Siemens 6MD85, Manual

Page: 888 / 1256

Parameter:
Imax thermal
•
Default setting
(_: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. The selected threshold current of 2.5 I
rated, obj
is a practicable value.
Parameter:
Imin cooling
•
Default setting
(_:108) Imin cooling
=
0.500 A
If only the thermal time constant (parameter
Thermal time constant
) must provide protection, set the
current parameter
Imin cooling
to 0 A.
Parameter:
Temperature rise at Irated
•
Default setting
(_:109) Temperature rise at Irated
=
70 K
As a value, set the overtemperature that is the result if the equipment is continuously operated with the rated
current and at an ambient temperature of 40°C. Here, the rated current refers to the protected object. You can
find the temperature value in the technical data of the equipment or measure it. If you use a temperature
sensor when measuring at the rated current, deduct the actual ambient temperature or the coolant tempera-
ture from the measured value.
When selecting the setting value, you can also use the specified temperature class for orientation. Usually, you
will find the overtemperature expressed in Kelvin (K), which can be accepted as is. If the absolute temperature
is given, the ambient temperature must be deducted. As a rule, this is 40°C.
The overtemperature at maximum permissible current (
ϑmax
) and the
Temperature rise at Irated
(
ϑrated,obj.
) can be converted by using the following formula:
[fo_ueb_for_Irated, 3, en_US]
EXAMPLE:
Temperature class B for continuous operation: permissible overtemperature = 80 K
From this, a temperature for I
rated
of 120°C (80 K + 40°C) can be derived when using a temperature sensor for
the measurement.
Temperature class F as thermal limiting value: permissible overtemperature = 105 K.
From this, a maximum temperature of 155°C (105 K + 40°C) derives.
From these values, the K factor can be derived:
[fo_bsp_kfaktor, 3, en_US]
If you select a setting value of 1.1 for the
K-factor
, your selection can be considered as conservative.
i
i
NOTE
For electrical machines, the limits can vary depending on the type of coolant.
Consult the machine manufacturer to agree on a setting value for the overtemperature.
Parameter:
Storage of thermal replica
•
Default setting
(_:113) Storage of thermal replica
=
no
If a continuous auxiliary voltage for the bay units is ensured, the bay default setting can be retained.
Protection and Automation Functions
7.26 Thermal Overload Protection, 3-Phase - Advanced
888 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017