ABB Relion 670 Series Applications Manual page 360

Section 24
Glossary
WEI
VT
X.21
3I
O
3V
O
354
Weak end infeed logic
Voltage transformer
A digital signalling interface primarily used for telecom equipment
Three times zero-sequence current.Often referred to as the residual or the
ground-fault current
Three times the zero sequence voltage. Often referred to as the residual
voltage or the neutral point voltage
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1MRK 511 407-UUS Rev. J
Phasor measurement unit RES670
Application manual