Siemens siprotec SJ62 User Manual page 145

2 Functions
Undervoltage Pro-
tection with Phase
Voltages
Dropout Threshold
of the Undervoltage
Protection
Current Criterion
for Undervoltage
Protection
143
The time delay settings should be set that tripping results when voltage dips occur,
which could lead to unstable operating conditions. On the other hand, the time delay
should be long enough to avoid tripping due to momentary voltage dips.
Undervoltage protection includes two definite time 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.
The smallest of the phase-to-phase voltages Vphph can also be configured as mea-
sured quantity for the undervoltage protection with three-phase connection by means
of parameter 615 OP. QUANTITY 27 instead of the positive sequence component
(V1). The threshold values have to be set as phase-phase quantities.
The time delay settings should be set that tripping results when voltage dips occur
which could lead to unstable operating conditions. On the other hand, the time delay
should be long enough to permissable short voltage dips.
Undervoltage protection includes two definite time 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.
The dropout thresholds of the 27-1 element and the 27-2 element can be set via the
dropout ratio r = V
dropout
RATIO). In this, the following marginal condition always holds for r:
r · (configured pickup threshold ) ≤ 120 V with connection of phase-to-phase voltages
or
r · (configured pickup threshold ) ≤ 210 V with connection of 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.
The 27-2 and 27-1 elements 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 criterion must be fulfilled in addition to the correspond-
ing 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. Therefore, it is possible to achieve that pickup of undervoltage
protection drops out when the line is disconnected from voltage supply. Furthermore,
(5113 27–1 DOUT RATIO or 5114 27–2 DOUT
/V
pickup
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015