Undervoltage Protection (ANSI 27)
149
7UM62 Manual
C53000-G1176-C149-3
Figure 2-71
Logic Diagram of the Undervoltage Protection
2.19.2 Setting Hints
General
The undervoltage protection is only effective and accessible if it has been set during
the configuration of the protection functions (Section 2.2) at address
=
Enabled
. Set
Disabled
if the function is not required. Address
is used to switch the function
ON
or
OFF
, or to block only the
trip command (
Block Relay
).
Setting Values
It must be considered that the positive phase-sequence system of the 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
= 75 V. The user must
select a value for the
time setting that ensures that voltage dips affecting
the operating stability are disconnected. On the other hand, the time delay must be
long enough to avoid disconnection in case of permissible short-time voltage dips.
For the second stage, a lower pickup threshold
e.g. = 65 V should be
combined with a shorter trip time
e.g. = 0.5 s to perform an approximate
adaptation 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
FNo. 06508
FNo. 06503
&
FNo. 06533
FNo. 06539
FNo. 06540
Tripping
matrix
FNo. 06531
FNo. 06506
FNo. 06537
&
OR
FFM
refer Fig. 2-120 in
Subsection 2.38.1.4
FNo. 000361
TMin
TRIP CMD