ABB RELION REX640, Техническое руководство, Страница: 591 / 1960

Max Dur delta Calc (maximum duration for delta calculation). After this time is
elapsed from initial fault detection moment, then the validity of delta-calculation
is not considered to be valid anymore and thus fault current estimation is done
without delta calculation i.e. based on real time measurement of threefold negative-
sequence component (
Equation 109
). The memorized pre-fault negative-sequence
component values are reset when function is reset.
In practical compensated networks, earth-fault current may include a large share of
harmonic components, especially during low ohmic faults. In IFPTOC the estimation
of earth-fault (EF) current can be done with or without harmonic components.
Refer to Figure 5 for illustrating the effect of harmonics on earth-fault current
estimate. Measurement of harmonic components can be enabled with setting
Enable harmonics = “Enable”, “Disable”.
Fundamental frequency component is always included into fault current
magnitude estimation, even when setting
Enable harmonics = “Disable”.
When setting
Enable harmonics = “Enable”, the included harmonics are
(if their magnitudes are sufficient for an accurate measurement): 2
nd
, 3
rd
,
5
th
, 7
th
and 9
th
.
Figure 338: Illustration of earth-fault current estimate with and without harmonics calculation enabled
(zoomed view on right hand column)
The harmonic components are only included in the earth-fault current estimate if
their magnitudes are sufficient for an accurate measurement i.e. their values exceed
minimum predefined value (0.3% from I
n
). Also, the effect of harmonics is only taken
into account, if the magnitude of fundamental frequency fault current estimate or
touch voltage exceeds set start thresholds.
For the earth-fault current estimate magnitude, , can be written:
When setting Enable harmonics = “Disable”:
1MRS759142 F Protection functions
REX640
Technical Manual
591