ABB Relion 670 series - Longer Route Switching Interruptions; Detecting Accumulated Time Delay Changes with Echo Timing

After communication channels are restored, a re-synchronization with initial 20 μs
clock adjustment steps takes place for each clock synchronization message. The
clock adjustment steps gradually decrease as the internal clock differences are
reduced.
2.3.2 Longer route switching interruptions
GUID-3AB55816-1D98-4D07-8526-7201E2EF2E1E v1
When echo timing is used and route switching takes longer than 2 s, internal clocks
are synchronized with asymmetric delay included. Influence from asymmetric
delay is 2 s/40 ms x 10 μs (average 20 ms and 1 μs) = 0.5 ms, which can cause an
unwanted trip depending on the sensitivity set for the protection function.
When global time (GPS) is used, communication failure in the range of 10–30
seconds can cause a synchronization loss of the internal clocks. Communication
failure longer than 30 seconds always requires a re-synchronization of the internal
clocks. If synchronization is lost, 5–15 seconds of healthy communication is
required to get the internal clocks synchronized again and to get them working with
normal tripping times.
2.3.3 Detecting accumulated time delay changes with echo
timing
GUID-F9ED604A-1E97-4354-BD30-93C010D3313C v1
Echo timing has an additional feature that detects accumulated time delay changes
below the MaxtDiffLevel of ±200-2000 μs. This is done to avoid small changes
from creating an accumulated asymmetry which can cause an unwanted trip. Due
to asymmetry in communication channel delay, jitter and wander, and buffer
memory, this feature is restricted to four time delay changes.
The parameter used for detecting the accumulated time delay changes (sensitivity)
is DeadbandtDiff, and its setting must be coordinated with that of MaxtDiffLevel.
The influence of MaxtDiffLevel on sensitivity is shown in Figure
5.
0%
1500
3000
4500
6000
0 5 10 15 20
kA
1 ms
0.8 ms
0.6 ms
0.4 ms
0.2 ms
A
0%
1500
3000
4500
6000
0 5 10 15 20
kA
1 ms
0.8 ms
0.6 ms
0.4 ms
0.2 ms
A
IEC07000225-1-en.vsdx
Fault current at external faults
IEC07000225 V1 EN-US
Figure 5: Virtual error in amperes at different asymmetric delay times in a
telecommunication network
Section 2 1MRK 505 382-UEN B
Telecommunication networks and line differential protection
18 Communication set-up 670/650 series 2.2
Application Guide