth Avenue still used 110 volts DC in the
1960s, and were the cause of numerous destroyed small appliances (typically hair dryers and
phonographs) among Boston University students who were unmindful of the warnings given
them when the students occupied buildings so supplied. New York City's electric utility
company, Consolidated Edison, continued to supply direct current to customers who had
adopted it early in the twentieth century, mainly for elevators. The New Yorker Hotel,
constructed in 1929, had a large direct-current power plant and did not convert fully to
alternating-current service until well into the 1960s. In January 1998, Consolidated Edison
started to eliminate DC service. At that time there were 4,600 DC customers. By 2006, there
were only 60 customers using DC service, and on November 14, 2007, the last direct-current
distribution by Con Edison was shut down. Customers still using DC were provided with onsite AC to DC rectifiers.
While DC distribution systems over significant distances are essentially extinct, DC power is
still common when distances are small, and especially when energy storage or conversion
uses batteries or fuel cells. These applications include:
Electronics, including Integrated circuits and Computers
Vehicle starting, lighting, and ignition systems
Hybrid and all-electric vehicle propulsion
Telecommunication plant power (wired and cellular mobile)
"Off-grid" isolated power installations using wind or solar power
In these applications, direct current may be used directly or converted to alternating
current using power electronic devices. In the future this may provide a way to supply
energy to a grid from distributed sources. For example, hybrid vehicle owners may rent the
capacity of their vehicle's batteries for load-leveling purposes by the local electrical utility
company.
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 5
Questions/Prompts:
1. Advocating for Direct Current
a. Who was the individual responsible for developing and championing direct
current technologies and power transmission?
b. What is one of the reasons he advocated for direct current?
c. What is one of the reasons he denigrated alternating current?
d. What important US Company did he help found?
2. Advocating for Alternating Current
a. Who was the engineering/mathematical individual responsible for developing
alternating current technologies?
b. Who was the champion of alternating current power transmission?
c. What is one of the reasons these two advocated for alternating current?
d. What important US Company did they help found?
3. What historical event marked the selection of alternating current over direct current
for energy distribution?
4. Provide an example of a system that still utilizes direct current and explain why direct
current is still a viable alternative for that example.
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5. The following table contains the important variables for electrical systems
Variables
Length/Distance
Charge
Mass
Time
Acceleration
Force = mass x acceleration
Energy=force x distance
Current=charge/time
Voltage=energy/charge
Resistance
Power=energy/time
Label(s)
L, d, or x
Q
m
t
a
F
E
I
V
R
P
Derived Units
Newton (N)
Joule (J)
Ampere (Amp)
Voltage (V)
Ohms (Ω)
Watt (W)
Fundamental Units
meter (m)
coulomb (c)
kilogram (kg)
seconds (sec)
m/sec2
kg-m/sec2
N-m
c/sec
N-m/c
N-m-sec/c2
N-m/sec
a. Use the factor label method (railroad tracks) to show that the product of
Current and Resistance yields the units of Voltage (V= IR). What is the name
of this equation?
b. Use railroad tracks to show that the product of Voltage and Current yields the
units of Power (PAVAILABLE = VI). This equation is called Watt’s Law.
c. Use the factor label method to show that the product of current squared and
resistance yields the units for Power (PLOSS = I2R)
d. Example: Suppose a power station that generates 12.4 MegaWatts at 345
KiloVolts is connected (by a 98% efficient transformer) to a 34.5 KiloVolt
distribution line and that there is a resistance of 1.0 Ohm along the
distribution line:
Determine the electrical current generated by the power station
Determine the power lost in the transformer
Determine the current in the distribution line
Determine the power lost in the distribution line
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 7
6. Transformers: As discussed in the article, alternating current electric power lines can
transport electricity at low costs across great distances at high voltages.
Transformers are then utilized to reduce the voltage (step-down transformers) to an
appropriate level for customers. A typical scenario is illustrated below:
http://www.altenergymag.com/articles/09.04.01/smartgrid/grid.jpg
A step-down transformer is analogous to a simple gear train with a gear ratio < 1:
Step-Down Gear Train:
Step-Down Transformer:
Variables:
N = Number of Teeth
P = Power
τ = Torque
ω = Rotational Speed
Assume 100% efficient:
Where, by design:
Outcomes:
Pin = Pout
Nin > Nout
τin > τout
ωin < ωout
Power Remains Constant
Torque Decreases
Rotational Speed Increases
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Variables:
N = Number of Turns
P = Power
V = Voltage
I = Current
Assume 100% efficient:
Where, by design:
Outcomes:
Pin = Pout
Nprimary > Nsecondary
Vprimary > Vsecondary
Iprimary < Isecondary
Power Remains Constant
Voltage Decreases
Current Increases
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 8
 Electrical Energy Distribution Case Study: The images on the next two pages detail the Major
PSNH Transmission and Distribution Systems in the Manchester-Hooksett Region of NH.
Respond to the following prompts, based upon these images and additional research:
Name:
o
Shade the region on the map of NH that corresponds to the geographic area covered by
the Manchester-Hooksett Region of the PSNH Transmission and Distribution System.
o
Name at least three power plants in the Manchester-Hooksett Region of NH and identify
the energy resource utilized by each of them.
o
Identify the major energy resource that provides power to within this region of NH
o
Identify a portion of the grid where energy is “lost”. Where does the energy “go”?
o
Identify the Transmission Substation in this region and indicate its output voltages.
o
Identify at least one Distribution Substation and indicate the input and output voltages for
each.
o
Where is the electric panel located in your home? What output voltages does it provide to
appliances in your home? What is the current rating on the main breaker?
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 10
Lesson 1.3.B: Electrical Circuit Diagnostics
Purpose
Electrical energy is everywhere! All engineering/science minded individuals should understand the basics
of electrical circuits in order to safely realize the very important desired outcome of diagnosing electrical
problems and taking appropriate steps to correct them. This has a number of benefits:
 Safety
 Becoming more self-sufficient
 Saving money
 Reducing waste
 Demonstrating engineering prowess
Procedure


Review basic concepts of Ohm’s Law for series and parallel circuits
Review basics regarding the use of a multimeter as a diagnostic tool electrical circuit components
 Ohm’s Law – Study and take notes on the Introduction to Electricity Power Point in the shared
folder with special emphasis on Ohm’s Law, Watt’s Law, and the placement of resistors in series
or parallel.
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 11
Series Circuit: Based upon the given information and Ohm’s Law, find the voltages and currents
identified in the figure (Note that RT is the *total* or *equivalent* resistance of the circuit).
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 12
Parallel Circuit: Based upon the given information and Ohm’s Law, find the voltages and currents
identified in the figure (Note that RT is the *total* or *equivalent* resistance of the circuit).
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 13
 Multimeter – Study and take notes on the Introduction to Electricity Power Point in the shared
folder with special emphasis on the use of a multimeter as a voltmeter, an ammeter, and an
ohmmeter.
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 14
 Theory to Practice – Series Circuit
o Use the materials provided (bread board, 5 Volt DC power supply, wires, resistors) to create a
simple series circuit. Sketch the circuit below.
o Use Ohm’s Law to predict the value of the current that should flow through each resistor
(make sure it does not exceed 100 mA) and the voltage drop across each resistor. Indicate
any necessary changes to your circuit on your sketch.
o After verifying the proper use of the multi-meter to measure voltage drops across components
and currents through them, use the multi-meter to measure the voltage drop across each
resistor as well as their respective currents. Record the observed values on your sketch.
o Disassemble the circuit and use the multimeter to measure the resistors resistances.
o Calculate the relative differences between your predicted and observed currents and voltages.
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 15
 Theory to Practice – Parallel Circuit
o Use the materials provided (bread board, 5 Volt DC power supply, wires, resistors) to create a
simple series circuit. Sketch the circuit below.
o Use Ohm’s Law to predict the value of the current that should flow through each resistor
(make sure it does not exceed 100 mA) and the voltage drop across each resistor. Indicate
any necessary changes to your circuit on your sketch.
o After verifying the proper use of the multi-meter to measure voltage drops across components
and currents through them, use the multi-meter to measure the voltage drop across each
resistor as well as their respective currents. Record the observed values on your sketch.
o Disassemble the circuit and use the multimeter to measure the resistors resistances.
o Calculate the relative differences between your predicted and observed currents and voltages.
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 16
 Theory to Practice – Series-Parallel Circuit
o Use the materials provided (bread board, 5 Volt DC power supply, wires, resistors) to create a
simple series circuit. Sketch the circuit below.
o Use Ohm’s Law to predict the value of the current that should flow through each resistor
(make sure it does not exceed 100 mA) and the voltage drop across each resistor. Indicate
any necessary changes to your circuit on your sketch.
o After verifying the proper use of the multi-meter to measure voltage drops across components
and currents through them, use the multi-meter to measure the voltage drop across each
resistor as well as their respective currents. Record the observed values on your sketch.
o Disassemble the circuit and use the multimeter to measure the resistors resistances.
o Calculate the relative differences between your predicted and observed currents and voltages.
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 17
Lessons 1.2 & 1.3 Key Term Crossword
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www.CrosswordWeaver.com
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POE@BHS-Unit 1: Energy and Power, Topic 1.3 Electrical Distribution System & Circuits Page 18
ACROSS
DOWN
1 A fundamental entity of nature that is
transferred between parts of a system in
the production of physical change within the
system and usually regarded as the
capacity for doing work.
3 A system that links electricity produced in
power stations to deliver it to where it is
needed.
8 The production of an electric or magnetic
state by the proximity (without contact) of
an electrified or magnetized body.
11 A natural fuel such as coal or gas, formed
in the geological past from the remains of
living organisms.
12 The rate at which work is performed or
energy is expended.
13 The rotating member of an electrical
machine.
14 The unit of electric current in the meterkilogram-second system of units. Referred
to as amp and symbolized as A.
16 States that the direct current flowing in an
electric circuit is directly proportional to the
voltage applied to the circuit.
23 The production of electricity in conductors
with the use of magnets.
27 The opposition that a device or material
offers to the flow of direct current.
30 The potential difference measured in volts.
The amount of work to be done to move a
charge from one point to another along an
electric circuit.
31 A result of a force moving an object a
certain distance.
32 A circuit in which all parts are connected
end to end to provide a single path of
current.
33 The state when objects are not yet in
motion.
34 A resource that cannot be replaced once
used.
2 An organization that works to develop and
enforce regulations that implement
environmental laws enacted by Congress.
4 A resource that can be replaced when
needed.
5 The unit of potential difference symbolized
as V.
6 Plant materials and animal waste used
especially as a source of fuel.
7 An energy source that will never run out.
9 The net transfer of electric charge (electron
movement along a path) per unit of time.
10 A closed electrical circuit in which the
current is divided into two or more paths
and then returns via a common path to
complete the circuit.
15 The unit of electric resistance in the meterkilogram-second system of units.
Symbolized as ?.
17 The ratio of the useful energy delivered by
a dynamic system to the energy supplied to
it
18 The use of heat from within the Earth or
from the atmosphere near oceans.
19 Energy which a body possesses by virtue of
being in motion.
20 The flow of electrical power or charge.
21 Changing one form of energy to another.
22 A machine for producing power in which a
wheel or rotor is made to revolve by a fastmoving flow of water, steam, gas, or air.
24 Any source of energy other than fossil fuels
that is used for constructive purposes.
25 Changes one form of power to another.
26 A dynamo or similar machine for converting
mechanical energy into electricity.
28 Energy caused by the movement of
electrons.
29 The energy that a piece of matter has
because of its position or nature or because
of the arrangement of parts.
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