ABB RELION REX640 Technical Manual page 891

1MRS759142 C
REX640
Technical Manual
Impedance measurement
DSTPDIS provides three independent phase-to-earth and phase-to-phase measuring
elements per zone. The three-phase fault is measured with a dedicated measurement
element.
The impedance measurement is done similarly regardless of the zone shape. The
operation is based on impedance mapping where the fault loop impedance is first
calculated and then compared with the zone boundaries. If impedance is recognized
inside the operation zone, the corresponding operate output is activated after the
operate time has elapsed.
Phase-to-earth impedance measuring elements
The phase-to-earth impedance measuring elements provide the basic earth-fault
protection in direct or low-impedance earthed networks. The earth-fault protection is
enabled with the setting Op Mod Gnd loops Znx (x = 1...5) = "True". The enabling
requires that all three phase-to-earth voltages are measured. Otherwise, the release of
the earth-fault measuring elements is automatically blocked.
The reach of phase-to-earth measuring elements is based on loop impedance
R
0

Z Z RF R
1 + N + = 1 +

3

GUID-2D66C10E-FE4F-41A2-930F-EB0477DE621F V1 EN
The earth return path impedance is included in the calculated fault
loop impedance of the phase-to-earth measuring element.
R X X
− 1 0 − 1
  
j X
 + ⋅ 1 +  +

3
  
Section 4
Protection functions
RF
(Equation 221)
885