Planning your Power Requirement

Living in India, we are used to power problems, but our equipment isn't, and therefore needs protection. The sensitivity level of all equipments is not the same and, therefore, the level of protection it requires also varies. For example, network servers need better power protection than desktops do, possibly longer back up and cleaner power. So, when planning your power requirement, decide the level of protection and the uptime your equipment needs as both will affect the overall cost. Plus, consider the maintenance and consumables cost for the power equipment. 

In this article, we'll look at important factors that an SME needs to consider while planning its power requirement. We'll first consider UPSs (Uninterruptible Power Supply) and then briefly look at other equipments such as power enhancers and power synthesizers.

UPSs



When deciding on a UPS, a commonly used equipment to provide back up to IT equipment, such as computers and servers, you need to first decide whether you need distributed, centralized or selective backup. Distributed backup means spreading multiple UPSs across your office to back up all or some of the computers. This strategy is good for small organizations having a handful of computers. You even have a choice of technology in smaller UPS systems, online or line interactive, and there can be a wide fluctuation in prices there.

If you have a reasonably sized network, of say 100-200 nodes, then centralized backup is the best bet. Here, you'll go for one or two large UPSs to provide back up to all the load. Here selecting a good UPS involves much more than a simple load calculation. So, we recommend hiring a professional power consultant for the job. First have your electrical installation analyzed to determine wiring faults, quality of electrical equipment, etc. 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. Similarly, other electrical equipment such as MCBs (Miniature Circuit Breakers) need to be of the right class. The fastest ones, known as magnetic breakers, can switch at a fraction of the mains input cycle. The UPS vendor would install these with the UPS to prevent it from being damaged.

Selective backup is a mix of centralized and distributed backup. A good case here can be companies that may initially be using distributed backup, but may later need to shift to centralized backup due to growth. In this case, you could judiciously use the smaller UPSs for a part of the load and use centralized backup for the rest. 

Besides computers, network equipment such as hubs, switches and routers also need power protection and must, therefore, be included in your plan. Capacity planning comes next, wherein you decide what capacity of UPS to buy. In capacity planning, power factor is an important aspect, as it helps calculate the total power consumed in Watts by the equipment that you want to protect. In electrical terms, this is the ratio of the effective power (Watts) to the apparent power (volt-amps or VA). Mathematically it is:

Power Factor = Effective Power (Watts)/Apparent Power (VA)






Alternately: 





Effective Power = Power Factor x Apparent Power (VA)










Resistive load, such as light bulbs have unity power factor, so its apparent power 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 multiplied by the VA). 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 the power consultant to help you calculate the power factor for your load using a power analyzer. 

When choosing a UPS, you not only need to keep your current requirements in mind, but also your future ones. So, if your organization is likely to grow significantly in the near future, then the UPS should be able to scale up to handle the extra load.

In that case, look for a modular UPS system, in which you can add capacity as per your requirement. In any case, it's a good idea to buy a UPS that has 15-20% excess capacity over your actual rated load. You may also need to provide redundancy for your UPS, depending upon how critical the load is. For instance, while you may have a large UPS to back up all computers on your network, you may want to put a separate UPS for your servers. So, even if the main UPS fails, the servers don't go down. 

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 shut down all systems, then you probably need 5-10 mins worth of backup. For extended backups, consider getting a generator along with the UPS. 

Here, identify the major cost heads besides the UPS. First, is the one-time implementation cost, which includes 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. If it's highly sensitive equipment, you might have to go for an online UPS system conforming to all EMI standards, which costs much more than a line-interactive one. Plus, you'll need a generator backup for those prolonged power cuts, because the UPS shouldn't be stretched for this. 

Running costs come next, which can be quite significant for large UPS systems. Large UPS systems generate heat, which can reduce battery life. Therefore, you should plan for proper air conditioning for the same, and also take into account the electricity bill for it. Then there's the cost of batteries, as the average life of SMF (Sealed Maintenance Free) batteries used by most UPS systems is three years. Even a small 30 to 40 kVA UPS could use about twenty batteries. If each battery costs Rs 10,000, then just the cost of replacing these batteries can run into lakhs of rupees. Finally, there's the cost of support and AMC for the UPS system, which depends upon how important it is for your systems to be back on after a failure. 

Other equipment



Power conditioning doesn't just mean installing a UPS. There's a range of other equipment to protect your IT infrastructure from different types of power problems. This is divided into two categories, power enhancers and power synthesizers.

Enhancers include things such as surge suppressors, line filters, voltage regulators and isolation transformers, while synthesizers are different kinds of UPSs, motor generators and even magnetic synthe- sizers. Each power-conditioning equipment can protect your load from certain types of power problems, but it's unlikely that any one would solve all your power

problems.

TYPE OF POWER PROBLEMS

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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 

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

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