Siemens siprotec 7SD5 User Manual page 315

Figure 2-131
The synchronism check function in the 7SD5 usually operates in conjunction with the
integrated automatic reclose, manual close, and the control functions of the relay. It is
also possible to employ an external automatic reclosing system. In such a case, signal
exchange between the devices is accomplished via binary inputs and outputs.
When closing via the integrated control function, the configured interlocking conditions
may have to be verified before checking the conditions for synchronism. After the syn-
chronism check grants the release, the interlocking conditions are not checked a
second time.
Furthermore, switching is possible with synchronous or asynchronous system condi-
tions or both. Synchronous switching means that the closing command is issued as
soon as the critical values (voltage magnitude difference Max. Volt. Diff, angle
difference Max. Angle Diff, and frequency difference Max. Freq. Diff) lie
within the set tolerances. For switching with asynchronous system conditions, the
device calculates the correct timing of the closing command from the angle difference
Max. Angle Diff and the frequency difference Max. Freq. Diff such that the
voltages on the busbar and the feeder circuit have exactly the same phase relationship
at the instant that the circuit breaker primary contacts close. For this purpose the
device must be informed on the operating time of the circuit breaker for closing. Differ-
ent frequency limit thresholds apply to switching under synchronism and asynchro-
nous conditions. If closing is permitted exclusively under synchronous system condi-
tions, the frequency difference limit for this condition can be set. If closing is permitted
under synchronous as well as under asynchronous system conditions, a frequency dif-
ference below 0.01 Hz is treated as a synchronous condition, a higher frequency dif-
ference value can then be set for closing under asynchronous system conditions.
The synchro check function only operates when it is requested to do so. Various pos-
sibilities exist for this purpose:
• Measuring request from the internal automatic reclosure device. If the internal au-
• Measuring request from an external automatic reclosure device. The measuring
7SD5 Manual
C53000-G1176-C169-1
Synchronism check across a transformer
tomatic reclosing function is set accordingly (one or more reclosing attempts set to
synchronism check, see also Section 2.15.2), the measuring request is accom-
plished internally. The release conditions for automatic reclosing apply.
request must be activated via the binary input „>Sync. Start AR" (No. 2906).
The release conditions for automatic reclosing apply.
2.16 Synchronism and Voltage Check (optional)
315