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
159. This locus can enter the
operating characteristic of a distance protection and cause, if no preventive measures
have been considered, its unwanted operation.
R
jX
Operating characteristic
Impedance locus at
power swing
IEC09000224_1_en.vsd
IEC09000224 V1 EN
Figure 159: Impedance plane with Power swing detection operating characteristic
and impedance locus at power swing
Basic characteristics
Power swing detection function (ZMRPSB, 78) detects reliably 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 operate conditions as well as during dead time of a single-pole automatic
reclosing cycle.
ZMRPSB (78) function is able to secure selective operation for internal faults during
power. 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 ZMRPSB (78) 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.
1MRK504116-UUS C Section 3
IED application
357
Application manual
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