Short-Time Protection

The short-time protection function helps to protect the distribution system against impedant short-circuits.
This function carries out true rms measurements.
The short-time time delay and the I²t ON and I²t OFF options can be used to obtain selectivity with a downstream circuit breaker:
- I²t OFF selected: the protection function implements a constant time curve.
- I²t ON selected: the protection function implements an I²t inverse-time curve up to 10 Ir. Above 10 Ir, the time curve is constant.
Zone selective interlocking (ZSI).

The short-time and ground-fault protection functions enable time selectivity by delaying the upstream devices to provide the downstream devices the time required to clear the fault. Zone selective interlocking can be used to obtain total selectivity between circuit breakers using external wiring.

For the characteristics and external wiring of the zone selective interlocking function, refer to Zone Selective Interlocking in the technical appendix.
Intermittent faults are taken into account by the trip unit and may lead to shorter tripping times than those set.
For the factory settings, the setting ranges, increment steps and setting accuracies, refer to Threshold and Time-Delay Settings.

Short-Time Pick-Up Isd

Pickup (accuracy ± 10%)

Isd = Ir x ...

1.5

2.5

Time Delay tsd

tsd time delay (s)	I²t OFF	0	0.1	0.2	0.3	0.4
tsd time delay (s)	I²t ON		0.1	0.2	0.3	0.4
Tripping time at 10 x Ir (ms) with I²t ON or I²t OFF	Maximum resettable time	20	80	140	230	350
Tripping time at 10 x Ir (ms) with I²t ON or I²t OFF	Maximum break time	80	140	200	320	500

If the rating plug without long-time protection is used and the long-time protection function is disabled, the short-time pickup Isd is automatically multiplied by In instead of Ir as is the standard case.