Hitachi Relion 650 Series Technical Manual page 285

1MRK 511 557-UEN Rev. A
IEC19000911 V2 EN-US
Figure 122: Voltage zero 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
transient increases as the pre-strike instant moves away from intended gap voltage zero 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 pre-
strike voltage is minimal.
The solution approach depends on the circuit breaker properties:
• If the minimum RDDS is lower than the maximum system voltage gradient (1 pu) the optimal
target energization instant is obtained by avoiding the previous half cycle of gap voltage. This is
achieved by shifting the energizing target to the right until the 'earliest probable pre-strike
instant' is no more located in, but still close to, the previous half cycle of gap voltage. See
121(b).
• If the minimum RDDS is greater/equal to the maximum system voltage gradient (1pu) the
optimal target energization instant is obtained by minimizing the probable pre-strike voltage on
both half cycles adjacent to the zero crossing. This is achieved by shifting the energizing target
to the right until the 'earliest probable pre-strike instant' and 'latest probable pre-strike instant'
are both at the same distance from the gap voltage zero target. 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
123.
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 zero. (b) shifted closing target for minimum pre-strike voltage.
Figure 121(a) and Figure
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Angle
Earliest probable pre-strike instant
Latest probable pre-strike instant
Nominal prestrike instant
122(a), the actual instants at which the current is established
Angle
(b)
IEC19000911-2-en.vsdx
Figure 122 (b).
Section 12
Monitoring
Figure
Figure
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