body model so that deviations can occur. The following figure shows an example of a predefined overload
characteristic curve and 2 standard characteristic curves based on the single-body model.
[dw_TOLP_UserCurve_characteristic, 1, en_US]
Figure 6-169
User-Defined Characteristic Curve with Replica of Standard Characteristics
The calculation is identical to the realization of the standard Thermal overload protection, 3-phase -
advanced function. You can find more information in the function description Thermal overload protection,
3-phase - advanced starting from chapter 6.19.1 Overview of Functions.
The main deviations are as follows:
•
The thermal characteristic is set with a flexible characteristic (t
trip
= f(I/I
rated,obj
)).
– The first point of the characteristic curve is important and is used to calculate the internal k-Factor.
– The point at I/I
rated,obj
= 1.5 is used to calculate the internal thermal time constant. If there is no point
at I/I
rated,obj
= 1.5, the point which is the closest to I/I
rated,obj
= 1.5 from I/I
rated,obj
= 1.1 is used to calcu-
late the internal thermal time.
– The points are set according to the maximum permissible load current.
•
The Curve based on preload parameter describes for which thermal preload the user-defined char-
acteristic curve is valid. Normally, such a curve is given for protected objects under rated load.
•
The Cool-down factor Tau parameter is used for the determination of the cooling time constant.
The set factor is multiplied with the internal calculated time constant.
•
The thermal model is based on a constant ambient temperature of 40 °C. It cannot be corrected via the
external measurement.
Protection and Automation Functions
6.20 Thermal Overload Protection, User-Defined Characteristic Curve
SIPROTEC 5, Overcurrent Protection, Manual 667
C53000-G5040-C017-8, Edition 07.2017
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