ABB Relion 670 Series Applications Manual page 495

1MRK 511 401-UUS F
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IEC18000078 V1 EN-US
Figure 222: Transformer capability curve for category IV
Low values of 3.5 or fewer times normal base current may result from overloads rather than faults.
For such cases, loading guides may indicate different allowable time durations, that is given in
Figure 222. The short-circuit currents shown in
currents. The line currents that relate to these winding currents depend upon the transformer
connection and the type of fault present. The protection curves only apply to transformers
described in the IEEE C57.12.00-1993 standard. For transformers built the prior to early 1970s,
consult the manufacturer for short circuit withstand capabilities.
17.12.3 Setting guidelines
17.12.3.1 Setting procedure on the IED
Parameters for the PTRSTHR (51TF) function are set via the local HMI or PCM600.
17.12.3.2 Consideration of zero sequence currents
Transformer withstand capability against through faults are determined based on fault current
flows through the windings. If the winding and CT connections are in wye, then CT measures the
winding currents which can be used directly for calculations. However, if any one of the windings
or the CT is delta connected, then the measured current cannot be used directly for the
calculation. This is due to the fact that the zero sequence current cannot be measured if any one of
the windings or CT is delta connected. It is important to consider zero sequence currents in order
to calculate the
Calculation of zero sequence current is difficult when more than one measured current does not
have zero sequence current. The function is able to calculate zero sequence current for a winding
Bay control REC670
Application manual
12 10 8 7 6 5 4
% Transformer impedance
2 5 10 20
Times normal base current
IEC18000078-1-en.vsdx
2
I t accurately.
© Copyright 2017 ABB. All rights reserved
50
Figure 222 is the balanced transformer winding
Section 17
Monitoring
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