Specifications

overload is in excess of the set current amplitude, the load power shall be

transferred to the bypass source without interruption.

4.2.6 Inverter Current Limit

The Inverter output shall also be limited to 150% of rated load current. The two

sensing locations shall operate separately and independently thus 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.

4.2.7 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.

4.3 Bypass and Static Switch

4.3.1 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.).

4.3.2 Automatic Re-transfers