UPS mission critical installations

Installing an Uninterruptible Power System ( UPS) can demand more than simply finding a space large enough in which to site it. For critical installations special considerations need to be given to the following areas:

Alarm Reporting

If the UPS is to be installed in a secure access room basement or confined environment consideration must be given to monitoring of the UPS status and alarms.

Most UPS incorporate some form of system and battery testing to warn of potential problems prior to a system failure. A UPS may seem to be performing normally but if the battery is very old it may only be capable of supplying 10% of its originally installed capacity when new. The UPS will have raised an alarm condition that the battery needs to be checked or replaced but this will be ignored if no remote monitoring is installed. A further complication can arise where the UPS has an automatic system bypass. In this case the UPS may have failed due to a system overload or fault condition. The load will have been automatically transferred to an unprotected mains supply. To the UPS users the system will appear normal but the load will be at risk. In either scenario only a mains failure highlights the fact that the UPS was actually in an alarm condition and was unable to support the load. It may have been operating for weeks in a near-to-fail or failed state.For critical applications the solution is to make use of the built-in communications port on the UPS. This normally provides both RS232 communications and signal contacts. It allows the UPS to report changes in its operating status to a Building Management System (BMS) remote status panel or Local Area Network (LAN). Failure to monitor the state of the UPS or to take advantage of automatic system and alarm reporting will seriously undermine the integrity of the UPS.

Ambient Temperature

Most UPS datasheets indicate that the UPS can work in ambient environments which range between 0 and 40C.

Such high ambients can occur when the UPS is installed in a control panel or a small unventilated room. In such environments reliability problems will occur. Most UPS will only work up to 40C for short periods. If the UPS has not been designed and manufactured to work continuously inside such a temperature range users should assume that the actual expected ambient is nearer 25C. At higher ambients the UPS will almost certainly alarm and may shut itself down automatically to protect itself. Ambients above 25C will also dramatically reduce battery life by as much as 90%. For high ambient environments either choose a UPS designed for long term high ambient use or install forced air cooling.

Automatic System Bypass

On-line UPS have an automatic bypass. This is a safety feature which allows the UPS to fail safely to mains without disrupting the supply to the load.

Such a transfer will occur when the UPS is overloaded to the extent that it cannot supply the requested capacity or it develops an internal fault condition. The load sees no break during the transfer.

Parallel Redundancy

The integrity of an on-line UPS installation can be further enhanced by installing two UPS in a parallel redundant configuration.

In such a scenario each UPS is capable of supporting the full load should one of the UPS fail.

External Maintenance Bypass

A maintenance bypass allows the UPS to be manually bypassed.

When activated the load is transferred from the output of the UPS to the raw mains. The load sees no break during the transfer from UPS to mains and vice versa. The process allows the UPS to be isolated for maintenance or simply swapped out. Whilst some UPS have a maintenance bypass built-into their design an external wall mounted bypass is more practical. An external maintenance bypass allows the UPS to be fully isolated and switched off. It also allows the UPS to be physically replaced without disruption of supply to the load.

External Maintenance Bypass Supply Conditioning

When powered through an external maintenance bypass the load is not protected from mains disturbances. Such a scenario can last for several hours.

The solution is to install a power conditioner in the external maintenance bypass circuit. Whilst a power conditioner cannot protect the load from a complete mains failure it can be specified to provide Galvanic Isolation and/or mains voltage regulation.

Line connection

Care should be taken to ensure supplies do not share common fuses.

Load Connection

Where a UPS powers a dedicated circuit some consideration should be given on how to control and restrict access to socket outlets on the circuit.

Without restricted access loads may be connected to the UPS which cause an overload and failure of the UPS. Access can be restricted through the installation of specially designed plugs and sockets colour coding and clear warning labels.