Typical Things to Keep in Mind while selcting a UPS

When selecting an uninterruptible power system (UPS), maintenance and engineering managers must consider the following factors that can make or break the success of the system:

The size of the critical load determines the capacity of the initial installation. The UPS must have adequate capacity to reliably serve the critical load and additional loads, without immediate expansion. The excess capacity of a UPS will depend on the facility’s plans for expansion of the supported load.

Earlier the approach was to keep provision for future expansion of the load. While this approach is still valid – the % buffer to be kept for expansion plans have to be revisited. The modern day approach is to plan for only immediate expansion plans. (Say for up to 6 months to 1 year). Any expansion beyond an year – can always be supported with an additional UPS as this ensures that all eggs are not put into one single basket – impacting the reliability/availability.

Further with the vertical modular topology available today with less space consumed by the UPSs it makes sense to parallel additional units to the existing UPS thereby achieving both redundancy and capacity handling as and when required.

System-reliability requirements will determine the configuration of the power system. Very high requirements will lead to a system with multiple UPS modules and multiple battery banks. The system also should have at least one redundant module so it can reliably serve the load if one module fails or undergoes maintenance.

A single UPS module with a static bypass switch can serve loads with lower requirements to provide utility or generator power during periods when the module is down. The consequences of a power failure tend to dictate reliability needs. If an outage would result in lost revenue, the failure to meet contractual obligations, or lost customer goodwill, it is appropriate to install a redundant system

The battery run time of a UPS is the length of time the UPS can reliably supply power to the critical load after input power has failed. Run time usually is defined as the length of time required for connected data-processing equipment to save data files and shut down in an orderly fashion, along with a margin of safety. Typical battery run time is 15 minutes.

Batteries are heavy and can present a large dead load to a structure, so managers must make sure a structural engineer reviews the proposed installation to determine if modifications are necessary to support the load.

Requirements for future expansion affect UPS configuration and determine space requirements for future modules and battery banks. Depending on the timing of the expansion, it might be more economical to install a single module and add modules as needed, rather than installing a single, larger module.

Managers who intend to install more capacity later should consider the electrical infrastructure required to support the maximum load, and they must carefully guard spaces allocated for expansion to ensure those spaces are not filled with other equipment.

Budgetary constraints play a key role in determining the final UPS design. Often, a system that satisfies other considerations simply will be too expensive to implement, and some functionality or system reliability will have to be sacrificed to keep costs in line

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