Functions
2.6 Voltage Protection 27, 59
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
148
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 =
V
dropout
/V
pickup
(
5113
27-1 DOUT RATIO
or
5114
27-2 DOUT RATIO
). The following marginal condition
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.
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