Electricity has permeated every aspect of our lives - be it at work, at home or at play. It powers our modes of transport, communication and the mediums through which we conduct business. Every device, from the mainframe in teh basement of your bank, to the PC on your desktop or the traffic lights that govern the flow and ebb of traffic, depends on electronic circuitry fed by electrical power.
While it is safe to say power supplies to the majority of countries in the Western world are reasonably stable the same cannot be said for Third world nations which, more often than not, experience power outages as a frequent occurrence.
Studies show that some 60% of all computer problems on the African continent can be traced to faulty electrical supplies. Within an office building there are many things that occur to affect this supply; lifts can momentarily drain the power load as can storms or nearby lightning strikes.
To protect their electronic equipment from potential power hazards users must implement an uninterruptible power supply (UPS). Potential users must first identify the applications keeping the business ticking over. Following this, they must isolate the hardware that must remain operational to facilitate this.
Compile an equipment list
The next step is to compile a list of the equipment involved. This could be anything from the switchboard to security doors, from photocopiers to escalators. Once this has been established it is then a simple matter of quantifying the power demand by totalling the expected power consumption of this vital equipment and multiplying this by the length of time the company wishes this equipment to stay online.
At this stage it is possible to identify the type of UPS best suited to a company's needs. An entry-level system will provide power to equipment in the event of a total power failure giving users time to save data and shut down files. A more sophisticated unit will condition and filter the electrical supply so that the power reaching the equipment is 'clean' and continuous. Units vary in size from small desktop systems that protect a single PC to very large UPSs which can provide power to an entire building.
UPS technologies
There are three types of UPSs - off-line, line-interactive and on-line. An off-line UPS is effectively a standby source of power - meaning that all equipment is connected directly to mains power and when the UPS detects a failure, it kicks in for long enough to allow systems to be shut down normally.
Key advantages of this are that the UPS is small and inexpensive. Disadvantages include a short back-up time - it only comes on stream when there is a power outage, no isolation from mains, power rating generally limited to 1500 VA, no intelligent interface and quasi-sine wave output. An off-line UPS will usually produce a stepped square wave which could cause damage to internal components of some devices if used in the wrong application.
By far the most important disadvantage of this type of UPS is that in most cases it provides no filtering or surge protection. It is considered to be an ideal power back-up solution for the SOHO environment. Thanks to its pricing it is also popular throughout Africa. However, it is mostly unsuitable for this region and its myriad of power-related problems.
Line-interactive UPS
Generally offering ratings of up to 3 kVA, line-interactive technology lies somewhere in between off-line and on-line UPSs in terms of protection and pricing. It offers protection in the event of an outage but also line conditioning which smoothes out peaks and troughs in the power supply. For example, if the voltage drops below a predetermined level the UPS will 'boost' it back to normal.
These units work by operating the inverter in reverse during times when the input AC power is normal to charge the battery. If the power fails a transfer switch is triggered and the battery power flows to the UPS output to power equipment.
Line-interactive UPS are best employed wherever power conditioning is not crucial to effective operation of the equipment and budgets are a consideration.
On-line UPS
An on-line UPS isolates the load completely from the mains supply - which means that nearly all electrical problems found with commercial appliances are halted at the UPS, enabling the load to run on clean power.
On-line is widely recognised as the best UPS for backing up mission-critical applications such as those found in hospitals, banks and air traffic control systems. While more expensive than the other two technologies, it ensures there is never a break in the power supply. This is thanks to its judicious use of a double-conversion technique which continuously converts the AC mains to DC, which trickle charges the battery and then feed through an inverter which transforms it into AC for the critical equipment load.
An ideal operational situation is to have electricity flowing as a pure sinewave. When raw power comes in from the mains it will inevitably be corrupted and have irregularities. On-line systems clean and filter the power so that pure sinewave electrical power is being output to the equipment. With online systems there is no switchover and the effect of spikes and surges in mains supply can be completely eliminated.
Battery quality
The performance and reliability of a UPS rests heavily on the quality of its batteries. Some UPS manufacturers use sub-standard automotive batteries that have a shorter life span and lower current rating than proper UPS high cycle batteries.
Batteries that have been designed for use in UPS systems are zero maintenance and have a five-year design life compared with one or two year life expectancy that most automotive batteries can give.
On high-end systems, the number of batteries used becomes a major portion of the total cost of ownership. As batteries are placed under maximum load during a power outage, this is the worst time to discover that the batteries are in a poor state and the back-up time required can not be provided or, worse still, there is no back-up at all.
Trying to cut costs by choosing inferior batteries can lead to the UPS under-performing or even failing completely, leaving the client high and dry.
On large systems the batteries are continually tested, while the UPS is in operation to protect against unexpected failure. This is managed by circuitry on the UPS which electronically reduces the incoming power, thus forcing the UPS battery-bank to compensate. After a short while the UPS restores full power again and logs the time taken for the battery bank to recharge itself, all without risk to the critical load.
By logging the rate at which the batteries lose power while under load and how quickly they recover and then comparing this to recommended figures, the UPS is able to identify when a particular bank of batteries requires attention.
Monitoring software
Another area to be considered when making the initial purchase of an on-line UPS is that of monitoring software. There are various levels of sophistication of monitoring software. An IT manager will want to know immediately of any potential power problems which could affect the operation of his network.
Power management software can carry out a number of functions including:
* Detailed monitoring of the utility power supply to detect spikes, brownouts, sags and other variations.
* Controlled shutdowns of equipment including selection of specific load segments of the network which need to be kept running longer. Users are normally informed via an on-screen message that they have X minutes to shut down their applications and save data.
* Maintenance checks of UPS equipment including battery status and readiness of the equipment to take over in the event of a power break.
* Recording a log of events so that a pattern of power problems can be established.
* Automatically alerting those responsible for the network by pager or e-mail that there is a power problem.
Some top-of-the-range software suites also allow remote monitoring of the UPS from anywhere on the network to analyse its performance. In addition, it should carry out preventative work. This is accomplished either via serial port communications, SNMP (simple network management protocol) software or via the web. This means the IT manager in London can control and monitor UPSs on the network regardless of their location.
Whatever technology is employed the crucial fact is that the UPS should be regarded as an integral part of the network.
UPS planning
Installing a UPS on the network requires careful thought and planning. Many network managers feel that it is enough to protect the main server. However, they often neglect the routers, bridges and hubs which carry data traffic. Likewise there may be certain users processing data locally on their PC who require the added security of an individual UPS.
Ideally a UPS should be considered when an information technology installation is being planned or a building is first being constructed. Power protection specialists can advise on what equipment is needed to protect the load and any special considerations that must be taken into account. For example, networks running a Unix operating system need to be shutdown in a specific order otherwise it could take IT staff days to reboot the system and recover files once power is restored.
In organisations that need to guarantee continuity in the event of prolonged power outages, such as hospitals or financial institutions, the autonomy time of a UPS (typically 10 minutes to two hours) is not enough. In such cases a back up generator is required. However, even here a UPS is essential as there is always a time lag before the generator reaches sufficient output to produce the required current and a switchover to emergency power can be implemented.
Choosing the correct power protection solution can be confusing. There are a number of different types of UPS each offering different levels of protection. Moreover, one has to consider how the UPSs are to be monitored and controlled with the correct software and what level of support and advice can be expected from your supplier.
For details contact Mike Kersten of Meissner on tel: (011) 392 1642 or e-mail: [email protected]
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