ABB RELION REX640 Technical Manual page 1194

Protection and control

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Protection related functions

Function block

Figure 681: Function block

Functionality

The fault locator function SCEFRFLO provides impedance-based fault location. It is

designed for radially operated distribution systems, and it can locate short circuits

in all kinds of distribution networks. Earth faults can be located in effectively

earthed and in low-resistance or low-reactance earthed networks. With certain

limitations, SCEFRFLO can also be used for locating an earth fault in unearthed

distribution networks. Moreover, SCEFRFLO can be applied to compensated

(resonant earthed) networks where an earth-fault current raising resistor is

connected in parallel with the arc suppression coil. The location of the continuous

low-ohmic earth fault can be determined by using the switching of the parallel

resistor of the coil during an earth fault.

The fault distance calculation is based on the locally measured fundamental

frequency current and voltage phasors. The full operation of SCEFRFLO requires

all phase currents and phase-to-earth voltages to be measured.

The fault distance estimate is obtained when SCEFRFLO is externally or internally

Analog channel configuration

SCEFRFLO has three analog group inputs which must be properly configured.

Table 1147: Analog inputs

There are a few special conditions which must be noted with the configuration.

Can be connected to GRPOFF if

See the preprocessing function blocks in this document for the possible

signal sources. The GRPOFF signal is available in the function block called

Phase voltage Meas is set to "Ph-to-ph without Uo"

Three-phase currents

Three-phase voltages

Residual voltage (measured), necessary when the phase-to-

phase voltages are measured and Phase voltage Meas is set

to "Accurate"

1MRS759142 F

Technical Manual