Function Block; Functionality - ABB RELION 620 Series Technical Manual

1MAC504801-IB E
4.7.1.2
4.7.1.3
620 series ANSI
Technical Manual

Function block

GUID-E50B9C93-A9EF-421B-8B8D-581C0AC67E89-ANSI V1 EN
Figure 229: Function block

Functionality

The phase step distance protection function 21P can be used for the short circuit protection
of distribution networks. 21P operates selectively for two-phase and three-phase short
circuits.
21P supports mho (circular) characteristics. It has five flexible and configurable zones for
protection (Z1...Z5). Directionality, reach and line angle for each zone can be set
independently from each other.
21P has a separate and independent impedance measurement for phase-to-phase and
three-phase fault loop in each distance protection zone. The memory voltage is used with
the three-phase impedance measurement elements to secure the correct directional
measurement in case of close-in three-phase faults.
The operation of 21P is based on the impedance-mapping approach, where the fault loop
impedance is calculated first and then compared to the zone boundaries. If the impedance
is recognized inside the operation zone, the corresponding trip output is activated after the
trip time has elapsed.
The impedance measurement is based on the full-cycle DFT-filtered current and voltage
phasors. Thus, the typical operating times are less than two cycles.
Section 4
Protection functions
489