TEPCO's experiences of automatic voltage controllers and SIPS as measures to prevent massive power outages

Transcription

1 TEPCO's experiences of automatic voltage controllers and SIPS as measures to prevent massive power outages Shinichi Imai, P.E. Teruo Ohno The Tokyo Electric Power Company, Inc. 1

2 The Tokyo Electric Power Company, Inc Wholesale: J-POWER (EPDC) The Japan Atomic Power Company, etc. Chugoku EPCO Okinawa EPCO Hokuriku EPCO Chubu EPCO Hokkaido EPCO Kansai EPCO Shikoku EPCO Kyushu EPCO Tohoku EPCO Tokyo EPCO North Latitude East Longitude Corporate Outline as of March 31, 2006 Date of Establishment: May 1, 1951 No. of Shareholders: 801,025 Electricity Sales: 4,630 billion (Approx. US$38.6 bil.) No. of employees: 38,235 No. of Customers: 27,780 thousand 75.3 GW Generations 14.1GW; Hydro 10.3GW; Oil Fired 3.2GW; Coal Fired 27.7GW; Gas Fired 18.2GW; Nuclear 1,572 Transmission Substations 28,693 circuit kilometers of transmission lines million electric customer accounts. Peak System Load 64.3 GW, 280 GWh 2

3 Contents Background; TEPCO s SIPS Observations on recent blackouts and related controllers & schemes in TEPCO August 14, 2003 Northeastern U.S. blackout Automatic Voltage Controllers and UVLS in TEPCO November 4, 2006 European blackout Adaptive load mitigation schemes & UFLS in TEPCO TEPCO s SIPS against short term instability and actual operational experiences Islanding protection system with P&Q balancing control 1999 and 2006 Tokyo power outages Summary 3

4 Background TEPCO s System Integrity Protection Schemes 4

5 TEPCO s SIPS Automatic actions by SIPS Overloading Voltage Instability Frequency Drop Transient Instability System Islanding Bus-coupler switching Tripping of pumped-hydros Generation runback/pickup Load shedding High side voltage control; PSVR Shunt switching; VQC Load shedding; UVLS Tripping of pumped-hydros BTB controls Load shedding; UFLS Fast generation rejection Shunt switching Load shedding 5

6 Features of TEPCO s SIPS Flat and centralized architecture inside substations or covering coherent subsystems Response based actions using on-line information rather than pre-determined actions like traditional RAS 2 out of 3 or 3 out of 4 voting redundancy ensuring security and dependability Custom designed microprocessor based relay and controller without using SCADA based information rather than utilizing industrial purpose Programmable Logic Controllers Based on co-development project with Japanese relay manufactures 6

7 Observations on recent blackouts and related controllers & schemes in TEPCO 7

8 Observations on 2003 US Blackout The loss of the Eastlake 5 unit did not put the grid into an unreliable state. However, the loss of the unit required the utility to import additional power to make up for the loss of the unit s output (612 MW), made voltage management in northern Ohio more challenging, and gave FE operators less flexibility in operating their system. (Final Report by US-Canada TF) After the loss of Sammis-Star 345kV line (Event 8), the voltage began a severe decline, which means n-8 contingencies caused voltage instability. (ECAR report) Installing shunt capacitors to transmission level can avoid tripping of critical generator 8

9 Coordination of voltage schedule and automatic voltage controllers in TEPCO PSVR AVR AVR AVR AVR PSVR PSVR PSVR 550kV Summer Peak 535kV Summer Peak Switching 545kV Normal 500kV power grid Shunt Shunt 525kV Normal Tap changing Switching Shunt Shunt VQC Transmission voltage schedule maintained High & Flat by reactive supplies from Gens and MSCs at S/Ss 50% at Gens and 20% of MSCs reserved in peak demand High side voltage control (PSVR) at reinforces reactive supply capabilities of Gens Fast switched shunts with numerical controllers can be regarded as dynamic resources Power system performance can be ensured against unexpected contingencies by a response-based control Automatic controllers effective to relieve operator s burden during emergency to stop or limit cascading 9

10 UVLS as Last Resort Installed just after 1987 Tokyo Blackout: Longest operation history of the world Microprocessor-based relaying Voltage collapse is detected: by central units located in the 500kV network, because 275kV or lower voltage are regulated by tap changing based on 3 out of 4 decision making logic to avoid unwanted operation Central units detect: Voltage Drop (Under Voltage) Rate of Voltage drop (dv/dt) CU 275kV,154kV radial network 500kV Main Grid Communication; Measured 500kV voltages CU CU Communication; Voltage collapse detection result RTU RTU CU Sub-Station 275,154/66 Sub-Station 275,154/66 (CU: Central Unit) 10

11 Observations on 2006 European Blackout Overloading; The overloading mitigation action led to result which was contrary to what operators expected Possible solution for overloading; Automatic mitigation to relieve operator s burden during emergency and to avoid cascading Actions would be adaptive in step by step manner with priorities until the overloading would be relieved. Frequency decay in western Europe Missing import from the East of 8940MW resulted total shedding of 17000MW of loads and 1600MW of pumps Coordination of underfrequency shedding/tripping schemes among TSOs may be reviewed to reduce the customer interruptions as much possible. 11

12 TEPCO s OLR (Overload Relay) Automatic load mitigation scheme When transmission lines or transformers are overloaded Generation Stations Rapid Output Control Selective Generator Shedding OLR Send out control signal Substations Load Shedding Generation controls with faster time delays executed prior to load shedding with slower time delays Automatically Relieve Overload in Network Facilities Prevent Unnecessary Trippings and Outages 12

13 TEPCO s UFLS with various time delays Increase timer settings for each frequency level. Settings Time Delay Shed loads s 4% (58.2) 1.0s 4% Hz 2.0s 4% 3.0s 4% 40% (Level2) 9.0s 4% 48.0 (57.6) Hz (Level3) 0.2s 8% 0.5s 8% 1.0s 4% 2.0s 4% 6.0s 4% 40% Shed load step by step. 13

14 TEPCO s SIPS against short term instability and actual operational experiences 14

15 Power system supplying to central Tokyo area SAIDI for Central Tokyo Area is less than one minute Radial operated to avoid high fault current and can be switched to adjacent system from different 500kV substations. Neither series reactors nor FCLs. Easy to know contingency flows, no loop flow problems and no cascading outages. No need for on-line contingency processor. Loss of parallel circuits on single tower can cause power outage in downstream system, which can be restored within 30 to 60 minutes by manually switched to adjacent system in each voltage level of 275, 154 and 66kV. Some amounts of generators connected to 154kV power systems in Tokyo bay area. Some systems including power stations are intentionally islanded with vital area by SIPS(UPSS). Training for operators is critical for fast system restoration. 15

16 TEPCO s bulk power grid 500kV 500kV 275kV 500kV 500kV; Meshed configuration and meshed operation 275kV and below; Meshed configuration and Radial operation Metropolitan Area including Tokyo 16

17 Bulk power system configuration 275kV OH Double Circuit Tower Caps; 3 to 4 GW in central Tokyo area 500kV Bulk Power Backbone Central Tokyo Area 275kV UG Triple Circuit Lines Caps; 1 to 2 GW 17

18 Bulk power system configuration in central Tokyo area Normally Opened 18

19 (NOTE) CU RTU Conceptual Diagram of UPSS 500kV & 275kV Overhead Transmission Line 275kV Under-ground Cable Line 154kV Under-ground Cable Line 66kV Under-ground Cable Line Central Unit Detects system separation. Calculates the balance of P and Q. Sends commands to RTUs. Remote Terminal Unit Measures P and Q. Trips feeders based on the command from CU. Opens or closes shunts and cables based on the command from CU. 500kV Power Grid 500kV 275kV Loss of mains Grid Network Radial System Metropolitan Area RTU UVR, UFR, f D ps CU C ss A ss B ss ShR 275kV L 154kV Load Shedding RTU ShR switching Intentional Islanding UVR, UFR, f L L L L L L Generators Sh.R Load UVR, UFR, f Load Shedding RTU Load Load Shedding RTU UVR, UFR, f 19

20 UPSS Controls both P and Q balance of Islanded System P Balance To Maintain the Frequency of the Islanded System. Shed Proper Amount of Load. Q Balance To Maintain Proper System Voltage. Switch on and off shunt capacitors and reactors. Switch off Cables if shunt control is not enough. UPSS watches the system condition every 2 seconds and determines how to control if the system becomes islanded. 20

21 Actual Operation of UPSS on August 14, 2006 Outline of the Outage Date: August 14, 2006 Interrupted Power: 2,160MW (1.39 million households are affected.) Area: A portion of Tokyo metropolitan area and neighboring area Duration: 0-59min Cause: One of 275kV major routes is Lost. Islanded System Scale: 620MW (310MW ACC Generator x 2) No.1 Line No.2 Line No.1 line No.2 line Faults Faults Faults 21

22 A Crane Vessel Crashed into Transmission Lines. No.1 Line No.2 Line Upper Pha ses Middle Phases Lower Phases 16.2m (53feet) Distance between lower phases and surface of the river Conductors of lines were severely damaged 22

23 Outline of UPSS Operation Result UPSS controlled PQ balance to maintain the islanded system Shed Load 66kV Bus Main Grid 275kV Bus 154kV Bus Shed Load: 666.5MW, MVar Switch on Shunt Capacitors: 80MVar Switch on Shunt Reactor: 70MVar Trip Cable including Tr: 163MVar Outage Area: 839MW 275kV Cable 154kV Bus Shed Load Shed Load Shed Load Shed Load No.1 Cable Off Q1: 146MVar Q2: 311MVar P: 620MW 154kV Bus 2 ACC Units SC On 66kV Bus 275kV Bus Main Grid P: 1,440MW Q: -40MVar Double circuit lines triped Shed Load ShR On P: 668MW Q: -345MVar 154kV Bus 66kV Bus Shed Load 66kV Bus 154kV Bus ShR On 23

24 UPSS Detected System Separation in 0.4 Second by Exceeding Phase Angle Difference. Frequency[Hz] Frequence[Hz] Main Grid Frequency System Separation Phase Angle Difference 0.4Sec :37:52.0 7:37:52.5 7:37:53.0 7:37:53.5 7:37:54.0 Time Setting (110 ) Islanded System Frequency Phase Angle Difference Phase Angle Difference 24

25 The Frequency and Voltage of the islanded system recovered in a few seconds Frequency[Hz] Nominal Frequency(50Hz) Islanded System Frequency 48.4 System Separation 7:37:50 7:37:52 7:37:54 7:37:56 7:37:58 7:38:00 7:38:02 Time Voltage[PU] Voltage of BUS A Voltage of BUS B Nominal Voltage(1PU) 0.7 Fault 0.6 7:37:50 7:37:52 7:37:54 7:37:56 7:37:58 7:38:00 7:38:02 Time 25

26 Air Plane Crash Another UPSS Operation history on November 22, GW Lost Hz Hz System Separation Synchronized to main grid Outage Area 498 Main grid Islanded system Hz 13 minutes 13:40 13:42 13:44 13:46 13:48 13:50 13:52 13:54 13:56 Islanded Area The Most Important Area 400MW 26

27 Islanded System Automatic Synchronizer Now: We rely on manual operation for system reconnection. Near Future: System reconnection will be done automatically. Main Grid Synchronizing Point 275kV 275kV Islanded Area fm, θ m Open Close fi, θi Power Plants 154kV 154kV Loads Substations 66kV Islanding System Automatic Synchronizer UPSS (Urban Power System Stabilizer) UPSS activate Detect the system islanding Command to close disconnectors Command to reconnect the islanded area and Main grid Check the synchronizing condithion < 0.3Hz is decreasing Close circuit breakers at the timing of fm, θ is m nearly 0. ISAS is now under development and will commence operation in July,

28 Challenges for future Retaining and keeping expertise especially for system design and testing Accelerated obsolescence of microprocessor based technology and spare parts problem Utilization of standardized technologies, products and communication protocols Sophisticated automated system restoration Coordinated setting and tuning among voltage controllers and SIPS by conducting many numerical calculations by more efficient manner Utilization of fast, reliable and high accurate data and information collected from whole of TEPCO s power system with synchronization. 28

29 Questions or Comments 29

30 VQC (Voltage Q Controller) 500kV Bus Detect Voltage Basic concept of VQ Control 275kV Bus voltage 275kV Bus Tap change SC, ShR switch VQC Down Tr tap SC on ShR off DEAD BAND SC off ShR on Raise Tr tap VQ Controller automatically controls Tr tap and Shunts according to Bus Voltages 500kV Bus voltage 30

31 Relaying Algorithm for Rate of Change of Frequency Detect high-speed rate of frequency decline. ROCOF settings Shed loads s 8% (58.8) Hz 1.0s 16% 48.0 (57.6) Hz 0.5s 24% 0.4s 32% For fast load shedding in case of large L-G imbalance. Measures Tc instead of df/dt. 31

32 Effect of ROCOF and Level+Timer Time Frequency characteristic Lowest tolerant frequency (in TEPCO s policy) Lowest frequency is raised (improved). Accommodate to TEPCO s policy in case of severe L-G imbalance such as 40%. 32

33 How to Detect System Separation? Phase Angle Difference between Islanded System and Main System Phase Angle Difference >110 Voltage Sag of Islanded System Voltage of Islanding system < 0.6pu (Sagged) Voltage of Main grid > 0.94pu (Normal) & >1 & Activate UPSS Distance Relay (Avoid Unnecessary UPSS operation during faults.) Note: Not Just Checking Status of the specified CBs. Whatever the system configuration is, UPSS must be able to detect system separation properly. 33

34 Measurement of phase angle difference Synchronized Sampling Master unit Slave unit Calculation of Phase Angle Difference Va Vb Va(m-3)= VaSin( ) Vb(m-3)= VbSin( -90 ) T Sampling Interval Tm Timing Flag Sampling Interval Synchronized 90 T Timing Flag Ts Va(m)= VaSin( + ) Vb(m)= VbSin( ) T Sampling = Ts - Tm 0 (Adjust Sampling Timing) 2 Assume delay times of both Upstream and Downstream are the same. -1 Va(m)Vb(m) + Va(m-3)Vb(m-3) =Cos ( ) Va Vb x x VaSin( + ) VbSin( ) + VaSin( ) x VbSin( -90 ) =VaSin( + ) VbSin( ) + VaCos( + ) x VbCos( ) =VaVbCos( + - ) =VaVbCos( ) Note: We don t rely on GPS for vital protection systems. 34

35 Power Station 66 kv 66 kv L L Substation Simplified Power System Model for Active & Reactive Power Balance Calculation L SC L Substation 154kV L L L Substation 154kV L Substation β1 Q1 L 275kV ShR L α 275kV X β2 Q2 P Failure 275kV Main Grid P: Excess Active Power which was received from the main grid. The same amount of load must be shed to maintain the frequency. Q1, Q2: Reactive Power which was passing the central transformer of the islanded system must be maintained to keep voltage proper. α : Detection point of receiving Active Power which is used for Load shedding Calculation. β : Detection points of passing Reactive Power which is used for Voltage Control Calculation. 35