ABB RELION REX640 Technical Manual page 870

Hide thumbs Also See for RELION REX640:

Table of Contents

Protection functions

The earth-fault detection is indicated with the EARTH_FLT monitored data. The

earth-fault detection criterion can be defined with the EF detection Mod GFC setting.

The fundamental criterion is based on the residual current. The residual voltage and

reference neutral current, measured from the transformer neutral point, can be used for

the earth-fault detection criteria.

Selection of earth-fault detection criteria

EF detection Mod GFC

If the residual current Io is derived from the phase currents either by the summation

connection of CTs, that is, the Holmgreen connection, or by internally summing the

phase currents, there is a risk of a false earth-fault detection due to apparent residual

current from the current transformer errors. This risk can be eliminated using a

stabilized residual current measurement. The stabilization is enabled by setting the EF

Cur stabilization setting to "True". The stabilization increases the residual current

Gnd Op current GFC threshold setting when the maximum phase current exceeds the

nominal current. The increase is defined with the Stab slope 1 GFC setting. The

apparent residual current may exist during short circuits and in inrush current

situations if the CTs saturate partially. The earth-fault detection function takes the CT

saturation into account with additional stabilization settings Gnd Op current 2 GFC,

A Ph Stab value GFC and Stab slope 2 GFC.

Setting EF Cur stabilization to "False" disables the stabilization of the residual current

measurement and should be used only when the residual current is measured with a

cable current transformer. The residual current threshold setting for earth-fault

detection is Gnd Op current GFC. If the residual current is measured from a

transformer neural point, Gnd Op A Ref GFC is used. This is valid when the setting EF

detection Mod GFC is "Io AND IoRef".

Enumerator name

Io AND IoRef

1MRS759142 C

Technical Manual

Show Quick Links

Chapters

Table of Contents