Undervoltage Seal-In Function - ABB REG670 Applications Manual

1MRK 502 071-UEN -
8.9.2.6
8.9.2.7
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual

Undervoltage seal-in function

For faults close to generating terminals the CTs might go in to saturation. The problem
is due to very long DC constant of the generators. The persistent DC component of
primary currents even if relatively small has a tendency to drive current transformers
into saturation. The ZGVPDIS under this condition might reset for some duration. A
reliable backup protection is provided under these conditions by providing an
undervoltage seal-in feature.
The undervoltage function is enabled from zone 2 or zone 3 start.
Load encroachment for zone 2 and zone 3
As zone 2 and zone 3 have larger reaches, there is a possibility of load impedance
encroaching into mho characteristics during heavy load conditions. Hence zone 2 and
zone 3 are provided with load encroachment blinder feature which is to be enabled by
the user. This feature measures the impedance based on positive sequence voltage and
current. As the load from the generator corresponds to the positive sequence signals.
Positive sequence voltage and current will be used for load encroachment blocking
logic,
Figure 166 shows the implemented load encroachment characteristic.
Load encroachment characteristic
ArgLd
-RLd
ArgLd
IEC11000304 V1 EN
Figure 166: Load Encroachment characteristic in under Impedance function
The resistive settings of this function is also provided in percentage of ZBase.
jX
ArgLd
R
RLd
ArgLd
IEC11000304_1_en
Section 8
Impedance protection
313