Short-Time Protection

• The short-time protection function helps to protect the distribution system against impedant short-circuits.

• The short-time time delay can be used to help ensure selectivity with a downstream circuit breaker.

• This function carries out true rms measurements.

• The I²t ON and I²t OFF options enhance selectivity with downstream protection devices.

• Use of I²t curves with short-time protection:

  • 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 (ZSI).

Short-Time Pickup Isd

Time Delay tsd