Siemens SIPROTEC 7SK80 Manual page 104

Functions
2.5 Voltage Protection 27, 59
Figure 2-28
Upon the closing of the circuit breaker, current criterion is delayed for a short period of time. If the voltage cri-
terion drops out during this time period (about 60 ms), the protection function does not pick up. Therefore no
fault record is created when voltage protection is activated in a healthy system. It is important to understand,
however, that if a low voltage condition exists on the load after the circuit breaker is closed (unlike Figure 2-28),
the desired pickup of the element will be delayed by 60 ms.
The following figure shows the logic diagram of the undervoltage protection function.
104
Typical fault profile for load side connection of the voltage transformers (with current supervi-
sion)
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010