Liebert Series 600T manual Modes of Operation

1.4Modes of Operation

Refer to 2.0 - Theory of Operation and 3.0 - Operation for more details.

1.4.1Normal (Load on UPS)

The utility AC source provides power to the rectifier/charger in each UPS module. Each rectifier/charger con- verts the utility AC power to DC and supplies DC power to the UPS module inverter while simultaneously float charging the battery plant. Each UPS module inverter converts DC to AC and furnishes AC power to the critical bus. The System Control Cabinet (SCC) is the tie point for the paralleled modules and monitors and controls the critical bus performance.

1.4.2Input Power Failure

If the utility source power fails or is outside the acceptable range, the battery plant becomes the primary supplier of DC power to the inverter.

1.4.3Recharge

After the utility source power is restored, or an alternate power source becomes available, each rectifier/charger slowly walks-in to once again power the inverters and recharge the battery plant.

1.4.4Overload

Overloads in critical systems may be caused by inrush currents during connected equipment start-up or by faults in the critical load. The Liebert Series 600T UPS system can maintain full output voltage regulation while sus- taining the following overloads:

•Up to 150% for 30 seconds

•Up to 125% for 10 minutes

•Up to 104% for an indefinite period of time

Also, for clearing momentary faults above 155% of rated SCC current, the static switch turns on for 40 millisec- onds to supply power from the bypass source. Up to 1000% of the rated current can be supplied for less than one cycle, while up to 500% of rated load can be sustained for the full 40 milliseconds of pulsed-parallel operation. The critical load remains on the UPS modules for the above conditions. If the UPS system overload capacity is exceeded, an automatic transfer to bypass is initiated, which closes the system bypass circuit breaker (SBB) and opens the UPS output circuit breaker.

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

1.4.5Redundant

If the multi-module UPS system includes one more module than the number required to supply the critical load, the UPS system can operate in the redundant mode. This means that the load will remain on the UPS system if one of the modules is disconnected because of an overload, an internal fault, or for maintenance. If the additional module is not included in the system design, or if the additional module is disconnected from the critical bus, the UPS system operates in the non-redundant mode.

1.4.6Bypass (Internal)

The SCC control logic initiates an automatic transfer to the bypass source if the overload-current-versus-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 maintenance.

The SCC internal maintenance bypass will allow most key components and operating modes to be checked with- out disturbing the critical bus. However, certain key power-carrying components, such as the output and bypass circuit breakers, will require complete system shutdown or isolation through an external maintenance bypass cabinet for 100% service.

1.4.7Maintenance Bypass

The installation of a Maintenance Bypass Cabinet, Panelboard or Switchboard is recommended to allow you to totally isolate the UPS from all power sources. Use of the Maintenance Bypass is described in 3.0 - Operation.

1.4.8Off-Battery

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

Introduction 9

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