Achieving Smarter Grid Operation With On-Line DSA Technology Powercon 2014 October 20-22, 2014, Chengdu, China Lei Wang Powertech Labs Inc. 12388 88 th Avenue Surrey, BC, Canada
A very simple version of Smart Grid Transmission grid Smart transmission network Smart substation Information technologies Smart control center Renewablebased systems Demand management Situational awareness Real-time modeling and validation Real-time and predictive analyses Optimization Controllability Interactions with power market
Smart Control Center Modernization of control centers involves development and deployment of technologies in many areas This has been proven critical with lessons learned from recent blackouts Example: the Sep 8, 2011 blackout in the US Pacific Southwest caused by an N-1 outage One of such technologies is the On- Line Dynamic Security Assessment ( On-Line DSA )
What is on-line DSA? Objective: ensuring secure operation of a power system Dealing with issues such as thermal loading, voltage, transient, oscillation, frequency, etc. What s the difference from the conventional approach? Start from a real-time captured, or forecast, system condition Consider all applicable security criteria and credible contingencies Include high fidelity system models ( model-based analysis ) Perform analyses automatically, periodically, and efficiently Present results in simple, straightforward way security margin, operational limits, remedial actions required, etc.
Applications in North America AESO IESO MISO ISO NE PJM CAISO ERCOT
Why on-line DSA? Improved grid security... prevent blackout! Better situational awareness in control rooms Maximizing transmission capabilities Management of renewables Assisting power market operation Fast and accurate controls Improved operational planning Handling of system operation after severe disturbances (due to hurricane, tornedo, flood, ice storm, etc.) More...
How did we come here From the idea room The concept of on line DSA is not new First proposed more than 40 years ago Intensive research and development have since been made Main focus was on algorithm and solution method development Due to the computer technology limitation, achieving on line DSA used to be a dream of power system engineers
How did we come here To the show room The development of the on line DSA technology sped up from mid 1990s There was motivation from utilities to adopt this technology Appropriate analysis methods were available Advances in IT helped make this feasible However, lack of the required infrastructure prevented this from practical applications
How did we come here To the control room The widespread applications of online DSA took off in the recent decade or so Significant progress has been made Regulatory requirements System operational requirements Matching infrastructure (SE, PMU, model and data, IT, etc.) Success in many application areas Measureable benefits observed
Three key elements in on-line DSA Algorithm On line DSA Modeling Integration
Algorithm Static analysis P-V Q-V Continuation powerflow Modal analysis OPF Dynamic analysis Time-domain simulations Direct methods (EEAC, BCU, etc.) Eigenvalue analysis Trajectory sensitivities New methods are being proposed and applied continuously Special analysis Transfer limit analysis Remedial controls Distributed/ parallel/cloud computations Big data analysis Probabilistic analysis AI methods
Modeling In addition to the models considered in the conventional security analysis of power systems, additional models or modeling techniques are required for on-line DSA Examples: Dynamic rating Node/breaker modeling Realistic contingency sequences RAS and SPS models Renewables Real-time closed loop controls Real-time equipment status External system equivalencing
Integration Real time Training Forecast Lookahead Market PMU/ WAMS Testing Study Redundant /Backup Result depository Integrated control room applications RT model recondition/match Auxiliary data management Resource & data sharing Analysis scenario creation Performance monitoring Result processing & display Failover & security Distributed/parallel/ cloud computing
Application areas The on-line DSA technology has been applied in the following areas System security status and margin monitoring Stability limit determination Recommendations for preventive/corrective control actions Impact assessment of renewables on system security Verification of system protection schemes (SPS) Transaction settlement in power market Determination of active and reactive power reserve Scheduling of equipment maintenance Support to PMU/WAMS applications Calibration and validation of power system models Preparation of models for system studies Post-mortem analysis of incidents System restoration
Illustration of power transfer limit analysis Assume that a system is operating at a condition ( A ) Measured by some system parameters (e.g. interface flows) Determined to be secure for all credible contingencies We need to know what is the secure region within which the system can move If the system needs to move to an insecure point for some reason, what needs to be done to ensure the system security For example, special protection system settings Interface Y Stability limit Extended security region Y 0 A Stability limit X 0 Interface X
What do we gain with such limit analysis? Increased degree of system security More opportunities for power market participants Real-time calculated limits are generally higher than the planning limits Lower cost for congestion management The monthly credit paid by IESO (the ISO in Ontario, Canada) averaged $11.7m during 2003-2007 Higher level of renewable export A recent study by ERCOT (the ISO in Texas, USA) discovered that the limits based on-line DSA could allow as much as 400 MW more wind export from its western region (this is more than 10% of the total transfer capacity) Transfer on the interface Real-time limit Planning limit Time
Does on-line DSA fit for the job? Two model validation examples done by ISO New England Fault at a 345 kv line followed by successful reclosing Bus voltage shown PMU recording On-line DSA simulation Blocking of one pole of an HVDC link due to a fault followed by the blocking of the second pole MW flow on an AC line shown
Application Example: BC Hydro Major transfers are constrained by stability SPS (generator tripping) is used to ensure system security Real-time generator tripping arming requires on-line lookup table A pattern matching (PM) method has been used which relies on off-line computed lookup tables This no longer meets the demand from system operation The PM method is being phased out with the on-line DSA technology Both voltage and transient criteria are examined
Application Example: BC Hydro (Cont d) The on-line DSA system runs every 4 minutes to determine Gen tripping required for the current transfer Gen tripping required to achieve max transfer Gen tripping requirement Secure Insecure Min gen tripping Min gen tripping Power transfer Current transfer Max transfer
Application Example: National Grid UK Motivation for on-line stability analysis (OSA) 60 GW island system with DC Interconnection to Europe Renewables brought more uncertainty Off-line studies no longer adequate Capabilities of the OSA Including both transient stability and damping criteria 3,000 bus system model 2,000 contingencies (N-1, N-2, detailed) 15-min computation cycle with 40 CPU cores
Application Example: National Grid UK (Cont d) A special study mode enables engineers to quickly perform studies for various scenarios based on real-time system conditions Benefits achieved Transient stability risks identified, which were not previously known Damping risks identified including one involving a group of 8 GW generation, which were not previously known Instability risks at special operation conditions (hydro units in pumping mode, circuit switching for voltage control, etc.)
Application Example: Transpower New Zealand Ensuring acceptable frequency response after the loss of a large unit or HVDC bi-pole is critical to system operation Appropriate active power reserve is required A Reserve Management Tool (RMT) is used for this purpose in New Zealand Electricity Market RMT runs in the market settlement cycle Full time-domain simulations with reduced network model but detailed dynamic models About 30 sec to solve 6 contingencies Tight integration with market data Expected cost saving in New Zealand Electricity Market in 10 years US$12m
Looking ahead Development of on-line DSA technology is still very active A particularly exciting direction is to combine the power of the measurement-based technology (PMU or WAMS) and the modelbased technology (on-line DSA) to offer the total solution for power system security We may also witness the day when on-line DSA becomes a mandatory and standard function in control rooms... and hopefully we will never see this scene again August 14, 2003, Manhattan, New York City