Thermal Overload Protection, Two Time Constants Trpttr (49); Identification; Application - ABB REB670 Applications Manual

1MRK 505 370-UUS A
7.5
7.5.1
7.5.2
Busbar protection REB670 2.2 ANSI
Application manual
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
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:
• OA: The air is naturally circulated to the coolers without fans and the oil is
naturally circulated without pumps.
• FOA: The coolers have fans to force air for cooling and pumps to force the
circulation of the transformer oil.
The protection can have two sets of parameters, one for non-forced cooling and one for
forced cooling. Both the permissive steady state loading level as well as the thermal
IEC 61850 IEC 60617
identification identification
TRPTTR
SYMBOL-A V1 EN-US
Section 7
Current protection
IP14513-1 v4
M14877-1 v2
ANSI/IEEE C37.2
device number
49
M15341-3 v5
211