2 Functions
104
7UM61 Manual
C53000-G1176-C127-3
Figure 2-31 Logic diagram of the undervoltage protection
2.15.2 Setting Notes
General The undervoltage protection is only effective and available if this function was set
during protective function configuration (Section 2.2, address 140, UNDERVOLTAGE is
set to Enabled. If the function is not required Disabled is set. Address 4001
UNDERVOLTAGE serves to switch the function ON or OFF or to block only the trip
command (Block relay).
Settings It must be note that the positive phase-sequence voltages and thus also the pickup
thresholds are evaluated as phase-to-phase quantities (terminal voltage ·√3
). The first
undervoltage protection stage is typically set to about 75% of the nominal machine
voltage, i.e. address 4002 U< is set to 75 V. The user must select a value for the 4003
T U< time setting that ensures that voltage dips which would affect operating stability
are disconnected. On the other hand, the time delay must be large enough to avoid
disconnections during admissible short-time voltage dips.
For the second stage, a lower pickup threshold 4004 U<< e.g. = 65 V should be com-
bined with a shorter trip time 4005 T U<< e.g. = 0.5 s to achieve an approximate ad-
aptation to the stability behaviour of the consumers.
All setting times are additional time delays which do not include the operating times
(measuring time, drop-out time) of the protective function.
The drop-out ratio can be adapted in small steps to the operating conditions at address
4006 DOUT RATIO.
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