Siemens SIPROTEC 7SJ62 Instruction Manual page 254

Functions
6-114
27-1
Anregung
Pickup
U<
V(t)
U(t)
Vn
Un
27-1 DO
U< Rf
U< AK
27-1 PU
U<
I(t)
In
Addr. 0212
LS I >
27 Delay
TU <
Anregung Pickup
Drop Out
Auslösung
Current Criterion Met
Stomkriterium erfüllt
27-1 Pickup and Current Criterion Met
Pickup
Anregung = Anregung U< und Stromkriterium erfüllt
Minimum Command Time
T
T AUSKOM = Mindestauskommandozeit
MIN COM
Figure 6-50 Typical Fault Profile for Load Side Connection of the Voltage Transformers
The instant after a circuit breaker is closed, the load side voltage begins to increase
and current begins to flow through the circuit breaker. To ensure that the 27-1 element
does not pickup, the element remains dropped out for a short period of time (about
20ms) until both the current flowing through the circuit breaker and the load side volt-
age stabilize. It is important to understand, however, that if a low voltage condition ex-
ists on the load after the circuit breaker is closed (i.e. a fault exists on the load side of
the circuit breaker), pickup of the 27-1 element will be delayed by 20 ms.
Figure 6-51 shows the logic diagram for the undervoltage protection.
Tripping
Closing
27-1
AUS EIN Anrege-
Signal
Signal
Befehl Befehl rückfall Drop Out
U<
T
20 ms
T AUSKOM
20 ms
MIN COM
27-1 Pickup
Anregung U<
Drop Out Setting
Rückfallschwelle
Pickup Setting
Anregeschwelle
t
Current Flow Monitoring
Setting
Schwelle Stromkriterium
t
t
t
Current Criterion Met
Stomkriterium erfüllt
t
7SJ62 Manual
C53000-G1140-C121-1