Alstom MiCOM P545 - 2.3.16 Out of step protection (Distance option only); 2.3.17 Critical stability angle (Distance option only)

P54x/EN AP/La4 Application Notes
(AP) 6-24 MiCOM P543, P544, P545 & P546
AP
In case the OST is enabled the R5, R5’, Z5 and Z5’ settings will be adequate for very slow
swing detection. If, however, the OST protection is disabled, set:
R5=R5’=0.85 x Z<
Z5=Z5’=2 x Zline
where Z< is load blinder radius determined in the 2.3.13 Section.
The user d
ecides which zones are required to be blocked.
Two timers are available:
The PSB Reset Delay
is used to maintain the PSB status when I naturally is low during the
swing cycle (near the current maxima and minima in the swing envelope). A typical setting
of 0.2 s is used to seal-in the detection until I has chance to appear again.
The PSB Unblock Dly
is used to time the duration for which the swing is present. The
intention is to allow the distinction between a stable and an unstable swing. If after the
timeout period the swing has still not stabilized, the block for selected zones can be released
(“unblocking”), giving the opportunity to split the system. If no unblocking is required at the
location of this relay, set to maximum (10 s).
PSB can be disabled on distribution systems, where power swings would not normally be
experienced.
2.3.16 Out of step protection (Di
stance option only)
P54x provides an integrated Out of Step protection, therefore avoiding a need for a separate
stand alone Out of Step relays. Unlike the power swing detection, the Out of Step protection
requires settings and is completely independent from the setting free Power swing detection.
This section provides a discussion and a guidance of how to set the Out of Step protection.
Settings based on system studies must be applied when ‘Predictive OST’ operation mode is
selected as the high setting accuracy is needed to avoid premature system splitting in the
case of severe power oscillations that do not lead to pole slip conditions. For the ‘OST’
setting the same method may be used but an exhaustive stability study may not be required
as it will be shown later that the total system impedance ZT and system split points
are
adequate to set the relay for this scenario.
The MiCOM P54x Out of Step protection can operate as a stand alone protection, i.e.
Distance protection may be completely disabled under Configuration column.
2.3.17 Critical stability angle (Di
stance option only)
What is the angle between two ends when a power system oscillation could be declared as a
pole slip?
Consider the power angle curves as in Figure 6.