Functions
2.5 Voltage Protection 27, 59
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
108
The time settings should be selected such that tripping occurs in response to voltage dips that lead to unstable
operating conditions. On the other hand, the time delay should be long enough to avoid tripping on short-term
voltage dips.
Dropout threshold of the undervoltage protection
The dropout thresholds of the 27-1 Element and the 27-2 Element can be configured via the dropout ratio r =
V
Dropout
/V
Pickup
at addresses 5113 27-1 DOUT RATIO or 5114 27-2 DOUT RATIO. The following marginal
condition applies to r:
r · (configured pickup threshold ≤ 130 V of instantaneously measured voltages (phase-to-phase voltages or
phase-to-ground voltages or
r · (configured pickup threshold ≤ 225 V for evaluation of values calculated from measured voltages (e.g. cal-
culated phase-to-phase voltages from the connected phase-to-ground voltages).
The minimum hysteresis is 0.6 V.
Note
If a setting is accidentally selected so that the dropout threshold (= pickup threshold · dropout ratio) results in
a value greater than 130 V/225 V, it will be reduced automatically. No error message occurs.
Current Criterion for Undervoltage Protection
The 27-1 Element and the 27-2 Element can be supervised by the current flow monitoring setting. If the
CURRENT SUPERV. is switched ON at address 5120 (factory setting), the release condition of the current cri-
terion must be fulfilled in addition to the corresponding undervoltage condition, which means that a configured
minimum current (BkrClosed I MIN, address 212) must be present to make sure that this protective function
can pick up. Thus it can be achieved that pickup of the undervoltage protection drops out when the line is dis-
connected from voltage supply. Furthermore, this feature prevents an immediate general pickup of the device
when the device is powered-up without measurement voltage being present.
Note
If parameter CURRENT SUPERV. is set to disabled at address 5120, the device picks up immediately if the
measuring-circuit voltage fails and the undervoltage protection is enabled. Furthermore, configuration can be
performed by pickup of measuring-circuit voltage or blocking of the voltage protection. The latter can be initiat-
ed via device operation in DIGSI and via communication from the control center by means of a tagging
command for blocking the voltage protection. This causes the dropout of the pickup and parameterization can
be resumed.
Please note that the pickup threshold BkrClosed I MIN (address 212) also affects the overload protection,
the load jam protection, the cold load pickup function and the CB maintenance.
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