ABB Relion 670 Series Applications Manual page 114

Section 6
Differential protection
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 50.
Series resistor thermal capacity
The series resistor is dimensioned for 200 W. Care shall be exercised while testing to ensure that if
current needs to be injected continuously or for a significant duration of time, check that the heat
dissipation Vxxx Series Resistance value does not exceed 200 W. Otherwise injection time shall be
reduced to the minimum.
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1MRK 511 358-UUS A
SEMOD54734-336 v6
Application manual