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The Latest in the MIT “Future of…” Studies
Recognizing the growing importance of energy issues
and MIT’s role as an honest broker, MIT faculty have
undertaken a series of in-depth multidisciplinary studies.
Previous studies have focused on energy supply
technologies; our focus is on energy delivery – the
electric grid. Also, unlike other “Future of…” studies, we
do not focus on carbon constraints.
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New Technologies Offer Great Opportunities
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Control Centers:
Improved System State Estimation Phase Angle Monitoring/Alarms Improved System Simulation Models Oscillation Detection New System Control Approaches
Transmission and Substations:
Phasor Measurement Units (PMUs) Flexible AC Transmission Systems (FACTS) New Sensor Technologies High Voltage DC Lines Superconducting Lines Fault Current Limiters Dynamic Line Rating Systems Energy Storage
Distribution and Customers:
Distribution Management Systems Outage Management Systems Volt/VAR Optimization Conservation Voltage Reduction Automated Fault Detection, Isolation, &
Restoration Advanced Metering Systems Microgrids
WESTERN INTERCONNECTION TRANSMISSION TECHNOLGOY FORUM
Outline
Some system trends
Transmission line technologies
Solid state control technologies
PMU and synchrophasor systems
Balancing area topologies
Renewable (wind) integration issues
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The U.S. Grid Performs Well
Losses have fallen over time, are in line with other nations’
Reliability also seems in line with other developed countries
Performance data are very weak
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U.S. Transmission and Distribution Losses 1926-2009
0%
2%
4%
6%
8%
10%
12%
14%
16%
18%
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1996
2001
2006
T&
D L
osse
s (
% o
f To
tal G
en
era
tio
n)
Year
Transmission Investment in New England
Source: ISO New England Transmission Project List, through October 2013v Update.
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Payments to Maintain Reliability
Reliability Agreements ended in June 2010
Source: ISO New England Transmission Project List, through October 2013 Update.
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$0
$50
$100
$150
$200
$250
$300
$350
$400
2005 2006 2007 2008 2009 2010 2011 2012
Dollars in millions
Regional Total Reliability Payments
Reliability Agreements NCPC
Congestion Costs
Source: ISO New England Transmission Project List, through October 2013 Update.
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0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
$0
$50
$100
$150
$200
$250
$300
2005 2006 2007 2008 2009 2010 2011 2012
Dollars in millions
Congestion Costs Congestion as % of Energy Market
“Peakier” Load Duration Curves Raise Cost
Air conditioning, shift away from industrial load have reduced capacity utilization.
Electric vehicles charged in late pm could make this worse.
Moving charging, other loads off peak could flatten curve and lower cost.
But most current demand response programs focus on emergencies, not load leveling.
Dynamic pricing would help smooth demand peakiness.
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Three Constraints of Transmission Lines
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Renewables’ Effect on System Inertia
System inertia necessary to ride through
transients
Inertia provided by large rotating masses of
conventional generators
Solar provides no system inertia
Wind provides inertia but no recovery
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AC Lines
Three conductor bundles (3 phases)
Length limited by stability margin
Compensating devices required to maintain
voltage stability
AC cables severely length limited
Charging currents, resonance
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High Temperature Superconducting Cable
Liquid nitrogen: 65 K (–208o C)
Demonstrated by LIPA in 2008:
138 kV ac,
574 MVA
600 m
Increase capacity of existing cables
Possible fault current limiter
Allows increased line loading
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Installation of the First Phase Conductor
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From Maguire et. al., “Installation and Testing Results of Long Island Transmission Level HTS Cable,” IEEE Trans. Applied Superconductivity, vol. 10, no. 3, June 2000.
Solid State Transformer Concept
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Examples of Static VAR Compensators
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Current injection orthogonal to
line voltage
Voltage injection orthogonal to
line current
DC vs. AC Transmission
DC lines not limited by stability considerations
Cost and losses are issues
Cost tradeoff a function of length
Converter vs. line losses
DC attractive for renewables located far from
load centers
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HVDC
Requires complex and expensive converter
terminals.
Excellent for long distance transmission.
Line costs/losses less than AC
For 800 mile/6000 MW line:
765 kV ac twice as expensive as +/- 800 kV dc
Ac losses twice those of dc
Comparable cost and losses for 200 mile line
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HVDC Converter Structures
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Current Source Converter Terminal(CSC)
Voltage Source Converter Terminal(VSC)
AC DC
Voltage Source Converter
Greater control flexibility
Aids stability, integration of remote renewables
Permits use of solid dielectric cables
Attractive for interconnects, not generator leads
Higher losses than CSC
Currently limited power rating
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VSC HVDC (cont’d)
Doesn’t require strong ac bus for
commutation.
Ideal for long cables
Underground or under water
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ABB HVDC Breaker
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WHAT ABOUT RENEWABLES?
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But New Transmission For Renewables
Will Not Necessarily:
Reduce congestion
or
Increase reliability
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Renewables Require New Transmission
The Challenge of Ramping Wind
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Wind output more variable than load, imperfectly predictable.
Work on better forecasting in progress.
System operators studying, implementing other changes to facilitate more wind.
Few incentives exist for flexibility today.
BPA Total Wind Generation 12/3/2009 – 12/10/2009
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Another Ramping Example
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Larger Balancing Areas
Real Time Contingency Analysis (RTCA)
should be expanded beyond boundaries of
BAs. Need wide area system model.
Standardization of models, e.g.,
nomenclature.
Minimize ramping requirements for wind.
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USING AMI + PRICING TO LEVEL LOAD
Dynamic pricing + automated response can shift
demand, but more research on consumer behavior is
needed.
Substantial ARRA-supported, state-mandated AMI
investments provide a very important learning
opportunity.
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Introduction to Synchrophasors
A network of phasor measurement units (PMUs)
situated at strategic locations throughout the
system. The data collected by the individual
PMUs are synchronized using a GPS time
stamp, making visible parameters such as phase
relationships.
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How Interconnected? The 2008 Florida Blackout
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PMU Data Could Warn of Blackouts
• PMUs give frequent, GPS-synchronized measures of current, voltage,
and phase angle at their locations.
• Ex-post analysis of 2003 blackout:
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Benefits of a Synchrophasor Network
System diagnostics and real-time analysis
Increased transmission line capacity
Operation closer to stability limits
Determination of more accurate system
model parameters
Detection of anomalous system conditions
E.g., low frequency oscillations
Many others yet to be discovered
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Synchrophasor Integration Issues
Prior to SGIG few applications or standards, and
interoperability difficult.
Data quality
Communication protocols
Security concerns
Post SGIG initiatives addressing these issues.
NASPI
Numerous IEEE standards
Communication, calibration, hardware requirements, etc.
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PMU Application Challenges
Baselining – what is “normal” operation?
Turning data into actionable information
Limited application software
Communication latency in wide-area
applications
Cost/authority/maintenance
Security and proprietary concerns
Training
Employing AI to determine/take actions
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Recommendations from Chapter 2
R&D efforts should be undertaken to develop:
1) The analysis tools necessary to generate
actionable information from data acquired from
PMUs, and
2) The control schemes necessary to make use of
this information by realizing the complementary
potential of PMUs, FACTS, and other hardware
devices.
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Recommendations from Chapter 2 (cont’d)
NERC should continue to encourage relevant
entities to participate in PMU data-sharing
efforts necessary for the effective
development and use of PMUs and wide-area
measurement systems
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“Power Outages Caused by Squirrels”
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NYT Headline Sunday Sept. 1, 2013