Alstom MiCOM P54 Series, Technical Manual, Page: 474 / 1024

P54x/EN AP/La4 Application Notes
(AP) 6-30
MiCOM P543, P544, P545 & P546
AP
2.3.17.4 Tost (trip delay) setting (Distance option only)
Tost must be set zero for setting Option 2 and 4 above.
For setting Option 3, Tost should normally be set to zero. It is only the case if a user wants
to operate breaker at the angle closer to 360 degrees (when voltages are in phase) when
time delay could be applied.
2.3.17.5 Blinder angle setting (Distance option only)
Set blinders angle ‘ α ’ same as total system impedance ZT angle.
2.3.17.6 Out of step operation on series compensated lines (Distance option only)
The maximum phase currents during out of step condition rarely exceed 2xIn RMS, which
corresponds to the minimum swing impedance passing through zone 1. Since the
Metal-Oxide Varistors (MOV) bypass level is normally set between 2-3In, they will not
operate during the power oscillations and therefore in majority of applications will not make
any impact on Out of Step operation.
Consider a worst case scenario when the power oscillations are triggered upon fault
clearance on the parallel line. In that case approximately twice the load current will start
flowing through the remaining circuit, increase further and eventually exceed the MOV
threshold. Since the R6-R5 region is usually set far from zone 1 the chances that the
positive sequence impedance’s trajectory may traverse in and out of the set
∆ R region due
to MOV’s operation, are remote. If MOV’s do operate within the ∆ R region (see Figure 9), a
timer, that has been initiated, may reset and be re-initiated or the impedance may remain
within
∆ R region for a slightly longer duration. This is due to the fact that resistive and
capacitive components will be added to the measured impedance during MOV operation as
per Figure 9. This effect may have an impact on the ‘Delta t’ measurement if ‘Predictive
OST’ setting is used. If the recommendation to set R5
MIN
as close as practically possible to
the R6
MAX
is followed, the chances that the swing currents will exceed MOV threshold within
the ∆ R region is very remote. If a study shows that the MOV’s could operate within the ∆ R
region, it is recommended to set ‘Predictive OST and OST’ operating mode to cover all
eventualities.