PHYS 1110

Lecture 25

Professor Stephen Thornton

December 4, 2012

Reading QuizHow many nuclear reactors are currently under construction in the United States?

A) None B) 1 C) 2 D) 3 E) 5 or more

Reading QuizHow many nuclear reactors are currently under construction in the United States?

A) None B) 1 C) 2 D) 3 E) 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

QuizWhich 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

QuizWhich 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 22

loss 2 2

P P RP I R R

V V= = =

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 Tier 3 Tier 4 Tier 5Up to the 101% to 131% to 201% to Excess ofBaseline 130% of 200% of 300% of 300% ofAmount Baseline Baseline Baseline Baseline

Lowest Higher rate Higher rate Higher rate Highest rate rate than Tier 1 than Tier 2 than Tier 3

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 self-monitor 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.