ABB REG316 4 Series - Page 114

ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. F
3-76
Undervoltage setting “Hold-Voltage”
Providing the overcurrent unit has picked up and the undervol-
tage unit picks up as well, the undervoltage unit “Hold-Voltage”
latches it in the pick-up state should the fault current fall below
its pick-up setting. The setting of the undervoltage unit must be
such that it can clearly distinguish between a normal load and a
fault condition. Because of the different conditions prevailing
during symmetrical and asymmetrical faults, the positive-
sequence component of the three-phase system is evaluated. A
setting well below the lowest voltage that can occur during
normal load conditions is chosen (Fig. 3.5.5.3).
"Hold-Voltage"
settin
g
for latchin
g
HEST 905 014 C
U
N
U
Minimum short-time
load voltage
Fig. 3.5.5.3 Operating characteristic of the undervoltage control
unit
U
N
= rated voltage of the undervoltage unit
Reset time “Hold-Time”
The reset time defined by the parameter “Hold-Time” determines
how long the overcurrent unit remains latched to ensure a
tripping signal of sufficient duration. The delay starts at the in-
stant of tripping.