Functions
2.2 Voltage Protection 27, 59
SIPROTEC, 7RW80, Manual
C53000-G1140-C233-1, Release date 10.2010
46
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 asymmetries.
Overvoltage protection includes three elements. Thus, with configuration of the negative system, a longer time
delay (Adresse
5004
,
59-1 DELAY
) may be assigned to the lower element (address
5015
,
59-1 PICKUP
V2
) depending on whether phase-ground or phase-phase voltages are connected) and a shorter time delay
(address
5007
,
59-2 DELAY
) may be assigned to the upper element (Address
5016
,
59-2 PICKUP V2
). A
third element can be activated at address
5033
59 Vp> V2
, which works with a user-defined curve (address
5035
).
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
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 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 with evaluation of the positive sequence components consists of two definite time el-
ements. 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 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.
