ABB ret650, Руководство по применению

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7.5 Thermal overload protection, two time constants
TRPTTR
IP14513-1 v4
7.5.1 Identification
M14877-1 v2
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Thermal overload protection, two time
constants
TRPTTR
SYMBOL-A V1 EN-US
49
7.5.2 Application
M15341-3 v5
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:
• 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 time constant is influenced by the cooling system of the transformer. The
two parameters sets can be activated by the binary input signal COOLING. This
1MRK 504 169-UEN A
Section 7
Current protection
Transformer protection RET650 2.2 IEC 133
Application manual