ROLE OF PROTECTION SYSTEMS IN CATASTROPHIC FAILURES IN POWER SYSTEMS. A. G. Phadke

Transcription

1 ROLE OF PROTECTION SYSTEMS IN CATASTROPHIC FAILURES IN POWER SYSTEMS A. G. Phadke

2 Presentation outline: Some past blackouts in North America Why do blackouts occur? Defensive strategies Impact of evolving technologies Future prospects

3 Some past blackouts in North America

4 NORTH AMERICAN SYSTEM AT A GLANCE: 870 GW capacity Thermal: 71 % Hydro: 14 % Nuclear: 13 % Transmission: 320,000 circuit-km Transmission Voltages: 765, 500, 345, 138 kv

5 SOME MAJOR BLACKOUTS IN HISTORY: 1. North-East blackout of New York City blackout of Western blackout of North-East blackout of 2003

6 1. North-East blackout of New York City blackout of 1977

7 Buchanan Millwood Sprainbrook Farragut Ravenswood Sprainbrook

8 3. Western blackout of North-East blackout of 2003

9 Hurricane and Earthquake Losses Flood Losses times per year Once a year Outages Electric Network Outages 1984 Present Model Data Floods D = Earthquakes D = 0.41 Hurricanes D = 0.98 ~ about 38 years ,000 10,000 Loss Per event (million 1990 dollars) ~ about 50 million people

10 Why do blackouts occur?

11 WHY Blackouts DO BLACKOUTS are Rare Events: OCCUR? Nature of the synchronous AC power system Stressed system Outages Inappropriate control actions Cascading Loss of synchronism and blackout

12 Inappropriate control actions (1) Inappropriate protection system operations (2) Inappropriate control system operations (3) Inappropriate operator actions

13 (1) Inappropriate protection system operations Some Statistics from NERC Reports Report Year Cases with Relay system Involvement % % % % %

14 (1) Inappropriate protection system operations NERC report for % Event 1 Event 2 Event 3 Event 4 Event 5 Event 6 Power System Facilities X X X X Protection Systems X X X X X System Monitoring X X X Operators X X Operational Planning X X System Reserve Response Preventive Maintenance X X Load Relief Restoration X X

15 (1) Inappropriate protection system operations Hidden failures in a directional overcurrent relay: + Fault Transmission line with directional overcurrent relaying overcurrent TC 52a directional Control Circuit -

16 (1) Inappropriate protection system operations Hidden failures in three zone step distance relays Z2 T2 Z1 Z3 T3 Timer 2 TC 52a Timer 3

17 (1) Inappropriate protection system operations Concept of region of vulnerability due to hidden failures Relay with hidden failure

18 (1) Inappropriate protection system operations Loadability of backup zones X Power Swing Relay Characteristic Line Impedance Load increase R Loss-of-field

19 (2) Inappropriate control system operations Equipment malfunctions: excitation systems, HVDC, FACTS, SVC Tap changer controls Faulty control circuits: lockouts, etc. Faulty synchronizing controls

20 (3) Inappropriate operator actions Usually a contributing factor in all blackout scenarios. Recent examples: New York City blackout of 1977 August 14, 2003 blackout in North America Post-maintenance energization sequences (AEP) Inappropriate manual intervention (AEP)

21 Defensive strategies

22 CAN BLACKOUTS BE MADE LESS LIKELY? Stressed system Outages Inappropriate control actions Power system design to make stress less likely Random events beyond control More intelligent controls Cascading Design of a ductile system instead of a brittle system Loss of synchronism and blackout

23 Power system design to make stress less likely These are long term solutions, well known to power system engineers: - Sufficient generation margin - Adequate transmission access to load centers - Adequate reactive support - Accurate real-time monitoring - Security against N-k contingencies

24 More intelligent controls (1) Use of wide area measurements (2) Remedial action schemes (3) Adaptive protection

25 The main operational control we are concerned with are the HIGH SPEED controls, including protection High speed protection equipment Autonomous for speed Very large numbers High speed wide area measurements

26 A phasor measurement unit Analog Inputs GPS receiver Phase-locked oscillator Modems Anti-aliasing filters 16-bit A/D conv Phasor microprocessor

27 ADVANCED CONTROL FUNCTIONS Phasor based: Feedback based control Measurements Controller Controlled Device

28 Example of control with phasor feed-back Power demand Controller System A System B δ A - δ B Desired performance Performance with constant power control law time

29 Example 1: HVDC Controller G MVAR 3 phase fault cleared in 3 cycles 1640 MW 590 MVAR (200+j20) MVA 820 MW G 2

30 Example 1: HVDC Controller Control law 1: Constant current, constant voltage on HVDC Control law 2: Optimal controller δ 1 δ 2 t (seconds) 5

31 Adaptive Relaying Controlled Security & Dependability Protection No 1 Protection No 2 Protection No 3 System State Logic Arbitration Or And Vote Breakers To Circuit

32 Supervisory control for managing hidden failures Inputs from other IEDs R Relay with a high index of vulnerability Analog signals Hidden failure Monitoring and Control device Supervisory output

33 Remedial Action Schemes Wide Area Protection Schemes SPS or RAS System Protection Schemes came into being as control functions which required protection system interventions. Often the inputs may be derived from protection systems, and certainly the outputs of protection systems are used to execute the controls. Wide Area Protections The role is to prevent major system failures. Voltage instability, angular instability are the main driving considerations.

34 Remedial Action Schemes Wide Area Protection Schemes Example: S 1, S 2, S 3 L Large System P t P g If P t > P 0 And If P g > P 0 And If S 1 OR S 2 OR S 3 open Then Drop load L

35 Intelligent islanding possibilities (1) Traditional out-of-step relaying Blocking Tripping Zone andtimer settings (2) PMU based out-of-step relaying Pre-fault S-PMU Relay S-PMU Relay Post-fault Interval Observation Interval Prediction

36 Intelligent islanding possibilities (3) Real-time coherency determination Observation window PMU data

37 Intelligent islanding possibilities (4) Intelligent load shedding Under-frequency triggers Voltage stability margin triggers Supervisory control Remedial action schemes Islanding systems

38 Design of a ductile system instead of a brittle system (1) Concept of a brittle system (2) Use of high power electronic systems (3) Intelligent load shedding (4) Remedial Action Schemes (5) Intelligent islanding (6) Improved operator aids (7) Improved restoration strategies

39 Design of a ductile system instead of a brittle system Ductile and Brittle structures Initiating event Brittle System To achieve ductility, Initiating event New network elements New configurations Renewable architectures Ductile System

40 Strategic placement of controllable elements: Brittle System Contingency set which leads to catastrophic failures Contingency set which leads to catastrophic failures with strategically placed controllable elements

41 Monitoring signals Control Center Activation Signal Initiating Event Dormant Elements D P

42 EFFECTS OF OPEN ACCESS AND DEREGULATION A paradigm shift in load generation relationship Public good vs. stockholder good Lack of incentives for infrastructure improvements Restrictions on information exchange Lack of signals for future technical manpower needs