ABB RELION REX640 Technical Manual page 1585

1MRS759142 C
REX640
Technical Manual
(one third connected in each phase)
• The natural asymmetry in a real network is due to differences in individual phase
admittances and it is presented with an asymmetry admittance concentrated into
phase A and presented with admittance
Y G j B
asymm = asymm + ⋅
GUID-9A982A5A-78E0-43CB-8069-73773CD0CE5E V1 EN
(only connected in phase A)
• The single-phase earth fault in the network is presented with admittance Y
+ j · B . Fault impedance can be assumed to be purely resistive (fault resistance
f
R ) which is connected between phase A, B or C and earth depending on the
f
faulted phase.
• The zero-sequence impedance of the earthing (or main) transformer with the
neutral point connected to the coil is represented with impedance Z
three-phase equivalent scheme one third must be applied).
asymm
Section 9
Control functions
(Equation 348)
= G
f f
(in the
oTr
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