E02704
voltage
generator
represents
voltage change
at fault location
Z
S1
Z
L1
I
1
I
F1
Z
R1
Z
S2
I
2
V
1
Z
L2
I
F2
Z
R2
V
2
Z
S0
I
0
Z
L0
I
F0
Z
R0
V
0
I
F/3
E
Figure 80: Sequence networks connection for an internal A-N fault
The fault is shown near to the busbar at end R of the line, and results in a connection of the positive, negative, and
zero sequence networks in series. The delta diagram shows that any fault is a generator of D, connected at the
location of the fault inception. The characteristics of the deltas are:
●
The DI generated by the fault is equal to the total fault arc current.
●
The DI splits into parallel paths, with part contribution from source “S” and part from remote end “R” of the
line. Therefore each element measures a lower proportion of DI.
●
The DV generated by the fault is equal to the fault arc voltage minus the pre-fault voltage, so it is in anti-
phase with the pre-fault voltage.
●
The DV measured by the protection is the voltage drop across the source impedance behind the protection
location. This is generally smaller than the DV measured at the fault location, because the voltage collapse
is smaller nearer to the source than at the fault.
●
For fault detection, the measured DI and DV associated with the fault must be greater than the Dir I Fwd
and Dir V Fwd settings respectively.
5.2
DELTA DIRECTIONAL DECISION
Delta quantities are generated when a fault starts. The following criteria characterise the fault direction:
P543i/P545i Chapter 7 - Distance Protection
P54x1i-TM-EN-1 177
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