Emerson NX manual Automatic Transfers to Bypass Overload Condition

Operation

2.6.2Automatic Transfers to Bypass (Overload Condition)

The UPS system will initiate an automatic load transfer to the bypass line if an overload condition exceeds the current-versus-time curve of overload capacity or if specified UPS system faults occur.

The Overload Transfer and Output Undervoltage alarm messages will initiate an automatic transfer to bypass. Other UPS system faults will initiate an automatic transfer to bypass followed immediately by the shutdown and isolation of the UPS system. Refer to 2.6.3 - Automatic Transfers to Bypass, UPS System Faults.

NOTE

A load transfer to the bypass line will be completed whenever an automatic transfer to bypass is initiated. If the OK to Transfer condition is present, the load transfer will be uninterrupted. If the Static Switch Unable alarm message is present for any reason, the automatic transfer will be interrupted for 40 to 120 milliseconds. Because of the reliability of the UPS components, an interrupted load transfer is a very unlikely occurrence.

2.6.3Automatic Transfers to Bypass, UPS System Faults

For specified UPS system faults, the control logic will initiate an automatic transfer to bypass followed immediately by a shutdown and isolation of the UPS system. The DC source (MBD) and input circuit breakers are open. The bypass static switch will be closed if the bypass line is available.

NOTE

The bypass line is usually not available during Low Battery Shutdown.

The following UPS system faults will initiate an automatic transfer to bypass:

•DC Overvoltage Shutdown

•Inverter Fault

•Low-Battery Shutdown

•Output Overvoltage and Undervoltage

•Overload Shutdown

•Equipment Overtemperature

•Rectifier Fuse Blown

NOTE

A load transfer to the bypass line will be completed whenever an automatic transfer to bypass is initiated and the bypass line is available. If the OK to Transfer condition is present, the load transfer will be uninterrupted. If the Static Switch Unable alarm message is present for any reason, the automatic transfer will be interrupted for 40 to 120 milliseconds. Because of the reliability of the UPS components, an interrupted load transfer is a very unlikely occurrence.

Some installations may include a Remote Emergency Power Off mode that can be initiated automatically by a contact closure in the critical load equipment. Refer to 2.4.4 - Remote Emergency Power Off.

25 Liebert®NX™