Transcript Lecture 25.v1.12-4-1..

PHYS 1110
Lecture 25
Professor Stephen Thornton
December 4, 2012
Reading Quiz
How many nuclear reactors are currently
under construction in the United States?
A)
B)
C)
D)
E)
None
1
2
3
5 or more
Reading Quiz
How many nuclear reactors are currently
under construction in the United States?
A)
B)
C)
D)
E)
None
1
2
3
5 or more
Remaining schedule:
Today, Dec. 4: HW 7 on Ch. 10 due
Quiz on Chs. 9 and 10
Thursday, Dec. 6: HW 8 on Ch. 11 due
Quiz
Which of the following is not characteristic of a
Small Nuclear Reactor?
A) Can be factory built and delivered as needed
B) Can be left in place after decommissioning
C) Can be used in specialized places like islands
or for Disney World.
D) Standard, not custom, designed
E) Do not necessarily need water for cooling
Quiz
Which of the following is not characteristic of a
Small Nuclear Reactor?
A) Can be factory built and delivered as needed
B) Can be left in place after decommissioning
C) Can be used in specialized places like islands
or for Disney World.
D) Standard, not custom, designed
E) Do not necessarily need water for cooling
Chapter 11
Energy Transmission and
Storage
Electricity Generation Electricity is normally generated at values
of 1000s of volts, but that is not ideal to transmit, so we first have to
use transformers to increase the voltage.
Electric Power Transmission We will explain in this chapter why
it is best to transmit electricity at values of 500,000 volts or higher.
After being transformed at the power plant, the electricity is
carefully connected to transmission lines which carry it sometimes
long distances, even across international borders like from Canada
to the United States or from France to Italy. The high voltage lines
send the electricity to an electrical substation.
Electric Power Distribution Once the electricity reaches a
substation normally owned by the local utility, the voltage is
reduced substantially before being delivered to a local transformer
when the voltage is reduced again before being delivered to the
customer.
2
2
P
P R
Ploss = I R = 2 R = 2
V
V
2
For a given transmitted power P and resistance
R of the transmission line, we minimize the
power loss by using the highest possible
voltage V. That is why overhead transmission
lines have voltages above 100 kV. Values
include 230, 345, 500 and 765 kV.
Transmission lines – electrical grid
Electrical energy must be generated as needed; a complex
control system is required to match the electrical
generation with the demand. The normal supply is
provided by the base load, which consists of power
plants like nuclear, coal, wind, and solar that cannot be
turned on and off quickly. When the demand exceeds the
supply, generating plants must be brought online for more
supply. When the demand far exceeds the supply, then
serious problems can occur, and generating plants and
transmission lines shut down. This causes blackouts
which have occurred in the US Northeast in 1965, 1977,
1996, 2003, and 2011. Sometimes rolling blackouts are
engineered to prevent more widespread blackouts.
Northeast power blackout in 2003 was the worst in the
USA. Affected 55 million people in Canada and 8
states. Everybody blamed each other.
Eventually FirstEnergy Corp was at fault. Hot day,
power monitor failed and was not reset. Eventually
256 power plants went off line.
Single phase 120 V AC. Peak is 170 V, rms is
120 V, 60 Hz. Nikola Tesla is mostly
responsible.
AC power transmission and distribution has several
advantages over DC including
• Electrical generators naturally produce AC.
• Transformers operate only using AC, not DC. The
power distribution grid must have the ability to change
voltages.
• It is easier to convert AC to DC than vice versa.
For these and other reasons, Edison lost his early lead with
DC power generation, and power plants produce AC
power that is transmitted and distributed as AC. However,
there are efforts now to transmit electricity as DC that we
will discuss later.
The three-phase power is produced by the
electrical generator at the power plant and goes to the
transmission substation which converts the power using
large transformers to the high voltages that will be carried
by the overhead transmission lines.
Overhead transmission lines
Substation
Utility pole
Electricity at home. We use
single phase. Have two wires,
120 V, that are out of phase, so
there is 240 V between them
for your hot water heater,
range, electric dryer.
Circuit breakers can be reset after resolving the problem that
caused it to trip. Plug fuses have a metal alloy ribbon inside that
melts when the current in the circuit is too great; this breaks the
circuit to prevent damage or even possibly a house fire. When the
ribbon melts, the fuse has to be thrown away and replaced.
Read about your electric bill:
generation, transmission, fuel, distribution,
customer charge, demand, taxes, other
charges.
Tier 1
Tier 2
Up to the 101% to
Baseline 130% of
Amount Baseline
Lowest
rate
Tier 3
131% to
200% of
Baseline
Tier 4
201% to
300% of
Baseline
Higher rate Higher rate Higher rate
than Tier 1 than Tier 2 than Tier 3
Tier 5
Excess of
300% of
Baseline
Highest rate
Smart Grid
Computers receive data from tens of thousands
of points in the electrical grid system. For example, too
much current passing through a line can overheat the wire,
cause it to expand and perhaps sag too close to a tree limb
where it may short out. The system measures the
temperatures of the conducting wires. If the demand for
electricity increases too much, the frequency of the voltage
may drop below 60 Hz. If the frequency drops below 59.95
Hz, a message goes out to the power plants for greater output.
If the frequency goes above 60.05 Hz, the message asks to
reduce power output. All this should be automated with
checks and balances.
Consider what would happen if smart meters were installed
at our homes. We would be able to determine the cost of
electricity at different times of the day. It costs more to
generate electricity at the peak demand times during the day,
because older, inefficient power plants must be turned on. If
we knew how much we were being charged during the day
for electricity, we would be more likely to use our electric
clothes dryer and dishwasher only at night. Some utilities
already offer cheaper rates to consumers if the utilities can
raise our thermostat settings higher on a hot summer day.
Making these changes would be easier with the smart grid
and smart meters. Smart meters are expensive and only
about 10% of Americans have even simple smart meters.
The American Society of Civil Engineers
reported in April 2012 that the nation’s electrical grid is a
patchwork system that will ultimately break down unless
more than $600 billion is spent on it before 2020. This
would amount to an increase of at least $11 billion each year.
The electrical grid now consists of 5,800 major power plants,
750,000 km (450,000 miles) of high voltage transmission
lines and many more overhead and underground wires in the
distribution system to the light switch. The US power
generation system is in much better condition than the
electrical grid. Experts say that both federal and private
funds are available to repair the system, but that there seems
to be little inspiration to build the new infrastructure.
Time Magazine reported in July 2012 that one of the first
things President Barrack Obama wanted to do when he took office in
2009 was give the country a digital smart grid that would selfmonitor and self-heal power outages by diagnosing them
electronically and rerouting power around them. He envisioned the
smart grid described here that would give Americans real-time
feedback and control over our energy use. The electrical grid would
be merged with the Internet so we could adjust our thermostats,
program our appliances, charge our electric cars, and sell back excess
electricity to our utility company from our rooftop solar panels.
Obama wanted to pour in $100 billion dollars in his economic
stimulus package towards the smart grid to be his “moon mission” or
“Interstate highway program” legacy. He was disappointed when he
learned it was not that simple. Utilities own the grid, and it would
take years or decades to convert the analog grid to digital and run the
high-voltage transmission lines necessary. Obama was surprised and
frustrated over his inability to cause change.
Quiz
Which of the following is not an advantage of AC
over DC power?
A) Electrical generators naturally produce AC.
B) It is not possible to transmit DC power.
C) Transformers only operate by AC, not DC.
D) It is easier to convert AC to DC than vice versa.
Quiz
Which of the following is not an advantage of AC
over DC power?
A) Electrical generators naturally produce AC.
B) It is not possible to transmit DC power.
C) Transformers only operate by AC, not DC.
D) It is easier to convert AC to DC than vice versa.
Quiz
The utility poles on the street where you live do not
likely carry which of the following?
A) Cable TV.
B) Telephone lines.
C) 7200 VAC power lines.
D) 240 VAC power lines.
E) 135 kVAC power lines.
Quiz
The utility poles on the street where you live do not
likely carry which of the following?
A) Cable TV.
B) Telephone lines.
C) 7200 VAC power lines.
D) 240 VAC power lines.
E) 135 kVAC power lines.