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Operation 81
3.2.3 Momentary Overloads
An overload in the critical load will continue to be supplied by the UPS system if the overload condition does not
exceed the current versus time curve of overload capacity for either the SCC rating or for the number of modules
on-line.
For momentary overloads exceeding 155% of rated system (SCC) current, the static switch turns on for 40 milli-
seconds to provide current from the bypass line in parallel with current from the UPS system output. Up to
1000% of rated current can be supplied for less than one cycle, while up to 500% of rated load can be sustained
for the full 40 milliseconds of pulsed-parallel operation. By providing two power sources simultaneously, high
current can be supplied to the critical load with full output voltage regulation. The critical load can be supported
through inrush currents and momentary faults without operating the motorized circuit breakers.
If an overload situation exceeds 40 milliseconds, the UPS system continues to supply power to the critical load if
it remains within the current versus time curve of overload capacity. If the system overload capacity is exceeded,
the UPS control logic at the SCC initiates an automatic transfer to the bypass line by operating the static bypass
switch and the motorized system circuit breakers (SBB and UPS Output).
Refer to 3.4 - Automatic Operations.
Figure 50 Momentary Overload (Pulsed Static Bypass Switch)
BIB
SKRU
MIB
MBB
I
R
#2UPS
CB1
CB2
I
R
#1UPS
CB1
System
Controls
I
R
#3UPS
CB1
CB2
RIB RIB
CB2
RIB BFB
Output
SBB
SBS
SCCT
SCCT
(can accommodate up to 6 UPS modules)
To CriticalLoad
Battery
MBD
Battery
MBD
Battery
MBD