ABB Relion 670 Series Applications Manual page 108

Section 7
Impedance protection
the voltage difference between the oscillating generating units in the power system, which
reflects further on in oscillating power flow between two parts of the system - the power swings
from one part to another - and vice versa.
Distance IEDs located in interconnected networks see these power swings as the swinging of the
measured impedance in relay points. The measured impedance varies with time along a locus in an
impedance plane, see figure 46. This locus can enter the operating characteristic of a distance
protection and cause, if no preventive measures have been considered, its unwanted operation.
IEC09000224 V1 EN-US
Figure 46: Impedance plane with Power swing detection operating characteristic and
Basic characteristics
Power swing detection function (ZMBURPSB, 68) reliably detects power swings with periodic time
of swinging as low as 200 ms (which means slip frequency as high as 10% of the rated frequency
on the 50 Hz basis). It detects the swings under normal system operation conditions as well as
during the dead time of a single-pole automatic reclosing cycle.
ZMBURPSB (68) function is able to secure selective operation for internal faults during power
swing. The operation of the distance protection function remains stable for external faults during
the power swing condition, even with the swing (electrical) centre located on the protected power
line.
The operating characteristic of the ZMBURPSB (68) function is easily adjustable to the selected
impedance operating characteristics of the corresponding controlled distance protection zones as
well as to the maximum possible load conditions of the protected power lines. See the
corresponding description in
7.1.3.2 Fault detection during power swing and unblocking distance protection
zone
Power swing unblocking feature of ZMBURPSB function unblocks or releases distance protection
zones with reliable phase selection for faults that occur during power swing.
There are methods such as zero sequence current supervision and negative sequence current
supervision used to inhibit PSB detection in case of faults during power swing so that the distance
protection zone, if blocked because of power swing, may trip and clear faults. However, power
system continuity and reliability is impacted:
102
jX
Operating characteristic
Impedance locus at
power swing
IEC09000224_1_en.vsd
impedance locus at power swing
"Technical reference manual" for the IEDs.
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Application manual