ABB 615 series Technical Manual page 820

Section 5
Protection related functions
814
Result quality indicator
The quality of the estimated fault distance is judged and reported in recorded data as the
Flt Dist quality together with the fault distance estimate. The Flt Dist quality is a bit vector
indicating detected sources of inaccuracy in the fault distance estimate. In case Flt Dist
quality equals 1, the result is not affected by error sources. This results in good quality for
fault distance estimate. If factors affecting negatively to fault distance estimation are
detected, the Flt Dist quality is according to
distance, Flt distance value is given in HMI in parenthesis.
Table 711: Fault distance quality indicator Flt Dist quality
Value
2
4
8
16
32
64
128
256
1) Xloop is the total loop reactance according to settings
For example, if fault point resistance exceeds 500 Ω and Flt to Lod Cur ratio is below 1.0,
Flt Dist quality is "36". As another example, if no error sources are found, but stability
criterion is not met, the value of Flt Dist quality is "2".
Impedance settings
The fault distance calculation in 21FL is based on the fault loop impedance modeling. The
fault loop is parametrized with the impedance settings and these can be set at maximum
for three line sections (A, B and C). Each section is enabled by entering a section length,
which differs from zero to settings Line Len section A, Line Len section B or Line Len
section C in the order section A-> section B-> section C.
The ground-fault loops require both positive-sequence and zero-sequence impedances,
for example, R1 line section A and X1 line section A, R0 line section A and X0 line section
A. For the short circuit loops, only positive-sequence impedances are needed. Even these
can be omitted in the short circuit loops, if the setting Enable simple model equals
"TRUE".
Table 711. In this case estimated fault
Corresponding inaccuracy description
Estimation stability criterion has not been reached
Fault point resistance exceeds 500 Ω
Fault point resistance exceeds 5 × X
Fault point resistance exceeds 20 × X
Flt to Lod Cur ratio is below 1.00
Fault distance estimate outside tolerances (<-0.1 pu
or >1.1 pu)
Distance estimate calculation is not done due to too
low magnitudes of I or V
Distance estimate calculation cannot be performed
(for example avoiding internal division by zero)
1MAC059074-MB A
1)
loop
1)
loop
615 series ANSI
Technical Manual