Teleprotection over packet f 30 8-11

Teleprotection over Packet Slide 1

Network Migration for Utilities: Teleprotection over Packet


Agenda

• Power Utility Communications: Networks in Transition

• Teleprotection Connectivity and Delay Considerations• Ensuring Communications Performance for Teleprotection over

Packet

• Teleprotection over Packet Use Case

• Conclusion

• Appendix: Pseudowire EmulationLatency Sources in Teleprotection


Power Utility Communications


Networks in Transition

• Power utility networks are mostly self-owned, privately operated

• Require SDH/SONET-level reliability for mission-critical communications

• Slow migration to IP, but Ethernet transport and IP/Packet-based networks gradually gain traction for higher throughput and lower OpEx

Upgrades to Smart Grid foster transformationNew applications: Substation automation (IEC 61850), NG-SCADA systems, WASA synchrophasors, IP video surveillance


• Control CapEx and avoid over-burdening network operations and management

Especially where SDH/SONET and PSN co-exist

• Ensure smart communications over packet and service assurance for mission critical apps in PSN environment:

Low end-to-end delay High availabilitySDH/SONET-level resiliencyTeleprotection, in particular, has stringent communications performance requirements !

Migration Challenges


Teleprotection Connectivity


What is Teleprotection

• Used for power line protection• Protect equipment from severe damages resulting from faulty HV

lines • Common schemes:

Distance (impedance) protectionCurrent differential protectionDirect Transfer TripCombination


Teleprotection Communications

• Distance Protection: Trips breakers when impedance measurements vary from those taken under normal conditions

Traditionally, no communication was required Pilot-aided distance relays use a communication channel to improve fault clearance

• Differential Protection: Disconnects faulty line segments if differential current measurements on both ends of the protection zone are higher than a setpoint

Requires communication between the end-point relays


• Traditionally, relays communicated (via a separate comm channel or a multiplexer) over the SDH/SONET backbone, power line carrier (PLC) or a dedicated fiber optic connection

• Communication channel interfaces: X.21, E1/T1, V.35, E&M; modern relays use IEC C37.94 fiber optic

Teleprotection Connectivity


Two options when migrating to packet communications:

• Continue using TDM connectivity for Teleprotection in parallel to new packet network installations for non-critical substation traffic

Hybrid TDM/PSN multiplexers and access nodes save on network equipment costs

• Use Ethernet or packet network for Teleprotection, provided it can guarantee required performance

Delivery of TDM-based Teleprotection signals over packet requires pseudowire emulation (see appendix I)

Teleprotection Connectivity (Cont’)


Teleprotection Communications –Key Performance Criteria (IEC 60834)

• Between the moment of change of state at the transmitter input and the receiver output

Transmission Time

• Valid commands in the presence of interference and/or noise, by minimizing the probability of missing command (Pmc)

Dependability

• Preventing false tripping due to a noisy environment, by minimizing the probability of unwanted commands (Puc)

Security

• Bandwidth consumption and resiliency also impact performance

Other

Performance criteria pose a challenge over non-deterministic packet transport and require enhanced, carrier-grade capabilities


Teleprotection Communications Performance: Latency Budget

• Most power line equipment can withstand a brief shortage/irruption

Typical requirement for total fault clearance time = 100ms

• Actual operation time of protection systems = 70-80% of this period

Including fault recognition, command transmission and line breaker switching

Large electromechanical switches take up the majority of time

• In modern applications, contact transfer is expected in 10ms or less

• For latency sources in Teleprotection communications, see Appendix II


Teleprotection Communications Performance: Asymmetric Delay

• Differential protection requires same channel delay in transmit and receive paths

Requires special attention in jitter-prone packet networks

Typical relays can tolerate discrepancies of up to 250 μs

• The main tools available for lowering delay variation:A jitter “buffer” at each end of the line for queuing sent and received packets

Traffic management: Ensure highest transmission priority for Teleprotection

Standard PSN-specific synchronization technologies maintain stable networks by disciplining the communications elements to a highly accurate clock source


Ensuring Teleprotection Performance over Packet


Communications Channel Resiliency

• Hardware redundancy:No single point of failure (NSPF) design with redundant, hot-swappable power supplies

Redundant control plane and switch fabric cards

• Link redundancy:1+1 protection topology with automatic switchover between links

Link aggregation group (LAG) per IEEE 802.3-2005 LACP (link aggregation control protocol) for Ethernet-based services

• Path protection:Ethernet Linear protection Switching (G.8031) , AKA “EVC (Ethernet Virtual Connection) protection”

Ethernet Ring Protection Switching (G.8032 ERPS) to provide Five Nines (99.999%) availability


Traffic Management and Quality of Service

Provide deterministic quality of service and priority for protection signals with multi-level Ethernet traffic management for predictable latency and jitter performance across the service path:

• Classification of incoming traffic into flows

• Metering and policing to regulate traffic with different bandwidth profiles

• Advanced scheduling and queue management to ensure minimal latency and jitter

• Shaping to smooth out bursts and avoid buffer overruns in subsequent network elements

• Packet editing and marking to signal proper handling instructions for subsequent network elements


Performance Monitoring and Testing

ServiceTurn-up

On-going Monitoring

Fault Management& Recovery

Connectivity Verification

Diagnostic Loopbacks

Performance Verification

& Testing

Performance Monitoring

Threshold Reporting

Statistics Collection Reporting

Fault Detection & Isolation

Fault Propagation & Notification

Resiliency & Repair

• A wealth of carrier-grade Ethernet tools to remotely test, monitor and troubleshoot the communications links operation

• Utility network operators anticipate service degradation ahead of time, as well as cut down truck-rolls and on-site technician calls


Teleprotection over Packet Use Case


Teleprotection over Packet Proof of Concept Program

• RAD’s Megaplex-4100 multiservice access platform was successfully tested by a major energy utility

• TDM data received from protection units was converted into packets, then transmitted over an MPLS network employing static routing

• The line differential protection equipment featured a variety of TDM communications interfaces, including G.703, X.21, RS-232, E&M, C37.94, Native E1

• End-to-end communication delay requirement of 8-10ms in a packet network environment experiencing a jitter of 2.5ms

Also required symmetrical latency with maximum tolerance of 100-250μs


Teleprotection over Packet Test Results

RAD’s Teleprotection multiplexers have successfully met requirements:

• Up to 5ms delay with quality of service for signal priority via shaping and traffic engineering tools

• Clock accuracy was rigorously maintained throughout transmission

• High degree of resiliency through various protection schemes, including DS1-level redundancy


Conclusion

• Critical Teleprotection applications require special attention in the move towards Smart Grids and next-generation networks

• Viable alternatives to existing deployments need to meet exacting performance criteria of minimal transmission time, reliability and security

Extremely low, symmetrical delay, robust clock accuracy, QoS assurance, resiliency, and on-going performance monitoring are “must have” elements for any Teleprotection over packet system

• Hybrid TDM/Packet solutions allow utility operators the freedom to choose the migration path that best suits their needs and budgets

Download comprehensive Teleprotection over Packet Solution Paper

http://www.rad.com/21/Teleprotection-over-Packet/22027/


Appendix


Appendix I:What is Pseudowire Emulation?

• The synchronous bit stream is segmented

• Headers are added to each segment to form the Packet

• Packets are forwarded to destination over the PSN network

• At destination, the original bit stream is reconstructed by removing headers, concatenating frames and regenerating the timing

• The most common pseudowire emulation standards are CESoPSN, SAToP, TDMoIP


Appendix II: Latency Sources in Teleprotection

•Includes the relay’s fault identification, command initiation and decision time

Teleprotection Equipment Delay

• Minimized via optimal design of ICs, DS0 xconnect, and• High-performance buffering and forwarding technology

Substation Multiplexer (TDM interface)

• 1-5ms, depending on packet size and # of TDM frames/packet• Smaller packets increase bandwidth overhead, but reduce

latency

Pseudowire Encapsulation and Packetization Delay

• Each element adds processing and queuing delay• Variable delay poses a greater threat and requires advanced

traffic managementPSN Network Elements


Thank You For Your Attention

www.rad.com

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Teleprotection over packet f 30 8-11