Application - ABB RED615 Technical Manual

1YHT530004D05 D
6.3.5
615 series
Technical Manual

Application

Communication principle
Analog samples, trip-, start- and user programmable signals are transferred in each
protection telegram and the exchange of these protection telegrams is done eight
times per power system cycle (every 2.5 ms when F
Master-Master communication arrangement is used in the two-terminal line
differential solution. Current samples are sent from both line ends and the
protection algorithms are also executed on both line ends. The direct-intertrip,
however, ensures that both ends are always operated simultaneously.
Time synchronization
In numerical line differential protection, the current samples from the protections
which are located geographically apart from each other must be time coordinated
so that the current samples from both ends of the protected line can be compared
without introducing irrelevant errors. The time coordination requires an extremely
high accuracy.
As an example, an inaccuracy of 0.1 ms in a 50 Hz system gives a maximum
amplitude error of approximately around 3 percent. An inaccuracy of 1 ms gives a
maximum amplitude error of approximately 31 percent. The corresponding figures
for a 60 Hz system are 4 and 38 percent respectively.
In the IED, the time coordination is done with an echo method. The IEDs create
their own time reference between each other so that the system clocks do not need
to synchronize.
The figure shows that in the time synchronization the transmission time to send a
message from station B to station A, T1→T2, and the time to receive a message
from A to B, T4→T5, are measured. The station A IED delay from the sampling to
the start of send, T3→T4, and the local delay from receive to the station B IED
sampling T5→T6 time, are also measured for the station B IED, and vice versa.
This way the time alignment factor for the local and remote samples is achieved.
GUID-2DDF64E2-D635-4783-854A-A62E5EFB7186 V1 EN
Figure 321: Measuring sampling latency
( T − T ) ( + T − T )
2 1 5 4
P =
d
2
GUID-0CB3B365-7081-43D4-90F5-91A8082522FE V2 EN
Section 6
Supervision functions
= 50 Hz).
n
(Equation 79)
591