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 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
.
Note that angle between U
3N
and U
3T
is typically close to 180°.
Section 9
1MRK502052-UEN B
Voltage protection
536
Technical manual
Содержание Relion REG670
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