Introduction to IEEE 1588 v2

1

Jim McGhee, Utility Market Manager, RuggedCom Inc.

(JimMcGhee@RuggedCom.com)

Grid-Interop 2010

IEEE 1588 standard overview• It is a high precision time synchronization (<1us) standard that uses

Ethernet communication network• Also called PTP – Precision Time Protocol• IEEE 1588 version 2 Release mid 2009• Unlike NTP/SNTP network devices (switches) actively participate in

order to minimize network and internal delays• No need for separate cabling (IRIG-B, 1PPS)• Fault tolerance using Redundant Clocks with BMC (Best Master Clock

Selection Algorithm)• Low cost to implement in IEDs• Reduce reliance on GPS• Hardware time-stamping is a key feature

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Problem of Path Delay• Ethernet switches introduce jitter from queuing• Queuing unpredictable; QoS helps a little• 100Mbps, 64byte packet -> 5us• 100Mbps, 1500byte packet -> 120us• 1588 v2 provides two solutions:

– Boundary clock: re-sync at every hop– Transparent clock: add correction field– Transparent clock: add correction field

Must address path delay jitter introduced by switches or even 1ms accuracy in jeopardy.

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Peer-to-Peer Path Delay Measurement• Similar delay_req/delay_resp mechanism as End-to-End delay

measurement

SWITCH FABRIC

PTP

Transparent ClockGrandmaster

Clock

PTP

Ordinary Clock

PTPt3 is t4 is t1 is

capturedt2 is

captured

PHY

MAC

PHY

MAC

PHY

MAC

PHY

MAC

Timestamp Unitst1t2 t3 t4

pdelay_req and pdelay_resp Messages

GM to TC Path Delay = (t2 – t1 + t4 – t3) / 2

t3 is captured

t4 is captured

capturedcaptured

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What is a Transparent Clock?

MAC

SWITCH FABRIC

MAC

PTP

Transparent ClockGrandmaster

Clock

MAC

PTP

Ordinary Clock

MAC

PTP

Timestamp

t1 inserted to

message

t2 is capture

upon ingress

Packet in queue

t3 upon egress,

correction = t3 – t2

t4 is captured

up ingress

Time is updated

• TC measures residence time of sync/delay messages in switches and adds to correction field of sync or follow-up messages

• TC causes less jitter in highly cascaded networks

PHY PHY PHYPHY

Timestamp Unitst1 t2 t3 t4

Sync Message

Sync Correction Field = t3 – t2

ingress

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Benefits of IEEE 1588 v2 for Substations• Eliminates the extra cabling requirements of

IRIG-B by using common Ethernet cabling

• Achieves guaranteed millisecond accuracy for substation sequence of event timing

• Sub-microsecond accuracy for critical applications like:– IEC 61850-9-2 Process Bus– IEC 61850-9-2 Process Bus

– Synchrophasors

• Eases the deployment of precision timing networks in modern ‘All-Ethernet’ substations

• Facilitates migration path from legacy solutions and paves the way towards IEC 61850 Edition II

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Clock Sourcese.g. GPS, NTP, Local

– IEC 61850-9-2 (Process Bus) application requires timing accuracy in range of 1us

– Critical power system parameters (e.g. current and voltage) are sampled , time stamped and multicast over the substation Ethernet LAN or the “Process Bus”

SubstationIEC 61850-9-2(Process Bus)

Ethernet Switch with1588 Master Clock

IEC 61850 Precision Timing Applications

IED- IntelligentElectronic Device

Power System

A

B

C

MU

MU

Merging Unit

Ethernet LAN

Ethernet Switch with1588 Transparent clock

IEDs with1588 Slave Clock

SampledValues

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Conventional Approach for Time Synch

Communications with IEDs based on Ethernet

Beside Ethernet network there is a dedicated wiring for time synch signal

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Migration Path for IEEE 1588 Time Synch

Time synch distributed over IEEE 1588 enabled Ethernet network

IEEE 1588 converted to IRIG-B on “last meter” for non-IEEE 1588 capable IEDs

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Full Implementation of IEEE 1588 Time Synch

All devices in the substation implement IEEE 1588

New generation of IEDs with specialized communications card is needed

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– Synchrophasors put measurements from across any portion of the power system on the same, absolute

time base.

– Synchrophasor applications require precise time synchronization of the parameters measured

throughout the power system

Synchrophasor Applications

– Synchrophasor measurements enable measurement-based analysis of power system stability and can give early evidence that the system is becoming unstable

– Critical in helping avoid blackouts

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Thank You!

Grid-Interop 2010