Siemens Siprotec 7UM611, Руководство пользователя

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2 Functions
64
7UM61 Manual
C53000-G1176-C127-3
A current-related alarm level is also available (address
1610 I ALARM
). The level is
set in secondary amperes and should be set equal to, or slightly less than, the permis-
sible continuous current
K-FACTOR
· I
N sec
. It may be used instead of the thermal alarm
level by setting the thermal alarm level to 100 % and is then practically inactive.
Extension of Time
Constants at
Machine Standstill The time constant programmed at address
1603
is valid for the running machine. On
slowing down or standstill, the machine may cool down much more slowly. This be-
haviour can be modeled by prolonging the time constant by the
K τ -FACTOR
(address
1612
) on machine standstill. In this context, machine standstill is detected when the
current falls below the threshold value
BkrClosed I MIN
(see margin heading "Cur-
rent Flow Monitoring" in section
P.System Data 1
).
If no distinction between time constants is necessary, the prolongation factor
K τ -
FACTOR
can be left as 1.0 (default).
Current Limiting The parameter
1615 I MAX THERM.
specifies up to which current value the trip times
are calculated in accordance with the prescribed formula. In the trip characteristics of
the following figure, this limit value determines the transition to the horizontal part of
the characteristics, where there is no further trip time reduction for increasing current
values. The limit value must ensure that even for the highest possible short-circuit cur-
rent, the trip times of the overload protection exceed the trip times of the short-circuit
protection devices (differential protection, impedance protection, time overcurrent pro-
tection). As a rule, a limitation to a secondary current corresponding to roughly three
times the nominal machine current will be sufficient.
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