Download Slides for Smart Grid and Transmission

EE 295
Smart Grid and the
Transmission System
Dr. Paul Hines
University of Vermont
School of Engineering
NY City, Nov. 9, 1965 © Bob Gomel, Life Where are we?
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1. Electromechanical grid 2. SG & power supply, renewables, etc 3. Basics of comm systems, scada, etc. 4. SG & retail electricity 5. SG & distribuJon, microgrids, storage, etc. 6. SG & Transmission 2 Main topics
•  Synchronized Phasor Measurement Units •  Flexible AC Transmission Systems •  Improved operaJons centers, controlling cascading failures 3 4 5 6 Basics of PMU measurement
•  Sinusoidal AC •  Measure magnitude •  Measure phase •  Methods of measurement •  hTps://www.naspi.org 7 Phasor data concentrators
8 F-Net
•  hTp://fnetpublic.utk.edu 9 Key concepts
•  PosiJve sequence •  Purpose: get an average phasor representaJon of the three-­‐phase system. •  There are also zero sequence and negaJve sequence components, but we’ll focus on the posiJve sequence. 10 11 PMU Applications (model validation)
•  Power systems live and die by their models. •  Dynamic models exist. •  However, it was previously extremely difficult to impossible to validate them •  A “scan” of convenJonal RTU data could take 30 seconds to 5 minutes (or more). •  Dynamics are much faster. •  A few PMUs allow one to determine if your model works or not. •  Many PMUs should allow you to calibrate your model. 12 PMU Applications (state estimation)
•  To be redundant: • 
A “scan” of convenJonal RTU data could take 30 seconds to 5 minutes (or more). •  State esJmaJon is the process of combining measurements, each with some error, to esJmate the “true” state of the system. •  The state esJmator is key to idenJfying overloads, as well as conJngency analysis. •  In power systems, voltage magnitudes and angles are typically considered the state variables. •  Once these are known, all other values can be computed from the power flow equaJons. •  Voltage angles were previously only available from the state esJmator. •  Now they can be “measured” •  There is some conversaJon about “state measurement” rather than “state esJmaJon” but this is misleading. All measurements have error, requiring esJmaJon. •  With a few phase angle measurements, state esJmaJon can be improved greatly. 13 PMU Applications (wide area
monitoring)
•  The angles between areas tend to drij, indicaJng large power flows. •  Monitoring these angles can be a useful measure of stress in the system. 14 15 PMU Applications (protection)
•  Zones of protecJon 16 Example…
17 PMU Applications (protection)
•  Out-­‐of-­‐step relays •  Look for major angle differences (generators that our out-­‐of-­‐phase with the system) •  What do you do with them when you find the problem? 18 PMU Applications (real time stability)
19 Real-time coordination of relay actions
20 Open PMU problems
•  PMU placement •  Where do we place the PMUs to get the most informaJon? •  ExtracJng informaJon from noisy data. •  PrevenJng instability from large-­‐scale stochasJc sources. 21 Nature, Sept. 2009:
As large, complex systems approach “collapse” they shows signs of criJcal slowing down. Ecological models, climate models, epilepJc seizure Hines, May 23, 2012 From Scheffer et al., 2009
•  Signs of CSD: noise amplified, lower-­‐frequency elements in noise filtered, autocorrelaJon Eigenvalues far from the origin Hines, May 23, 2012 Eigenvalues
near the origin Autocorrelation and variance in a single
machine infinite bus system
Low stress case Hines, May 23, 2012 High stress case 1-machine, infinite bus model
Bus 1 Infinite bus, but noisy voltage Bus 2 Hines, May 23, 2012 2 bus network model Time -­‐> Hines, May 23, 2012 9 bus network model Hines, May 23, 2012 What about the WSCC on
August 10, 1996?
•  Lines sagged into trees, triggering a cascading failure •  7.5 million customers lost power. 7 states + Canada. Hines, May 23, 2012 WSCC (WECC, BPA) on August 10, 1996 Hines, May 23, 2012 Can we use this to predict
distance to transition?
Use a simple regression model to esJmate parameters. Test on separate data Hines, May 23, 2012 Flexible AC transmission systems
•  The problem •  We cannot (easily) control the flow of power in a transmission system. •  Do 2-­‐bus example. •  AcJvely controlling voltages requires •  Switched capacitors, which are relaJvely expensive and can only be used in discrete chunks. •  Could be rather slow •  Synchronous condenser •  A generator that doesn’t produce acJve power •  Expensive. •  Can we control voltages and currents using power electronics? 31 Distributed FACTS
32 Concepts from the readings
•  Loop flow •  CongesJon 33 High Voltage DC
34 HVDC
35 36 Celilo Converter Station in 1989
37 38 Advantages
•  Advantages •  No skin effect=> less resistance •  about 3.5% per 1,000 km [wikipedia] •  Smaller capaciJve losses to ground •  Fully controllable •  Transmission lines are less expensive (2-­‐wires) •  Disadvantages •  Circuit breakers •  Lower reliability •  Expensive converter staJons 39