Thermal Overload Protection, One Time Constant Fahrenheit Celsius Lfpttr/Lcpttr (26) - ABB REC670 Applications Manual

Section 8
Current protection
8.7
8.7.1
8.8
8.8.1
8.8.2
202
tVN is the definite time delay for the trip function of the residual voltage protection,
given in s.
Thermal overload protection, one time constant
Fahrenheit/Celsius LFPTTR/LCPTTR (26)
Identification
Thermal overload protection, two time constants
TRPTTR (49)
Identification
Function description
Thermal overload protection, two time
constants
Application
Transformers in the power system are designed for a certain maximum load current
(power) level. If the current exceeds this level the losses will be higher than expected.
As a consequence the temperature of the transformer will increase. If the temperature
of the transformer reaches too high a value, the equipment might be damaged;
• The insulation within the transformer experiences forced ageing. As a
consequence of this, the risk of internal phase-to-phase or phase-to-ground faults
increases.
• There might be hot spots within the transformer, which degrades the paper
insulation. It might also cause bubbling in the transformer oil.
In stressed situations in the power system it can be required to overload transformers
for a limited time. This should be done without the above mentioned risks. The thermal
IEC 61850 IEC 60617
identification identification
TRPTTR
SYMBOL-A V1 EN-US
1MRK 511 401-UUS A
IP14512-1 v7
IP14513-1 v4
M14877-1 v2
ANSI/IEEE C37.2
device number
49
M15341-3 v5
Bay control REC670 2.2 ANSI
Application manual