ABB REG670 - Operation Principle

Name Type Values (Range) Unit Description
ANGLE REAL - deg Angle between 3rd
harmonic votage
phasors, radians
DU3
REAL - kV Diff. between 3rd harm.
volt. at both sides of gen.,
Volts
BU3
REAL - kV Bias voltage, a part of
voltN3rdHarmonic,
primary Volts
UN
REAL - kV Fund. frequency voltage
at generator neutral,
primary Volts
9.6.7 Operation principle
The protection is a combination of the 95% fundamental frequency earth fault
protection and the 3
rd
harmonic based stator earth fault protection, (STEFPHIZ). The
3
rd
harmonic based 100% stator earth fault protection is using the 3
rd
harmonic voltage
generated by the generator itself. To assure reliable function of the protection it is
necessary that the 3
rd
harmonic voltage generation is at least 0.8 V RMS on VT
secondary side.
The 3
rd
harmonic voltage generated by the generator has the same phase angle in the
three phases. It has the characteristic of a zero sequence component. If the generator
is connected to the power system via a block transformer that cannot transform zero
sequence voltages between the voltage levels, the 3
rd
harmonic voltage, that is U
3N
and U
3T
in fig 258, in the generator system is not influenced by the external power
system. At normal operation the generator third harmonic voltage characteristic can
be described as in figure 258.
Note that angle between U
3N
and U
3T
is typically close to 180°.
Section 9 1MRK502052-UEN B
Voltage protection
536
Technical manual