Hitachi Relion 650 Series Technical Manual page 284

Section 12
Monitoring
RDDS
max
IECEQUATION19050 V2 EN-US
as ScatterRDDS is specified in percent of nominal RDDS.
The settings that determine the optimized energizing angle are listed in
Table 268: Scatter based settings of ACBMSCBR
Setting
RDDS
ScatterMechCl
ScatterRDDS
GapVoltage
The following subsections explain how ACBMSCBR optimizes the mechanical closing target for
different application scenarios.
Closing at gap voltage zero
The objective of considering breaker scatter for gap voltage zero target is to minimize the pre-striking
voltage.
Aiming for current making precisely at gap voltage zero may actually result in high switching
overvoltages.
defined above) is lower than the maximum system voltage gradient.
behavior of the breaker when the minimum RDDS of the CB is greater/equal to the maximum system
voltage gradient.
IEC19000910 V2 EN-US
Figure 121: Voltage zero closing with low-RDDS circuit breaker: (a) closing target at gap
278
 
ScatterRDDS
 
RDDS 1
100
Description
Rate of decay of dielectric strength of the breaker. It is negative in nature and the dielectric
strength reduces as the contacts approach each other. It is the statistical average of several
measured RDDS values.
Standard deviation of mechanical closing time scatter.
Percentage difference between the nominal and observed minimum/maximum RDDS values.
Expected gap voltage across the corresponding phase circuit breaker just prior to the target
making instant.
Figure 121(a) displays the behavior of the breaker when the minimum RDDS (as
(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.
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Angle
Earliest probable pre-strike instant
Latest probable pre-strike instant
Nominal prestrike instant
1MRK 511 557-UEN Rev. A
Table 268.
GUID-6208EB83-FD39-4B26-826D-0F3BEC03488B v2
Figure 122(a) displays the
Angle
(b)
IEC19000910-2-en.vsdx
Technical Manual