IEC10000062 V1 EN-US
Figure 4:
Setting the MaxtDiffLevel in PCM600
The setting range for
MaxtDiffLevel is ±200-2000 μs, and it must be coordinated with
reference to the sensitivity of the protection function. This setting is only relevant for echo
timing.
MaxtDiffLevel is defined and measured at a sudden change in time difference between the line
ends induced by route switching. If the set value for
MaxtDiffLevel is exceeded, the protection
function gets blocked. To avoid unwanted trips produced by a number of small changes below
the set value, these small changes are summated and checked to be below
MaxtDiffLevel.
The line differential protection IED has no supervising function that could detect the
difference between asymmetric delay, buffer memory delay, telecommunication network jitter
and wander, and internal clock drift. The sum of these factors is supervised by observing the
deviation between the internal clocks in all IEDs.
GPSSyncErr denotes GPS synchronization error, and it is activated when GPS global time and
internal clock time deviate by more than 16 μs. If activated, the differential protection function
can be set to be blocked or the echo mode can be set to be activated.
In an SDH network (≥ 2 Mbit/s) with an acceptably small asymmetric delay, for example G.703
E1, maximum time deviation of 2 x ±300 μs can be used. In a PDH network (n x 64 kbit/s) with a
buffer memory of for example 100 μs, typical maximum time deviation is 2 x ±400 μs. The
actual setting value is to be calculated accordingly.
2.3.1.2
Reference clock deviation from the set maximum time deviation
GUID-0FC23ED9-2CDB-48EE-ADDB-81D39E334F56 v1
Reference clock deviation lower than the set maximum time deviation
Route switching that causes the virtual difference between the internal clocks of respective
line differential protection IEDs to be lower than the set maximum time deviation due to
asymmetry in the communication channel delay, jitter and wander, and buffer memory, does
not cause a communication failure alarm or blocking of the protection function. The deviation
is considered to be within the accuracy requirements, and will be compensated for by the
normal synchronization mechanisms of the internal clocks.
If route switching takes longer than 2 s, master and slave IEDs start to re-synchronize after a 4
s delay incorporating the new channel asymmetry. Synchronization adjusts the internal clock
differences of differential protection IEDs at different line ends to be within ±1 μs. Time
synchronization messages are evaluated every 5 ms. If maximum time deviation is set to ±200
μs, it takes approximately 10 seconds to reach new synchronization. Synchronization reaches
the ±1 μs accuracy after an additional 10-15 seconds.
Section 2
1MRK 505 382-UEN E
Telecommunication networks and line differential protection
14
Communication set-up, 670/650 series
Application Guide
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