ABB REG670 - Page 320

and the real part gives the fault conductance:
1 1 1
Re
f ref
R Z Z
æ ö
= -
ç ÷
ç ÷
è ø
EQUATION2421 V1 EN
In the settings there are given two resistance levels:
• RAlarm given in Ω. If
f Alarm
R R<
EQUATION2524 V1 EN
an alarm signal ALARM is given after a set delay tAlarm.
• RTrip given in Ω. If
f Trip
R R<
EQUATION2523 V1 EN
a start signal START is given.
If the fault resistance is slightly below the set value RTrip the trip time will be about
10 s with default filter length of 1 s. If the fault resistance is estimated to 0 Ω the trip
delay will be 2 s with default filter length of 1 s. For values in between the delay will
follow linear interpolation describing the fault resistance time relation, as shown in
figure 142.
Note that actual tripping time is dependent on the set parameter FilterLength which
has default value of 1s.
Section 7 1MRK502052-UEN B
Impedance protection
314
Technical manual