Functions
2.6 Voltage Protection 27, 59
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
147
Overvoltage Protection - Negative Sequence System V2
In a three-phase transformer connection, parameter 614 OP. QUANTITY 59 can determine that the negative
sequence system V2 can be evaluated as a measured value for the overvoltage protection. The negative se-
quence system detects voltage unbalance and can be used for the stabilization of the time overcurrent protec-
tion. In backup protection of transformers or generators, the fault currents lie, in some cases, only slightly above
the load currents. In order to obtain a pickup threshold of the time overcurrent protection that is as sensitive as
possible, its stabilization via the voltage protection is necessary to avoid false tripping.
Overvoltage protection comprises two elements. Thus, with configuration of the negative system, a longer time
delay (address 5004, 59-1 DELAY) may be assigned to the lower element (address 5015, 59-1-V2 PICKUP
and a shorter time delay (address 5007, 59-2 DELAY) may be assigned to the upper element (address 5016,
59-2-V2 PICKUP). There are not clear cut procedures on how to set the pickup values 59-1-V2 PICKUP or
59-2-V2 PICKUP as they depend on the respective station configuration.
The time delays of the overvoltage elements are entered at addresses 5004 59-1 DELAY and 5007 59-2
DELAY, and should be selected in such manner that they make allowance for brief voltage peaks that are gen-
erated during switching operations and also enable clearance of stationary overvoltages in due time.
Dropout Threshold of the Overvoltage Protection
The dropout thresholds of the 59-1 element and the 59-2 element can be configured via the dropout ratio r =
V
Dropout
/V
Pickup
at addresses 5017 59-1 DOUT RATIO or 5018 59-2 DOUT RATIO. The following marginal
condition applies to r:
r · (configured pickup threshold) ≤ 150 V with connection of phase-to-phase voltages and phase-to-ground
voltages or
r · (configured pickup threshold) ≤ 260 V with calculation of the measured values from the connected voltages
(e.g. phase-to-phase voltages calculated from the connected phase-to-ground voltages).
The minimum hysteresis is 0.6 V.
Undervoltage Protection - Positive Sequence System V1
The positive sequence component (V1) can be evaluated for the undervoltage protection. Especially in case of
stability problems, their acquisition is advantageous because the positive sequence system is relevant for the
limit of the stable energy transmission. Concerning the pickup values there are no specific notes on how to set
them. However, because the undervoltage protection function is primarily intended to protect induction ma-
chines from voltage dips and to prevent stability problems, the pickup values will usually be between 60% and
85% of the nominal voltage. Please note that in case of frequency deviations of > 5 Hz, the calculated RMS
value of the voltage is calculated too low and the device may thus tend to overfunctioning.
The threshold value is multiplied as positive sequence voltage and set to √3
, thus realizing the reference to the
nominal voltage.
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.
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