ABB RELION REX640 Technical Manual page 591

Protection and control

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1MRS759142 F

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 (

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".

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

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,

When setting

Technical Manual

Equation 109

Fundamental frequency component is always included into fault current

magnitude estimation, even when setting

Enable harmonics = "Enable", the included harmonics are

When setting

(if their magnitudes are sufficient for an accurate measurement): 2

Enable harmonics = "Disable":

). The memorized pre-fault negative-sequence

Enable harmonics = "Disable".

). Also, the effect of harmonics is only taken

, can be written:

Protection functions