Siemens 6MD85, Manual

Page: 786 / 1256

Parameter:
Operate delay
•
Default setting
(_:181:6) Operate delay
=
3 s
The
Operate delay
must be set for the specific application.
Parameter:
Dropout ratio
•
Recommended setting value
(_:181:4) Dropout ratio
=
0.95
The recommended set value of
0.95
is appropriate for most applications. To achieve high measurement preci-
sion, the
Dropout ratio
can be reduced, to 0.98, for example.
Parameter:
Pickup mode
•
Recommended setting value
(_:181:101) Pickup mode
=
1 out of 3
With the
Pickup mode
parameter, you define whether the protection stage picks up if all 3 measuring
elements detect the overvoltage condition (
3 out of 3
) or if only 1 measuring element detects the over-
voltage condition (
1 out of 3
).
Parameter Value Description
1 out of 3
Select the setting for protection applications or for monitoring the voltage
range.
Siemens recommends
1 out of 3
as the default setting. This reflects how
the function behaved in previous generations (SIPROTEC 4, SIPROTEC 3).
3 out of 3
Select this setting when using the stage to disconnect from the power
system (in the case of wind farms, for example).
Operation as Supervision Function
If you want the stage to have a reporting effect only, generation of the operate indication and fault logging
can be disabled via the
Operate & flt.rec. blocked
parameter.
EXAMPLE
Example for 2-stage overvoltage protection
The example describes the possible settings for a 2-stage overvoltage protection function. We will look at the
settings of the parameters
Threshold
and
Operate delay
.
•
1. Stage:
To detect stationary overvoltages, set the threshold value of the first overvoltage-protection element at
least 10 % above the max. stationary phase-to-phase voltage anticipated during normal operation. When
setting the parameter
Measured value
to phase-to-phase voltage and a secondary rated voltage of
100 V, the secondary setting value of the first overvoltage-protection element is calculated as follows:
Threshold value: 10 % above V
rated
V
threshold, sec
= 1.1 V
rated, sec
= 1.1 × 100 V = 110 V
This requires that the primary rated voltages of protected object and voltage transformer are identical. If they
are different, you have to adjust the pickup value.
For the
Operate delay
set a value of 3 s.
•
2. Stage:
The second overvoltage-protection stage is intended for high overvoltages with short duration. A high
pickup value is selected here, for example, 1.5 times the rated voltage. A time delay setting of 0.1 s to
0.2 s is sufficient then.
Stage Setting Values
Threshold value Time delay
1 1.1 V
rated
3 s
Protection and Automation Functions
7.13 Overvoltage Protection with 3-Phase Voltage
786 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017