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8.14.2
Application
IP14969-1 v1
8.14.2.1
General
M13874-3 v3
Various changes in power system may cause oscillations of rotating units. The most
typical reasons for these oscillations are big changes in load or changes in power
system configuration caused by different faults and their clearance. As the rotating
masses strive to find a stable operate condition, they oscillate with damped oscillations
until they reach the final stability.
The extent of the oscillations depends on the extent of the disturbances and on the
natural stability of the system.
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
. 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-US
Figure 227:
Impedance plane with Power swing detection operating characteristic
and impedance locus at power swing
8.14.2.2
Basic characteristics
M13874-11 v5
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
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI
449
Application manual
Summary of Contents for RELION RET670
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