Hitachi Relion 650 Series Technical Manual page 287

1MRK 511 557-UEN Rev. A
IEC19000913 V2 EN-US
Figure 125: Voltage peak closing with high-RDDS circuit breaker: (a) Closing target at gap
As shown in
in the circuit can vary from 'earliest probable pre-strike instant' to 'latest probable pre-strike instant'.
This variation depends on the electrical and mechanical scatter of the breaker. The magnitude of the
inrush current asymmetry increases as the pre-strike instant moves away from intended gap voltage
peak target. Thus, for given mechanical and dielectric scatter, it is desirable to obtain a combination
of 'earliest probable pre-strike instant' and 'latest probable pre-strike instant' for which the highest
expected inrush current asymmetry is minimal.
The solution approach depends on the circuit breaker properties:
• If the maximum RDDS is lower than the maximum system voltage gradient (1 pu) the optimal
target energization instant is obtained by avoiding the next half cycle of gap voltage. This is
achieved by shifting the energizing target to the left until the 'latest probable pre-strike instant' is
no more located in the next half cycle of gap voltage. See
• If the maximum RDDS is greater/equal to the maximum system voltage gradient (1pu) the
optimal target energization instant is obtained by maximizing the probable pre-strike voltage on
both sides of the gap voltage peak. This is achieved by shifting the energizing target to the left
until the 'earliest probable pre-strike instant' and 'latest probable pre-strike instant' are both at
the same distance from the gap voltage peak. See
ACBMSCBR performs the scatter correction as explained above and evaluates the expected pre-
arcing time in the shifted optimized energizing target. The shift of the optimized energizing angle from
the ideal target angle (TGTANGLX) is given at the SCATTERLX output and the expected pre-arcing
time in the shifted optimized energizing target is given at the PPREARCLX output as shown in
126.
Technical Manual
(a)
Nominal dielectric strength with slope
RDDS
Mechanically scattered dielectric strength
Electrically scattered dielectric strength
with slope RDDS
max
Electrically scattered dielectric strength
with slope RDDS
min
voltage peak. (b) Shifted closing target for maximum pre-strike voltage.
Figure 124(a) and Figure
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Angle
Earliest probable pre-strike instant
Latest probable pre-strike instant
Nominal prestrike instant
125(a), the actual instants at which the current is established
Figure
Angle
(b)
Figure 124(b).
125(b).
Section 12
Monitoring
Figure
281