ABB Relion 670 Series Applications Manual page 521

1MRK 511 401-UEN Rev. K
effects are cumulative over the transformers lifetime. They are based principally on informed
engineering judgment and favorable, historical field experience as said in IEEE standard.
2000
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IEC18000078 V1 EN-US
Figure 251: 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
winding 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.
18.12.3 Setting guidelines
18.12.3.1 Setting procedure on the IED
Parameters for the PTRSTHR function are set via the local HMI or PCM600.
18.12.3.2 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 star, 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 by knowing the zero sequence currents of other winding(s). The zero sequence
Bay control REC670
Application manual
12 10 8 7 6 5 4
% Transformer impedance
2 5 10
Times normal base current
IEC18000078-1-en.vsdx
Figure 251. The short-circuit currents shown in
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20 50
Figure 251
2
I t accurately.
Section 18
Monitoring
is the balanced transformer
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