This document discusses using IEEE 1588 Precision Time Protocol (PTP) for time synchronization in power substations and smart grids. It recommends having a timing strategy that uses PTP according to defined profiles like IEEE C37.238 for power systems. This provides more accurate time synchronization than older methods like IRIG-B, with redundancy and management capabilities. The document also warns that relying solely on GPS for timing leaves systems vulnerable and that a single timing solution will not scale for power grids of the future.

1. Confidential © Copyright 2013
Doug Arnold
Principal Technologist, Symmetricom & IEEE 1588 Study Group Co-Chair
23 May 2013
Time Synchronisation

2. 2Confidential © Copyright 2013
IEEE C37.238-2011 Timing
(PTP Power Profile)
IEC 61850 Smart Substation:
Industrial Ethernet Infrastructure With PTP
Relay
Relays
Phasor
Measurement
Units
Control Center
Bay
Controller
Bay
Controller
Gateway
Communication
Bus
NO INDEPENDENT TIMING DISTRIBUTION
Communication
Bus
Intelligent
Switchgear
NextGeneration
CT/PT(VT)
IEEE C37.238-2011 Timing
HMI
Station Controller
Substation Clocks
Station Bus
Merging Unit
CT/PT (VT)
Switchgear
Process Bus
Relays

3. 3Confidential © Copyright 2013
Traditional
Smart Grid
Substation Applications:
Time Accuracy Requirements
AccountingOperationsForensics
Phasor Measurements
Sampled Values
Traveling Wave Fault Locator
Lightning Strike Correlation
SCADA/EMS
Frequency Measurement
Protection Relaying Events
Event/Disturbance Recorders
Quality of Supply Metering
Bulk Metering
Customer Premises Metering
1.0 second 0.5 second 1 millisecond 1 microsecond
Application
Accuracy

4. 4Confidential © Copyright 2013
Do you have a timing strategy?
If not, you may have issues and not know it.
• Improper antenna installations
• Damaged antennas causing interference
• Environmental conditions
• Intentional and unintentional sabotage
such as jamming and spoofing
GPS antenna farms are created from multiple point
solution implementations. Some of the issues that
can impact your timing reference:

5. 5Confidential © Copyright 2013
IEC 61850 Smart Substations:
Process Bus To The Switchyard
Current Practice
• Parallel copper cabling between
switch yard & control building
• Analog samples to protection
equipment
• Coaxial cables for IRIG timing
Source
GE Protection & Control Journal
October 2008
Future Systems
• Fiber optic network IEC 61850
Process Bus
• Digitized sampled values to
protection equipment
• Timing on data network
• Increases reliability & control
• Provides isolation
• Lowers cost

6. 6Confidential © Copyright 2013
Benefits of having a timing strategy
The benefit of having a timing strategy is to ensure that you have a single
accurate and reliable time reference within and across your substations.
IEEE 1588 Telecom
Profile Grandmaster
IEEE 1588 PTP
WAN synchronization
#1
#2
#3 Rubidium
Holdover
GPS
Substation Master Clocks
Alarm Status
SNMP Monitoring
#4
Remote Management
Your timing architecture should consider
the following elements:
1. Redundant hardware and primary
reference
2. Backup time references
3. Holdover
4. Management

7. 7Confidential © Copyright 2013
Time Transfer Technologies
IRIG-B (S)NTP PTP
Accuracy (typical) 1-10ms 1ms – 10 ms 100ns-1ms
Transport media Dedicated cables Ethernet cables Ethernet cables
Protocol style Master-slave Client-server Master-slave
Built in latency
correction
No Yes Yes
Set-up Configured Configured
Self-organizing, or
configured
Update intervals 1 second Minutes 1 second
Specialized hardware Required No Required
Redundant masters
for N-1 contingency No Yes Yes

8. 8Confidential © Copyright 2013
What a Network Looks Like to PTP

9. 9Confidential © Copyright 2013
Transparent Clock
Cable delay Cable delay
Residence Time
Total delay = cable delays + switch residence time
SYNCFollow Up

10. 10Confidential © Copyright 2013
PTP Profiles
• PTP options
– Many optional features
– Works over many network types
– Used in several different industries
– Interoperability between PTP enabled devices is not guaranteed!
• Profiles
– Purpose is to ensure interoperability and meet performance
requirements for a specific application
– More restrictive set of rules than PTP
– Popular profiles
• Power Profile, IEEE C37.238-2011
• Telecom Profile, ITU G8265.1
• Audio-Visual Profile, IEEE 802.1AS

11. 11Confidential © Copyright 2013
IEC 61588 - Power Profile Standard
• IEEE C37.238-2011 Standard
- Profile for IEEE 1588 Precision Time
Protocol in power system applications
• Profile Characteristics:
- LAN (Layer 2 Ethernet Mapping)
- Multicast addressing only
- Switches must be PTP enabled
- Time transfer accuracy and holdover
time defined
• IEC 61850 will add C37.238-2011 as a
requirement in the future.
• http://standards.ieee.org/findstds/stan
dard/C37.238-2011.html

12. 12Confidential © Copyright 2013
Backup Primary Reference
with Telecom Profile PTP
Substation
• GPS primary reference
• PTP Grandmaster
• Telecom Profile slave
IEEE 1588 Telecom
Profile Grandmaster

13. 13Confidential © Copyright 2013
• 25 substations with PMUs in northern
California, USA
• Transmission elements monitored by PMUs
– Broad regional footprint monitored by
PMUs
– Voltage monitored at 60-500kV
– Many installations line voltage
• PDCs in 13 field locations, fully redundant
• Communication System availability
–Redundant architecture
– Production system (designed for
99.95% - outage of 4.5 h/year)
Synchrophasor Project
Oregon
California
Lake
Tahoe
COTP
AC
INTERTIE
Nevada - Oregon Border
(NOB)
DC
PMU locations
Super PDC locatios

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PG&E Timing Objectives for the
Synchrophasor Project

15. 15Confidential © Copyright 2013
PG&E Deployment

16. 16Confidential © Copyright 2013
Smart Substation WAN/LAN Timing Solution
IRIG-B Bus
RELAY ROOM
Event
Recorder
IRIG-B
C37.118.1-2011
Protection Schemes
Remote
Terminal
Unit (RTU)
PPS, PPM
SubstationClock
GPS/GNSS
ADM
DS1
G.703 9/13
COMMUNICATION ROOM
IEEE 1588 GMC
TP5000, SSU 2K,
Time Hub
IEEE 1588 PTP
Telecom Profile
Utility WAN
SONET/SDH
Protection
Relay
Alarm
Annunciator
Substation
Gateway
Substation Switch
(Transparent Clock)
LAN
 IEEE 1588 PTP
Power Profile
PMU
PDC

17. 17Confidential © Copyright 2013
Summary
• Using PTP for time distribution in substations is most
accurate with lowest TCO
• GPS vulnerability is real and needs to be mitigated
• Point solutions will not scale and will become
impossible to manage
• Don’t limit your options. Have a strategy to transition
from a traditional substation to a smart substation.
• Time sync will continue to increase in importance.
Quality and expertise matter.

18. 18Confidential © Copyright 2013
Thank You Doug Arnold
darnold@symmetricom.com
707-537-7902
Debbie Henderson
dhenderson@symmetricom.com
408-428-7911