GE Multilin
T60 Transformer Protection System
8-1
8 THEORY OF OPERATION
8.1 DIRECTIONAL PRINCIPLE
8
8 THEORY OF OPERATION 8.1DIRECTIONAL PRINCIPLE
8.1.1 CURRENT DIRECTIONAL PROTECTION
The directional principle responds to a relative direction of the fault currents. This means that a reference signal, such as
transformer
voltage, is not required. The directional principle declares that
•
if all of the fault currents flow in one direction, the fault is internal,
or
•
if at least one fault current flows in an opposite direction compared with the sum of the remaining currents, the fault is
external.
The directional principle is implemented in two stages.
First, based on the magnitude of a given current, it is determined whether the current is a fault current. If so, its relative
phase relation has to be considered. The angle check must not be initiated for the load currents as the direction will be out
of the
transformer
even during internal faults. The auxiliary comparator of this stage applies an adaptable threshold. The
threshold is a fraction of the restraining current. The current from a particular feeder is used for bus directional comparison
if its magnitude is greater than
0.2 ×
I
restraint
or it is greater than 2 times its CT rating.
Second, for – and only for – the selected fault currents, the phase angle between a given current and the sum of all the
remaining currents is checked. The sum of all the remaining currents is the differential current less the current under con-
sideration. Therefore, for each, say the
p
th, current to be considered, the angle between the
and
phasors is to be
checked.
Ideally, during external faults, the said angle is close to 180° (see below); and during internal faults - close to 0 degrees.
Figure 8–1: DIRECTIONAL PRINCIPLE OPERATION DURING EXTERNAL FAULTS
Figure 8–2: DIRECTIONAL PRINCIPLE OPERATION DURING INTERNAL FAULTS
The T60 implementation calculates the maximum angle for the considered currents and compares it against a fixed thresh-
old of 90°. The flag indicating whether the directional protection principle is satisfied is available as the FlexLogic operand
XFMR PCNT DIFF DIR A/B/C.
I
P
I
D
I
P
–
836726A2.CDR
BLOCK
OP
E
RAT
E
BLOCK
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
p
D
p
I
I
I
real
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
p
D
p
I
I
I
imag
I
p
I
D
- I
p
E
xternal Fault Conditions
OP
E
RAT
E
836727A2.CDR
BLOCK
BLOCK
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
p
D
p
I
I
I
real
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
p
D
p
I
I
I
imag
I
p
I
D
- I
p
Internal Fault Conditions
OP
E
RAT
E
OP
E
RAT
E
Summary of Contents for T60
Page 6: ...vi T60 Transformer Protection System GE Multilin TABLE OF CONTENTS ...
Page 14: ...xiv T60 Transformer Protection System GE Multilin TABLE OF CONTENTS ...
Page 34: ...1 20 T60 Transformer Protection System GE Multilin 1 5 USING THE RELAY 1 GETTING STARTED 1 ...
Page 490: ...5 344 T60 Transformer Protection System GE Multilin 5 10 TESTING 5 SETTINGS 5 ...
Page 522: ...6 32 T60 Transformer Protection System GE Multilin 6 5 PRODUCT INFORMATION 6 ACTUAL VALUES 6 ...
Page 536: ...7 14 T60 Transformer Protection System GE Multilin 7 1 COMMANDS 7 COMMANDS AND TARGETS 7 ...
Page 568: ...10 12 T60 Transformer Protection System GE Multilin 10 6 DISPOSAL 10 MAINTENANCE 10 ...
Page 596: ...A 28 T60 Transformer Protection System GE Multilin A 1 PARAMETER LISTS APPENDIX A A ...
Page 716: ...B 120 T60 Transformer Protection System GE Multilin B 4 MEMORY MAPPING APPENDIX B B ...
Page 762: ...E 10 T60 Transformer Protection System GE Multilin E 1 IEC 60870 5 104 PROTOCOL APPENDIX E E ...
Page 774: ...F 12 T60 Transformer Protection System GE Multilin F 2 DNP POINT LISTS APPENDIX F F ...