Parameter: Emerg. start T overtravel
•
Default setting (_:112) Emerg. start T overtravel = 300 s
The Emerg. start T overtravel parameter is used to set the time for which blocking of the tripping has
to remain active after an outgoing binary input signal >Emergency start. With an outgoing input signal,
the load on the protected object is removed. The emergency start T-overtravel must be set long enough to
allow the thermal memory to fall below the dropout threshold after cooling. Select a time on the order of
magnitude of the Cooling time constant. In the example, 5 min (300 s) have been assumed.
Parameter: Imax thermal
•
Recommended setting value (_:107) Imax thermal = 2.5 A at I
rated
= 1 A
The Imax thermal parameter allows you to set the threshold current for the Behav. at I> Imax
therm. parameter. If you calculate with relatively long start times for motors (longer than 25 s), the current
limiting must be reduced to 2 I/I
rated, obj
.
Parameter: Imin cooling
•
Recommended setting value (_:108) Imin cooling = 0.5 A at I
rated
= 1 A
When defining the minimum current Imin cooling, you can use the no-load current for orientation. If no
data is available, set 0.5 I/I
rated, obj
. If the current falls below this value, the internal thermal time constant τ
automatically switches to the internal cooling time constant with the Cool-down factor Tau parameter.
Parameter: Storage of thermal replica
•
Recommended setting value (_:113) Storage of thermal replica = no
If a continuous auxiliary voltage for the bay units is ensured, the default setting can be retained.
Parameter: Behav. at I> Imax therm.
•
Recommended setting value (_:114) Behav. at I> Imax therm. = current limiting
The Behav. at I> Imax therm. parameter is used to select the process by which the function reacts to
short-circuit currents. To prevent premature tripping of the overload protection at low time constants, high
preloading and high short-circuit currents, the thermal replica can be modified. As overcurrent due to a
starting of the motor also leads to a certain heating of the stator winding, limiting the input current is recom-
mended for machines.
Parameter Value
Description
current limiting
The input currents are limited to the value set in the Imax thermal
parameter. If the measured current exceeds the set current value, the
limited current value is supplied to the thermal replica. An advisable current
threshold is approx. 2 to 2.5 I
rated, obj
.
freeze therm. rep.
If input currents exceed the Imax thermal parameter, the thermal replica
will be frozen for the time the parameter is exceeded.
Parameter: Curve based on preload
•
Default value (_:101) Curve based on preload = 100 %
The Curve based on preload parameter is used for a certain load case. In most cases, it applies for an
operation under rated conditions. For that, it is assumed that rated current is flowing permanently. This is
referred to as warm condition. In this case, the default setting 100 % is applied.
Thus, the thermal behavior is also correct for different preloads.
For cases without preload or cold condition, set the parameter to 0 %.
Protection and Automation Functions
6.20 Thermal Overload Protection, User-Defined Characteristic Curve
SIPROTEC 5, Overcurrent Protection, Manual 671
C53000-G5040-C017-8, Edition 07.2017
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