Pos Description
1 Scheme earthing point
Ensure that only one earthing point exists in this scheme.
2 One-phase plate with stabilizing resistor and metrosil. Protective earth is a separate 4 mm
screw terminal on the plate.
3 Necessary connection for the metrosil.
4 Position of optional test switch for secondary injection into the high impedance differential IED.
5 Necessary connection for stabilizing resistor.
6 How to connect the high impedance restricted earth fault protection scheme to one CT input in
IED.
7.1.4 Setting guidelines
IP14945-1 v1
M13076-3 v2
The setting calculations are individual for each application. Refer to the different
application descriptions below.
7.1.4.1 Configuration
M13076-5 v4
The configuration is done in the Application Configuration tool.
7.1.4.2 Settings of protection function
M13076-10 v6
Operation: The operation of the high impedance differential function can be
switched On or Off.
U>Alarm: Set the alarm level. The sensitivity can roughly be calculated as a
certain percentage of the selected Trip level. A typical setting is 10% of U>Trip
This alarm stage can be used for scheme CT supervision.
tAlarm: Set the time delay for the alarm. A typical setting is 2-3 seconds.
U>Trip: Set the trip level according to the calculations (see examples below for a
guidance). The level is selected with margin to the calculated required voltage to
achieve stability. Values can be within 20V - 400V range dependent on the
application.
SeriesResistor: Set the value of the used stabilizing series resistor. Calculate the
value according to the examples for each application. Adjust the resistor as close as
possible to the calculated value. Measure the value achieved and set this value for
this parameter.
The value shall always be high impedance. This means for
example, for 1A circuits say bigger than 400 ohms (400 VA) and
Section 7 1MRK 506 369-UEN B
Differential protection
138 Line distance protection REL670 2.2 IEC
Application manual
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