Mimic Display, Chg, SYS. Status | Liebert 30-130kVA guide

Introduction

1.3.4Overload

Overloads in critical systems may be caused by inrush currents during connected equipment startup or by faults in the critical load or distribution network. The Liebert Npower UPS system can maintain full output voltage regulation while sustaining the following overloads:

•Up to 125% for 10 minutes

•Up to 150% for 1 minute

•Up to 200% for 10 cycles

For momentary faults above 200% of rated current, the static switch turns on for 10 cycles to supply power from the bypass source. Up to 6,000 amps of current can be supplied for the first half cycle.

The critical load remains on the UPS module for the above conditions. If the UPS system overload capacity is exceeded, an automatic transfer to bypass is initiated, which keeps the static switch on and opens the inverter output contactor.

Whenever you have an overload condition, you should determine the cause of the overload.

1.3.5Bypass (Internal)

The UPS control logic initiates an automatic transfer to the bypass source if the overload-current-ver- sus-time curve is exceeded or if specified UPS system faults occur. You can also manually transfer the load to the bypass (without interruption) if you must take the UPS module out of service for mainte- nance.

With the rotary switch in the Bypass position, most key components and operating modes can be checked without disturbing the critical bus. However, certain key power-carrying components will require complete system shutdown or isolation through an external maintenance bypass cabinet for 100% service.

1.3.6External Maintenance Bypass

The installation of an External Maintenance Bypass Cabinet or panel board is recommended to allow you to totally isolate the UPS from all power sources. Use of the External Maintenance Bypass is described in SIB External Maintenance Bypass on page 30.

1.3.7Off-Battery

The battery plant can be disconnected from the rectifier/charger by using an external Module Battery Disconnect (MBD) circuit breaker. The UPS continues to function normally, though it does not have power outage back-up capability until the battery plant is reconnected.