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

1MRK 511 401-UEN A
8.7
8.7.1
8.8
8.8.1
8.8.2
Bay control REC670 2.2 IEC
Application manual
Thermal overload protection, one time constant,
Celsius/Fahrenheit LCPTTR/LFPTTR
Identification
Thermal overload protection, two time constants
TRPTTR
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-earth 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 overload protection provides information and makes temporary
overloading of transformers possible.
The permissible load level of a power transformer is highly dependent on the
cooling system of the transformer. There are two main principles:
Current protection
IEC 61850 IEC 60617
identification identification
TRPTTR
SYMBOL-A V1 EN-US
Section 8
IP14512-1 v7
IP14513-1 v4
M14877-1 v2
ANSI/IEEE C37.2
device number
49
M15341-3 v5
191