Uninterruptible power supply systems

Mike Rea, MD of AEC UK, explains about keeping the power on and shows how uninterruptible power supplies save data from corruption and ultimately save companies time and money.

Until recently, companies were barely curious in evaluating UPS before purchase, whereas purchasing a computer involved detailed appraisal.

The attitude of the user was that the vendor knew what was best for the system and was the best judge of what was required.

From the point of view of a professional installer, a UPS system was a grudge purchase for most customers and was quite likely to be added as an afterthought (usually after several expensive malfunctions had been diagnosed as power problems).

Nowadays, anyone managing a network knows that uninterruptible power supplies are essential to save data corruption and ultimately for saving their company time and money.

If the power to servers is turned off without properly shutting down the server, data can be corrupted, so all servers and any PCs that run critical applications should be protected from power outages.

The cost to the company in the time that it takes to restore the data from backups, plus the interruption of service while the server is rebooted, can easily run to thousands or even hundreds of thousands of pounds per hour.

Besides powering servers when the main electrical power is lost, UPSs also protect against power spikes (high pulses of energy) and brownouts (a lowering of voltage without total power loss).

UPSs can also provide surge protection for network or telephone connections.

Research on power supply disturbances conducted in European countries show great differences from place to place and between different types of installations.

On average a computer site experiences around 20 blackouts each year which, in general, are far more common in rural areas.

Most blackouts arise in the local, low voltage distribution network.

An online double-conversion UPS is a combination of inverters, rectifiers, specialised electronic controls and energy storage (for example batteries) constituting a power system for maintaining continuity of load power in case of input power failure.

The most commonly used battery, for UPS purposes, is the VR (valve regulated) lead acid battery.

The UPS is designed to ensure that the battery has a long and trouble-free operation.

Recharging is smooth and the voltage of the total battery string is kept very stable.

Batteries in UPS will eventually fail.

Too often, administrators discover that the battery has failed only after the power goes out and the UPS doesn't keep the system running.

New features intended to combat this problem include monitoring systems built into the UPS, as well as software to extend monitoring and reporting capabilities.

At the present time, the commercial mains power supply is not capable of providing clean and consistent electric power demanded by sensitive equipment.

Such equipment requires a consistent supply of power of the correct specifications for their operation, hardware protection, continuity of process, storage and transfer of information and safety of personnel.

Computer networks, communication links, electronic medical equipment, industrial process control, remote installations like offshore operations, online applications such as airline reservations, etc.

are examples of such critical loads.

Beyond any dispute the installation of an uninterruptible power supply (UPS) system is nowadays accepted as being a vital element in the protection of sensitive equipment.

A UPS uses RS-232 communication to interface with computer systems.

Various details can be interrogated from the UPS at any time and some messages are automatically sent from the UPS to the computer.

Sophisticated software in the form of an USHA card (universal SNMP and HTTP adapter) provides an easy to use sophisticated management solution offering an interface between the UPS and the network.

The embedded HTTP server is capable of processing, forwarding and receiving HTTP commands whilst the embedded SNMP chips allows the UPS to be monitored from anywhere on the network rather than only through the server's serial port.

Both facilities can be carried out simultaneously.

An SNMP module also allows the monitoring of UPS without having to run the UPS software on the server, and the monitoring of network devices such as routers or switches where running UPS is not an option.

There are three types of UPS products: standby, or offline, which provide utility power during normal operation; line-interactive UPS, which offers a measure of voltage regulation; and online UPS which is ideally suited to networks running mission-critical applications.

Online supplies a highly stable, low-distortion AC supply to the critical load, eliminating mains borne interference altogether.

Line-interactive or offline UPS, whilst boasting gimmicky software, will, however, only serve to reduce the impact of mains borne interference.

Discerning customers are now switching towards on-line UPS systems and away from the cheaper line-interactive or offline UPS.

Technologically, UPS are becoming far more advanced.

AEC UK's recently launched Power Station provides up to 12 hours of continuous power yet takes up to 75% less floor space than traditional systems.

The bespoke system is modular in design and can be provided in variable support times ranging from 700VA to 6kVA to meet customers' specific requirements.

It has been specially engineered to offer ease of servicing through rapid and easy access to all internal components.

Field upgradeable in both power and backup times, the Power Station has full power module hot-swap capability and a dedicated power charger module, that also includes extra booster charger, switch gear and charger indicator light to show that the unit's batteries are functioning correctly.

Nevertheless, any device that can interrupt this critical supply will always need an emergency bypass system (EMBS) to allow for maintenance, upgrades or simply as a fail safe device.

The user can easily install the EMBS, allowing normal mains supply to be restored in an emergency by bypassing the whole UPS system.

The manual bypass system has a simple "make before break" rotary switch that reconnects the load in an emergency or for maintenance or upgrade.

The range of UPS products available makes the choice of UPS systems somewhat bewildering.

Users need to be knowledgeable so that they are able to be discerning on the type of UPS required and not fooled by technical jargon and the over-hyped claims of some UPS manufacturers.

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