Precision Time Protocol (Ptp) Functional - GE T1000 Technical Manual

GE Reason Switches
Figure 65: Synchronization classes, shown at IEC 61850-90-4 Technical Report, section 14.1
12.2

Precision Time Protocol (PTP) Functional

Although PTP protocol allows to use both Ethernet (multicast) or IP (UDP transport mechanism), IEC 61850-90-4 Technical
Report advert that only layer 2 communication has accuracy for power system applications, such as synchronization of IED
equipment. Thus, it is recommended that Ethernet protocol is used for power system communication applications.
REASON SWITCHES-TM-EN-3

PPS (pulse-per-second) and IRIG-B signals for non-Ethernet synchronism
networks;

NTP (Network Time Protocol) and PTP (Precision Time Protocol) for
synchronism network over Ethernet.
In addition, IEC-61850-90-4 shows a table containing synchronization classes of
accuracy, to separate critical synchronism application from less critical applications.
The following table is the one shown in section 14.1 of the IEC 61850-90-4 Technical
Report.
When using time synchronization over Ethernet network, only PTP has accuracy to
fulfill all classes. PPS signals can be used in T4 class applications, the same class that
IRIG-B signals are included. Although not mentioned explicitly at IEC 61850-90-4
Technical Report, PTP signals accuracy fulfills T5 class applications.
Precision Time Protocol (PTP) uses the Ethernet frames to transport synchronism
messages, to do time synchronization of several IED connected to the network. The
protocol itself allows to be used layer 2 (Multicast transport mechanism) or layer 3
(UDP transport mechanism) messages, which the chosen one will remain on the
application requirements.
The messages are transmitted in a master-slave method. Different from NTP
protocol, where the slave sends a request to the master to receive time data, in a PTP
network the master multicasts its synchronization messages throughout the
network, and slaves receive the messages cyclically, while the master remains
sending it to the network. The next figure exemplifies a PTP-aware network.
Chapter 4 – Functions
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