PowerPoint Presentation clearwater

1
Stability and Security of Power Networks G. T.
Heydt Arizona State University ECEDHA 2004
Annual Meeting
March, 2004 Orlando, Florida
2
Outline

• Stability and security a general discussion
• Weaknesses and strengths of the North American
  grid
• Some theoretical considerations
• Solutions short range and long range
• Propaganda power engineering education
• Conclusions

3
Stability

• Power system stability basically refers to the
  ability of operating an AC network with all
  generators in synchronism, retaining synchronism
  even after a large disturbance

4
Stability

• Each synchronous generator has a Newtons law
  second order nonlinear differential equation that
  describes the machine angle and control systems
  (e.g., power system stabilizers) also contribute
  a higher order nonlinear controller to the
  dynamics
• A large interconnection (WECC, e.g.) may have
  about 200 generators 150 PSSs about 1000 to
  10000 order nonlinear differential equations

5
Stability

• The basic analysis technique is state space
  analysis / eigenvalues for the linearized system,
  or simulation for the nonlinear system.
  Typically, the dimension is very high in the
  1000 10,000 range. The interconnection is
  modeled as Ibus Ybus Vbus which is reduced to
  eliminate the non-dynamic nodes (i.e., remove the
  non-generation nodes).

6
Power system stabilizers

• A PSS is a controller that uses (usually local)
  measurements to provide a signal to one generator
  so that damping torque is produced by the machine
  field winding. The basic concept is that a
  linear controller is used with standard feedback
  control technology to place the poles of the
  linearized system solidly in the LHP. Virtually
  all large generating units in North America are
  fitted with PSSs.

7
Power system stabilizers

• The main weaknesses of this approach are that
  the nonlinear system may respond poorly, and also
  dynamics external to the generator PSS are not
  modeled (nor included in the measurements).
  Therefore modes that result from inter area
  dynamics may not be damped.

x
x
x
x
x
x
x
x
x
8
By injecting the appropriate signals from distant
measurements in the system, transmitted through
LEOS, the controller is able to obtain superior
performance in terms of damping interarea
oscillations compared to use of conventional
local signals. The main concept is to use
interarea signals for interarea controls
Wide area robust power system stability control
Low Earth Orbit Satellites LEOS
REGIONAL MEASUREMENTS
LOCAL
SPSS
MEASUREMENTS
9
Hierarchical robust power system controller
Management Level

• Execution Level
• Signal pre-processor
• Actuator / Distributor
• Operation Level
• System modal identifier
• SPSS damping loop
• Management Level
• Fuzzy logic based parameter tuner

Operation Level
Execution Level
Control
Input Data
Power System
10
Voltage Regulator With PSS and SPSS
Remote Signals
SPSS
Vt
PSS
??,?f, or Pa

Generator Excitation System
?
Ref

Voltage Regulator
Gen
-
Generator Field
11
(No Transcript)
12
Key issues

• Full scale nonlinear solution (transient
  stability study)
• Eigenvalues of the linearized system near the
  operating point (small signal stability)
• Line and component ratings
• Voltage ratings (maximum and minimum)
• Coherency - groups of generators swinging
  together
• Synchronizing torque, PSSs
• Acceptable operating conditions (including
  operation within about 50 mHz of 60 Hz)

13
Security
Market
Network
Communication systems
Internal Sources
Information decisions
Natural calamities
Intentional human acts
External Sources
Security refers to the ability of the system to
respond only to intended operator commands,
blocking all unintended operations
14
Electric power system is vulnerable to failure
due to

• Natural disasters
• Deliberate attack
• Equipment failures
• Operator error
• Accidents

Tree-related events High load periods Software
failures
15
Monitoring of electric power networks
Reduce Vulnerability
Underground Transmission Lines
Substations
Advanced
PMU
Transformers
EMS
Sensor Systems
Overhead Transmission Lines
16
Energy management systems
Archiving
Sensory information
E M S
Generator controls
Command and control
Operator interaction
State estimator
17
Network vulnerability reduction through virtual
sensor utilization
EMS
EMS
Virtual Data
Virtual Sensor Present
18
Tradeoffs betweenvirtual and physical sensors
Low Cost Less Accurate
High Cost Greater Accuracy
Z H X
V
I
Physical Sensors
Virtual Sensors
19
What is needed to enhance both security and
stability

• Ability to acquire and interpret extensive
  real-time information from diverse sources,
  ranging from sensors to satellites. Sensory data
  used in Hx z state estimators to enhance system
  performance.
• Ability to quickly evaluate system vulnerability
  with respect to catastrophic events in a market
  environment involving competing, self-serving
  agents
• Ability to adapt protective device performance
  based on system-wide and external system
  assessment
• Ability to reconfigure the power network to
  minimize system vulnerability
• Ability to develop system restoration plans to
  minimize the impact of disruption

20
Strategic Power Infrastructure Defense System
21
Communication system for strategic power
infrastructure defense
Time synchronization (GPS) / Self healing /
Info. Exchange (LEO)
GPS or LEO satellite communication
Internet based communication channel
Internet based or more direct and faster
communication channel
Strategic power infrastructure main system
Intranet Ethernet or model based network is used
in the Intranet. Each Intranet can have a
gateway that handles IP addresses in the
Intranet
Internet or any other communication channel for a
number of Intranets
22
The North American grid
NERC policies, rules, reliability, plans,
synchronous interconnections
23
North American Electric Reliability Council

• Sets standards for the reliable operation and
  planning
• Monitors, assesses and enforces compliance with
  standards
• Provides education and training
• Assesses, analyzes and reports on bulk electric
  system adequacy
• Coordinates with Regional Reliability Councils
• Coordinates the provision of applications, data
  and services
• Certifies reliability service organizations and
  personnel
• Coordinates critical infrastructure protection
• Enables the reliable operation by facilitating
  information exchange and coordination among
  reliability service organizations
• Administers procedures for appeals and conflict
  resolution

24
Weaknesses and strengths of the North American
grid

• Basic transmission design is over 40 years old.
  Some basic distribution circuits are over 60
  years old.
• Never designed to handle high levels of bulk
  power
• Both transmission and generation constrained
• The impact of market driven exchange of power has
  stressed the transmission grid
• The transition to market based infrastructure has
  stressed the newly created control entities
  (e.g., ISOs) in an industry that is rapidly
  loosing corporate memory

25
The Northeast blackout of 2003
Time 8/14/2003 40957 PM EDT  The first
significant events were initially recorded in
Michigan and Ohio
26
The Northeast blackout of 2003
Time 8/14/03 041039 PM EDT The disturbance
was then recorded all over Michigan , Ohio , and
the city of Buffalo, NY
27
The Northeast blackout of 2003
Time 8/14/03 041058 PM EDT 19 seconds later,
the disturbance had propagated to the eastern
seaboard.
28
The Northeast blackout of 2003

• Main causes
• Failure of state estimator in MISO to model
  external system changes
• Combination of heavy power exchanges, high
  reactive power flows, planned outages of
  transmission circuits and planned outage of a
  main generating facility (none of which are
  unusual)
• Operator error / training of MISO operators /
  imprudent operation of an Ohio utility
  (generation outages)
• Unplanned unit and line outages

29
The Northeast blackout of 2003
30
The Northeast blackout of 2003
31
Generation building boom of the past
200
180
160
140
120
GW Installed in Five Year Period
100
80
60
40
20
0
1950
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
Coal
Oil
Gas
Nuclear
Other
32
A hindsight view of the past building boom
Generation Building Boom Follows the Baby Boom
Labor Force Entry
35
200
180
30
160
25
140
120
20
Percent Change in Labor Force
100
GW Installed in Five Year Period
15
80
60
10
40
5
20
0
0
1950
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
Coal
Oil
Gas
Nuclear
Other
33
Generation building boom of the future
1400
Total System Generation Capacity
1200
1000
By 2020, the U.S. will need 1300 new power plants
at 300 MW each
GW
800
600
Cumulative Additions
400
200
0
2000
2005
2010
2015
2020
2025
2030
34
Employment at major IOUs
35

• TRANSMISSION
• DISTRIBUTION

36
The N9s problem

• Electric power quality
• Extreme bus voltage reliability, for example
  'five nines' (i.e., 0.99999 availability), or six
  nines or even higher
• Utilization of new transmission and distribution
  technologies for improvement of reliability
• Utilization of distributed energy sources (DERs)
  to improve reliability
• Working with manufacturers of information
  technology equipment to reduce load vulnerability

37
24/7 UTILIZATION OF POWER SYSTEM ULTRA HIGH
RELIABILITY
INFORMATION PROCESSING, FINANCIAL SERVICES,
AIRLINES, POLICE, MILITARY
38
Reliability enhancement

• Distributed rather than concentrated loads
• Loop circuits for distribution systems
• Information Technology and sensitive
  manufacturing loads
• Independence of energy sources
• Environmental issues

39

• AS A RESPONSE TO THE 1993 TERRORIST BOMBING OF
  THE WTC, THE PRIMARY DISTRIBUTION SYSTEM IN THE
  BUILDING WAS IMPROVED TO KEEP THE POWER ON IN THE
  CASE OF SEVERE DISRUPTION OF THE SUPPLY /
  INTERRUPTION OF THE IN-BUILDING PRIMARY
  DISTRIBUTION. THERE WERE TEN SUBSTATIONS IN EACH
  WTC TOWER, ON FLOORS 7, 41, 75, AND 108, AND THE
  SOUTH TOWER HAD AN ADDITIONAL TENANT OWNED DOUBLY
  FED SUBSTATION ON FLOOR 43

40

• THE USE OF MULTIPLE FEEDS, MULTIPLE SUBSTATIONS,
  AND ISOLATED POWER SUPPLIES KEPT THE POWER ON IN
  MOST OF THE WTC FOR 102 MINUTES AFTER THE INITIAL
  STRIKE. IT IS BELIEVED THAT THIS WAS THE MAIN
  FACTOR IN SAVING THE LIVES OF AS MANY AS 18,000
  PEOPLE WHO ESCAPED FROM THE TOWERS BEFORE COLLAPSE

41
Independence of sources

• The dependence of the sources will result in a
  much higher outage rate than (1-P1)(1-P2)

42
Modeling dependence of sources

• The dependence effect of multiple sources can be
  modeled using a difference equation of the form
• qn1 Cqn(1-C)(q1)1/n qn
• where qn 1-pn outage rate of circuit upon
  addition of nth feeder, C is a correlation
  coefficient
• The (q1)1/n term is called a discounting term
  and it accounts for increased potential for
  dependence for cases of large n (large numbers of
  feeders)

43
Discounted model

• C 0 indicates no correlation between multiple
  feeders
• C 1 indicates the feeder outages among several
  feeders are common mode

44
Reliability of multiple feeds
The addition of feeders to improve reliability
has a diminishing effect. For practical cases,
use of more than three independent feeders of
100 capacity is counter- productive.
45
(No Transcript)
46
Probabilities of uncommon events
COMMON (?) Event_______
Loosing at roulette in Las Vegas bet on
00 Loosing the PowerBall lottery FAA design
criteria for aircraft
LIFE Probability, N 97.368,
1.6 99.99995, 6.3 0.999999999
0.999999999999, 9 to 12
POWER SYSTEM RELIABILITY Reliability N
Outage time 99.9 3 8h 45 min
/ yr 99.998631 4.9 1 day / 200 yrs 99.999
5 5 min 15 s / yr 99.99999 7
3.2 s / yr 99.999999 8 18.9 cycles /
yr 99.9999999 9 1.8 cycles / yr
47
Solutions short range

• Distributed generation
• Added small generation units at all levels
• Conservation / electronic control of loads
• Investment in distribution systems
• Sharp increase in research in both transmission
  and distribution engineering
• Recruiting of students to the power area at all
  levels
• Improvement of software tools

48
PROTON EXCHANGE MEMBRANE FUEL CELL - 7.5 kVA

• PHOSPHORIC ACID 250 kVA FUEL CELL

49
Microturbines

• Low capacity, high speed units with electronic
  interface with 60 Hz bus
• Alternative fuel sources (e.g., biogas, gasifier,
  pyrolysis, fuels that have less than 10 of heat
  content compared to fossil fuels)
• Catalytic combustor to reduce nitrous oxide
  production
• Heat recovery
• Lower capacities -- e.g.,
• 5 - 300 kVA
• High efficiency small units
• New IEEE standard requires disconnection from the
  distribution system within a few cycles during
  low voltage or outage events

50
Solutions long term

• Added generation in larger units
• Local solutions for high reliability requirements
• Added capacity in distribution systems
• Adaptive islanding of interconnected systems
• Coordinate national energy policy with system
  realities

51

• The educational aspect of the problem

52
U. S. Power engineering undergraduate
enrollments
53
U. S. Power engineering graduate enrollments
200
M.S.E.E.
graduate degree recipients
150
100
50
Ph.D.
0
year
Source G.T. Heydt and V. Vittal, Feeding Our
Profession, IEEE Power Energy

Magazine, vol.1, issue 1, Jan/Feb 2003, pp 38-45
54
The general electrical engineering reality

• There is a certain ebb and flow to the enrolments
  in engineering nation-wide since the all-time
  low in undergraduate engineering in 1998, there
  has been an uninterrupted growth in enrolments
• In many electrical and computer engineering
  programs, the growing tendency to select the
  computer engineering option has resulted in the
  majority of students seeing little or no subject
  matter relating to energy and power

55
The general electrical engineering reality

• Given the decreasing number of electrical
  engineering undergraduates, there is good
  progress in stopping the precipitous decline in
  the undergraduate power engineering enrolments to
  the point where many power programs are
  experiencing record levels

56
Encouraging developments on the curriculum
front

• A determined movement away from the old straight
  jacket curriculum to new enriched course
  offerings with broadened choice
• New developments are evident in three principal
  thrusts
• addition of microeconomic/finance elements
• introduction of energy, environment and public
  policy aspects
• wider array of power systems, power electronics
  and machines/drives courses

57
The impact of recent events

• Restructuring of electricity and the California
  crisis sharpened public interest in electricity
• The September 11, 2001 tragedy brought to
  prominence the issue of the security of the North
  American interconnected power system
• The 2003 mega-blackout produced keen interest in
  the reliability of the interconnected grid

58
Conclusions

• Stability of power systems is a well understood
  phenomenon, but complex numerical problem.
• Stability enhancement controls are very complex
  to design, but the present research thrusts and
  engineering practice have yielded in-service
  designs (or designs nearly in-service) that are
  suitable to the task
• The transition to a market based energy
  infrastructure may not have been well thought
  out, and system implications are just now being
  remedied

59
Conclusions

• Distribution engineering, long a step-child of
  power engineering, is a focus of research
  mainly related to high reliability, cost
  reduction, and distributed generation sources
• System security is a point of focus in
  contemporary power engineering
• Research on sensory systems is needed to enhance
  system security
• Power engineering education and the production of
  power engineers at all levels seems to have a
  significant impact on the health of the national
  power system. It is unclear that the number of
  engineers needed will be attained by US
  educational institutions.