Example System With Power Transformers - GE D90 Plus Instruction Manual

CHAPTER 15: THEORY OF OPERATION

Example system with power transformers

PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
Transformer Loop
connection
Yd5 AB
BC
CA
Yd7 AB
BC
CA
Yd9 AB
BC
CA
Yd11 AB
BC
CA
Equations from the current transformation and voltage transformation columns are used to
derive inputs to the three (AB, BC, and CA) phase distance elements. For example, if the CTs
are located at the delta side of the delta-wye 11 (Dy11) transformer, and a given zone is set
to look through the transformer into the system connected to the wye winding, the CT
location setting for that zone shall be set to "Dy11" and the relay would use –√3I
of a traditional I – I for the AB phase distance element.
A B
The current supervision pickup setting applies to the currents specified in the current
transformation columns.
A distance zone originates at the location of the VTs (regardless of the location of the CTs).
Consider the system shown below. To respond to the indicated fault, a distance relay is
normally applied at the relay point X.
PHASE DISTANCE APPLIED TO POWER TRANSFORMERS
Current transformation
1
( )
I = I - I - I
_21P 2
AB B A C
3
1
( )
I = I - I - I
_21P 2
BC C A B
3
1
I = ( I - I - I )
_21P 2
CA A B C
3
1
( )
I = I + I - I
_21P 2
AB B C A
3
1
( )
I = I + I - I
_21P 2
BC A C B
3
1
I = ( I + I - I )
_21P 2
CA A B C
3
1
( )
I = I - I - I
_21P 2
AB C A B
3
1
( )
I = I - I - I
_21P 2
BC A B C
3
1
I = ( I - I - I )
_21P 2
CA B A C
3
1
( )
I = I + I - I
_21P 2
AB A C B
3
1
( )
I = I + I - I
_21P 2
BC A B C
3
1
( )
I = I + I - I
_21P 2
CA B C A
3
Voltage transformation
V _21P = V
3
AB B
V _21P = V
3
BC C
V _21P = V
3
CA A
V _21P - = V
3
AB A
V _21P - = V
3
BC B
V _21P - = V
3
CA C
V _21P = V
3
AB C
V _21P = V
3
BC A
V _21P = V
3
CA B
V _21P - = V
3
AB B
V _21P - = V
3
BC C
V _21P - = V
3
CA A
instead
B
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