• Fundamental frequency-based residual overvoltage protection 59N, 59G
• Third harmonic voltage-based protection 27/59THN
Neutral
side
x E
3H
R
f
(1-x)E
3H
x1- x
59N/59G protection
27/59THN
protection
R
N
Step-up unit
Generator CB Circuit breaker
Terminal
side
Stator winding
Fault at distance ‘x’
from generator neutral
GUID-D96A0B1A-E8AB-4B59-ABE8-37DC055BE0FE V1 EN
Figure 206: Complete stator ground-fault protection
Third harmonic voltage-based differential protection
The voltage generated by a generator is not a perfect sinusoidal wave but contains triplen
harmonics voltages. These triplen harmonics appear in each phase with the same
magnitude and angle, due to which they do not sum to zero and thus also appear in the
neutral side of the generator as a zero-sequence quantity. Among all the triplen harmonics
voltages generated, the third harmonic voltage has the highest magnitude with the
magnitude varying between 1% and 10% of the terminal voltage, depending on the
generator design philosophy. However, for a particular generator the magnitude of third
harmonics on the neutral side and terminal side depends also on the active power
generated.
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 429
Technical Manual
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