Siemens 6MD85, Manual

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Parameter:
Method of measurement
•
Recommended setting value
(_:11491:8) Method of measurement
=
fundamental comp.
With the
Method of measurement
parameter, you define whether the stage uses the
fundamental
comp.
(standard method) or the calculated
RMS value
.
Parameter Value Description
fundamental comp.
Select this method of measurement if harmonics or transient current peaks
are to be suppressed.
Siemens recommends using this method as the standard method.
RMS value
Select this method of measurement if you want the stage to take harmonics
into account (for example, at capacitor banks). Consider that aperiodic DC
components present in the secondary circuit are measured and can cause
an overfunction.
For this method of measurement, do not set the
threshold value
of the
stage to less than 0.1 I
rated,sec
. If currents from more than one measuring
point are added up in the current interface of a function group, the setting
value should not be set lower than 0.1 I
rated,sec
multiplied by the number of
added currents.
Parameter:
Threshold
•
Default setting
(_:11491:3) Threshold
=
1.500 A
The recommended setting value of 1.500 A is suitable for most applications.
Set the
Threshold
and
Type of character. curve
parameters for the specific application.
The setting depends on the maximum occurring operating current. Pickup by overload must be excluded since
overcurrent protection operates with short tripping times as short-circuit protection and not as overload
protection.
Set the
Threshold
parameter for lines to approx.10 %, for transformers and motors to approx. 20 % above
the maximum expected load.
Note that a safety margin is set between pickup value and threshold value. The stage only picks up at approx.
10 % above the
Threshold
.
Parameter
Type of character. curve
•
Default setting
(_:11491:101) Type of character. curve
=
IEC normal inverse
The device offers all the usual inverse-time characteristic curves according to IEC and ANSI. Select the
Type
of character. curve
required for your specific application.
Parameter:
Reset
•
Default setting
(_:11491:102) Reset
=
disk emulation
The
Reset
parameter allows you to define whether the stage decreases according to the dropout character-
istic curve (behavior of a disk emulation = rotor disc) or instantaneously.
Parameter Value Description
disk emulation
Select this setting if the device is coordinated with electromechanical
devices or other devices which perform a dropout after a disk emulation.
instantaneous
Select this setting if the dropout does not have to be performed after a disk
emulation and an instantaneous dropout is desired instead.
Parameter:
Time dial
•
Default setting
(_:11491:103) Time dial
=
1
You can use the
Time dial
parameter to displace the characteristic curve in the time direction.
Protection and Automation Functions
7.12 Voltage-Dependent Overcurrent Protection
778 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017