Siemens SIPROTEC 7RW80 Manual page 47

Undervoltage Protection with Phase-to-phase or Phase-to-ground Voltages
For undervoltage protection with phase-to-phase or phase-to-ground voltages you have to configure at address
5109 27 Phasesthe measured quantity that is to be evaluated for the undervoltage protection. While being
configured All phases all voltages have to underrun their threshold. At Smallest phase only one voltage
has to underrun its threshold.
The threshold values are set in the value to be evaluated (see Chapter 2.2, Table 2-2).
Undervoltage protection includes three elements. The pickup value of the lower threshold is set at address
5110 or 5111, 27-2 PICKUP (depending on the voltage transformer connection, phase-to-ground or phase-
to-phase), while time delay is set at address 5112, 27-2 DELAY (short time delay). The pickup value of the
upper element is set at address 5102 or 5103, 27-1 PICKUP, while the time delay is set at address 5106,
27-1 DELAY (a somewhat longer time delay). Setting these elements in this matter allows the undervoltage
protection function to closely follow the stability behaviour of the system. A third element can be activated at
address 5131 27 Vp<, which works with a user-defined curve (address 5133). The corresponding delay time
can be configured at address 5132 27 T Vp<.
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 and the 27-2 element can be configured via the dropout ratio r =
V /V
dropout pickup
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. calcu-
lated phase-to-phase voltages from the connected phase-to-ground voltages).
The minimum hysteresis is 0.6 V.
Note
If a setting is selected such that the dropout threshold (= pickup threshold · dropout ratio) results in a greater
value than 130 V/225 V, it will be limited automatically. No error message occurs.
SIPROTEC, 7RW80, Manual
C53000-G1140-C233-1, Release date 10.2010
(5113 27-1 DOUT RATIO or 5114 27-2 DOUT RATIO). The following marginal condition
Functions
2.2 Voltage Protection 27, 59
47