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Communications Technology for Protection Systems January 14, 2013 Communications Technology for Protection Systems Power System Relaying Committee Relaying Communications Subcommittee Special report prepared by WG H9 Assignment Prepare a document that would assist engineers in understanding the communications technology for protective relaying. Members of the Working Group René Midence, Chair Moh Sachdev, Vice Chair Members Antonova, G. Ariza, J. Bell, T. Benou, M. Bolado, O. Brahma, S. Brettschneider, S. Castro, L. Chaparro, R. Chelmecki, Chris Dahlin, T. De La Quintana, A. Ebrecht, J. Gauci, A. Gers, J.M. Harada, R. Hamilton, R. Higinbotham, B. Huerta C. Iadonisi, D. Ince, B. Kwan, M. Li, T. Lu, Y. MacKie, B. McHale, E. McLaren, P. Murphy, J. Niemira, J. Nordell, D. Oba, E. Pathirana, V. Rizvi, I. Sambasivan, S. Sidhu, T. Simon, M. Thompson, S. Tournier, J.C. Ward, S. Yang, Y. Date Printed: 1/15/2013 Page 1 of 225 Table of Contents 1. Introduction ........................................................................................................................... 10 1.1 The Introduction of Digital Communications ............................................................... 13 1.2 Data Communications for Protection and Control........................................................ 13 1.3 Substation Automation Examples ................................................................................. 22 1.4 Substation Automation with Electromechanical Relays ............................................... 22 1.5 Substation Automation with Numerical Relays ............................................................ 26 1.5.1 Numerical Relays and Serial Communications RS-232 ........................................... 27 1.5.2 Numerical Relays and Serial Communications RS-485 ........................................... 28 1.5.3 Numerical Relays and Ethernet Networks ................................................................ 30 2. Analog and Discrete Signals ................................................................................................. 31 3. Synchronous communication ................................................................................................ 33 4. Asynchronous communication.............................................................................................. 34 5. Bit Error and Bit Error Correction ........................................................................................ 34 5.1 Bit Errors ....................................................................................................................... 34 5.2 Bit Error Correction ...................................................................................................... 35 5.3 Alarms ........................................................................................................................... 36 6. Channel Delay ....................................................................................................................... 36 6.1 Resynchronization......................................................................................................... 37 7. Jitter and wander ................................................................................................................... 37 7.1 Why jitter is important .................................................................................................. 38 7.2 Symptoms of Jitter/Wander Issues................................................................................ 38 8. Basic Considerations in Digital Communications ................................................................ 39 8.1 Speed / Delay ................................................................................................................ 39 8.2 Dependability and Security ........................................................................................... 41 8.3 Redundancy................................................................................................................... 41 8.4 Reliability and Availability of Communications Networks .......................................... 42 8.5 Noise ............................................................................................................................. 44 8.5.1 Noise in Digital Circuits ........................................................................................... 44 8.5.2 Noise in Analog Circuits ........................................................................................... 44 8.5.3 Power system coupled noise ..................................................................................... 45 8.5.4 Noise Detection ......................................................................................................... 45 9. OSI Protocol Model .............................................................................................................. 45 10. Multiplex Channel, SDH, PDH, SONET.......................................................................... 47 10.1 Multiplexing .................................................................................................................. 47 10.1.1 Frequency Division Multiplexing ......................................................................... 47 10.1.2 Wave Division Multiplexing................................................................................. 47 10.1.3 Time Division Multiplexing ................................................................................. 48 10.1.4 Code Division Multiplexing (Spread Spectrum) .................................................. 48 10.2 Digital Hierarchies ........................................................................................................ 48 10.2.1 PDH - Plesiochronous Digital Hierarchy .............................................................. 49 10.3 SONET (Synchronous Optical Network) and SDH (Synchronous Digital Hierarchy) 50 10.3.1 Basic SONET Signal............................................................................................. 51 10.3.2 Synchronous Digital Hierarchy (SDH) ................................................................. 51 10.3.3 SONET/SDH network topologies and network resilience .................................... 52 Date Printed: 1/15/2013 Page 2 of 225 10.3.4 GR-1230 4-Fiber Bi-directional Line Switched Ring (BLSR) ............................. 58 10.3.5 SONET Delay Characteristics .............................................................................. 58 10.3.6 SONET Restoration Characteristics ..................................................................... 58 10.4 SONET/SDH for power system protection................................................................... 59 10.4.1 PDH/SONET/SDH Networks ............................................................................... 59 10.5 SONET Synchronization .............................................................................................. 61 10.5.1 Stratum Clock Hierarchy ...................................................................................... 61 10.5.2 Synchronization Status Messages (SSM) ............................................................. 62 11. Physical Communications Media- Electrical .................................................................... 63 11.1 Serial Communications RS-232 .................................................................................... 63 11.1.1 Voltage levels ........................................................................................................ 64 11.1.2 RS-232 Data Structure .......................................................................................... 65 11.1.3 RS-232 Physical Properties ................................................................................... 66 11.1.4 Maximum cable lengths ........................................................................................ 66 11.1.5 Error detection ...................................................................................................... 68 11.1.6 Disadvantages of the parity system....................................................................... 68 11.2 Serial Communications RS-485 .................................................................................... 69 11.2.1 Uses of EIA-485 ................................................................................................... 70 11.2.2 Differential signals with RS-485 .......................................................................... 70 11.2.3 Network topology with RS-485 ............................................................................ 72 11.2.4 RS-485 functionality ............................................................................................. 73 11.3 Electrical Interfaces ...................................................................................................... 73 11.3.1 Metallic media (coax and twisted pair) ................................................................. 73 11.3.2 Digital Electrical Interfaces .................................................................................. 74 11.3.3 RS-232 Electrical Interface ................................................................................... 75 11.3.4 RS449 Electrical Interface .................................................................................... 75 11.3.5 V.35 Electrical Interface ....................................................................................... 77 11.3.6 G.703 Electrical Interface ....................................................................................
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