Siemens siprotec SJ62 User Manual page 140

SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
The undervoltage protection works in an additional frequency range. This ensures that
the protective function is preserved even when it is applied, e.g. as motor protection
in context with decelerating motors. However, the r.m.s. value of the positive-se-
quence voltage component is considered too small when severe frequency deviations
exist. This function therefore exhibits an overfunction. If applications are anticipated in
which the frequency range of f
not return a correct result and must be switched off.
Figure 2-44 shows a typical voltage profile during a fault for source side connection of
the voltage transformers. Because full voltage is present after the circuit breaker is
opened the current supervision CS described above is not necessary in this case.
After the voltage drops below the pickup setting, tripping is initiated after time delay
27-1 DELAY. As long as the voltage remains below the drop out setting, reclosing is
blocked. Only after the fault has been cleared, i.e. when the voltage increases above
the drop out level, the element drops out and allows reclosing of the circuit breaker.
Figure 2-44 Typical fault profile for source side connection of the voltage transformer (with-
out current supervision)
Figure 2-45 shows a fault profile for a load side connection of the voltage transformers.
When the circuit breaker is open, the voltage disappears (the voltage remains below
the pickup setting), and current supervision is used to ensure that pickup drops out
after the circuit breaker has opened (BkrClosed I MIN).
After the voltage drops below the pickup setting, tripping is initiated after time delay
27-1 DELAY. When the circuit breaker opens voltage decreases to zero and under-
voltage pickup is maintained. The current value also decreases to zero so that current
supervision is reset as soon as the release threshold (BkrClosed I MIN) is exceed-
ed. Thanks to the AND-combination of voltage and current criteria pickup of the pro-
tective function is also reset. As a consequence, energization is admitted a new when
the minimum command time elapsed.
± 10%, will be exceeded, the current criterion will
Nom
2.6 Voltage Protection 27, 59
138