ABB RELION REX640 Technical Manual page 521

1MRS759142 C
REX640
Technical Manual
• Fundamental frequency-based residual overvoltage protection ROVPTOV
• Third harmonic-based stator earth-fault protection H3EFPSEF
GUID-20EF93CC-3D90-4A44-9510-3D408B5EE534 V1 EN
Figure 281: Complete stator earth-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.
Section 4
Protection functions
515