ABB RELION REX640 Technical Manual page 1329

Protection and control

Hide thumbs Also See for RELION REX640:

Table of Contents

1MRS759142 F

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 protection relay, the time coordination is done with an echo method. The

protection relays 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 protection relay delay from the

sampling to the start of send, T3→T4, and the local delay from receive to the

station B protection relay sampling T5→T6 time, are also measured for the station B

protection relay, and vice versa. This way the time alignment factor for the local and

remote samples is achieved.

Figure 756: Measuring sampling latency

Technical Manual

Supervision functions

(Equation 317)

(Equation 318)