ABB RELION 670 Series Applications Manual page 227

1MRK 504 152-UEN B
Auxiliary
Transformer
Transformer
IEC10000102 V1 EN-US
Figure 122: Application example for generator under-impedance function
The first under-impedance protection zone shall cover 100% of the step-up transformer
impedance with a time delay of 1.0s.
Calculate the step-up transformer impedance, in primary ohms, from the 13kV side as follows:
=
X
T
IEC-EQUATION2318 V1 EN-US
Then the reach in primary ohms shall be set to 100% of transformer impedance. Thus the reach
shall be set to 0,26Ω primary.
Application manual
HV Substation
HV CB
65MVA
Step-up
123/13kV
Transformer
x =10%
t
Generator CB
Excitation
Y
Y
@
VT: 13,5kV/110V
70MVA
~ 13,2kV
3062A
CT: 4000/5
2
2
x U 10 13
× = ×
t r
100 S 100 65
= W
0, 26
Section 7
Impedance protection
REG670
21 Z<
ZMH PDIS
221