ABB ret650 - Transformer Application Example

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EQUATION1189 V1 EN-US (Equation 31)
Further description can be found in the technical reference manual.
tPRCrvx, tTRCrvx, tCRCrvx: Parameters for user programmable of inverse reset
time characteristic curve. Further description can be found in the technical
reference manual.
7.4.3.6 Transformer application example
SEMOD55591-4 v8
Two main cases are of interest when residual overcurrent protection is used for a
power transformer, namely if residual current can be fed from the protected
transformer winding or not.
The protected winding will feed earth-fault (residual) current to earth faults in the
connected power system. The residual current fed from the transformer at external
phase-to-earth faults is highly dependent on the total positive and zero-sequence
source impedances. It is also dependent on the residual current distribution between
the network zero-sequence impedance and the transformer zero-sequence
impedance. An example of this application is shown in Figure
54.
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alt
Three phase CT
summated
Single CT
YN/D or YN/Y
transformer
en05000490.vsd
IEC05000490 V1 EN-US
Figure 54: Residual overcurrent protection application on a directly earthed
transformer winding
In this case the protection has two different tasks:
1MRK 504 169-UEN A Section 7
Current protection
Transformer protection RET650 2.2 IEC 129
Application manual