Electric Power Network
By udhayaforu
@udhayaforu (8)
India
October 12, 2006 2:19am CST
Electric Power Network Tutorial:
Basic Steady State & Dynamic
Models for Control, Pricing
and Optimization
Christopher DeMarco
Electrical and Computer Engineering
& Power Systems Engineering Research Center
www.pserc.org
University of Wisconsin-Madison
Madison, WI 53706
(608) 262-5546
demarco@engr.wisc.edu
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 2
Components of my talk:
* Evangelism: for an audience likely
focused on mathematical problems in
communications networks, show what
makes electric power networks different,
and (hopefully) what makes them
interesting.
* Start with some "fun facts" - just general
nature of technology involved,
(opinionated) overview of nature of
industry.
* Move on to mathematical modeling -
construct underlying dynamics,
associated equilibrium for steady state.
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 3
Highlight:
- state equations associated with nodes;
- role of network structure;
- peculiar coordinate system used in
dynamics and steady state;
- policy/control decisions available;
- market driven control & pricing.
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 4
Old Assumptions under Regulated or State
Monopoly
* Ever increasing economies of scale for
central generation plants - lowest
production cost associated with central
generating plants of increasing size.
These economies of scale (historically)
justified "natural monopoly" for
generation.
* Parallel independent transmission and
distribution firms seen as highly
inefficient. Long historic trend toward
single interconnected synchronous grid
covering large geographic area. Again,
natural monopoly.
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 5
What has Changed?
i) Public perception of significant mis-steps
in generation investment for many
state/regulated monopoly firms (notable
in US). Examples of billions of dollars of
investment in partially constructed
nuclear plants abandoned (interestingly,
quite commensurate with billions of
dollars of waste in CA markets ...)
ii) Significant expansion of availability of
natural gas, beyond estimates of one or
two decades earlier.
iii) Significant improvements in natural gas
based prime movers; combined cycle gas
turbines achieving efficiencies in high
50% range, from plants of medium size.
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 6
iv) Strong political trends in many nations
favoring market-based solutions over
central planning solutions. Belief that
private firms would make better
investment decisions (editorial comment -
evidence in US to date suggest private
firms unable to make any investment
decisions in transmission).
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 7
Common Features Emerging in Power
Production in Many Parts of the World:
* Assumption that distribution systems and
(most of) transmission grid are still
natural monopolies. Hence, these remain
regulated, or state held.
* Assumption that real time operation of
transmission grid must lie in hands of
centralized coordinating body, with
considerable authority; oft-termed
"Independent System Operator," or ISO.
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 8
* Assumption that generation should be
provided through competitive markets
(though exact structure and rules for
markets vary widely, and in many cases,
are still evolving).
* Many (not all) markets share a rough
structure of day ahead offers made by
independent generation companies, with
a central market entity (ISO or Power
Exchange) making initial plan of
schedule/purchases.
* Some markets allow independent
arranged transactions between buyer &
seller, "bilateral transaction."
Coordinated with ISO, but not with central
market.
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 9
* Emerging efforts to bring larger number
of power consumers to active participation
into market, possibly down to retail level
(terms: "retail competition," or "customer
choice")
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 10
Generation Technology Overview
* Key observation: conversion of
mechanical energy to electrical energy via
rotating machines is a highly refined
technology - in excess of 98% efficient in
modern machines.
* But wide variations in efficiency lie in
conversion process from chemical (or
nuclear) energy to rotating mechanical
power.
* Large percentage of new generation
around the world (and overwhelming
majority in US) within last decade has
natural gas as primary fuel; large
percentage as gas turbines (irony - in
1970’s in US, natural gas was outlawed
as a fuel for electric generation).
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 11
* Huge market demand for these units;
before economic slowdown of 2001,
growing concern regarding world-wide
manufacturing capability - could it keep
up with demand?
* Increasing maximum size of units (e.g.,
1000 MW - so apparent economies of
scale showing up in this technology as
well)
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 12
New Technologies in GT Units
* Much advance due to improved materials,
and improved computer tools for
modeling and optimizing combustion and
fluid flow designs.
* Better materials allow higher firing
temperatures, yields higher efficiency,
while limiting NOx emissions. Potential
efficiencies of 60% in combined cycle gas
turbines.
* Some manufacturers also examining
steam cooling to raise efficiencies in
simple cycle units (an example in partial
operation: Lakeland Electric, Florida, USA
site - 262 MW unit claiming 39%
efficiency).
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 13
Aerospace Derivative Gas Turbines
* "Aero" units often serve in smaller
capacity (say ~5 to 50 MW) applications,
where start/stop cycling for peaking may
be necessary.
* Simple cycle units, hence lower
efficiency; however, some manufacturers
claiming technology improvements
bringing efficiency close to 40%.
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 14
Heat Recovery Steam Generators (HRSG)
Typical technology of older coal fired plants
* Historic efficiencies in coal plants topped
out around 35-39%
* Advances in gas turbine technology also
driving incremental improvements in
HRSG designs.
* Significant efficiency enhancement can
be gained in retrofit/upgrades of old
generation steam turbines (opportunity
here - in US, more than 1300 major steam
generating plants over 30 yrs old!)
* New blade designs, new coatings offer
significant enhancements - efficiency
improvements of up to 10% claimed by
vendors.
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 15
Emerging Technologies
* Tremendous interest being created by socalled
"micro-turbines," and by fuel cell
advances.
Some debate as to classification of
microturbine, but rough characteristics:
* power range of 10 kW to 500 kW;
* turbomachinery based on radial flow
designs, often derived from automotive
turbocharger technologies;
* usually just one rotating unit, with
compressor, power turbine, and
generator all on common shaft;
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 16
* high speed operation, 10,000 to 100,000
rpm;
* modest pressure and temperature
operation, yielding fairly low emission
(catalytic converters can be added);
* very compact construction, suitable for
transport by small truck;
* generator allowed to operate at variable
speed, at high frequency, into power
electronic rectifier and internal DC bus,
inverted to grid frequency AC.
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 17
Questions:
* Will units achieve low maintenance, "turnkey"
operation desired for target markets?
* Cost, efficiency, and cumulative
environmental impact of large numbers of
these units?
* Interconnection standards, and impacts
on grid stability and reliability?
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 18
Fuel Cell Technologies
* Growing experience with test installations
- fuel cells in use in some reliability critical
backup applications (e.g. Citibank, NYC),
as well as US military test sites.
* Very high capital cost remains key barrier
to market acceptance.
* Some analysts see possibility of price
reductions coming from "spillover"
automotive developments - major auto
manufacturers placing large R&D
budgets on fuel cells. However,
significant difference in thermal
management challenges for mobile vs.
stationary power.
* Technical applications questions for grid
application - similar to microturbines -
IMA Tutorial: Electric Power Grids
Minneapolis, MN, March 7, 2004
C. L. DeMarco, University of Wisconsin-Madison; page 19
what should be the interconnection
standards? what are units’ dynamic
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