ABB MDAR, Инструкция по эксплуатации

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I.L. 40-385.5
6-2
Figure 9 — 3Ø faults
Figure 10 — ØG faults
6.2 FAULTED PHASE SELECTION UNITS
Faulted phase selection includes determining if the
fault is between phases or between one or more
phases and ground, and also identifies the specific
phase or phases involved in the fault.
Faulted phase identification is necessary for imple-
mentation of SPT for ØG faults and for providing
information for fault location computation.
The current phasors I
A
, I
B
, I
C
and I
o
are utilized in the
fault identification algorithm. When a fault occurs, the
last set of current phasors prior to the fault are saved
as the pre-fault load current values.
The following conventions are used:
3I
o
=I
A
+ I
B
+ I
C
Calculated zero sequence current
from the measured post-fault current phasors
I
AL
, I
BL
, I
CL
,Measured pre-fault load current phasors
I
A
, I
B
, I
C
, 3I
o
Measured post-fault current phasors
DI
A
, DI
B
, DI
C
,Resultant fault current phasors
To determine the resultant fault current, remove the
zero sequence current from the measured post-fault
current and subtract the measured pre-fault load cur-
rent. The resulting fault current is the sum of the pos-
itive sequence current and the negative sequence
current of the fault.
DI
A
= (I
A
- I
o
) - I
AL
= I
A1
+ I
A2
DI
B
= (I
B
- I
o
) - I
BL
= I
B1
+ I
B2
DI
C
= (I
C
- I
o
) - I
CL
= I
C1
+ I
C2
Compare the magnitude of the resultant fault current
phasors using the following table to determine the
fault type.
If none of the nine fault types in the table are identi-
fied, then the fault must be identified as a three-
phase fault.
6.3 FORWARD DIRECTIONAL OVERCURRENT
PHASE UNIT, (FDOP)
The inordinately high influence of ct lead resistance
for a low voltage MPS test with the Motor-Generator
set as one of the test sources, produces virtually a 90
phase shift in the polarizing voltage with the angle
between the sources, causing undesired operation.
Even though this is an MPS-related phenomenon
and would pose no problem for an actual power sys-
tem, a forward directional overcurrent phase function
FDOP and logic which includes AND-144C and
AND-144Ø, as shown in Figure 25, has been added
to each phase for supervising the Z1P and PLTP 3Ø-
unit trip paths. The performance of the FDOP ele-
ments (FDOPA, PDOPB and FDOPC) is 90 -60 ,
which is similar to the directional unit of the type CR
relay, except always use prefault voltage for polariz-
ing quantity. Its sensitivity is 0.5 amperes.
6.4 FORWARD/REVERSE DIRECTIONAL OVER-
CURRENT GROUND UNITS (FDOG/RDOG)
There are 2 directional overcurrent ground units,
FDOG (forward directional overcurrent ground) and
RDOG (reverse directional overcurrent ground), in
the MDAR (REL-300) system. The operating princi-
ple of these units can be selected based on the appli-
cation. By scrolling the functional field to DIRU
(directional unit) and selecting the ZSEQ (zero
Fault Type
A
G B
G C
G A
B B
C C
A
A
B
G B
C
G C
A
G
|∆
IA| > 1.5 x
|∆
IB| x x x
|∆
IA| > 1.5 x
|∆
IC| x x x
|∆
IB| > 1.5 x
|∆
IA| x x x
|∆
IB| > 1.5 x
|∆
IC| x x x
|∆
IC| > 1.5 x
|∆
IA| x x x
|∆
IC| > 1.5 x
|∆
IB| x x x