Siemens SIPROTEC 7SJ62 Manual page 148

Functions
2.6 Voltage Protection 27, 59
Undervoltage Protection with Phase-to-phase or Phase-to-ground Voltages
In parameter 615 OP. QUANTITY 27 you can determine foor undervoltage protection in a three-phase con-
nection that instead of the positive-sequence system V1, the smallest of the phase-to-phase voltages Vphph
or the smallest phase-to-ground voltage Vph-n is configured as a measured quantity. The threshold values are
set in the quantity to be evaluated (see Section 2.6, table 2-11).
Undervoltage protection comprises two 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 way allows the undervoltage pro-
tection function to closely follow the stability behavior of the system.
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.
Note
During configuration of a single-phase voltage transformer connection (parameter 240 VT Connect. 1ph not
equal to NO), parameters 213 VT Connect. 3ph and 615 OP. QUANTITY 27 are not evaluated. In this
case, exclusively parameters 5103 27-1 PICKUP or 5111 27-2 PICKUP are relevant for the threshold values
of the undervoltage protection.
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 =
(5113 27-1 DOUT RATIO or 5114 27-2 DOUT RATIO). The following marginal condition
V /V
dropout pickup
applies to r:
r · (configured pickup threshold) ≤ 120 V with connection of phase-to-phase voltages and phase-to-ground
voltages) or
r· (configured pickup threshold) ≤ 210 V with calculation of the measured values from the connected voltages
(e.g. calculated 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 120 V / 210 V, it will be limited automatically. No error message occurs.
148
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008