ABB Relion Technical Manual page 177

1MRK 502 048-UUS A
Technical manual
When the apparent impedance reaches the zone Z2 this zone will operate, normally with
a longer delay. The zone is related to the static stability of the generator.
LEXPDIS (40) protection also has a directional blinder (supervision). See figure 71.
In LEXPDIS (40) function the zone measurement is done as shown in figure 72.
Offset
XoffsetZ1
Z1diameter
IEC06000456 V2 EN
Figure 72: Zone measurement in LEXPDIS (40) protection function
The impedance Z1 is constructed from the measured apparent impedance Z and the
impedance corresponding to the centre point of the impedance characteristic (Z1 or Z2).
If the magnitude of this impedance is less than the radius (diameter/2) of the characteristic,
this part of the protection will operate.
If the directional restrain is set Disabled the impedance zone operation will start the
appropriate timer and LEXPDIS (40) will trip after the set delay (tZ1 or tZ2).
If the directional restrain is set Enabled the directional release function must also operate
to enable operation. A new impedance is constructed from the measured apparent
impedance Z and the XoffsetDirLine point on the y-axis. If the phase angle of this
impedance is less than the set DirAngle LEXPDIS (40) function will be released, see
figure 73.
Impedance protection
R
Z (apparent impedance)
Z1 = Z - (XoffsetZ1 +
Z1diameter/2)
Z1 or Z2
en06000456-2.vsd
Section 7
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