ABB REG670 Applications Manual

9.7.1 Identification
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
49
9.7.2 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:
• 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 can be
used for transformers where forced cooling can be taken out of operation, for example
at fan or pump faults.
The thermal overload protection estimates the internal heat content of the transformer
(temperature) continuously. This estimation is made by using a thermal model of the
transformer which is based on current measurement.
If the heat content of the protected transformer reaches a set alarm level a signal can
be given to the operator. Two alarm levels are available. This enables preventive
1MRK 502 071-UEN - Section 9
Current protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 367
Application manual

ABB REG670 Specifications

General

Brand	ABB
Model	REG670
Category	Protection Device
Language	English