GE Multilin g60, Instruction Manual

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9-14 G60 Generator Protection System GE Multilin
9.2 PHASE DISTANCE THROUGH POWER TRANSFORMERS 9 APPLICATION OF SETTINGS
9
9.2PHASE DISTANCE THROUGH POWER TRANSFORMERS 9.2.1 OVERVIEW
a) APPLICATION DESCRIPTION
Phase distance elements of the G60 could be set to respond to faults beyond any three-phase power transformer. The
relay guarantees accurate reach and targeting for any phase fault. Moreover, the current and voltage transformers may be
located independently on different sides of the transformer.
The following setting rules apply to this feature:
1. A given distance zone is terminated by location of the VTs, not the CTs.
2. Consequently, the positive-sequence impedance of a transformer must be included in the reach setting only if the
transformer is located between the potential source and the intended reach point.
3. The current signals require compensation if the transformer is located between the CTs and the intended reach point.
If this is the case the CT connection setting shall be set to transformer connection and vector group as seen from the
CTs toward the reach point. Otherwise, the CT connection setting shall be set to "None".
4. The voltage signals require compensation if the transformer is located between the VTs and the intended reach point.
If this is the case the VT connection setting shall be set to transformer connection and vector group as seen from the
VTs toward the reach point. Otherwise, the VT connection setting shall be set to "None".
5. The reach setting is entered in secondary ohms and as such must take into account location and ratios of VTs and CTs
as well as voltage ratio of the involved power transformer.
The following equations explain the setting rules. Consider two applications as shown in the figure below:
Figure 9–6: PHASE DISTANCE PROTECTION LOOKING THROUGH A POWER TRANSFORMER
where: Z
X
= intended reach impedance for Zone 1 (primary ohms)
Z
H
= intended reach impedance for Zone 3 (primary ohms)
Z
T
= positive-sequence impedance of the transformer
V
X
, V
H
= transformer rated voltages
n
CT
= transformation ratio of the CTs
n
VT
= transformation ratio of the VTs
Z1: Z1 reach setting (secondary ohms)
Z3: Zone 3 reach setting (secondary ohms)
830718A1.CDR
X H
Z
X
Z1
Z
H
Z
T
Z3
(a)
X H
Z
X
Z1
Z
H
Z
T
Z3
( b )