Siemens 6MD85, Manual

Page: 791 / 1256

Where
T
inv
Inverse-time delay
T
p
Time multiplier (parameter
Time dial
)
V Measured voltage
V
thresh
Threshold value (parameter
Threshold
)
k Curve constant k (parameter
Charact. constant k
)
α Curve constant α (parameter
Charact. constant α
)
c Curve constant c (parameter
Charact. constant c
)
When V/V
thresh
is equal to or greater than 20, the inverse-time delay does not decrease any further.
Dropout Behavior
When the voltage falls below the dropout threshold (0.95 × pickup factor × threshold value), the pickup signal
is going and the dropout is started. You can define the dropout behavior via parameter
Reset time
. Instan-
taneous reset takes place by setting
Reset time
to 0 s. A delayed reset takes place by setting the desired
delay time.
During the
Reset time
(> 0 s), the elapsed operate delay is frozen. If the pickup value is exceeded again
within this period, the stage operates when the rest of operate delay expires.
Blocking the Stage
In the event of blocking, the picked up stage will be reset. Blocking is possible externally or internally via the
binary input signal
>Block stage
.
Application and Setting Notes
Parameter:
Method of measurement
•
Recommended setting value
(_:8) Method of measurement
=
fundamental comp.
With the
Method of measurement
parameter, you define whether the tripping stage uses the fundamental
component (standard method = default setting) or the calculated RMS value.
Parameter Value Description
fundamental comp.
Select this method of measurement to suppress harmonics or transient
voltage peaks.
Siemens recommends this method of measurement as the default setting.
RMS value
Select this method of measurement if you want the stage to take harmonics
into account (for example, at capacitor banks). Do not set the threshold
value of the tripping stage under 10 V for this method of measurement.
Parameter:
Measured value
•
Default setting
(_:9) Measured value
=
phase-to-phase
With the
Measured value
parameter, you define whether the tripping stage monitors the phase-to-phase
voltages V
AB
, V
BC
, and V
CA
or the phase-to-ground voltages V
A
, V
B
, and V
C
.
7.13.8
Protection and Automation Functions
7.13 Overvoltage Protection with 3-Phase Voltage
SIPROTEC 5, High-Voltage Bay Controller, Manual 791
C53000-G5040-C015-9, Edition 11.2017