Operation 81
3.2.3 Momentary Overloads
Anoverload in the critical load will continueto be supplied by the UPS system if the overload condition doesnot
exceedthe current versus time curve of overloadcapacity for either the SCC ratingor for the number of modules
on-line.
Formomentary overloads exceeding 155% of rated system (SCC) current, thes taticswitch turns on for 40 milli-
secondsto 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
forthe full 40 milliseconds of pulsed-parallel operation. By providingtwo power sources simultaneously, high
currentcan be supplied to the critical load with full output voltageregulation. The critical load can be supported
throughinrush currents and momentary faults without operating the motorized circuitbreakers.
Ifan overload situation exceeds 40 milliseconds, theUP Ssystem continues to supply power to the critical load if
itremains within the current versus time curve of overload capacity.If the system overload capacity is exceeded,
theUPS control logic at the SCC initiates an automatictransfer to the bypass line by operating the staticbypass
switchand the motorized system circuit breakers (SBB and UPS Output).
Refer to 3.4 - Automatic Operations.
Figure 50 Momentary Overload (Pulsed Static BypassS witch)
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
(canaccommodate up t o 6UP S modules)
ToCriticalLoad
Battery
MBD
Battery
MBD
Battery
MBD
DISCONTINUED
PROD U C T