Specifications

providing redundancy and, in the event of a failure, prevent unnecessary

damage to power transistor components/fuses. Load current above 150%

shall cause an immediate transfer of the load to the bypass source for fault

clearing.

4.3.7. Inverter Overload Protection

The Inverter AC output shall utilize electronic current limiting for overload

conditions. The Inverter shall utilize a contactor to isolate its output from the

critical bus.

a. The Inverter fuses shall be the fast acting semiconductor type to clear

faults on the DC buss.

b. The Inverter output isolation contactor shall be located internal to the

UPS module and shall be controlled by the internal UPS module system

logic.

4.4. Bypass and Static Switch

4.4.1. 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 bypass source. The static switch shall only be

utilized for the time needed to energize the wrap-around contactor thus

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

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

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

energize within 150 microseconds thus providing an uninterrupted transfer

to the bypass source when any of the following limitations are exceeded:

a. Inverter output undervoltage or overvoltage.

b. Overloads beyond the capability of the inverter.

c. DC circuit undervoltage or overvoltage.

d. Final voltage of system battery is reached (bypass source present and

available).

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