Teleprotection signals from protective relays are among the most critical data transmitted across utility networks, as they help manage the power grid load, as well as to protect equipment within the power network from severe damages resulting from faulty HV lines. By enabling load-sharing, grid adjustments and immediate fault clearance, Teleprotection has a decisive role in ensuring uninterrupted power supply and therefore requires special attention with regards to network performance and reliability. Specifically, protection commands must be assured immediate delivery when problems are detected, so that faulty equipment can be disconnected before causing a system-wide damage.

1. Network Migration for Utilities:
Teleprotection over
Packet
Teleprotection over Packet Slide 1

2. 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 Emulation
Latency Sources in Teleprotection
Teleprotection over Packet Slide 2

3. Power Utility Communications
Teleprotection over Packet Slide 3

4. 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 transformation
New applications: Substation automation (IEC 61850), NG-SCADA systems,
WASA synchrophasors, IP video surveillance
Teleprotection over Packet Slide 4

5. Migration Challenges
• 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 availability
SDH/SONET-level resiliency
Teleprotection, in particular, has stringent communications
performance requirements !
Teleprotection over Packet Slide 5

6. Teleprotection Connectivity
Teleprotection over Packet Slide 6

7. What is Teleprotection
• Used for power line protection
• Protect equipment from severe damages resulting from faulty HV
lines
• Common schemes:
Distance (impedance) protection
Current differential protection
Direct Transfer Trip
Combination
Teleprotection over Packet Slide 7

8. 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
Teleprotection over Packet Slide 8

9. Teleprotection Connectivity
• 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 over Packet Slide 9

10. Teleprotection Connectivity (Cont’)
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 over Packet Slide 10

11. Teleprotection Communications –
Key Performance Criteria (IEC 60834)
Transmission Time
• Between the moment of change of state at the transmitter input and the
receiver output
Dependability
• Valid commands in the presence of interference and/or noise, by minimizing
the probability of missing command (Pmc)
Security
• Preventing false tripping due to a noisy environment, by minimizing the
probability of unwanted commands (Puc)
Other
• Bandwidth consumption and resiliency also impact performance
Performance criteria pose a challenge over non-deterministic
packet transport and require enhanced, carrier-grade capabilities
Teleprotection over Packet Slide 11

12. 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 over Packet Slide 12

13. 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
Teleprotection over Packet Slide 13

14. Ensuring Teleprotection
Performance over Packet
Teleprotection over Packet Slide 14

15. 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
Teleprotection over Packet Slide 15

16. 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
Teleprotection over Packet Slide 16

17. Performance Monitoring and Testing
• 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
Service On-going Fault Management
Turn-up Monitoring & Recovery
Connectivity Performance Fault Detection &
Verification Monitoring Isolation
Diagnostic Fault Propagation &
Loopbacks Threshold Reporting
Notification
Performance
Verification Statistics Collection
Reporting Resiliency & Repair
& Testing
Teleprotection over Packet Slide 17

18. Teleprotection over Packet
Use Case
Teleprotection over Packet Slide 18

19. 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 Slide 19

20. 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
Teleprotection over Packet Slide 20

21. 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
Teleprotection over Packet Slide 21

22. Appendix
Teleprotection over Packet Slide 22

23. 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
Teleprotection over Packet Slide 23

24. Appendix II:
Latency Sources in Teleprotection
Teleprotection Equipment • Includes the relay’s fault identification, command initiation
Delay and decision time
Substation Multiplexer • Minimized via optimal design of ICs, DS0 xconnect, and
(TDM interface) • High-performance buffering and forwarding technology
• 1-5ms, depending on packet size and # of TDM frames/packet
Pseudowire Encapsulation
• Smaller packets increase bandwidth overhead, but reduce
and Packetization Delay latency
• Each element adds processing and queuing delay
PSN Network Elements • Variable delay poses a greater threat and requires advanced
traffic management
Teleprotection over Packet Slide 24

25. Thank You
For Your
Attention
www.rad.com
Teleprotection over Packet Slide 25