GE T35, Инструкция по эксплуатации

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CHAPTER 5: SETTINGS PRODUCT SETUP
T35 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL 5-111
5
The relay can be configured to operate on some PTP networks that are not strictly PP. Time accuracy can be less than
specified for a PP network. Tolerated deviations from strict PP include 1) missing declaration of PP compliance in the
messages, 2) connection to a network device that does not support the PTP peer delay mechanism, 3) jitter substantially
greater than 1
µs in received event messages, and 4) certain non-compliant announce and sync message update rates.
The relay implements PTP according to IEEE Std 1588 2008 and the equivalent IEC 61588:2009(E), sometimes referred to as
version 2 PTP. It does not support the previous version of the standard (version 1).
PTP is a protocol that allows multiple clocks in a network to synchronize with one another. It permits synchronization
accuracies better than 1 ns, but this requires that each and every component in the network achieve very high levels of
accuracy and a very high baud rate, faster than normally used for relay communications. When operating over a generic
Ethernet network, time error can amount to 1 ms or more. PP is a profile of PTP which specifies a limited subset of PTP
suitable for use in power system protection, control, automation, and data communication applications, and thereby
facilitates interoperability between different vendor’s clocks and switches. PP specifies a worst-case delivered time error of
less than 1
µs over a 16-hop network.
In a PTP system and in a PP system, the clocks automatically organize themselves into a master-slave synchronization
hierarchy with the “best” clock available making itself the "grandmaster" at the top of the hierarchy; all others make
themselves “slaves” and track the grandmaster. Typically the grandmaster clock receives its time from GPS satellites or
some other link to the international time standard. If the grandmaster fails, the next “best” clock available in the domain
assumes the grandmaster role. When a clock on start-up discovers that it is “better” than the present grandmaster, it
assumes the grandmaster role and the previous grandmaster reverts to slave. The T35 qualification mechanism accepts a
potential master clock as a new grandmaster, when in a four-second interval it has received three announce messages
from it, all better than the present grandmaster clock and better than any other announce in this interval.
Time messages issued by the grandmaster are delayed as they pass through the network both due to the finite speed of
the signal in the interconnecting fiber or wire, and due to processing delays in the Ethernet switches. Each clock and switch
implementing PP measures the propagation delay to each of its PP neighbors, and compensates for these delays in the
time received. Each network device implementing PP measures the processing delay it introduces in each time message
and compensates for this delay in the time it transmits. As a result, the time delivered to end-devices such as the UR are
virtually identical to the grandmaster time. If one of the network devices in the hierarchy does not fully implement PP, the
associated propagation delay and/or latency may not be compensated for, and the time received at the end-device can be
in error by more than 100
µs.
See the preceding Real Time Clock section for a description of when time values received via PTP are used to update the
relay’s real time clock.
The following settings are available for configuring the relay for PTP. The PTP menu displays only when the option was
purchased.
STRICT POWER PROFILE
— Power profile (IEEE Std C37.238 2011) requires that the relay only select a power profile compliant
clock as a grandmaster, that the delivered time have worst-case error of ±1 µs, and that the peer delay mechanism be
implemented. With the strict power profile setting enabled, the relay only selects as master the clocks displaying the
IEEE_C37_238 identification codes. It uses a port only when the peer delay mechanism is operational. With the strict power
profile setting disabled, the relay uses clocks without the power profile identification when no power profile clocks are
present, and uses ports even if the peer delay mechanism is non-operational. This setting applies to all of the relay’s PTP
capable ports.
PTP DOMAIN NUMBER
— Set this setting to the domain number of the grandmaster-capable clock(s) to be synchronized to. A
network can support multiple time distribution domains, each distinguished with a unique domain number. More
commonly, there is a single domain using the default domain number zero.
This setting applies to all of the relay’s PTP capable ports.
PTP VLAN PRIORITY
— This setting selects the value of the priority field in the 802.1Q VLAN tag in request messages issued
by the relay’s peer delay mechanism. In compliance with PP the default VLAN priority is 4, but it is recommended that it be
set to 7 in accordance with PTP. Depending on the characteristics of the device to which the relay is linked directly, VLAN
Priority can have no effect.
This setting applies to all of the relay’s PTP capable ports.