Liebert 130 kVA user manual UPS Power switches configuration, Bypass Supplies

User Manual

Hipulse - Single Phase ‘1+N’ UPS System 130 kVA - 110V

During normal operation both the rectifier and inverter sections are active and provide regulated load power whilst simultaneously float charging the battery. In the event of a mains power failure, the rectifier becomes inoperative and the inverter is powered solely from the battery. Critical load power is maintained under these conditions until battery is fully discharged, where upon the UPS shuts down. The end of battery discharge is assumed when the battery voltage falls below a preset value (i.e. 330 / 340V d.c. for a 400 V a.c. system).

The period for which the load can be maintained following a mains power failure is known as the ‘System’s Autonomy Time’ and is dependent upon both the battery A/Hr capacity and the applied percentage load.

1.2.2 Bypass Supplies

The circuit block annotated ‘Static Switch’ in figure 1-2 contains an electronically controlled switching circuit which enables the critical load to be connected either to the inverter output or to a bypass power source via the ‘static bypass line’. During normal system operation the load is connected to the inverter and the ‘inverter -side’ of the Static Switch is closed; but in the event of a UPS overload, or inverter failure, it is automatically transferred to the static bypass supply line.

Bypass Supply

Mains Supply

Maintenance Bypass

Isolator

Maintenance Bypass Line

Bypass Isolator		STATIC
Static Bypass Line
		SWITCH
RECTIFIER	INVERTER	STATIC
		SWITCH
Input
		Output
Isolator	Battery	Isolator
	Isolator
	BATTERY

UPS

Output

Supply

Fig 1-2 : UPS Power switches configuration

To provide a clean (no-break) load transfer between the inverter output and static bypass line, the static switch activates connecting the load to the bypass supplies. To achieve this, the inverter output and bypass supply must be fully synchronized during normal operating conditions. This is achieved through the inverter control electronics which make the inverter frequency track that of the static bypass supply provided that the bypass remains within an acceptable frequency window. The synchronizing window is pre-selected to 2% of nominal frequency, giving an acceptable frequency window ±1 Hz.

A manually controlled, ‘Maintenance Bypass’ supply is also incorporated into the UPS design. Its purpose is to enable the critical load to be powered from the mains (bypass) supply while the UPS is shut down for routine maintenance.

Note: The load equipment is not protected from normal supply aberrations when operating on Bypass side or in the maintenance bypass mode

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