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Section 8
Impedance protection
306
Q [pu]
Motor
Generator
A
0.8
0.6
Overexcited
37
0.2
Underexcited
-0.3
E
-0.5
D
IEC06000451 V1 EN-US
Figure 148:
Capability curve of a generator
where:
AB
= Field current limit
BC
= Stator current limit
CD
= End region heating limit of stator, due to leakage flux
BH
= Possible active power limit due to turbine output power limitation
EF
= Steady-state limit without AVR
X
= Source impedance of connected power system
s
Loss of excitation protection can be based on directional power measurement or
impedance measurement.
The straight line EF in the P-Q plane can be transferred into the impedance plane by
using the relation shown in equation 162.
*
2
×
V
V V
V
V
=
=
=
=
Z
*
*
×
I
I V
S
S
EQUATION1723 V1 EN-US
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
B
S
o
1
0.8
0.4
0.6
o
18
F
X
C
H
F
X
=0
s
en06000451.vsd
2
2
2
×
×
×
S
V
P
V
Q
=
+
j
*
2
2
2
×
+
+
S
P
Q
P
Q
1MRK 502 071-UUS A
P [pu]
=0.2
e
=
+
R
jX
2
Application manual
(Equation 162)
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