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If I were to give grades today… > 80 78-80 76-78 70-76 68-70 66-68 60-66 58-60 56-58 50-56 48-50 <48 A AB+ B BC+ C CD+ D DF 8 2 4 7 5 4 7 1 1 8 1 2 =(0.2*Ex1+0.2*Ex2+0.15*HW)/0.55 1 Notes on security assessment James D. McCalley 2 3 Types of security violations & consequences Security Overload Security Xfmr overload Line overload Cascading overloads Voltage Security Low Voltage Dynamic Security Unstable Voltage Slow voltage collapse Fast voltage collapse Earlyswing instability Oscillatory instability (damping) Smalldisturbance instability Largedisturbance 4 instability Types of security violations & consequences Overloaded xfmr/line has higher tripping likelihood, resulting in loss of another element, possible cascading, voltage or dynamic insecurity Overload Security Xfmr overload Line overload Cascading overloads Dynamic security can result in loss of generation; growing oscillations can Security cause large power swings to enter relay trip zones Voltage Security Dynamic Security Low voltageUnstable affects EarlyOscillatory Low swing instability load and generation Voltage Voltage instability (damping) operation. Voltage instability can result in widespread loss SmallLargeSlow Fast of load. voltage collapse voltage collapse disturbance instability disturbance 5 instability Traditional assessment & decision The NERC Disturbance-Performance Table DyLiacco’s operational decision paradigm System operating limits 6 NERC Disturbance-Performance Table 7 NERC Disturbance-Performance Table, cont 8 NERC Disturbance-Performance Table, cont 9 Normal One Element Out of Service Two of More Elements Out of Service Extreme Events (Two or More Elements Out of Service) Single Contingency (Forced or Maint) Category B Event B Results In: •No Cascading •No load loss •No overload •No voltage limit violation •Possible RAS operation Prepare for Contingency •Implement Limits Prepare for Next Contingency •Limit Import/Export •Curtail Generation •Shed Load B Single Line Ground (SLG) or 3-Phase (3Ø) Fault, with Normal Clearing on: 1. Generator 2. Transmission Circuit 3. Transformer Or loss of an element without a fault. 4. Single Pole Block, Normal Clearing of a DC Line Single Contingency (Category B Event) B Category C event: A first contingency, followed by adjustments, followed by a second contingency) •No Cascading •May Result In: •Generation curtailment •Load shedding •Import/Export reductions •Safety Net operation Prepare for Next Contingency •Limit Import/Export •Curtail Generation •Shed Load 10 Normal One Element Out of Service Two of More Elements Out of Service Extreme Events (Two or More Elements Out of Service) Multiple Contingencies – Category C Event C1-8 C1-3 SLG Fault, with Normal Clearing: 1. Bus Section 2. Breaker (failure or internal fault) SLG or 3Ø Fault, with Normal Clearing. 3. Category B (B1, B2, B3, or B4) contingency, manual system adjustments, followed by another Category B (B1, B2, B3, or B4) contingency C4-8 •No Cascading •May Result In: •Generation curtailment •Load shedding •Import/Export reductions •Safety Net operation Prepare for Next Contingency •Limit Import/Export •Curtail Generation •Shed Load 4. Bipolar (dc) Line Fault (non 3Ø), with Normal Clearing: 5. Any two circuits of a multiple circuit towerline SLG Fault, with Delayed Clearing and (stuck breaker or protection system failure): 6.Generator 7.Trans Circuit 8. Xmer 9. Bus Section Extreme (Category D) Event – May originate from any Operating State D1-14 D12-14 12. Failure of a fully D1 3Ø Fault, with Delayed Clearing (stuck breaker or protection system failure): 1. Generator 2. trans Circuit 3. Xmer 4. Bus Section 3Ø Fault, with Normal Clearing: 5. Breaker (failure or internal fault) 6. Loss of tower line with 3 or more ckts 7. All trans lines on a common right-of way 8. Loss of a subs (one voltage level +Xmer) 9. Loss of a switching st (one voltage + plus Xmer) 10. Loss of all generating units at a station 11. Loss of a large load or major load center redundant special protection system (or remedial action scheme) to operate when required 13. Operation, partial operation or misoperation of a fully redundant special protection system (or remedial action scheme) for an event or condition for which it was not intended to operate 14. Impact of severe power swings or oscillations from disturbances in another Regional Council. •No Cascading •May Result In: •Generation curtailment •Load shedding •Import/Export reductions •Safety Net operation Prepare for Next Contingency •Limit Import/Export 11 •Curtail Generation •Shed Load DyLiacco’s operational decision paradigm Normal (secure) Restorative Extreme emergency. Separation, cascading delivery point interruption, load shedding Alert, Not secure Take corrective actions Emergency 12 System operating limits (SOLs) The value (such as MW, MVar, Amperes, Frequency or Volts) that satisfies the most limiting of the prescribed operating criteria for a specified system configuration to ensure operation within acceptable reliability criteria. System Operating Limits are based upon certain operating criteria. These include, but are not limited to applicable pre- and post-contingency… •Facility Ratings •Transient Stability Ratings •Voltage Stability Ratings •System Voltage Limits There is a subset of SOLs that are known as Interconnection Reliability Operating Limits (IROL). IROLs are defined as, “The value (such as MW, MVar, Amperes, Frequency or Volts) derived from, or a subset of the System Operating Limits, which if exceeded, could expose a widespread area of the Bulk Electric System to instability, uncontrolled 13 separation(s) or cascading outages.” Cascading outages – the public perception…. 14 System operating limits 300 MW Question 1: Is it “secure”? Bus 2 X23=1 X12=1 900 MW X13=1 Bus 1 Bus 3 Continuous rating=1200MW Emergency rating=1300 MW 1200 MW Question 2: What is maximum cct 1-3 flow such that reliability criteria is satisfied? 15 Treating power as if it is current…. V1 V2 P12 PG2 jx12 PG1 PD1 PD2 A very basic relation for power system engineers expresses the real power flow across a transmission circuit as: P12 V1 I12 cos (1) Here, φ is the angle by which the voltage leads the current and is called the power factor angle. If we assume that electric loads are purely resistive, so that only real power flows in the network, then φ≈0 (φ will not be exactly zero because of line reactance). In this case, eq. (1) is: P12 V1 I12 (2) 16 Treating power as if it is current…. A basic fact of power system is that the voltages usually do not deviate significantly from their nominal value. Under a system of normalization (called per-unit), where all voltages are normalized with respect to this nominal voltage, it will be the case that |Vk|≈1.0. As a result, eq. (2) becomes: P12 I12 (3) In other words, the numerical value of the real power flowing on the circuit is the same as the numerical value of the current magnitude flowing on that circuit (under the system of normalization). If, again, the electric load is purely resistive, then all currents will have almost the same angle, and one can treat the current magnitude as if it were the current phasor. Useful conclusion: If we assume voltage magnitudes are all unity, and all loads are purely resistive, then whatever rules we have of dealing 17 with currents also work with real pu power flows! (or Sbase×pu pwr flws) Two good approximations for parallel flows 1. Current division: For 2 parallel paths A and B, power flows on path A according to PTotal XB XA XB Bus 2 300 1 900 300 2 1 X23=1 X12=1 900 MW X13=1 Bus 1 2 900 600 2 1 900 MW Bus 3 18 Two good approximations for parallel flows 1. Current division: For 2 parallel paths A and B, power flows on path A according to PTotal 300 MW 300 XB XA XB Bus 2 1 100 2 1 300 X23=1 X12=1 2 2 1 200 X13=1 Bus 1 100 Bus 3 300 MW 19 Two good approximations for parallel flows 2. Superposition: Results of 2 independent calculations will add Bus 2 300 MW 300 100 Total=500 300 200 Total=200 900 MW Total=700 Bus 1 600 100 Bus 3 1200 MW Continuous rating=1200MW Emergency rating=1300 MW IS IT SATISFYING RELIABILITY CRITERIA? 20 System operating limits 300 MW Bus 2 The answer to Question 1: Is it “secure”? Lose Cct 2-3! 900 MW Total=1200 Bus 1 Bus 3 1200 MW Continuous rating=1200MW Emergency rating=1300 MW IS IT SATISFYING RELIABILITY CRITERIA? YES!!! 21 System operating limits Bus 2 300 MW Total=500 Total=200 900 MW Total=700 Bus 1 Bus 3 Question 2: What is maximum cct 1-3 flow such that reliability criteria is satisfied? 1200 MW Depends on how flow is increased: assume stress direction of Bus1/Bus3. Desire precontingency limits to 22 reflect postcontingency effects System operating limits Bus 2 300 MW 333 100 Question 2: What is maximum cct 1-3 flow such that reliability criteria is satisfied? Total=533 333 200 Total=233 1000MW Total=767 Bus 1 667 100 Bus 3 1300 MW Continuous rating=1200MW Emergency rating=1300 MW IS IT SATISFYING RELIABILITY CRITERIA? 23 System operating limits 300 MW Bus 2 Lose Cct 2-3! 1000MW Total=1300 Bus 1 Bus 3 Continuous limit=1200MW Emergency limit=1300 MW IS IT SATISFYING RELIABILITY CRITERIA? 1300 MW It is right at the limit! 24 System operating limits Bus 2 300 MW Total=500 Total=200 900 MW Total=700 Bus 1 SOL=767 Bus 3 Question 2: What is maximum cct 1-3 flow such that reliability criteria is satisfied? 1200 MW Answer 25 Illustration of real-time calculation of operating security limits w/ DTS What is dispatcher training simulator? PTDF and OTDF Automatic calculation of SOL Sample system 26 What is the DTS? An off-line environment that: Emulates an energy control center's EMS Simulates the physical power system DTS uses the same interfaces and is composed of much of the same software as the real-time EMS 27 PTDF and OTDF Power transfer dist. factors: PTDFcct k bus b Change in Flow of cct k [Change in injection of bus b] Outage transfer dist. factors: OTDFcct k cct j Change in Flow of cct k Flow on outaged cct j 28 PTDF and OTDF Power transfer dist. factors: Change in Flow of cct k PTDFcct k [Change in injection of bus b] bus b Outage transfer dist. factors: Change in Flow of cct k OTDF cct k [Flow cct j on outaged cct j] We will later show how to compute SOL using PTDFs ali and LODF dl,k 29 Automatic calculation of SOLs More than identifying contingencies that result in violations, it identifies the LIMIT Overload security only Uses PTDFs, OTDFs, stress direction SOL for each cct computed as most restrictive of Normal condition, using continuous rating or All contingencies, using emergency rating Embedded in Areva’s DTS Updates SOL for all circuits every 8 sec 30 29 Outaged Line 24 25 26 30 27 28 Monitored Line 21 12 14 7 4 0 2 19 9 15 6 22 1 Outaged Line 17 23 20 16 10 3 18 31 310 MW 386 MW (7-28) 269 MW 825 MW (14-26) 37 MW 640 MW 269 MW (14-26) 797 MW (7-28) 143 MW 244 MW (27-28) 37 MW 269 MW (14-26) 195 MW 465 MW (21-24) More than identifying contingencies resulting in violations, it identifies LIMITS Current Time of DTS: 1/3/2000 3:01:01 AM 32 278 MW 319 MW (7-28) 139 MW 938 MW (14-26) 103 MW 301 MW (14-26) 610 MW 742 MW (7-28) 184 MW 280 MW (10-16) 103 MW 301 MW (14-26) 65 MW 457 MW (7-28) More than identifying contingencies resulting in violations, it identifies LIMITS Current Time of DTS: 1/3/2000 6:00:23 AM 33 89 MW 244 MW (7-28) 291 MW 716 MW (14-26) 163 MW 295 MW (14-26) 745 MW 834 MW (7-28) 267 MW 323 MW (10-16) 163 MW 295 MW (14-26) 75 MW 459 MW (25-26) More than identifying contingencies resulting in violations, it identifies LIMITS Current Time of DTS: 1/3/2000 8:00:05 AM 34 74 MW 224 MW (7-28) 311 MW 585 MW (14-26) 223 MW 839 MW 298 MW (14-26) 891 MW (7-28) 286 MW 341 MW (27-28) 223 MW 298 MW (14-26) 121 MW 438 MW (25-26) More than identifying contingencies resulting in violations, it identifies LIMITS Current Time of DTS: 1/3/2000 9:31:05 AM 35 56 MW 196 MW (7-28) 305 MW 759 MW (14-26) 325 MW 376 MW (14-26) 680 MW 779 MW (7-28) 392 MW 421 MW (10-16) 325 MW 376 MW (14-26) 285 MW 421 MW (25-26) More than identifying contingencies resulting in violations, it identifies LIMITS Current Time of DTS: 1/3/2000 11:01:31 AM 36 Flow vs. SOL (Picton:Brighton) 800 700 600 MW 500 400 300 200 100 0 1/3/2000 1/3/2000 1/3/2000 1/3/2000 1/3/2000 1/3/2000 1/3/2000 1/3/2000 1/3/2000 2:24 3:36 4:48 6:00 7:12 8:24 9:36 10:48 12:00 DTS time & day Line Flow SOL Security Margin Thermal Limit 37 SOL Equations: f 0 f f max We want f 0 that along with f would take the flow on the monitored cct to its max Computing SOL using PTDFs ali and LODF dl,k Following a P at node i and a - P at node j: f ai Pi aj Pj ai aj Pi Change on line k after a P on i and - P on j: f k aki akj Pi Outage of line k: f d , k f k0 d , k aki akj Pi Change on after P at node i and a - P at node j and outage of line k: f ai aj Pi d ,k f k0 d ,k aki akj Pi All the change on will be set to f max f 0 ai aj Pi d ,k f k0 d ,k aki akj Pi f max f max f 0 d ,k f k0 Pi ai aj d ,k aki akj f OSL f 0 ai aj Pi f OSL f 0 a i aj f max f 0 d ,k f k0 ai aj d ,k aki akj 38