APC Bypass Static User Manual download pdf (Page 7)

Page 7 10/05/09

the outlined time limitation; the critical load shall be switched to the automatic static bypass output of

the UPS.

C. Output Contactor: The output inverter shall be provided with an output mechanical contactor to

provide physical isolation of the inverter from the critical bus. With this feature a failed inverter shall

be removed from the critical bus.

D. Battery Protection: The inverter shall be provided with monitoring and control circuits to limit the

level of discharge on the battery system.

2.5 STATIC BYPASS

A. General: As part of the UPS, a system static bypass switch shall be provided. The system static

bypass shall provide no break transfer of the critical load from the inverter output to the static

bypass input source during times where maintenance is required, or the inverter can not support the

critical bus. Such times may be due to prolonged or severe overloads, or UPS failure.

B. Design: The design of the static switch power path shall consist of silicon controlled rectifiers

(SCR) with a continuous duty rating of 110 percent of the UPS output rating.

C. Automatic Transfers: An automatic transfer of load to static bypass shall take place whenever the

load on the critical bus exceeds the overload rating of the UPS. Automatic transfers of the critical

load from static bypass back to normal operation shall take place when the overload condition is

removed from the critical bus output of the system. Automatic transfers of load to static bypass shall

also take place if for any reason the UPS cannot support the critical bus.

D. Manual Transfers: Manually initiated transfers to and from static bypass shall be initiated through

the UPS display interface.

E. Overloads: The static bypass shall be rated and capable of handling overloads equal to or less

than 110 percent of the rated system output continuously. For instantaneous overloads caused by

inrush current from magnetic devices, or short circuit conditions, the static bypass shall be capable

of sustaining overloads of 800 percent of system capacity for periods of up to 500 milliseconds.

F. System Protection: As a requirement of UL 1778, back-feed protection in the static bypass circuit

shall also be incorporated in the system design. To achieve back-feed protection, a mechanical

contactor in series with the bypass SCR(s) shall be controlled by the UPS/static switch, to open

immediately upon sensing a condition where back-feeding of the static switch by any source

connected to the critical output bus of the system is occurring. One such condition could be a result

of a shorted SCR.

G. Dual Feed: For purposes of increased reliability, the static bypass shall be capable of being fed

from a separate feed from the input power converter.

2.6 INTERNAL MECHANICAL BYPASS

The UPS shall be equipped with an internal make-before-break bypass switch to isolate the UPS

during times where maintenance is required.

2.7 DISPLAY AND CONTROLS

A. Display Unit: A microprocessor-controlled display unit shall be located on the front of the

system. The display shall consist of an alphanumeric display with backlight, an alarm LED, and a

keypad consisting of pushbutton switches.

B. Metered Data: The following metered data shall be available on the alphanumeric display:

1. Year, month, day, hour, minute, second of occurring events.

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APC Bypass Static User Manual Page 7

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