ABB 650 series, Technical Manual

Page: 321 / 778

3T 3N
3N
V V V Beta
+ ³
EQUATION2359-ANSI V1 EN
(Equation 94)
V
3N
, and V
3T
are third harmonic phasors with real and imaginary parts. The factor Beta
must be set not to risk operation under non-faulted conditions.
The voltage V
3N
is measured via a voltage transformer between the generator neutral point
and ground. The voltage V
3T
can be measured in different ways. The setting TVoltType
defines how the protection function is fed from voltage transformers at the high voltage
side of the generator. If V
3T
is lower than the set level VT3BlkLevel , STEFPHIZ (59THD)
function is blocked. The choices of TVoltType are:
NoVoltage : There is no voltage measured from the generator terminal side. This can be the
case when there are only phase-to-phase voltage transformers available at the generator
terminal side. In this case the protection will operate as a simple neutral point 3
rd
harmonic
undervoltage protection, which must be blocked externally during generator start-up and
shut-down.
ResidualVoltage : The function is fed from a broken delta connection of the phase to
ground connected voltage transformers at the generator terminal side,
V
3T
=(1/3)*V_Broken_Delta.
AllThreePhases : The function is fed from the three phase to ground connected voltage
transformers at the generator terminal side. The 3
rd
harmonic voltage V
3T
is calculated in
the IED, V
3T
=(1/3)*(V3A+V3B+V3C).
PhaseA , PhaseB , or PhaseC : The function is fed from one phase voltage transformer only.
The 3
rd
harmonic zero sequence voltage is assumed to be equal to any of the phase
voltages, as the third harmonic voltage is of zero sequence type, V
3T
=V3x (x= AB or C.
A simplified block diagram describing the stator ground fault protection function shown
in figure
145 .
1MRK 502 048-UUS A
Section 9
Voltage protection
315
Technical manual