Specifications

98AEtypSMSspec_RevC.doc

SP-0012 Rev. C 09/05/09

F. The UPS Module Control power supply employs a redundant design configuration,

utilizing the UPS AC input (utility) and the UPS Module inverter output therefore

enhancing reliability.

2.2.4 Bypass and Static Switch

UPS module contains an automatic bypass static switch circuit and associated bypass

static switch transfer control circuitry.

A. General

A bypass circuit shall be provided as an alternate source of power other than the inverter.

A high speed SCR switch and wrap-around contactor shall be used to assume the

critical load during automatic transfers to the bypass circuit. The static switch and

wrap-around contactor shall derive power from an upstream bypass feed contactor

internal to the UPS module. The wrap-around contactor shall be electrically connected in

parallel to the static switch and shall, at the same time as the static switch, be energized

and upon closure maintain the critical load feed from the bypass source. The static

switch shall only be utilized for the time needed to energize the wrap-around contactor

therefore increasing reliability. The bypass circuit shall be capable of supplying the

UPS rated load current and also provide fault clearing current capabilities. The UPS

system logic shall employ sensing which shall cause the static switch to energize within

150 microseconds therefore providing an uninterrupted transfer to the bypass source

when any of the following limitations are exceeded:

1. Inverter output undervoltage or overvoltage.

2. Overloads beyond the capability of the inverter.

3. DC circuit undervoltage or overvoltage.

4. Final voltage of system battery is reached (bypass source present and available).

5. System failure (e.g.: logic fail, fuse blown, etc.).

B. Automatic Re-transfers

In the event that the critical load must be transferred to the bypass source due to an

overload, the UPS system logic shall monitor the overload condition and, upon the

overload being cleared, perform an automatic re-transfer back to the inverter output.

The UPS system logic shall only allow a re-transfer to occur three times within a one

minute period. Re-transfers shall be inhibited on the fourth transfer due to the likelihood

of a recurring problem at the UPS load distribution. All retransfers will be inhibited if the

inverter and static bypass line are not synchronized.

C. Manual Transfers

The UPS shall be capable of transferring the critical load to/from the bypass source via

the front control panel. If performing manual transfers to inverter or automatic

retransfers, the UPS system logic shall force the inverter output voltage to match the

bypass input voltage and then parallel the inverter and bypass sources providing a

make-before-break transition allowing a controlled walk-in of load current to the inverter.

Manual transfers will be inhibited if the inverter and static bypass line are not

synchronized.

D. Static Switch