ABB RELION RET670 Applications Manual page 481

1MRK 504 163-UUS A
Transformer protection RET670 2.2 ANSI
Application manual
The warning angle (StartAngle) should be chosen not to cross into normal operating
area. The maximum line power is assumed to be 2000 MVA. This corresponds to
apparent impedance:
2 2
U 400
= = =
Z 80 ohm
S 2000
EQUATION1967 V1 EN-US
Simplified, the example can be shown as a triangle, see figure 239.
IEC07000016 V1 EN-US
Figure 239: Simplified figure to derive StartAngle
ZB
³
angleStart arctan + arctan
Zload
EQUATION1968 V2 EN-US
In case of minor damped oscillations at normal operation we do not want the protection
to start. Therefore we set the start angle with large margin.
Set StartAngle to 110°
X
ZA
Zload
ZB
ZA 32 52
=
arctan + arctan
Zload 80 80
Impedance protection
en07000016.vsd
»
0 0
= 21.8 + 33.0 55
Section 8
(Equation 401)
R
(Equation 402)
475