Siemens 7SK80 Manual page 116

Functions
2.5 Voltage Protection 27, 59
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 PICKUP
V2 and a shorter time delay (address 5007, 59-2 DELAY) may be assigned to the upper Element (address
5016, 59-2 PICKUP V2). There are not clear cut procedures on how to set the pickup values 59-1 PICKUP
V2 or 59-2 PICKUP V2 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 /V
Dropout Pickup
condition applies to r:
r · (configured pickup threshold) ≤ 150 V with connection of phase-to-phase voltages and phase-to-Ground volt-
ages 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.
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.
Undervoltage Protection with Phase-to-phase or Phase-to-Ground Voltages
In parameter 615 OP. QUANTITY 27 you can determine for undervoltage protection in a three-phase connec-
tion 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 2.5, table 2-7).
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.
116
at addresses 5017 59-1 DOUT RATIO or 5018 59-2 DOUT RATIO. The following marginal
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012