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Display of measured variable:
The display of the measured variable in the case of the underre-
actance protection is an impedance vector which starts at the
centre of the circular characteristic. This vector and the vector of
the impedance measured at the generator terminals form a tri-
angle as shown in Fig. 3.5.14.5. The protection picks up, if the
displayed impedance equals or is less than the radius of the cir-
cle:
1
X
'
æ
ö
d
£
-
z
x
ç
÷
d
è
ø
2
2
Example:
x d = 2; X d ' = 0,2
1
(
)
z £
-
=
2 0 1
.
0 95
.
2
X '
d
2
x
d
Fig. 3.5.14.5
Display of the impedance measured by the un-
derreactance function
3-164
REG 316*4 1MRB520049-Uen / Rev. F
x
U
I
z
0
HEST 905 034 C
r
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