Hitachi Relion 670 Series Applications Manual page 105

1MRK511407-UUS Rev. N
The minimum load resistance R
equation 17.
=
R
L min
EQUATION1338 V1 EN-US
The system impedance Z
system, see figure 49. Its value is calculated according to equation 18.
=
Z Z
S
EQUATION1339 V1 EN-US
The calculated value of the system impedance is of informative nature and helps in determining the
position of the oscillation center, see figure 50, which is for a general case calculated according to
equation 19.
=
Z
CO
EQUATION1340 V1 EN-US
In particular cases, when
=
E
A
EQUATION1342 V1 EN-US
The center of oscillation resides on the impedance point according to equation 21.
=
Z
CO
EQUATION1341 V1 EN-US
Phasor measurement unit RES670
Application manual
Lmin
( )
j
× =
Z cos 144.4 0.95 137.2
L min max
is determined as a sum of all impedances in an equivalent two-machine
S
(
+ + =
Z Z 17.16
SA 1 L 1 SB 1
Z
-
S Z
SA 1
E
B
+
1
E
A
E
B
Z
(
- = +
S Z 7.43 j 33.9
SA 1
2
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at maximum load and minimum system voltage is equal to
× = W
)
+ W
j 154.8
)
W
Section 7
Impedance protection
(Equation 17)
(Equation 18)
(Equation 19)
(Equation 20)
(Equation 21)
99