ABB REX 521 Technical Reference Manual, Standard Configurations page 83

1MRS 751802-MUM
7.1.6.
Protection Relay
Technical Reference Manual, Standard Configurations
3U< and 3U<<
Abnormal busbar voltages can be caused by faults in the network or a faulty tap
changer or voltage regulator of a power transformer. The function blocks are
designed for the single-phase, two-phase and three-phase undervoltage protection
whenever the DT characteristic or, as concerns 3U<, the IDMT (Inverse Definite
Minimum Time) characteristic is appropriate. Suppression of harmonics is possible.
3U<
BS1
BS2
GROUP START
RESET TRIP
)LJ  )XQFWLRQ EORFN V\PEROV RI 8 DQG 8
Three-phase under voltage protection, low-set stage, 3U<
Start voltage
Operate time
Operation mode
Time multiplier
Measuring mode
Operation accurcy
Start time
Reset time
Reset ratio, typically
Retardation time
Operate time accuracy in DT mode
Accuracy class index E in inverse-time mode ± 35 ms or the accuracy appearing when the measured
3U<<
BS1
BS2
START
GROUP
TRIP
RESET
0.10...1.20 x Un
0.10...300.00 s
Not in use
Definite time
C curve
0.1...1.00
Mode 1 (Phase-to-phase voltages / Peak-to-peak meas.)
Mode 2 (Phase-to-phase voltages / Fundam.freq.)
Mode 3 (Phase-to-earth voltages / Fundam.freq.)
Note! The values below apply when f/fn = 0.95...1.05
±2.5% of set value
Injected voltages > 1.1 x start voltage:
internal time < 42 ms
total time < 50 ms
40...1000 ms
(depends on the minimum pulse width set for the trip
output)
0.96
(depends on the value of the "Oper. hysteresis"
parameter)
< 50 ms
±2% of set value or ±20 ms
voltage varies ±2.5%
REX 521
83