Phase Distance Applied To Power Transformers; Description - GE UR Series L90 Instruction Manual

9.4 PHASE DISTANCE APPLIED TO POWER TRANSFORMERS

9.4PHASE DISTANCE APPLIED TO POWER TRANSFORMERS
As a Wye-Delta transformer introduces discontinuity for the zero-sequence circuit, the ground distance protection cannot
be applied, except special circumstances, to respond to faults behind the transformer.
The phase distance elements, however, could be developed so that both accurate reach and correct fault phase identifica-
tion is retained for faults behind the power transformer as seen from the relaying point. Without appropriate compensation,
the relay's reach would depend on a type of fault, creating considerable difficulties in applying the relay.
The L90 provides for any location of the VTs and CTs with respect to the involved power transformer and the direction of
any given zone.
In the following equations, the VT and CT locations are referenced as "None" if the transformer is not present between the
CT/VT and the intended reach point. Otherwise, the location is to be selected as a type of a transformer as seen from the
VT/CT position towards the intended reach point. The following figure explains the adopted rules.
APPLICATIONS OF THE "PHS DIST XFMR VOL/CUR CONNECTION" SETTINGS
Table 9–9: PHASE DISTANCE INPUT SIGNALS FOR DELTA-WYE TRANSFORMERS
TRANSFORMER LOOP
CONNECTION
None AB
BC
CA
Dy1 AB
BC
CA
Dy3 AB
BC
CA
Dy5 AB
BC
CA
Dy7 AB
9
BC
CA
9-30
CURRENT
TRANSFORMATION
I I
A B
I I
B C
I I
C A
3I
A
3I
B
3I
C
I 3I
AB_21P C
I 3I
BC_21P A
I 3I
CA_21P B
I 3I
AB_21P B
I 3I
BC_21P C
I 3I
CA_21P A
I 3I
AB_21P A
I 3I
BC_21P B
I 3I
CA_21P C
L90 Line Current Differential System
9 THEORY OF OPERATION
VOLTAGE
TRANSFORMATION
V
AB
V
BC
V
CA
1
 
------ - V V
AB CA
3
1
------ - V  
V
BC AB
3
1
------ - V  
V
CA BC
3
1
------ - V  
V V
AB_21P BC CA
3
1
------ - V  
V V
BC_21P CA AB
3
1
 
------ - V
V V
CA_21P AB BC
3
1
 
------ - V
V V
AB_21P BC AB
3
1
 
------ - V
V V
BC_21P CA BC
3
1
 
------ - V
V V
CA_21P AB CA
3
1
 
------ - V
V V
AB_21P CA AB
3
1
 
------ - V
V V
BC_21P AB BC
3
1
 
V ------ - V V
CA_21P BC CA
3

9.4.1 DESCRIPTION

GE Multilin