Calculation of Required Stability Voltage Limits
The assigned through fault current is 31.5 kA.
[fo_function87GHApplication&SettingsFunction13, 1, en_US]
[fo_function87GHApplication&SettingsFunction14, 1, en_US]
[fo_function87GHApplication&SettingsFunction15, 1, en_US]
Calculation of Stabilizing Resistor Value
The required relay setting I
set
can be calculated from:
[fo_function87GHApplication&SettingsFunction21, 1, en_US]
[fo_function87GHApplication&SettingsFunction22, 1, en_US]
[fo_function87GHApplication&SettingsFunction23, 1, en_US]
The magnetizing current is dependent on the relay operate voltage (V
set
). This is not finalized yet so a provi-
sional value is chosen from the above i.e. 107.1 < V
set
< 150
Say V
setprov
= 120 V. From CT magnetizing curve: At 120 V I
MAGLCT
= 9 mA and I
MAGNCT
= 12 mA
[fo_function87GHApplication&SettingsFunction24, 1, en_US]
[fo_function87GHApplication&SettingsFunction25, 1, en_US]
Metrosil Specification
C Value
V
set
= 120 V (i.e. > 100 V) so a C value of 1000 is chosen
Short Time Power Rating
Using the empirical formula
[fo_function87GHApplication&SettingsFunction12, 1, en_US]
Protection and Automation Functions
5.29 87GH Restricted Earth-Fault Protection – High-Impedance
Reyrolle 7SR5, Overcurrent Protection Device, Device Manual 361
C53000-G7040-C014-1, Edition 11.2019
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