2 Functions
260
7SA522 Manual
C53000-G1176-C155-3
If a power transformer is located between the feeder voltage transformers and the bus-
bar voltage transformers (Figure 2-110), its vector group can be compensated for by
the 7SA522 relay, so that no external matching transformers are necessary.
Figure 2-110 Synchronism check across a transformer
The synchronism check function in the 7SA522 usually operates together with the in-
tegrated 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, closing is possible with synchronous or asynchronous system conditions
or both. Synchronous closing means that the closing command is issued as soon as
the critical values (voltage magnitude difference 0D[9ROW'LII, angle difference
0D[$QJOH'LII, and frequency difference 0D[)UHT'LII) lie within the set
tolerances. For closing with asynchronous system conditions, the device calculates
the correct timing of the closing command from the angle difference 0D[$QJOH
'LII and the frequency difference 0D[)UHT'LII 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. Different frequency
limit thresholds apply to closing at synchronism and asynchronous conditions: If
closing shall be permitted exclusively under synchronous system conditions, the fre-
quency difference limit for this condition can be set. If closing is permitted under syn-
chronous as well as under asynchronous system conditions, a frequency difference
below 0.01 Hz is treated as a synchronous condition, a higher frequency difference
value can then be set for closing under asynchronous system conditions.
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