ABB REC670 Applications Manual page 135

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
It should be remembered that the vectorial sum of the currents must be used (IEDs,
Metrosil and resistor currents are resistive). The current measurement is insensitive
to DC component in fault current to allow the use of only the AC components of
the fault current in the above calculations.
The voltage dependent resistor (Metrosil) characteristic is shown in Figure 54.
Series resistor thermal capacity
The series resistor is dimensioned for 200 W. Preferable the U>Trip
SeriesResistor should always be lower than 200 W to allow continuous activation
during testing. If this value is exceeded, testing should be done with a transient
faults.
Section 7
Differential protection
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