ABB REB500 - Page 61

1MRK 505 350-UEN Section 6
Additional functions
Technical Manual 53
Distributed busbar protection REB500
Figure 21 Voltage Release
Used as an undervoltage release criterion U< : The phase-to-neutral voltages (U
L1
,
U
L2
, U
L3
) are measured.
Used as a neutral overvoltage release criterion 3U0>: The neutral voltage is either
evaluated and is derived from the three phase voltages (3U
0
= U
L1
+ U
L2
+ U
L3
) or
is fed externally (3U
0
).
Should a voltage be interrupted either due to a tripped MCB or an open-circuit, a
voltage function configured for overvoltage will disable, while one configured for
undervoltage will enable.
An open VT circuit connected to an undervoltage function can be
detected by monitoring the signal “28805_Voltage criterion”.