ABB RELION RET670 Applications Manual page 215

1MRK 504 163-UUS A
Transformer protection RET670 2.2 ANSI
Application manual
Q
(Mvar)
600
400
Capacitive
200
200
Inductive
400
600
800
1000
IEC06000589 V1 EN-US
Figure 83: Self-regulating effect of reactive power balance
Increase in power transfer
The increase in power transfer capability as a function of the degree of compensation
for a transmission line can be explained by studying the circuit shown in figure 84. The
power transfer on the transmission line is given by the equation 55:
( )
d
× ×
V V sin
= =
A B
P
-
X X
Line C
EQUATION1994-ANSI V1 EN-US
The compensation degree K
A
P
A
-jX
C
+jX
L
V
A
Q
A
ANSI06000590 V1 EN-US
Figure 84: Transmission line with series capacitor
The effect on the power transfer when considering a constant angle difference (δ)
between the line ends is illustrated in figure 85. Practical compensation degree runs
500 1000
Transmission 500 kV
500 km
Line
Series
Compensation k = 50 %
( )
d
× ×
V V sin
A B
( )
× -
X 1 K
Line C
is defined as equation
c
D
V
V V
A B
B
P
B
d
V
B
Q
B
en06000590_ansi.vsd
Section 8
Impedance protection
(S.C.)
Power flow
(MW)
1500
(T.L. + S.C.)
(T.L.)
en06000589.vsd
SEMOD168320-45 v2
(Equation 55)
209