3/31/2009 1

Electric Power GridPerformance

Presentation

by Anthony J Spurgin

Independent Consultant

San Diego, CA

a-jspurgin@att.net

3/31/2009 2

Electric Power

• Electric power is a useful and flexible form of power that has allowed for the expansion of services to people, such hospital services, lighting, trains, cooking and heating capabilities as well as being used by industries of various kinds

• Energy and principally electric power has lead to the development of nations and civilization

• The grid is a method by which electric power can be used for the benefit of many

• The grid ensures that people are served with a reliable and relatively inexpensive source of power

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Electric Power Grid

• The Grid is an integrated power distribution system

• It is made up Power generation elements (power stations), power distribution lines (high voltage lines) and household and commercial distribution systems (low voltage lines), see Figure

• It functions to ensure reliable power reaches end-state users

• Issues to be considered are: reliability, and cost• Reliability is achieved by ensuring that power

outages are minimized, voltage and frequency are controlled within narrow limits.

• Costs are controlled by selection of power plants• There are also requirements for power shaping,

but this is not covered here

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Electric Power Gridfrom Wikipedia

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Electric Power Grid• Cost is an issue, reliability could be enhanced by the use

of redundant power stations, power lines, etc, but this has a cost.

• Having standby systems maybe necessary but the choice has to be prudent. What is enough?

• To allow for variable power needs, some power generators are kept at low loads, so-called spinning reserve, the concern here is that running a unit at part power can be expensive

• By enhancing the reliability of power plant operations one can also enhance the reliability of the grid, as a whole. The same goes for power lines

• Reliability of grid networks can be enhanced by connection to other grids. Loads can flow into and out of a given grid network, this is particularly useful when dealing with localized disturbances

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Electric Power Grid:Control of Grid Frequency

• Short term control of frequency is achieved by automatic action associated with the power plants

• Power stations generate electric power by the use of alternators driven by steam or gas turbines

• The rotational speed of the standard turbine is sensed by governors and used as a proportional controller, so if the grid frequency drops the controller opens the turbine valves to admit more steam

• In turn, power plant controllers sense the falling pressure and increases power output (firing rate) to match the demand

• The gain of the control maybe non-linear, different at different power levels

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Electric Power Grid:Frequency Control

• The objective of controlling the frequency is to try to account for minute to minute load variations on the grid

• Increasing load on the grid causes the frequency to drop and voltage to change

• Grid loads can vary in a number ways– Minute to minute load changes, washer/dryers turned on or off– daily variations to demand changes due to the activities of

people, such as lunch times from 12 to 1pm– Factory load requirements changing, production variations– Weather changes– For Daily and Yearly variations in power; see next figure

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Electric Power Grid:Load Variations

Percent Load

Time ofDay

12 mn 12 mn12 md

100

50

Base Load

Peak Power

• Daily and yearly power variations (symbolic)

100

50

Percent Max Power

January June December

Date of Year

HeatingHeating

Cooling

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Power Plants:Characteristics affecting response

capabilities and cost• Power plants capabilities vary according to their

fuel, their design and their age• The above aspects influence their ability to fit

into the needs of the organization operating the grid

• There are gas-fired power plants, coal-fired plants, nuclear plants, combined-cycle plants, supercritical pressure plants and hydraulic dam power units

• There is an increased probability of solar, wind, tidal plants to meet environmental imperatives

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Power Plants:Characteristics affecting response

capabilities and cost• Gas fired plants are very flexible and require less time to

build and license• Combined cycle plants are the most efficient fossil plants• Nuclear plants have low fuel costs• Coal plants are more expensive than both gas and

nuclear. They require extensive emission controls• Nuclear plants are less flexible than the others• Nuclear plants do not release carbon based gases• The size and cost of units depends on their

corresponding power density, fossil and nuclear plants are compact, whereas solar, and wind plants spread out

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Power Plants:response and cost

• From the point of view of the grid operator, one is interested in having the most economic plants, match load change requirements and are very reliable

• So the cost per Megawatt sent-out is important, but flexibility is important

• Cost is also a function of the percent time that the plant is at its most economical load

• The grid operator has to supply power over the whole year, so he has to factor daily, weekly, and yearly variations. Periods of low demand maybe a good time to maintain plants, but what reserves should be retained?

• One can appreciate now why, it may be difficult to incorporate solar and wind units into this mix.

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Electric Power Grid:Control Center

• In addition to the plant control systems, the grid is also controlled by the actions of the grid control center

• The grid center sends instructions to the power plants to increase or decrease power to meet predictions of upcoming load changes

• The center has the responsibility of trying to predict large load changes, correct grid frequency difference compared with standard, and stabilize the grid during severe losses of load

• The center monitors the power distribution to enhance the grid security and optimize the cost of power

• The cost of power depends on the type of power plant, fuel costs and age of plant. The cost picture is broken up into cost of capital, fuel cost and manpower costs

• Government action can modify the cost picture by adding costs like a carbon tax. Adding taxes for carbon increases cost of electricity, maybe some reduction is likely if taxes levied results in higher efficiency plants

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Electric Power Grid:Blackouts and Line losses

• The main power lines are limited in number, controlled by cost and politics, NIBY is an issue for both plants and lines. We want the power, but not the power lines or plants!

• If a line ceases to function, its load is redistributed among the remaining lines

• Each line has a load limit, determined by current limits which are ensured by the use of breakers

• One of the tasks of the control center is to monitor the health of the grid and take action to protect the integrity of the grid

• The grid controllers have to be aware of the potential for loss of power plants and increases in loads It is the duty of the power plant personnel to inform the center of actions that might lead to a loss of a power plant or loss of load output

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Electric Power Grid:Grid Controllers

• The grid controllers should have plans to step in to maintain the grid, as a whole, by isolating part of the grid

• Once such an event has occurred, the grid operations have to be recovered. This is not just the case of closing breakers.

• Depending on the power plants and the customers’ equipment limitations, this may take a while. In the case of nuclear power plants, one has to factor in impact of xenon impacts on the return to critical of the reactor

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Grid Operations• The objective of the presentation is to inform the audience on some of the

complexities of the Grid• The Grid operations are a complex mixture of plant operations, reliability

considerations and cost implications• In moving to a Smart Grid all of the above needs to be considered, plus the

fact that Green technologies need to be integrated into the Grid functions, so this increases the burdens on the Grid operations

• The grid has been operating effectively for a large number of years, but as the complexity of industry has increased the reliability of the grid has decreased because of the increased burden being placed upon it

• Steps have been taken to improve the reliability, but the move to the fully Smart grid will take time and it appears that it will cost a lot of money

• It will interesting to see how all of the requirements are going to be handled and how the improvements will be factored into the system

• This ends the first part of the three part series on the topic of Smart Grids and Metering

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Smart Grid :Thoughts

• Although the grid has functioned in present form for some while; technology has advanced in a number of ways and some of these can help in increasing the reliability and cost of operations

• Computer control systems allow for more predictive capabilities along with better sensing devices to help mitigate or prevent line and plant losses

• Communication improvements by wireless can inform central processes of sequential failures and the processes can step in to prevent cascading events

• Weather models tied into the central processes can be used to alert for the need to bring units on line and select the most cost effective way to do that

• It is expected that SDG&E will tell us about their concepts related to the SMART Grid and SMART Metering. I think that we are wondering what are the implementation details, what is the process of implementation, how long will it take and most importantly how much will it cost?