ABB COM600 series User's & Technical Manual page 27

1MRS758734 COM600 series 5.1
Substation Analytics Technical Manual
•
Saturation. The saturation of current or voltage transformers increases certain har-
monics, especially the second, the fifth and the seventh. Saturation deteriorates the
fault distance estimate.
• In unearthed networks, the ratio between the earth-fault current (Rfault = 0 ohms)
and load current magnitude is critical. The higher the ratio, the better the fault dis-
tance estimate.
Furthermore, the distribution networks have specific features which further complicate
and challenge fault localization algorithms. These include, for example, non-homogeneity
of lines, presence of laterals and load taps. The validity of the estimated earth fault dis-
tance is judged and reported together with the fault distance estimate. The EF_VALIDITY
output has various values:
Table 4.3-1 The EF_VALIDITY output values
N/A Indicator is not applicable (fault type is a short circuit).
High Result is not affected by error sources
Moderate Result is slightly affect by error sources. The additional error in the fault
distance estimate can be tens of percents.
Poor Fault distance algorithm is greatly affected by error sources and cannot
function properly. In this case, the result is only trend setting. The result
can only indicate, for example, whether the fault is in the beginning or
in the end of the feeder section.
ALARM indication
SCEFRFLO contains an alarm output for the calculated fault distance. If the calculated
fault distance FLT_DISTANCE is between the settings Low alarm Dis limit and High
alarm Dis limit, the ALARM output is activated.
The ALARM output can be utilized, for example, in regions with waterways or other
places where knowledge of certain fault locations is of high importance.
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