ABB RELION REX640 Technical Manual page 949

Protection and control

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1MRS759142 F

• The "Vol Dep Overcur" method combines overcurrent and undervoltage

conditions. An undervoltage condition allows lower current threshold settings

and increases the sensitivity of the fault detection.

• The "Under impedance" method uses fault loop impedance for identifying the

faulted phases. The underimpedance characteristic can be either quadrilateral

or circular in shape. The sensitivity of the fault detection is defined by an

independent setting in resistive and reactive reaches. The underimpedance

method is supervised by a load encroachment logic which ensures that the load

impedance does not interfere with the faulted phase selection.

The "OC AND Und impedance" method combines "Overcurrent" and "Under

impedance" methods so that both criteria have to be fulfilled.

All phase selection methods require that all three phase currents are measured

and all three phase-to-earth voltages are available. If only phase-to-phase voltages

are available (

measuring loops can be released for measurement. The release of phase-to-earth

fault measuring elements is then blocked, RELEASE_PE = "No fault".

The operation of the faulted phase selection function is highly dependent on the

earth-fault detection function. The phase preference or faulted loop selection logic

can be set to filter the faulted phases to be released for measurement in the

protection zones.

The general indication of a fault is given in the binary output START_GFC. The

faulted phase information can be found from the integer monitored data signal

Table 909: Enumeration values for integer monitored data signal STARTS_GFC

Enumeration name

The fault loops released for measurement are indicated with the integer monitored

data signals RELEASE_PE and RELEASE_PP. These signals may be filtered by the

phase preference of the faulted loop selection logic.

Table 910: Enumeration values for integer monitored data signal RELEASE_PE

Enumeration name

Table continues on the next page

Technical Manual

Phase voltage Meas = "Ph-to-ph without Uo"), only phase-to-phase

Protection functions