7.2.2
Functionality
The underimpedance protection for generators and transformers ZGCPDIS, has the
offset mho characteristic as a three zone back-up protection for detection of phase-to-
phase short circuits in transformers and generators. The full scheme three zones have
independent measuring phase-to-phase loops and settings that gives high flexibility
for all types of applications.
All three zones can be individually definite time delayed.
A load encroachment characteristic is available for the third zone as shown in figure
.
IEC07000117-2-en.vsd
jX
Operation area
Operation area
R
Operation area
No operation area
No operation area
IEC07000117 V2 EN
Figure 65:
Load encroachment influence on the offset mho Z3 characteristic
7.2.3
Function block
IEC10000122-2-en.vsd
ZGCPDIS
I3P*
U3P*
BLOCK
BLKZ
LDCND
TRIP
TRZ1
TRZ2
TRZ3
START
STZ1
STZ2
STZ3
IEC10000122 V2 EN
Figure 66:
ZGCPDIS function block
1MRK 502 048-UEN A
Section 7
Impedance protection
147
Technical manual
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