ABB REF615 - Application

A070443 V2 EN
Figure 74: Extended operation area in directional earth-fault protection
5.2.2.4 Application
The directional earth-fault protection (DEFxPDEF) is designed for protection and
clearance of earth faults and for earth-fault protection of different equipment
connected to the power systems, such as shunt capacitor banks or shunt reactors, and
for backup earth-fault protection of power transformers.
Many applications require several steps using different current start levels and time
delays. DEFxPDEF consists of two different stages:
• low (DEFLPDEF)
• high (DEFHPDEF)
DEFLPDEF contains several types of time delay characteristics. DEFHPDEF is used
for fast clearance of serious earth faults.
The protection can be based on the phase angle criterion with extended operating
sector. It can also be based on measuring either the reactive part I
0
sin(φ) or the active
part I
0
cos(φ) of the residual current. In isolated networks or in networks with high
impedance earthing, the phase-to-earth fault current is significantly smaller than the
short-circuit currents. In addition, the magnitude of the fault current is almost
independent of the fault location in the network.
The function uses the residual current components I
0
cos(φ) or I
0
sin(φ) according to
the earthing method, where φ is the angle between the residual current and the
Section 5 1MRS756378 D
Protection functions
152 REF615
Application Manual