amplitude increases. When the critical fault clearance time is reached the stability
cannot be maintained.
Un-damped oscillations occur in the power system, where generator groups at different
locations, oscillate against each other
. If the connection between the generators is too
weak the amplitude of the oscillations will increase until the angular stability is lost. At
the moment of pole slip there will be a centre of this pole slip, which is equivalent with
distance protection impedance measurement of a three-phase. If this point is situated in
the generator itself, the generator should be tripped as fast as possible. If the locus of
the out of step centre is located in the power system outside the generators the power
system should, if possible, be split into two parts, and the generators should be kept in
service. This split can be made at predefined locations (trip of predefined lines) after
function from pole slip protection (PSPPPAM ,78) in the line protection IED.
IEC06000314 V1 EN-US
Figure 235: Undamped oscillations causing pole slip
Section 8 1MRK 504 163-UUS A
Impedance protection
468 Transformer protection RET670 2.2 ANSI
Application manual
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