Siemens SIPROTEC 7SK80 Manual page 101

The positive and negative sequence voltages stated in the table are calculated from the phase-to-Ground volt-
ages.
Note
For capacitive voltage connections, the same values as with the connection type Van, Vbn, Vcn are used.
Current Criterion
Depending on the system, the primary voltage transformers are arranged either on the supply side or the load
side of the associated circuit breaker. These different arrangements lead to different behaviour of the voltage
protection function when a fault occurs. When a tripping command is issued and a circuit breaker is opened,
full voltage remains on the supply side while the load side voltage becomes zero. When voltage supply is sup-
pressed, undervoltage protection, for instance, will remain picked up. If pickup is to drop out, the current can
be used as an additional criterion for pickup of undervoltage protection (current supervision CS). Undervoltage
pickup can only be maintained when the undervoltage criterion satisfied and a settable minimum current level
(BkrClosed I MIN) are exceeded. Here, the largest of the three phase currents is used. When the current
decreases below the minimum current setting after the circuit breaker has opened, undervoltage protection
drops out.
Note
If parameter CURRENT SUPERV. is set to disabled in address 5120, the device picks up immediately without
measurement voltage and the undervoltage protection function in pickup. Apply measuring voltage or block the
voltage protection to continue with configuration. Moreover you have the option of setting a flag via device op-
eration for blocking the voltage protection. This initiates the reset of the pickup and device configuration can be
resumed.
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
Functions
2.5 Voltage Protection 27, 59
101