Liebert 1000kVA manual Momentary Overloads, Momentary overload, pulsed static bypass switch

Operation

3.3.3Momentary Overloads

An overload in the critical load will continue to be supplied by the UPS system if the overload condi- tion 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 milliseconds to provide current from the bypass line in parallel with current from the UPS sys- tem 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 volt- age regulation. The critical load can be supported through inrush currents and momentary faults without operating the motorized circuit breakers. Pulse paralleling also serves, under some circum- stances, as a backup in the event that an external bypass feeder breaker (e.g., BFB) trips open during this pulse-paralleling period, retaining the UPS inverter connection with the critical load.

If an overload condition 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 3.5 - Automatic Operations.

Figure 55 Momentary overload, pulsed static bypass switch

		RIB			RIB			RIB		BFB
UPS #3			UPS #2			UPS		#1
CB1			CB1			CB1
								SBS
										BIB
	R			R			R		SBB
	I			I			I				MBB
CB2			CB2			CB2		System		SKRU
								Controls

Output

MIB

					SCCT
	MBD				To Critical Load
			MBD		MBD
					SCCT
Battery
		Battery		Battery
					(can accommodate up to 6 UPS modules)

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