by March 1, 2005 0 comments



The nature of your business determines the kind of power you need. If you’re running, say, a call center or a data center that provides services to customers, then you’d want 100% guaranteed uptime. For this kind of a setup, you’d need to build redundancy in the power you use. Most large UPS manufacturers have UPS systems that provide redundant power. The amount of backup is another critical element here. That is, if there’s a power cut, how long it will be before the batteries drain out completely. If there are long power cuts in your area, then you may want to consider going for a long period of backup. For this, you’ll need extra batteries.

Know your load

The first step, therefore, is to create a list of all the equipment you need to provide power for, whether it needs backup or not, and the equipment’s sensitivity level. For instance, if you have telecom equipment that could take days to reconfigure if it reboots, you’ll have to ensure that it gets the cleanest possible power that’s free from any glitches, and possibly backed up by a redundant power supply. Or if you need a power backup solution for expensive medical equipment, then low electromagnetic emission would be of prime concern, and you’ll need something that strictly follows international EMI (Electromagnetic Interference) standards. Similarly, network servers would need better power protection than desktop nodes, and would even need power for proper cooling to prevent damage from overheating. Some other equipment that could need power protection may be printers, fax machines, local PBX, wireless equipment such as access points and routers, etc.

                                       
Effective Power 
Power Factor (Watts) = ———————–
                                    
Apparent Power (VA)
Alternately, 
Effective Power = Power Factor x Apparent Power (VA)

Calculate load power consumption

Having created a list of equipment, the next step is to determine how much power all equipment requires. In most cases, this can be obtained by reading the back plate of an electrical device. You may find the power consumption in Watts. To calculate power consumption from the value of current given in Amps, then you need to multiply it with the operating voltage of the electrical device. For instance, if a computer monitor specifies a current value to be 0.3 amps and operating voltage as 220 volts, then multiplying the two together will give you power consumtion as 66 Watts. You must add up the power consumed by each device to calculate your total load. 

Types
Of Power Problems

Power Cut
Loss of mains voltage for a long period of time
Power Glitch
Momentary loss of power, which could even be for a few milliseconds. This could cause computers to reboot, damage hard drives and corrupt important data
Over Voltage
Sustained voltages higher than the regular mains voltage
Ground Faults
These occur when earthing is not done properly, and can cause serious malfunctions
Miswiring
May not seem like a power problem, but can be for some equipment. Equipment can continue to function even with mis-wiring, but has the risk of shock and early failure of electronic devices
Spike
Spikes are like surges, but are caused by lightening strikes or when utility power comes back. They are very high momentary voltages and can be a big problem 
Power Surge
A sudden increase in mains voltage for about 1/20th of a sec, which usually occurs when heavy motors and machinery are switched off 
Frequency
Variation
Frequency of the power system changes beyond a certain acceptable limit, and can damage equipment. In India this is 50 Hz, so check your equipment’s tolerance level
EMI (Electromagnetic
Interference)
Emission of electromagnetic energy from equipments such as motors, power generation units, plain CRT monitors and UPSs. It can interfere with the operation of other equipments. International standards bodies like the IEC have defined EMI standards. So, make sure your power equipment conforms with standards
Power Sag/Brownout
Dip in mains voltage for less than a sec is a sag, else brownout. Surges occur when heavy machinery is turned off, brownouts when they are turned on. Spikes follow brownouts
Harmonic
Distortion
Harmonics are multiples of the mains frequency, which superimpose on its perfect sine wave and distort it. This affects the quality of power fed to your equipment
Total Harmonic Distortion
The ratio of the sum of powers of all harmonic frequencies above the fundamental frequency to the power of the fundamental frequency. It’s usually expressed in dB

Here, power factor is an important consideration in load calculations, especially when choosing a UPS. In electrical terms, this is the ratio of the effective power (Watts) to the apparent power (volt-amps or VA). Mathematically, it is:

Resistive load, such as light bulbs have unity power factor, so its apparent power (in VA) is equal to the effective power (in Watts). Computer load, however, is non-linear, so its power factor is less than unity, leading to a lower effective power than apparent power. Usually, a power factor value of 0.7 is good enough for computer load, though some servers also claim unity power factor. So if your projected load is 100 VA, then it will actually consume 70 Watts of power (power factor times the apparent power). This will also help you determine the actual battery ratings you need, so you don’t end up paying extra for higher rated batteries. Most UPS ratings are given in VA, so you must know the actual power consumed by your load and its power factor to determine what UPS rating to actually go for. Ask your vendor to calculate the power factor for your load using a Power Analyzer. When choosing a UPS, always choose a rating that’s slightly higher than your total load. The amount of extra buffer depends upon how much will your network grow over a period of time. 

Batteries come next. The number of batteries depends upon how much backup you’re planning to provide to your systems. If you just need enough time to shutdown all systems, then you probably need 5-10 minutes worth of backup. For extended backups, consider getting a generator along with the UPS. 

Understand power problems

The most common power problems that you should be aware of include power cut, glitch, over voltage, power sag or brownout, spikes and surges, electromagnetic interference, fast leading edge spikes, mis-wiring, ground faults, frequency variation and harmonic distortion. You must be aquainted with some of these like power cut, over voltage, sag and glitch. If you know the frequency at which these occur, you can put in the right equipment to protect against them.

Mis-wiring and ground faults are also terms you would be familiar with. For instance, in electrical wiring, the neutral wire takes three times more current than the live one. If your neutral wiring is thinner, it could overheat and burn out, unless you’re using three-phase input power. Have an electrician check these out. The common mains frequency in India is 50 Hz, and it normally doesn’t dip. For the rest of the power problems, it’s best to ask a professional power consultant to check out their presence in your area. EMI or Electromagnetic Interference, for instance, is the emission of electromagnetic energy from different types of equipment, which can interfere with the operation of other equipment. It can be caused by sources like motors, power generation units, plain CRT monitors and even UPSs. For this, there are international standards bodies like the International Electrotechnical Commission, which have defined various EMI standards that equipment must conform to. 

Choosing the right equipment

Understand different types of power conditioning equipment and the features to consider when buying. Once you know everything that needs power in your setup, it’s time to understand what power conditioning equipment you need. While most of your IT infrastructure can be handled by a UPS, there are a few other things that also need consideration. Let’s see each in a little more detail. 

UPS

A number of things need to be considered when going for a UPS. These start from calculating what rating you need and end with determining how much floor space you’ll need for it, and how will you provide cooling for it. That’s because temperature affects battery life. The rating depends upon what all you want to back up. We told you how to do that in the previous article. Whatever UPS you buy, ensure that its rating is at least 15% more than the load it’s trying to provide backup to. For a large UPS, even 15% should be sufficient to handle all possible future growth. 

Large UPS system needs a separate battery rack. Plan for the space, cooling and 
running costs for it

One of the most important aspects that must be thought about carefully while choosing a UPS is the technology. This has been written about many times, so we’ll try to focus more towards the key aspects here. Simply speaking, a UPS can be classified either as standby, line-interactive and online. The last type, online UPS, is the most complex of all UPS systems, and is meant to provide the best power protection. They’re also, therefore, the most expensive. So they can be used for your mission critical load such as servers, expensive telecom equipment, etc. 

However, there’s a difference in technology being followed by different UPS manufacturers. So you must ask the vendor to explain what technology they’re using and why you should choose it. Also check the level of protection it offers against all the power problems in your area. 

Can it, for instance, prevent transients or nasty spikes from passing through and affecting your load? A UPS should also be able to trip itself and remain undamaged during a short circuit. 

Line-interactive UPS systems offer slightly lesser protection than online ones, and are typically available in the 5-10 kVA rating. They are good for normal load
such as PCs and workstations. Standby is the simplest UPS technology, typically suited for single or 2-3 PCs load. 

You should also identify other major cost heads besides the UPS. First, is the one time implementation cost, which consists of the UPS system and the battery bank. As both items could take up a lot of floor space, you have to consider the room cost. If you plan to upgrade to a larger rating, then that would require additional floor space. Other features to consider are high temperature and overload protection. High temperatures can reduce battery life, and overloading can damage the UPS circuitry. 

The type of batteries used in UPSs is also important. Most UPSs come with SMF (Sealed Maintenance Free) batteries. Just ensure that the vendor gives you warranty for both the batteries and the UPS. Note that the average life of UPS batteries is around three years.

Other equipment

Besides a UPS, you would also need a lot of other equipment. This is divided into two categories-power enhancers and power synthesizers. A power enhancer is a device that can improve the mains supply you’re using for your load. Enhancers include equipment like surge suppressors, line filters, voltage regulators and isolation transformers. 

Surge suppressors are basically devices that can reduce the size of incoming spikes to levels manageable by your load. Isolation transformers, as the name suggests, are used to isolate sensitive equipment from noise in the mains voltage. They’re normally used to reject noise between line and ground and even reject transient voltage. Synthesizers take the incoming utility power and provide auxiliary power to your load. These include different kinds of UPSs, motor generators, and even magnetic synthesizers. 

Each power conditioning equipment can protect your load from certain types of power problems, but it’s unlikely that a single such equipment would solve all your power problems. 

Besides these, some other electrical equipment also needs to be kept in mind. MCBs or Miniature Circuit Breakers for instance, need to be of the right class. The fastest ones, known as magnetic breakers, can switch within a fraction of the mains input cycle. A UPS vendor, for instance, would prefer to install these with the UPS to prevent it from being damaged.

Distributed vs Centralized Power




There are three ways of distributing power in your organization. It could be centralized, distributed, or a combination of both. Centralized dis tribution of power means buying one large UPS for all your equipment. On the other hand, Distributed power distribution is like buying several smaller units and placing them across your organization to handle various equipments. The third option of combining both means going for a large UPS to handle all general load, and smaller UPSs to handle the critical load. 

The method you go for depends upon your organization’s span and nature of business. If it’s spread across a large area, then it may not be possible to provide centralized backup. It would be really difficult to carry over the backup power to all locations, so it would be better to go for distributed power. 

If it’s a small office with a handful of computers, then you may find distributed computing to be a cheaper option. Centralized backup could prove to be a more economical and reliable option for a large organization having lots of equipment located in the same building. So you could install one large UPS to provide backup to all systems. This would be more manageable than several smaller units scattered across the office. You may also need to put up separate units for critical elements such as servers, networking devices and other important equipment such as your local PBX, etc which are crucial to your business.

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