Application - ABB RELION REX640 Technical Manual

Section 4
Protection functions
4.2.2.10
436
-90 -75
GUID-95353022-78F0-47E8-A179-A79CC3F5DBA4 V1 EN
Figure 237: Phase angle 88 amplitude (Directional mode = Forward)

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 Iosin(φ) or the active
part Iocos(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 Iocos(φ) or Iosin(φ) according to
the earthing method, where φ is the angle between the residual current and the
reference residual voltage (-Uo). In compensated networks, the phase angle criterion
with extended operating sector can also be used. When the relay characteristic angle
RCA is 0 degrees, the negative quadrant of the operation sector can be extended with
the Min forward angle setting. The operation sector can be set between 0 and -180
degrees, so that the total operation sector is from +90 to -180 degrees. In other words,
the sector can be up to 270 degrees wide. This allows the protection settings to stay the
Io / % of I
n
100
Min forward angle
90
80
70
50
40
30
20
10
-60 -45 -30 -15 0 15
1MRS759142 C
88 deg
100% of In
85 deg
20% of In
73 deg
1% of In
30 45 60 75 90
Technical Manual
REX640