tVN is the definite time delay for the trip function of the residual voltage protection,
given in s.
9.7 Thermal overload protection, two time constants
TRPTTR
(49)
IP14513-1 v4
9.7.1 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
9.7.2 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-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.
1MRK 502 071-UUS A Section 9
Current protection
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062 395
Application manual
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