Fault Detection During Power Swing And Unblocking Distance Protection Zone - Hitachi Relion 670 Series Applications Manual

Section 7
Impedance protection
The oscillation rate depends also on the inertia of the system and on the total system impedance
between different generating units. These oscillations cause changes in phase and amplitude of 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:
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 "Technical reference manual" for the IEDs.
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:
94
jX
Operating characteristic
Impedance locus at
power swing
IEC09000224_1_en.vsd
Impedance plane with Power swing detection operating characteristic and impedance
locus at power swing
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Application manual