Ram Engineering Controls

Advantages of UPS Systems with Transformers

There are many good reasons for a manufacturer to develop a replacement technology. However, these drivers often relate more to manufacturing, cost and competitive considerations than to the product's intrinsic ability to undertake the primary task for which it was designed. While in some cases it may be acceptable to make compromises in absolute performance, especially when size and value for money are included in the equation, other applications require a more robust solution.

This exact scenario has existed for a number of years in the uninterruptible power system (UPS) marketplace.

Traditional technology, in the guise of the transformer-based online UPS is, at power ratings sub 40kVA, being usurped by the latest advancements in transformer less UPS design.

The advent of sophisticated microprocessor controlled electronics and advancements in power electronics has allowed UPS manufacturers to produce ever more capable devices at lower costs.

And, because the latest breed of transformerless online UPS dispense with conventional bulky and heavy transformers, they offer a highly compact and cost-effective solution for many modern power protection environments.

Make no mistake, in most circumstances these smaller, lighter and lower cost UPS offer an ideal solution for any organisation looking to provide back up power for their computer and telecomms equipment.

As with most things, however, there is a trade off between certain characteristics, some of which are an essential consideration for particular applications, while others assume a lesser importance.

An average transformerless online UPS with a reasonable specification can provide adequate power protection for a wide range of critical devices.

Because of the recent proliferation of transformerless UPSs, most customers will be able to find a suitable device within their budget, and which boasts a specification that appears to meet their needs.

Ram Engineering Controls

Advantages of UPS Systems with Transformers

However, comparative specifications can be misleading and users that operate in high risk mission critical sectors such as telecomms, healthcare and military environments, or those operating highly sensitive equipment such as mobile comms base stations and file servers, should examine exactly what they require from their UPS, before committing to a particular technology.

Briefly, a transformer-based online UPS boasts several intrinsic advantages compared to the more recent transformerless technology.

For many years, experienced electrical engineers have been aware of the fact that transformerless UPS devices are susceptible to interference from spikes and transients caused by a variety of devices such as photocopiers, laser printers and motors.

The 'dirty' mains that this produces can be transferred through a UPS, and feeds the connected load.

This means that, in practice, a transformerless UPS has to incorporate some sort of electronic mains filter.

Otherwise, it can do nothing to improve the quality of raw mains that, in most circumstances, can be variable to say the least.

In contrast, because the transformer itself constitutes a physical barrier, a transformer-based online UPS completely isolates the load from the worst vagaries of the mains supply.

Therefore, in circumstances where the load is likely to be affected by a very large variation in its power supply, a transformer-based UPS provides a safer and more robust solution than transformerless technology - simply because its size and construction affords some inertia between the input and output waveforms, with no additional electronic filtering required.

Also, because transformer-based UPSs inherently contain galvanic isolation the power supply fed to the load is invariably superior to the mains supply itself.

This attribute alone can be a major consideration for a number of crucial applications and installations.

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Advantages of UPS Systems with Transformers

In fact, the latest electrical standards for medical installations (BS-EN60601 and 61558-2) actually require that critical devices be connected through a Galvanic Isolation transformer, rather than directly to the raw mains.

Any electrical installation that requires the utmost reliability needs to deploy proven solutions to minimise the likelihood of potential equipment failure.

One of the major advantages of transformer-based UPS devices is their higher mean time before failure (MTBF).

Because these devices use traditional electrical engineering principles instead of a high concentration of electronic components, they are inherently more reliable by design than a corresponding electronic circuit board assembly.

By contrast, transformerless UPSs employ sophisticated electronic circuitry to mimic the online characteristics of a transformer-based device, as well as providing suitable standards of mains filtering.

As such, they can be more prone to failure on sites where there is a high degree of mains borne pollution such as transients, spikes and electrical noise.

That's why most experts will only recommend a transformer-based design within industrial and/or critical such as medical and transportation (Railtrack) environments.

However, it should still be noted that, because transformerless designs use plug-in circuit boards, they are actually quicker to repair than transformer-based units.

Of course, as we pointed out earlier there are some very compelling reasons to specify a transformerless UPS.

Among these is the fact that conventional transformer-based uninterruptible power systems are significantly larger than their transformerless brethren.

The main reason for this is that the transformer itself takes up a large amount of space within the cabinet, which results in the transformer-based UPS being significantly heavier, and therefore not as convenient or portable as the transformerless variant.

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Advantages of UPS Systems with Transformers

Moreover, transformer-based uninterruptible power systems operate typically 10% less efficiently than their transformerless stable mates, as the transformer itself causes heat to build up within the vicinity of the device, leading to greater care in terms of airflow and air conditioning.

Some transformerless online UPS also incorporate an extra economy mode to further boost efficiency up to 99%.

The potential antisocial characteristics of the transformer-based UPS are heightened by the noise they can make - frequently a loud and intrusive hum, which can often be compounded by their cooling fan noise.

In practice this means that this type of UPS is often unsuitable for siting in an office or small computer and telecomms rooms, particularly where the levels of noise and heat emitted might cause a problem for staff working in the vicinity.

Transformerless UPSs, on the other hand, are quieter in operation, and run considerably cooler.

Conversely, the heat and noise generated by transformer-based UPSs makes them significantly less efficient in operation than transformerless devices.

This makes them more costly to run, with a higher current drain than the electronic switching circuitry in a transformerless UPS.

Although transformerless UPSs are more complex in design, because the majority of components are electronic, they are cheaper to manufacture than the transformer-based variety.

Rather like mass-produced electronics, many transformerless UPS manufacturers can take advantage of significant economies of scale in their manufacturing processes, further reducing the costs of designing, developing and producing this type of uninterruptible power supply.

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Advantages of UPS Systems with Transformers

Transformer-based UPS devices differ significantly, in that they are more specialist electrical items, and therefore cannot benefit to the same degree from mass produced off the shelf electronic components.

This makes them typically up to 30% more expensive to purchase than transformerless devices.

What this suggests therefore is that, while the transformer-based UPS might be the ideal choice in certain circumstances, economic considerations, together with issues of space and environmental impact, may sway the decision towards a transformerless model.

There is no doubt that transformer-based devices are ideal for sites that experience heavily polluted mains supplies - particularly industrial, rural and complex infrastructure locations, such as hospitals.

In these circumstances, any UPS would be expected to offer dependable long-term protection from repetitive transients and electrical noise.

Despite containing sophisticated electronic circuits that smooth out such anomalies transformerless UPSs cannot fully isolate the load from the mains, unlike a transformer-based device.

This is why several transformerless online UPS manufacturers offer additional cabinets to house filters and isolation transformers so that their systems can approach the benefits required for industrial and heavily polluted environments.

In addition, a traditional transformer-based UPS will prove more reliable over an extended period than sophisticated but sensitive electronic component based filters.

This makes the transformerless UPS more suitable for circumstances where the incoming mains supply is less polluted.

In addition, a transformerless unit can provide input power factor correction capabilities as an integral part of its electronic circuitry.

As such, this type of UPS requires a separate filter or power factor correction device.

Ram Engineering Controls

Advantages of UPS Systems with Transformers

The corollary of this is that - because of the principle of Galvanic Isolation - a transformer-based unit is incapable of generating DC current that might be passed to the connected load.

In contrast, a transformerless UPS will pass on the DC current.

Because DC current causes up to a 10x heating effect compared to an alternating current, this inevitably stresses the unit.

Additionally, a transformer-based UPS will allow a load that has a high neutral current requirement to take such a current, by simply passing this through from its input.

In summary, therefore, deciding between transformer-based and transformerless UPSs is rather like the battle between diesel and petrol engines.

When selecting the right technology to employ, the user has to balance short and long term benefits against budget and overall life cycle costs.

Consultation from a supplier that can offer an impartial recommendation from both technologies should lead to the adoption of a secure and robust power solution.

This document is downloaded at → http://www.engineeringtalk.com/news/rlo/rlo149.html Yours truly, Ram Engineering Controls