4.5
Thermal protection
4.5.1
Three-phase thermal protection for feeders, cables and
distribution transformers 49F
4.5.1.1
Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Three-phase thermal protection for
feeders, cables and distribution
transformers
T1PTTR
3Ith>F
49F
4.5.1.2
Function block
A07069-ANSI V2 EN
Figure 141:
Function block
4.5.1.3
Functionality
The increased utilization of power systems closer to the thermal limits has generated a
need for a thermal overload function for power lines as well.
A thermal overload is in some cases not detected by other protection functions, and the
introduction of the thermal overload function 49F allows the protected circuit to operate
closer to the thermal limits.
An alarm level gives an early warning to allow operators to take action before the line
trips. The early warning is based on the three-phase current measuring function using a
thermal model with first order thermal loss with the settable time constant. If the
temperature rise continues the function operates based on the thermal model of the line.
Re-energizing of the line after a thermal overload operation can be inhibited for a time to
allow the line to cool. The time for the line to cool is estimated by the thermal model.
1MRS240050-IB C
Section 4
Protection functions
REF615R
295
Technical Manual
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