ABB RELION RET670 Applications Manual page 294

Section 8
Impedance protection
288
Calculate the step-up transformer impedance, in primary ohms, from the 13kV side as
follows:
2
x U 10 13
= × =
X t r
T
100 S 100 65
IEC-EQUATION2318 V1 EN-US
Then the reach in primary ohms shall be set to 100% of transformer impedance. Thus
the reach shall be set to 0,26Ω primary.
Set the first zone of Full-scheme distance measuring, Mho characteristic ZMHPDIS
(21) to disable phase-to-ground loops and enable phase-to-phase loops:
• The parameter GlobalBaseSel shall be set in order to select the global base value
group GBASVAL where the base voltage UBaseVBase and the base current IBase
are defined; UBaseVBase is the generator rated phase-phase voltage
(VBase=13,2kV) and IBase is the generator rated phase current (IBase=3062A).
• Parameter DirMode shall be set to Offset.
• Parameter OffsetMhoDir shall be set to Non-directional.
• The phase-to-ground measuring loops shall be disabled by setting
OpModePG=Disabled
• The phase-to-phase measuring loops shall be enabled and corresponding settings
in primary ohms for forward and reserve reach and time delay shall be entered
accordingly:
• Parameter ZPP shall be set to 0,260Ω.
• Parameter ZrevPP shall be set to 0,260Ω.
• Parameter tPP shall be set to 1,0000s.
• Parameter ZAngPP shall be set to default value 85 Deg.
Set the following for the directional element ZDMRDIR:
• The parameter GlobalBaseSel shall be set in order to select the global base value
group GBASVAL where the base voltage UBaseVBase and the base current IBase
are defined; UBaseVBase is the generator rated phase-phase voltage
(VBase=13,2kV) and IBase is the generator rated phase current (IBase=3062A).
• Parameter DirEvalType shall be set to Imp/Comp.
• Other settings can be left on the default values.
By doing this offset mho characteristic for zone one will be achieved as shown in
figure 136. Note that for this particular example ZPP=ZRevPP=0,26Ω. Thus the
operating characteristic for this particular application will be a circle with a centre in
the impedance plane origo.
By following the same procedure other mho zones can be set.
2
× = W
0, 26
1MRK 504 163-UUS A
Transformer protection RET670 2.2 ANSI
Application manual