PERFECT TIMING CRAIG PREUSS, P.E. HOW IEEE STANDARD PC IMPACTS SUBSTATION AUTOMATION

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1 PERFECT TIMING HOW IEEE STANDARD PC IMPACTS SUBSTATION AUTOMATION CRAIG PREUSS, P.E. ENGINEERING MANAGER UTILITY AUTOMATION BLACK & VEATCH CORPORATION SUBSTATIONS C0 SUBCOMMITTEE CHAIR WORKING GROUP C7 MEMBER

2 PERFECT TIMING Why is Timing Important to a Smart Grid? Trusted Time What Time is It Today? What Time is It Tomorrow? Origins of Perfect Time P E R F E C T T I M I N G

synchronization accuracy should be accurate to 1 ms and utilize the most accurate method suitable for the application In 2009, NIST gets involved with Priority Action Plan 13 in the Smart Grid

3 3 WHY IS TIMING IMPORTANT TO A SMART GRID? W H Y I S T I M I N G I M P O R T A N T T O A S M A R T G R I D? August 14, 2003 blackout revealed gaps in substation time synchronization Utilities implement synchronization different ways, including not at all In 2009, NERC guidelines [1] state that time synchronization accuracy should be accurate to 1 ms and utilize the most accurate method suitable for the application In 2009, NIST gets involved with Priority Action Plan 13 in the Smart Grid Interoperability Roadmap Release 1.0 Time synchronization is the key to many Smart Grid applications NIST is focused on PMUs and IEC sampled measured values [1] NERC Security Guideline for the Electricity Sector: Time Stamping of Operational Data Logs version 0.995, available at 11_Clean.pdf

4 4 ARE THERE MORE THAN TWO APPLICATIONS? W H Y I S T I M I N G I M P O R T A N T T O A S M A R T G R I D? 1. Fault and disturbance recording devices (DFRs and DME) are governed by NERC PRC to be within 2 ms of UTC 2. SOE (typically 1 ms) 3. PMU IEDs (typically 1 μs) 4. Test equipment for synchronized end-to-end testing (typically 1 ms) 5. Reporting to RTU, EMS, and SCADA systems (typically 1 ms) 6. Sampled measured values in IEC require 1 μs 7. Traveling wave fault detection (towers located 800 ft apart represent 1.7 μs, so 100 ns is practical) 8. Lightning correlation (1 ms) 9. Accurate correlation of substation events with communication network events (1 s??) 10. Special protection schemes (50 ms or less depending on scheme requirements) 11. Smart meters and revenue meters require from 1 ms to 1 μs 12. Control of fast acting switches and actuators as low as 1 μs 13. Use of Time Synchronized Measurements in Protective Relay Applications PSRC H14

5 TIMING DEPENDENT APPLICATIONS Future PMU Protection Apps Fast Acting Control W H Y I S T I M I N G I M P O R T A N T T O A S M A R T G R I D? Phasor Measurements Sampled Measured Values Special Protection Schemes Travelling Wave Fault Loc. SCADA/EMS/SAS/DMS/DA Test Equipment Comm. Network Correlation Lightning Strike Correlation Event/Disturbance Recorders SOE Metering Operations Forensics Accuracy 0.5s 1ms 1 s

6 6 WHAT DO STANDARDS REQUIRE? W H Y I S T I M I N G I M P O R T A N T T O A S M A R T G R I D? IEEE Std C Clocks be set an order of magnitude greater than the actual timing requirement A requirement for 1 ms requires the clock to be accurate to 0.1 ms PSRC H3 is working on PC Recommended practice for time tagging of power system protection events in protective relays Similar work starting in SUBS IEC Time Performance Ranges There is a need for sub-microsecond accuracy in the Smart Grid!

Measurement Telecommunication Protects equipment

SCADA/EMS/DMS DA SA Generation Metering at

current, phase Private SDH/SONET networks for

7 WHAT TIME IS IT? W H Y I S T I M I N G I M P O R T A N T T O A S M A R T G R I D? Protection Control Systems Metering & Measurement Telecommunication Protects equipment Includes event/disturbance recorders SCADA/EMS/DMS DA SA Generation Metering at substations / customer Transducers for voltage, current, phase Private SDH/SONET networks for secure voice and data communication (SCADA) By-product: Time stamped data Result: Time stamped data Result: Time stamped data Input: Frequency

ATTRIBUTES OF TRUSTED TIME T R U S T E D T I M E Absolute time matters when Applications function across the Smart Grid (beyond the substation) It changes the measurement quality The measurement

8 ATTRIBUTES OF TRUSTED TIME T R U S T E D T I M E Absolute time matters when Applications function across the Smart Grid (beyond the substation) It changes the measurement quality The measurement affects grid security (wide area control and protection) NERC PRC compliance counts Is our timing system trusted? Trusted time is accurate, secure, and deterministic GPS is the standard time source GPS is not under your control, and is subject to external influences PRC Disturbance Monitoring Equipment Installation and Data Reporting

9 IS GPS A TRUSTED TIME SOURCE? Satellite Outages T R U S T E D T I M E GPS Jammers Personal Privacy Devices RF, Climatic & Solar Interference

10 IS GPS SUFFICIENT? T R U S T E D T I M E Does the GPS system meet the N-1 contingency requirements Substations are designed to N-1 criteria Protection is designed to N-1 criteria Telecommunication networks assume GPS can fail (Cesium) Should we depend solely on GPS for time sensitive applications? How can we backup the time source? How can we survive temporary outages? N-1 Contingency Withstand the loss of any one item of plant/component without loss of load or adverse voltage outcome

BACKING UP THE TIME SOURCE Holdover Use a stable cesium oscillator to control drift over extended outages. This does not address clock failure.

11 BACKING UP THE TIME SOURCE Holdover Use a stable cesium oscillator to control drift over extended outages. This does not address clock failure. IRIG-B IRIG-B over TDM Transporting IRIG-B over the TDM communication network (VoIP does not transport IRIG-B well) NTP NTP over Ethernet Transporting NTP over the Ethernet/enterprise network (Not accurate enough) 1588-v2 IEEE A standards based time and frequency dissemination over Ethernet with a high rate of adoption (driven by mobile and industrial automations sectors)

12 SMART TIMING FOR A SMART GRID? NTP Multiple GPS (per Unit) GPS IRIG-B Generation Master Clock W H A T T I M E I S I T T O D A Y? Time Synchronization ASCII (NTP) Control Center(s) DNP3 IRIG-B Transmission & Distribution Multiple GPS (project based)

13 14 WHAT TIME IS IT? W H A T T I M E I S I T T O D A Y? IRIG-B de facto time synchronization standard in substations Achieves microsecond precision Supported by many satellite clocks and IEDs Requires Satellite clock and antenna Dedicated timing wire Engineering calculations Careful design Existing time distribution does not seem too smart!

14 15 SATELLITE CLOCK AND ANTENNA W H A T T I M E I S I T T O D A Y? US Department of Defense Global Positioning Satellite (GPS) system Accuracy better than 10 nanoseconds Signals received by antenna Clock calculates distance to at least four satellites Clock calculates propagation delay Inaccuracies introduce between 20 and 500 ns delay

15 16 DEDICATED TIMING WIRE W H A T T I M E I S I T T O D A Y? A separate timing wire is required Coax (with proper taps and terminations) Twisted shielded pair (TSP) Timing wire is installed next to serial and network connections to relays. Source: IEEE 1588 for Time Synchronization of Devices in the Electric Power Industry Fred Steinhauser, Christian Riesch, Manfred Rudigier ISPCS 2010, Portsmouth

16 17 ENGINEERING CALCULATIONS W H A T T I M E I S I T T O D A Y? Satellite clock outputs Need to calculate load so clock is not overloaded Need to ensure voltage drop is not below minimum input on IEDs Need to ensure voltage is not above maximum input on IEDs

17 18 CAREFUL DESIGN W H A T T I M E I S I T T O D A Y? Timing wire distances should be limited to between 50 and 100 feet Proper termination to avoid ringing and reflections Status of time synchronization May be available in some IEDs Not well documented Rarely implemented

Interlocking Logic GENERATION 1 SUBSTATION

IRIG-B IRIG-B Hardwired Parallel Copper Cabling

Relay Relay IED IED Hardwired Parallel Copper

18 Interlocking Logic GENERATION 1 SUBSTATION ARCHITECTURE Control Center RTU HMI/Mimic IRIG-B IRIG-B IRIG-B Hardwired Parallel Copper Cabling (Relay Room) W H A T T I M E I S I T T O D A Y? Relay Relay IED IED Hardwired Parallel Copper Cabling (HV Yard) Switchgear CT/PT (VT) Switchgear CT/PT (VT)

Substation Clock W H A T T I M E I S I T T O D A Y?

19 GENERATION 2 SUBSTATION ARCHITECTURE Control Center HMI Station Controller Gateway Communication Bus Vendor protocols such as LON, MVB, DPS, Profibus, FIP, DNP 3.0, Modbus, etc. Substation Clock W H A T T I M E I S I T T O D A Y? IED IED IRIG-B IRIG-B IRIG-B IRIG-B IRIG-B IRIG-B IED IED Hardwired Parallel Copper Cabling (HV Yard) Switchgear CT/PT (VT) Switchgear CT/PT (VT)

20 21 STATUS QUO W H A T T I M E I S I T T O M O R R O W? Not scalable to the smart grid Substantially more devices than a substation Highly distributed environment Lots of antennas because devices are too far apart

21 DISTRIBUTING TIME TOMORROW Atomic Clock Optical PHY 1588 Grandmaster 1588 Grandmaster IEEE 1588 IEEE Grandmaster IEEE 1588 W H A T T I M E I S I T T O M O R R O W? Atomic Clock IEEE 1588 Power Profile Legacy (IRIG-B, PPS..) 2.048Mhz / 2.048mbps Telecom Switch Relaying & IED s 1588 Slave/ Grandmaster IEEE 1588 Slave / GPS Backup Function Station Bus LAN RTU

22 THE SMART SUBSTATION Control Center HMI Station Controller Gateway Substation Clock IEEE C Timing (IEEE 1588 Power Profile) IEC / Station Bus W H A T T I M E I S I T T O M O R R O W? Communication Bus Bay Controller IEEE C Timing Intelligent Switchgear IED Relay Next Generation CT/PT (VT) Bay Controller Merging Unit IED IEC / Process Bus Switchgear CT/PT (VT)

23 LEGACY IEDS IN A SMART SUBSTATION W H A T T I M E I S I T T O M O R R O W? 1588 slave clocks can generate IRIG-B or SNTP for downstream devices. Ethernet switches an obvious place. Transition from IRIG-B and SNTP to 1588 will be gradual. A simple migration path is essential for success. Serial and Ethernet IEDs need bridge between 1588 and legacy time sync protocols.

24 25 BENEFITS OF SMART TIMING W H A T T I M E I S I T T O M O R R O W? Ethernet network protocol Re-use Ethernet network asset (should support 1588) Hardware assist and delay measurements provide high precision time synchronization (nanosecond) No need for separate cabling (IRIG-B,PPS) Fault tolerance using best master clock algorithm Low cost to implement in IEDs Reduce reliance on GPS

25 26 THE ORIGINS OF PERFECT TIME T H E O R I G I N S O F P E R F E C T T I M E Late 1980s computer networks need time Answer: NTP as RFC 1059 Recognized today as pretty good time 2002 members of the automation, robotics, test and measurement, time keeping industries, NIST, and the military recognize the need for more accurate time Answer IEEE 1588 (then version 1) Meant to provide sub-microsecond synchronization of real-time clocks in networked distributed measurement and control systems Early adoption in motion control, process control, robotics, packaging, printing presses, gas turbine control, telecommunications, and military applications Since 2007, the International IEEE Symposium on Precision Clock Synchronization for Measurement, Control and Communication (ISPCS) has been held every year IEEE 1588 does work, delivers high precision, has many committed vendors, and interoperability exists

26 27 THE ORIGINS OF PERFECT TIME T H E O R I G I N S O F P E R F E C T T I M E working group realizes that additional work is still needed Known issues, formal mechanism for extensions, conformance testing, redundancy, and security Working group starts updating 2007 IEEE PSRC subcommittee H task force 1 (HTF1) sees a need for a network time protocol that supports existing and developing requirements Identifies phasor measurement units or synchrophasors Identifies IEC Five performance classes Range from 1 ms to 1 μs

27 28 THE ORIGINS OF PERFECT TIME T H E O R I G I N S O F P E R F E C T T I M E 2008 IEEE 1588 Version 2 is ratified and introduces some key concepts Ordinary clocks, boundary clocks, transparent clocks, and slave clocks that address delays introduced by the communication network Peer to peer path delay measurement Higher sync message rates UDP protocol mapping Security Profiles are allowed by industries looking for specific capabilities that would foster compatibility between devices

28 29 THE ORIGINS OF PERFECT TIME T H E O R I G I N S O F P E R F E C T T I M E 2008/ IEEE PSRC HTF1 agrees a power profile to IEEE 1588 is required and working group forms (H7) to develop standard Later in 2009, IEEE Substations Committee requests a joint working group so scope can be expanded to whole substation End of 2009, first PSRC/SUBS plug fest 2010/2011 Second PSRC/SUBS plug fest Joint working group C7 and H7 are still working on standard Annexes, mappings to and C37.118, management, etc Balloting continues in 2011

29 IEEE is also referred to as version 2 defined for all applications and environments barrier to interoperability profiles define protocol elements to suit the intended application Profiles are not interoperable (by design) T H E O R I G I N S O F P E R F E C T T I M E Power Profile Defined by IEEE PSRC (C37.238) Substation LAN Applications Telecom Profile Defined by ITU-T (G ) Telecom WAN Applications Default Profile Defined in Annex J. of 1588 specification LAN/Industrial Automation Application (v1)

30 IEEE OVERVIEW T H E O R I G I N S O F P E R F E C T T I M E Functions over LAN and WAN Grandmaster sends time messages to slaves Slaves eliminate round-trip delay and synchronize Accuracy is improved High transaction rate Hardware time-stamping PTP aware switches/routers Best Master Clock Algorithm is self healing system Can meet Telecom & Utility accuracy needs Grandmaster Packet Flow Embedded Slave External Slave

IEEE 1588-2008 MESSAGE OVERVIEW T H E O R I G I N S O F P E R F E C T T I M E The Grandmaster (Server) sends the

message Follow_Up message Delay_Resp(onse) Message Headers entering the PHY are the on-time marker The Slave

31 IEEE MESSAGE OVERVIEW T H E O R I G I N S O F P E R F E C T T I M E The Grandmaster (Server) sends the following messages: Signaling (2 types) Acknowledge TLV (ACK) Negative Acknowledge TLV (NACK) Announce message Sync message Follow_Up message Delay_Resp(onse) Message Headers entering the PHY are the on-time marker The Slave (Client) sends the following messages: Signaling (3 types) Request announce Request sync Request delay_resp(onse) Delay_Req(uest)

32 IEEE 1588 ROUTING OPTIONS Unicast Multicast T H E O R I G I N S O F P E R F E C T T I M E Grandmaster sends PTP packets directly to PTP slaves Switches/Routers forward PTP packets directly to slaves Unicast Sync Interval; Telecom Profile: User defined Sync interval up to 128Hz Many subscribers supported Grandmaster broadcasts PTP packets to a Multicast IP address. Switches/Routers With IGMP snooping, forwards multicast packets to subscribers Without IGMP snooping all multicast traffic broadcast to all ports Multicast Sync Interval; Default Profile: 0.5 Hz, 1Hz & 2 Hz (1 packet/ 2 seconds up to 2 packets/second) Unicast (1:1)

Master/Server UNICAST STARTUP SEQUENCE Master Clock Slave Clock Slave/Client T H E O R I G I N S O F P E R F E C T T I M E IEEE 1588 Processor Network protocol stack & OS Processing Sync detector &

33 Master/Server UNICAST STARTUP SEQUENCE Master Clock Slave Clock Slave/Client T H E O R I G I N S O F P E R F E C T T I M E IEEE 1588 Processor Network protocol stack & OS Processing Sync detector & timestamp generator Physical layer Server clock sends: 2. Signaling (Announce granted) 4. Signaling (Sync granted) 6. Signaling (delay_resp granted) Time Switch/Router Layer Network Time PROCESS SETS UP THE RESERVATION Client clock sends: IEEE 1588 Processor Network protocol stack & OS Processing Sync detector & timestamp generator Physical layer 1. Signaling (Request Announce) 3. Signaling (Request Sync) 5. Signaling (Request delay_resp) The process is repeated before the lease expires (typically halfway through the lease period).

34 T H E O R I G I N S O F P E R F E C T T I M E MULTICAST STARTUP SEQUENCE In lieu of signaling, the Grandmaster is self-declared, based on user priority, clockclass and the lowest clockid Ordinary Clock is the IEEE 1588 term for Grandmaster and/or Slave Consider the example where OC1 loses the GPS reference: OC1 clockclass changes (6 to 7) OC2 assumes Grandmaster mode OC1 enters passive state clockclass Priority 2 GPS Reference Passive Grandmaster Mode Announce Ordinary Clock 1 Sync Delay_resp Network Delay_resp Sync Announce Ordinary Clock 3 Definition 6 Clock synchronized to a Primary Reference time source Priority 2 GPS Reference Grandmaster Ordinary Clock 2 7 Clock previously in clockclass 6 but is in holdover within holdover specs

35 Master Clock TIME TRANSFER TECHNIQUE Slave Clock Data At Slave Clock Round Trip Delay RTD = (t2 - t1) + (t4 - t3) t1 Leap second offset Offset: (slave clock error and one-way path delay) Offset SYNC = t2 t1 Offset DELAY_REQ = t4 t3 t2 t2 (& t1 for 1-step) We assume path symmetry, therefore One-Way Path Delay = RTD 2 T H E O R I G I N S O F P E R F E C T T I M E t4 Time Switch/Router Layer t3 Time t1,t2 t1, t2, t3 t1, t2, t3, t4 Slave Clock Error = (t2 - t1) - (RTD 2) The protocol transfers TAI (Atomic Time). UTC time is TAI + leap second offset from the announce message TAI instant 1 January :00: exactly was identified as UTC instant 1 January :00: The process is repeated up to 128 times per second. (Announce rate is lower than Sync rate)

Master Clock TIME TRANSFER EXAMPLE Slave Clock Data At Slave Clock Assume at an instant in time: Master clock value = 100 seconds Slave clock value = 150 seconds (the slave clock error = 50 seconds)

seconds (100+2+2+5) Sync message is sent at t = 100 seconds For illustration, Delay_Req is sent 5 seconds after the Sync message is received: Round Trip Delay RTD = (t2 - t1) + (t4 - t3) RTD =

36 Master Clock TIME TRANSFER EXAMPLE Slave Clock Data At Slave Clock Assume at an instant in time: Master clock value = 100 seconds Slave clock value = 150 seconds (the slave clock error = 50 seconds) One way path delay = 2 seconds T H E O R I G I N S O F P E R F E C T T I M E t1 t4 Time Switch/Router Layer 2s t2 t3 Time t1 = 100 seconds t2 = 152 seconds (150+2) t3 = 157 seconds (152+5) t4 = 109 seconds ( ) Sync message is sent at t = 100 seconds For illustration, Delay_Req is sent 5 seconds after the Sync message is received: Round Trip Delay RTD = (t2 - t1) + (t4 - t3) RTD = ( ) + ( ) RTD = 4 seconds Slave clock error eliminated. Slave Clock Error = (t2 - t1) - (RTD 2) = ( ) - (4 2) = 50 seconds Round trip error eliminated If the slave clock is adjusted by -50 seconds, the Master & Slave will be synchronized

37 Master Clock ANNOUNCE MESSAGE Slave Clock The announce message carries no Sync information. It does transport the leap second offset t1 t2 T H E O R I G I N S O F P E R F E C T T I M E t4 Time Switch/Router Layer t3 Time Flags Leap Second Information Grandmaster clockclass Grandmaster Accuracy Grandmaster Clock Type

38 Master Clock SYNC MESSAGE Slave Clock t1 t2 T H E O R I G I N S O F P E R F E C T T I M E t4 Time Switch/Router Layer t3 Time Flags (same as announce) t1

39 Master Clock DELAY_REQ(UEST) MESSAGE Slave Clock The delay_req(uest) message optionally carries timing information in the Timestamp field t1 t2 T H E O R I G I N S O F P E R F E C T T I M E t4 Time Switch/Router Layer t3 Time Flags (same as announce)

40 Master Clock DELAY_RESP(ONSE) MESSAGE Slave Clock t1 t2 T H E O R I G I N S O F P E R F E C T T I M E t4 Time Switch/Router Layer t3 Time Flags (same as announce) t4

interval Repeats @ Announce Interval rate Repeats @ Sync Interval rate

41 TIME TRANSFER (UNICAST) Grandmaster Slave Clock T H E O R I G I N S O F P E R F E C T T I M E Grandmaster/Server Lease duration interval Announce Interval rate Sync Interval rate t1 t4 Time t2 t3 Time Slave Initiated Process Lease establishment Slave/Client

TIME TRANSFER (MULTICAST) Grandmaster Master Clock Slave Clock T H E O R I G I N S O F P E R F E C T T I M E Grandmaster/Server Repeats @ Announce Interval rate

42 TIME TRANSFER (MULTICAST) Grandmaster Master Clock Slave Clock T H E O R I G I N S O F P E R F E C T T I M E Grandmaster/Server Announce Interval rate Sync Interval rate Grandmaster Initiated Process t1 t4 Time Time No signaling occurs Sync interval is pre-determined, lease is infinite t2 t3 Slave/Client

IEEE 1588-2008 TRAFFIC IMPACT Message Packet Sizes In-band Traffic Rate T H E O R I G I N S O F P E R F E C T T I M E Signaling (request) 96 bytes (54) Signaling (ACK/NACK) 98 bytes (56) Announce

43 IEEE TRAFFIC IMPACT Message Packet Sizes In-band Traffic Rate T H E O R I G I N S O F P E R F E C T T I M E Signaling (request) 96 bytes (54) Signaling (ACK/NACK) 98 bytes (56) Announce message 106 bytes (64) Sync message 86 bytes (44) Follow_Up message 86 bytes (44) Delay_Resp(onse) 96 bytes (54) Delay_Req(uest) 86 bytes (44) Using the following typical values: Announce interval 1 per second Sync interval 64 per second Lease duration 300 seconds Delay_Req(uest) 64 per second Delay_Resp(onse) 64 per second Peak traffic transmitted in one second: (96x3)+(98x3) x( ) = bytes = 0.017% of Fast Ethernet (100mbps) = % of GigE () 1588 only message size in bytes

44 IMPROVING ACCURACY 1-Step Clock 2-Step Clock Master Clock Slave Clock Master Clock Slave Clock T H E O R I G I N S O F P E R F E C T T I M E t1 t4 Switch/Router Layer Estimated value of t1 received at Slave Real value of t1 received at Slave t3 t1 t4 Switch/Router Layer Real value of t1 received at Slave t3 Time Time Packet encryption may prevent the real-time stamp from being inserted into the Sync message Time Time

IMPROVING ACCURACY Transparent Clock Boundary Clock T H E O R I G I N

delay inside the switch ( residence time ) Modifies (adds) residence

Correction field must be accurate PTP Packet Residence Time = Egress

built-in clock Internal clock synchronized via 1588 to the upstream

sync flow Regenerates 1588 messages Essentially a client one side

45 IMPROVING ACCURACY Transparent Clock Boundary Clock T H E O R I G I N S O F P E R F E C T T I M E Switch, not a clock Measures 1588 packet delay inside the switch ( residence time ) Modifies (adds) residence time to the correction field Limited to non-encrypted networks Correction field must be accurate PTP Packet Residence Time = Egress Time - Arrival Time Arrival Time Egress Time PTP Packet Switch with built-in clock Internal clock synchronized via 1588 to the upstream master Slave on 1 port, master on others Interrupts the Grandmaster sync flow Regenerates 1588 messages Essentially a client one side being used to discipline a GM on the other Slave GMC Transparent Clock Boundary Clock

46 48 CONCLUSIONS P E R F E C T T I M I N G PTP has demonstrated sub microsecond time synchronization The work by PSRC H7 and SUBS C7 will create a power profile for PTP Accuracy for all smart grid applications will be possible Redundancy will be possible Switch vendors have embraced work IED vendors need to get involved Migration path possible using hybrid solution that combines PC and IRIG-B Timing solutions sold today may not have migration path Timing s impact on bandwidth is minimal

47 49 FOR MORE INFORMATION IEEE PSRC working group website IEEE 1588 PTP website P E F E C T T I M I N G

48 PERFECT QUESTIONS CRAIG PREUSS, P.E. ENGINEERING MANAGER UTILITY AUTOMATION BLACK & VEATCH CORPORATION SUBSTATIONS C0 SUBCOMMITTEE CHAIR WORKING GROUP C7 MEMBER

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