ABB 650 series, Technical Manual

Page: 319 / 778

9.5.6 Monitored data
Table 182: STEFPHIZ (59THD) Monitored data
Name Type Values (Range) Unit Description
VT3 REAL - kV Mag. of 3rd harm. voltage at
generator terminal side
VN3 REAL - kV Mag. of 3rd harm. voltage at
generator neutral side
E3 REAL - kV Total induced stator 3rd
harmonic voltage
ANGLE REAL - deg Angle between 3rd harmonic
votage phasors
DV3 REAL - kV Diff. between 3rd harm. volt. at
both sides of gen.
BV3 REAL - kV Bias voltage, a part of UN3
V_N REAL - kV Fund. frequency voltage at
generator neutral
9.5.7 Operation principle
The protection is a combination of the 95% fundamental frequency ground fault
protection and the100% Stator ground fault protection, 3
rd
harmonic based, (STEFPHIZ,
59THD). The 3
rd
harmonic based 100% stator ground 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 V
3N
and
V
3T
in fig 144 , 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
144 .
Note that angle between V
3N
and V
3T
is typically close to 180°.
1MRK 502 048-UUS A
Section 9
Voltage protection
313
Technical manual