ABB Relion Technical Manual page 316

Section 9
Voltage protection
310
only 95% of the stator winding. They leave 5% close to the neutral end unprotected. Under
unfavorable conditions the blind zone may extend up to 20% from the neutral.
The 95% stator ground fault protection measures the fundamental frequency voltage
component in the generator star point and it operates when the fundamental frequency
voltage exceeds the preset value. By applying this principle approximately 95% of the
stator winding can be protected. In order to protect the last 5% of the stator winding close
to the neutral end the 3rd harmonic voltage measurement can be performed. In 100%
Stator E/F 3rd harmonic protection either the 3rd harmonic voltage differential principle,
the neutral point 3rd harmonic undervoltage principle or the terminal side 3rd harmonic
overvoltage principle can be applied. However, differential principle is strongly
recommended. Combination of these two measuring principles provides coverage for
entire stator winding against ground faults.
x E3 x E3
N N N
RN RN
uN uN
x
Samples of the
neutral voltage
from which the
fundamental and
3rd harmonic
Neutral point fundamental frequency
voltages are
over-voltage protection 5% - 100%
over- voltage protection 10% – 100%
filtered out
3rd harmonic
Differential
differential
0% – 30%
0% - 30%
ANSI10000202 V1 EN
Figure 142: Protection principles for STEFPHIZ (59TD) function
stator winding stator winding
(1- x) E3 (1- x) E3
Rf Rf
1 - x 1 - x
1 or 100 %
1MRK 502 048-UUS A
CB 1 may not exist CB 1 may not exist
CB 1 CB 1
T T
Transformer
uT uT
Samples of the
terminal voltage
from which the
3rd harmonic
voltage is filtered
out
ANSI10000202-1-en.vsd
Technical manual
CB 2 CB 2