Uninterruptible Power supply- UPS?

UPS is an electrical equipment providing an interface between the mains power supply and load .The UPS supplies sinusoidal/quasi sinusoidal AC power free of disturbances and within strict amplitude and frequency tolerances. It is generally made up of a rectifier/charger and an inverter together with a battery bank for backup power in the event of a mains failure/deviations .

UPS topologies?

There are three major topologies –Off Line ,Line Interactive and On Line UPS. These three major topologies perform a basic level of power protection for power sensitive equipments like Personal Computers ,control instrumentation etc.. Users who do not require the highest possible power availability to the critical load have options such as off-line or line-interactive UPS devices.

Off-line UPS - is so named because the battery and/or the inverter are not supplying power to the load except when the utility "fails." Or deviates within the range allowed .The failure of the utility requires the switch to transfer to inverter. The inverter then starts and runs the load. The total transfer time after the command to switch is usually well less than a half cycle or four –eight milliseconds . The required decision and transfer time are usually acceptable for most electrical loads. Off-line, (also called stand-by), is a cost-effective choice for small, non-critical stand-alone applications, for example, isolated PCs and peripherals.

Line-interactive UPS - utilizes the bi-directional inverter to perform two functions, namely to run the load and to charge the battery. As the name implies, the inverter "interacts" with the utility to maintain nominal output voltage to the load. An ability to interact with the utility supply improves the overall UPS performance over that of the off-line products. Line-interactive UPS devices offer protection against wide input voltage swings, sustained brownout and single-phase conditions. For many users, the line-interactive UPS represents a very good level of protection for a moderate investment.

On-line UPS - features an inverter that is on-line all the time, as well as a battery that is always in the energy power circuit and not separated from the inverter by switching means. The smooth, solid and repeatable performance of this topology yields a number of tangible benefits, particularly worthwhile for mission-critical applications.

Advantages of On Line UPS-

Line/load isolation, resulting in more stable output voltage.

Superior reliability with simple controls

Wide input voltage range which optimizes battery life

What are power problems?

Even small disturbances in the main electricity supply can cause damage to electronic equipment. Power problems can cause unplanned shutdowns and data loss. All these problems can cost your company a considerable amount of money. Transients ,sag ,brown outs ,under voltage ,over voltage ,distortion ,EMI ,RFI etc are called Power Problems –Electric Pollutions .

Frequency of power problems?

A recent Power Quality Study revealed that the average computer system is subjected to 289 potentially damaging power disturbances per year.

How to avoid power problems?
All essential electronic equipment should be connected to a voltage regulator, power conditioner or, best of all, a UPS. A UPS will maintain a steady supply of power irrespective of the mains supply quality.

What are the effects of Electric Pollutions ?
Apart from inconvenience and the hidden cost of re-programming, there are often real costs of physical damage . Computers react adversely to voltage reductions, some also respond badly if subjected to power surge or over voltages and the majority of electronic equipment is affected by frequency drift or instability.

Usually the loads react differently to erratic power; however, you can be sure that all computer based equipment, whether used for monitoring control, or simply data storage, is going to be affected in some way.

This inconvenient aspect usually appears during important programming exercises or on-line data transfer and, at a time when you can ill afford problems, a disturbance occurs which corrupts the process. This leads to the hidden costs of the program being re-run to a convenient point to re-start or in the case of an unmanned automatic data transfer, it may result in the error not being located for several hours or even days, culminating in many days of in correct processing.

Where we need the UPS ?
Industry and Commerce

Banks, money-brokers, stock market and finance houses

Shipping, airline handling and warehousing

Stock and inventory control

Process control and materials handling

Hospitals

Life support systems

Hospital logistics and management

Body and Brain Scanning Machines

Blood analysis equipment and data storage

Essential Public Services

Local Council/Government Offices

Telecommunications and satellite links

Defence installations

Police, Fire and Emergency services

Essential services – electricity, gas, water, etc

The solutions

Diesel generators provide a long term answer, enabling power to be drawn for as long as the engine has fuel. However, the major disadvantage is the lack of continuity of power whilst the machine starts and the inability to combat short-term fluctuations or disturbances.

To cover both short-term disturbances and general power failures, the most sensible and practical solution is the Uninterruptible Power Supply or UPS. This type of equipment produces its own output power by using either the incoming mains or storage batteries; the transition between the two is made without disturbance to the load. The UPS also acts as a permanently connected, high grade power conditioner between the load and the raw incoming mains to prevent any form of fluctuations, transients or other disturbance from affecting the critical load.

Justifying the investment - the costs

It follows that a device that can cope with any power problem, including complete power failure is going to represent a significant initial investment. However, when considering any expenditure it is essential to assess several factors and the associated costs involved.

Typically computer malfunctions can result in huge costs which will more than justify the investment in a UPS and some of these costs are given below:

Equipment down-time
Replacement/maintenance
Re-programming
Supplementary or additional processing
Unused manpower

These items are easily seen, but the problems which also occur as a result may be even more costly, such as business, processing backlogs, invoicing delays, incorrect stock control, process malfunctions. The list is endless and to think that peace of mind, reliability and reduced maintenance can all be achieved by the installation of a static UPS from Energy Systems, it follows that your investment is justified by the insurance it provides.

Considerations on buying a UPS
As with the computer and telecommunication industry, the choice of power protection equipment seems endless but it should always be remembered that the level of power protection remains directly related to the investment made, as is usual with capital equipment.

There are many considerations which can dictate the ideal level of power protection for a given installation. The following aspects should be given careful thought before purchasing equipment

New installations
If the installation is new it may be possible to consider a central back-up system which will eliminate the need for expensive re-cabling at a later date.

Existing installations
For existing installations involving processing and telecoms equipment, it would be relevant to assess the level of power protection required. As an example, some installations may demand that every item be supported by an uninterruptible power supply (UPS) which will provide protection against any form of power disturbance including computer power failure, whereas another application may only require a UPS for the central processor and one or two workstations.

Type of client
The level of automation will often dictate whether a system requires a UPS or whether a line conditioner or power filter will be acceptable. The final selection of power protection device is also governed by the type of application - Emergency services or financial institutions cannot tolerate power failure due to the nature of their business. Whereas many industrial companies are prepared to accept occasional power deficiencies as an inconvenience not a disaster.

Site
The location of the site may also have considerable bearing on the products required, since an inner city may be more susceptible to power fluctuations due to load shedding or power irregularities in heavily loaded areas. In rural areas the power may be regularly interrupted due to the effect of prevailing weather conditions on overhead power lines and some of the more remote areas may be located at the very end of a power line and suffer from poor mains voltage regulation.