If you need to know about batteries; you’ve come to the right place Chinese flag 点击这里访问我们的中文网站 Chinese flag

Power conditioning: UPS– - only for an outage?

Thu, 11/15/2012 - 17:36 -- Ruth Williams

2-26For most people the main reason for having a uninterruptible power supply (UPS) is to provide a back-up source of power if the primary source is lost or interrupted. Fear of losing power is of course understandable, especially as more and more businesses move online – any, even momentary, loss of power can cause significant losses and disruption. 

Yet, in reality, the likelihood of power outage is very low. Ordinarily, power supplies in the United States and other developed nations suffer an average of 8.8 hours of outage each year – not much. What’s more, focusing on power outage diverts attention away from more important power quality issues.

Poor quality power originates from a variety of sources. The utility providing the power can often be the source in the form of brownouts and outages. It can also come from much closer to home and can include things like overloaded transformers, circuits, blown circuit breakers and other electrical loads that create troublesome spikes, surges and noises. 

However, the effects are not always immediately obvious – equipment can cease to function inexplicably. It is a common myth that UPS systems protect electrical equipment from bad power – in fact most UPS systems are only designed to provide backup power in case of a failure.

Getting to the source

Modern electrical equipment used in a variety of settings, such as offices, hospitals, data centres, laboratories and dental surgeries to name but a few, relies extensively on microprocessor and semiconductor technology. Unfortunately these devices are vulnerable to electrical power transients, noise, spikes and other problems. 

Because so much of this microprocessor equipment operates on non-isolated, switch-mode power supplies, most of the time sudden changes in voltage tend to have little noticeable effect. Rather, voltage transients, electrical noise, common-mode voltages and neutral to ground problems have increasingly caused problems. 

Transients on the power line can smash through a sensitive semiconductor substrate, leading to the immediate failure of critical components. Unsurprisingly, lightning strikes cause the most severe transients. If a voltage spike caused by a strike nearby reaches a piece of equipment through power or communications cable, it can fry the electrical system. Large value transients can also be caused by transformer switching, electric motors or even something as small as a photocopier. 

The common-mode cure

Even systems that do not experience spikes and transients can be affected by common mode problems that corrupt data or prevent systems from communicating with one another. The majority of today’s sophisticated and sensitive electronic instrumentation and equipment is designed to run only on smooth, clean, transient-free and isolated voltage. A power supply which suffers continuously from electrical noise or branch electrical circuits with high levels of neutral to ground (common-mode voltage) can cause problems such as incorrect or unreliable test results, communications errors system lockups, and ‘no fault found’ service calls.

Neutral to ground noise is a particularly annoying problem because it prevents microprocessors from functioning correctly, but it is often difficult to identify or eliminate. Fortunately, it is very easy to mitigate with an isolation transformer, which eliminates all neutral to ground voltages and establishes a true zero-volt logic reference on the safety ground. Isolation transformers are used in all power conditioners and some UPS systems.

What do you need to protect against?

A typical office building will experience around 6 000 power disturbances a year, but only 3-5% will be brownouts or power failures. The rest are sags, surges, transients, spikes, lightning strikes, common and normal mode voltage events and low voltage impulses. These can actually be more damaging than a power loss, often resulting in disruption and long-term degradation, especially if equipment is not properly protected. 

Paradoxically, office facilities managers often invest large amounts to reap the rewards of increasingly sophisticated electronic instruments and analysers, but few take steps to protect this crucial equipment from damage or faulty operation caused by a poor quality power supply.

2-27One company which has seen the benefit of using power conditioners is James Hall & Company, a major retail wholesaler in the UK. James Hall and Company is one of six UK Spar wholesalers. It serves an area southward from the Scottish border to North Wales and eastward to Hull and Scunthorpe. It supports around 500 stores in this area, two-thirds of which are independents and one-third wholly owned. These outlets include corner shops and convenience stores, petrol forecourts and stores on army bases.

The company is responsible for supplying and supporting these Spar branded outlets with everything they need to function efficiently from store design, display systems and products through to accounts and business systems. It offers a one-stop shop that protects business efficiency, maintains Spar standards and saves retailers time and effort.

Forecourt expansion triggers focus on power quality

Like the other five UK-based Spar wholesalers, James Hall & Company is a family business. It maintains very high standards in procurement and the operation of their business systems. A firm belief in ‘added-value’ is reflected in a policy of buying on performance rather than on price.

2-28aMike Crompton, Technical Support Manager for Retail IT, is responsible for the support, maintenance and upgrade of the IT systems across the retail establishments, which support 5 000 staff generating a turnover at the wholesale level of around £320 million (US$495 million) per year. Crompton has been heavily involved in the company’s expansion into petrol forecourt retailing, which began ten years ago. There are currently 127 Spar forecourts. 

Because James Hall and Company’s previous forecourt experience involved third-party standalone systems with a software link to the wholesaler, it was necessary to find a solution to the challenge of integrating suitable petrol forecourt software into Spar’s existing, bespoke electronic point of sale (EPOS) systems. To do this, Spar nationally in association with BCP (Spar’s Retail Software provider) forged a partnership with HTec, the UK’s leading retail and loyalty systems provider for petrol forecourts.

2-28bLike James Hall & Co, HTec is focused on performance and quality rather than buying on price. It provided the forecourt software systems, while James Hall & Company managed the back-office systems and all of the relevant hardware.

Over the years Htec has learned the importance of protecting the quality of the power supply. Its policy is to install UPS units with built-in power conditioning. The UPS function is intended to protect vital IT systems, both front and back office, in the event of power failures. The power conditioning element is to protect the equipment from irregularities in the power supply.

Initially, Crompton was cautious about the function of these units. Some years before James Hall & Company had actually removed the UPS units from its retail premises because they had caused almost as many problems as the other equipment on the sites, requiring regular attention. However, with HTec’s insistence that the forecourt sites must be protected by power conditioning systems and that these units should be supplied by Powervar, Crompton took a new look at the performance and benefits it delivered.

Massive drop in data corruption problems

2-29a

It was not long before he noticed that hard disk corruption/failures on EPOS and back office systems were down by as much as 80% compared with the non-UPS protected community. Crompton was very surprised by this result and he began to re-examine the potential role for power protection systems across the company’s wider community.

He found, for example, that in one Spar shop at the University of Lancaster, an establishment with seven tills and a back office computer, there was an average 

of one service call a week over a prolonged period, all 

involving data corruption to the hard disk. Taking on board lessons from the forecourts, he 

installed power conditioning units, this time without the UPS components– one for each till and the back office unit– and the frequency of call outs dropped immediately.

2-29b

It was clear that the savings both in cost and convenience to the outlet and customers represented a very substantial return on investment. In fact, the entire investment in the installation of power conditioning units was paid for in a matter of months. Not only did the level of service call outs drop dramatically, when they did happen they were much easier to fix. This was because hard disk failures and data corruption were virtually abolished.

Power quality monitoring exercise

In order to establish the financial arguments in detail, Crompton initiated power quality monitoring across 20 stores over a two-week period. The results showed that in every instance there was at least one spike in the supply that was capable of taking out a hard drive, on top of that there were smaller events that were resulting in cumulative damage. The potential for at least one failure per fortnight was an unacceptably high level.

Across James Hall & Company’s region the power supply is highly variable, a fact that is true nationwide. The quality of power produced by the UK generators was set to meet a standard that was probably more than adequate before sensitive technology was in widespread use but today there are sufficient spikes and surges to cause costly damage. 

Sometimes the origin of a problem – disk failure or data corruption – is not obviously traceable, since power problems do not leave an easy trail to follow. However, the data from the monitoring exercise and the practical results on the forecourts were enough to persuade Mike Crompton that power conditioning equipment should be installed across the entire Spar community served by his company.

Potential to extend hardware life

Over a twelve-month period power conditioning has been rolled out to all the outlets whose equipment was due for renewal. The effect has been quickly seen. Callouts have halved and those problems that remain with the IT systems are easier to identify and quicker to repair.

In addition to protecting the quality of power feeding sensitive equipment, the power conditioners also have a beneficial effect on the general power supply to the stores. For example, some in-store equipment such as cardboard crushers draw so much power that they cause a large dip in the power supply, even causing the store lights to flicker. Powervar equipment helps to even this out and avoid critical system failures.

In total, James Hall & Company invested around £130 000 (US$202 000) in Powervar equipment and is confident that this initial investment will extend the trouble-free life of front and back office systems by 20% and deliver additional rental income of more than £2m.

Not all UPSs are equal

So for Crompton, the experience of using Powervar equipment has been completely different from previous UPS systems. UPSs are intended to provide a secondary source of power or a ‘back-up power supply’. 

However, it is important to understand what they are and are not able to do when it comes to protecting sensitive electrical equipment. In an online UPS, AC power is constantly converted from AC to DC and back to AC, which guarantees that output voltage is well-regulated in terms of both frequency and voltage and is free of normal mode (phase to neutral) transients. 

However, only an online UPS with an isolation transformer actually offers the total protection that most people believe that all UPS systems provide. When looking at a complete power protection solution, it is crucial to consider the following elements:

Voltage regulator. This regulates voltage to meet the precise needs of electronic equipment. 

Isolation transformer. This transformer guards against common mode noise voltage. 

Surge diverter. Protects equipment from spikes or transients in excess of 250V. 

Power line filter. Decreases low-voltage impulses. This is the one crucial piece of equipment which is missing from power protection systems.

Frequency regulator. This device, typically found in an online UPS, offers constant power by regenerating the AC waveform from a DC device.

Battery backup/UPS. This provides continuous power in case of a power failure or brownout.

It is clear, therefore, that different devices provide different elements and degrees of protection. While UPS are useful for ensuring power continuity, they often do not protect electrical systems from a variety of the other bad quality incidents.

Investment in power conditioning systems can only deliver a real return when the end user acknowledges the key issues and comprehends the often hidden negative effects that arise from not protecting systems effectively.