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Synchrophasor standards - Communications

Synchrophasor standards - Communications. Kenneth Martin Electric Power Group. Outline. Synchrophasor data system requirements C37.118 synchrophasor standards IEC 61850 STTP Other standards. Typical synchrophasor measurement system.

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Synchrophasor standards - Communications

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  1. Synchrophasor standards - Communications Kenneth Martin Electric Power Group

  2. Outline • Synchrophasor data system requirements • C37.118 synchrophasor standards • IEC 61850 • STTP • Other standards

  3. Typical synchrophasor measurement system • Measurements at substations, real-time data sent to control center • Data collected & aligned, sent to applications or higher levels • Processed in real-time or from recording

  4. Requirements for Phasor Data • Phasor data characteristics • Data is sent continuously on timed cycle, not polled • Requires constant bandwidth • Data is sent in frames, always same size • All measurements correspond to the frame timetag • Communication requirement considerations • Bandwidth for continuous data flow • Latency in data delivery • Data link reliability • Communication impairments – errors, dropouts, etc.

  5. Communication Chain • User equipment (terminal equipment) • PMU, DFR, recorder, display, etc. • Interface unit • Modems, CSU/DSU, SRU, etc. • Communication system User Equipment User Equipment Communication System Interface Unit Interface Unit

  6. Router Router Typical utility communication setup • Interface unit is Router • Port connection • Ethernet (100BaseT, FO) • Communication connection – WAN, Nx64K • Experience • Setup very solid, knowledge of router configuration required • Reliability – very good with reliable backbone system • Impairments – very little data loss; outages can be long • Security – changes & updates can create problems Digital channel or wideband Communication System PMU PDC

  7. Communication Systems • Utility owned • Analog radio & microwave • Digital – fiber & microwave • SONET (channel based) & wideband • Leased from telecomm • Voice grade channel (analog) including dial-up • Frame relay • Digital channel – 56/64K, ISDN, DDS, etc • Wideband – Nx64K, T1, area Ethernet • Wireless – owned or leased, local connections • Internet

  8. Bandwidth and Latency • Bandwidth is how much information can pass in a given period of time • Commonly called speed or baud • 14.4K modem can send/receive 14,400 bits/sec • Ethernet 10BaseT sends/receives 10,000,000 bits/sec • Latency defines how long information takes from one point to another • Time for a bit or message to leave one point and arrive at another • Latency is a concern for real-time & data synchronization

  9. Bandwidth considerations • A specified bandwidth can vary • Analog modems reduce speed for noise on line • Data compression increases effective bandwidth • Administration & other traffic reduce capacity • Admin such as security, IGMP, etc. • Other traffic on shared link • Protocol overheads reduce capacity • Small messages are less efficient than large ones • Ethernet - 22 bytes/packet, UDP – 28 bytes/packet • Overhead can exceed data!

  10. Bandwidth requirements • Depends on number of quantities, data type & rate • Floating point almost doubles data rate (below) • Overhead must be figured into calculation • Asynchronous serial – 2 bits/byte • With small packets, IP on Ethernet can have > 50% overhead PMU output – C37.118, all integer PMU output – C37.118, all floating point Data rate in bits/sec (BPS) is approximately 10X(rate in bytes/sec)

  11. Latency in communications Communication System Transmitting Device Receiving Device t comm system delay, Serializing Delay, Full message received, t1 t0 - start of transmission t1 t2 1st bit output 1st bit input Last bit input Communication system delay can be characterized as the time from when the first bit is sent at time t0 until it is received at time t1 creating a delay of (t1 - t0). With a data rate of B bits/sec and a message length of N bits: Delay = t1 - t0 = Dt1 + N/B. Typical async serial might be ∆t1 = 25 ms, B = 33,600 bps, N = 64 char x 10 bits/char: Delay = 25 + 640/33600 = 25 + 19 = 44 ms. Channel delay and data rate are both significant contributions.

  12. Signal Delay - PMU to PDC • Direct synchronous, 128 KBPS, 200 mile distance • Ave delay 19.5 ms, max 25 ms • V.34 analog modem, 300 mile distance • Average delay 93 ms, max 114 ms

  13. Signal Delay - PMU to PDC • Communication with Ethernet connections • 10M BPS system • Direct connection through local hub • Ave delay 4.4 ms, max 5.4 ms • Remote installation, 200 mi distance • 2 routers, synchronous WAN, 128 KBPS • Ave delay 17.5 ms, max 18.7 ms

  14. Delay Summary • Distance has little effect on overall delay • Delay on communication media 5.4 to 10 µs/mi • Higher bit rates decrease serializing delay • 56 KBPS – 140 µs/byte; 10 MBPS – 0.8 µs/byte • Average delays-- • Analog modems: Complex coding (V.32bis, V.34): 60 – 110 ms • Network, 10baseT: • Over WAN narrowband, 2 routers, 200 mi: 17-19 ms • Direct, no routers, minimal distance: 4 – 8 ms • Secondary PDC-PDC depend on routers, link BW, data management • Range: 100 ms to several seconds

  15. Latency & error requirements • Depend on application & user. Typical needs-- • Recorded data • Latency immaterial • Can tolerate some gaps • User displays • Latency < 2 sec usually ok, maybe more • Some gaps tolerable • Real-time controls • Latency critical • May tolerate some dropped samples, no outages

  16. System Reliability (actual measurement) • 2 weeks Statistics • Signal = PMU & communications • Sync = GPS lock Station Reliability (%) Notes (PMU) Signal Sync PMU1 97.52 99.974 PMU fail 2 days PMU2 99.929 99.996 Normal, modem PMU3 99.997 93.74 PMU clock failure PMU4 99.82 100 Comm sys problems PMU5 99.99 99.988 Normal, fiber, digital PMU6 99.983 99.74 PMU clock problems PMU7 99.996 99.95 Normal, modem

  17. Communications performance considerations • Applications determine performance requirements • Delays for data correction and replacement preferable for analysis (TCP) • Single point & short interval dropouts are tolerable for most monitoring (UDP or TCP) • All delay degrades high speed controls (UDP) • Reliability of data communication system • System outage - redundancy & fail over systems • Dual independent communication links or high reliability communication system (SONET rings) • Data loss - error detection & correction • Automatic by modems or TCP, or performed by the application under user control • Latency (delay) & variation of latency may be a problem for controls

  18. Standards for data communication • IEEE SYNCHROPHASOR • IEEE C37.118 & C37.118.1 • IEC 61850 -90-5 • STTP • Other standards: DNP-3, ICCP, OPC, Fieldbus, ModBus, FMS

  19. IEEE Synchrophasor Standard Communications • First Standard: IEEE1344-1995 • Basic communication messages • Second Standard: IEEE C37.118-2005 • Data transmission formats defined • Improved status and error indications • Includes single or multiple PMU data • Widely used & very few problems • Third Standard: IEEE C37.118.2-2011 • Backward compatible with 2005 standard • Added a few features • Currently being updated

  20. IEEE C37.118 communication • Communication messaging • Message definitions • Message sequence • Message contents & format • Identification of messaging participants • Does not specify • Communication medium • Communication system protocol • Communication security

  21. C37.118 Messaging • Command frame • Start/stop data, send other information • Data frame • Phasor and Frequency measurements • Analog data (user specified data type) • Digital indications (Boolean, 1-bit values) • Configuration frame • Describes data frame, with scaling & naming • Header frame • Text descriptions, user format Commands PMU PDC Data, Configuration, Header

  22. Message Construction • All message frames have the same basic format • SYNC word includes type & version • IDCODE identifies every message • SOC & FRACSEC accurately time each frame • CHK provides a reliable quality check

  23. Data Message • Data from one or more PMUs • Share same time stamp • Number of phasors, analogs, & digitals set in config • STAT – flags for data from PMU • Phasors – type and data format specified • Analogs – sample data values, open to user • Digitals – Boolean values for switch, status, etc. • Frequency/ROCOF – from PMU Overall data packet . . . Header PMU1 PMU2 PMU3 PMU K CRC Individual PMU data block ... ... ... STAT Phsr1 Phsr2 PhsrN Freq/Df Alog1 AlogJ Dig1 DigI

  24. B15 B14 B13 B12 B11 B10 B8-6 B5-4 B3-0 B9 STAT word – applies to all PMU measurements Data valid PMU error PMU sync Data time by arrival PMU trigger Configuration changed Data modify PMU_TQ Time Quality Unlocked time Trigger reason • Data Valid – bit set to indicate data not usable • PMU error – some error in PMU, unit specific • PMU sync – angle not valid if sync lost • Time by arrival – time stamp bad, local time applied • PMU trigger & Configuration change – alerts • Data modify flag – data changed by some process • PMU_TQ & Unlocked time – secondary time error Bit flag for each PMU

  25. Message extension for larger systems Configuration message extension (config3) Message is extensible to multiple frames Previous messages limited to one 64K frame Necessary for large data sets OVER-ALL . . . Header PMU1 PMU2 PMU K . . . PMU K+1 PMU J RATE . . . PMU J+1 PMU N CRC

  26. PMU ID PMUID identifies a particular data stream Commands for control, data source & configuration Allows multiple streams between devices PMUID also identifies original PMU Config, data Config, data PDC PMU PMU PDC Application PC host PMU Cmds Application Cmds

  27. Implementation • Independent of protocol (not specified by standard) • RS232 Serial • Original implementation, direct interpretation • IP protocol • TCP/IP direct both ways • UDP/IP direct both ways • TCP/IP for control, UDP/IP for data (shown below) PMU PDC TCP//IP – Control, Config UDP//IP - Data

  28. Operation Adaptation • Command/response – described in standard • Spontaneous data transmit • Data sent at power-on or by external command • Eliminates need for control signals • Less likely to be interrupted • Config sent periodically, spontaneously • Supports auto-config for remote devices (PDCs) • Solves some firewall security issues • Adaptations need user coordination

  29. Other Standards for Synchrophasor Data • IEC 61850 -90-5 • Extension of 61850 to wide area • Integrates directly into 61850 systems • More complex to develop • More bandwidth required • DNP-3, ICCP • Generally used for slower reporting • Support interface with EMS

  30. IEC 61850 • Substation configuration & control • IEC TC57, WG10 • Takes advantage of • Proliferation of Intelligent Electronic Devices (IED) • Wide bandwidth network communications • Primary focus is substation automation • Now increasing scope to include wide area • GOOSE & phasor wide area extensions defined

  31. IEC 61850 operation • Station bus • Configuration, controls, reporting, archiving, etc • Includes wide area GOOSE messaging • Process bus • Measurements, status, h/s commands, etc Outside World Substation bus 10/100/1000 MB Redundant Ethernet Substation Gateway Relay IED Relay DFR Process bus .1/1/10 GB Redundant Ethernet CLK A MU MU MU MU CLK B

  32. IEC 61850-90-5 TR key features - modeling • Communication needs are outlined • Tunneling & gateway approach for PDC • Modeling considerations for both approaches • Sample Values (SV) extended for route-ability Tunneling Gateway

  33. IEC 61850-90-5 TR added key features to 61850 • Security • Confidentiality, authentication, integrity • Refers to methods developed under 62351 • Application of security is optional – use where required • Services • Profiles • Data types and classes • R-SV & R-GOOSE (routable using UDP) • Modelling • Logical nodes & SCL types

  34. IEC 61850-90-5 vs. C37.118.2 • Messaging system only • Operates over other protocols, coordination outside of 37.118 • Configuration by vendor methods • Use standard API of communication interface; requires only 37.118 commands • Lightweight, required messages and content only • Complete communication protocol • Complete operability in protocol • Includes modeling and configuration • Uses MMS stack and requires 61850 functional implementation • Messaging standardized, some extra overhead but full functionality

  35. STTP Protocol • US Dept. of Energy sponsored development • Supported by 11 vendors & 12 utilities • Being developed as IEEE Standard P2664 • Address shortcomings of C37.118 & 61850 • Better on-line configuration control • More like other control center application operation • Benefits • Measurement oriented for more specific data selection & management • Easier to configure and change during operation • Includes built-in security & lossless compression

  36. STTP Protocol features • Uses publish-subscribe to establish connections • Measurement value selection (instead of PMU) • Establishes separate data and command channels • Small basic packet size simplifies fragmenting • Built-in optional security

  37. EMS-oriented Standards • DNP-3 • One of several protocols used primarily for SCADA systems • Query-response type system, not well adapted for multiple sample/second systems like WAMS • ICCP • A complex high-level protocol used to exchange data between control centers • Offers services not used in phasor data systems • Complexity does not lend itself to adapting to high-speed, small-processor WAMS devices

  38. Data system standards • OPC, OPC-DA • OLE for Process Control • Adapted from a Microsoft PC standard • Supports client/server data flow • Allows user data item selection • May be too slow for large data sets • FMS, ModBus, Field Bus, Profibus, etc • Data messaging systems • Could be used (I don’t know of any users)

  39. A few thoughts • Current systems focus on real-time & higher reporting rates but System phase angles can be used at any speed • Slower reporting for system analysis could serve in low bandwidth applications – power flow, state estimation, etc. • Standards need to support lower reporting rates • High-speed controls need minimum latency • Standards should support direct, low-latency applications (small data sets) • Synchrophasors represent the fundamental component • Some applications need higher order information (harmonics, power quality, etc) • Standards should support wider information reporting • Current standards report at rates related to system frequency • This has nice mathematical properties, but is not necessary • Consistent reporting rates are necessary to synchronize the data for accurate phase angle comparison

  40. Summary • IEEE C37.118 series • Messaging for synchrophasor communications • Adapts to communication medium • Well established • Widely used • Other standards useful in some cases • IEC 61850-90-5 in 61850 systems • DNP3 and ICCP for EMS interface

  41. Application considerations • Fixed reporting rates • Phase angle determined by measurement time • For system angles data must be the same time • Fixed rates and times support comparisons • Data rates are sub-multiple of frequency • Data pushed to reduce delay & variation • Communication requirements • Continuous bandwidth • Low latency for real time

  42. Message Basic Details • All message frames have the same basic format • Easier for program interfaces • SYNC word includes type & version • Identifies message • Easy to add messages • Can intermix messages of old new standard revisions • SOC unique for 130 years (until 2101) • FRACSEC – fraction of second or interval • Delineated by TIME_BASE in configuration • CHK is quality check in message, independent of communication quality

  43. OSI communication model • 7 layer model • Used to characterize any system • C37.118 interfaces at layer 6 or 7 where the data reaches the application • Lower levels by RS-232, TCP/IP, UDP/IP, DNP3, 61850, etc.

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