ABB RELION 670 Series Technical Manual page 1430

Section 27
Glossary
WEI
VT
X.21
3I
O
3V
O
1424
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
1MRK 502 066-UUS B
Technical manual