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[ Spotlight: UPS ]

has better voltage stabilisation and power conditioning and lower running costs than the offline version. It is also energy efficient. Moreover, the lifetime is better because of the way the inverter and batteries are run. However, less protection is provided against frequency changes and harmonics. Under normal operation, mains power is fed through a voltage stabiliser and conditioner to the load, feeding a battery charger linked directly to the standby batteries. If a mains failure occurs, the load is switched to the standby batteries, providing power via a DC/AC inverter. Rotary UPS – This uses the inertia of a high-mass spinning flywheel for energy storage to provide short- term ride-through if mains power is lost. Protection is also provided against spikes and sags. However, the flywheel typically provides only 10–20 seconds of protection before it slows, so is often operated with a standby diesel genset – the rotary UPS providing backup power only for the short time the engine needs to start and stabilise power. Rotary system sine wave quality is high, harmonics are negligible, while efficiency, fault clearing and high inrush load capability are all good. The type is relatively expensive and is usually used for critical applications needing larger powers, especially above 400 kVA. Rotary Diesel UPS – This comprises diesel engine,

generator, kinetic energy storage module and coupling choke operating together to provide power conditioning and ride through energy for the UPS. The diesel engine offers longer-term backup. These systems provide extremely high availability and reliability, plus high efficiency during stand-by operation. Rotary UPS (including diesel) are niche in the global

UPS market, representing a mere 4.3 per cent of global UPS revenues in 2008 (IMS Research). The remaining 95.7 per cent was made up of static UPS – a ratio unlikely to have greatly changed since then. Emergency gensets – These are sometimes used to

provide extended run-time (autonomy) after the UPS has done its job of protection, but before mains power is restored. These are not UPS in themselves, but are important in the overall picture.

Choice When specifying a UPS, it is essential to choose the right topology – getting it wrong can severely affect performance and costs. Key factors include the business type, existing protection, how important the equipment is, the load to be protected, ambient conditions and future requirements.

Above, left: Eaton’s new compact offline 3S UPS offers affordable and reliable protection against the most common power quality problems for office and home computers. It also covers peripherals, such as printers

Above, right: Fig.3: A schematic of an offline UPS. The output is dependent on mains input voltage and frequency variations. The inverter is connected in parallel and simply backs up utility power (courtesy APC)

The range of applications for static UPS is very broad,

while those for rotary UPS are more limited. Static UPS are typically used in everything from the home and office to large public buildings and small to medium sized data centres. They are generally more energy efficient than rotary types, which are typically suited to applications where there are many short power inrushes, such as motor switching. However, some traditional rotary UPS advantages have been somewhat eroded by recent static UPS advances. Where high network security is essential (as it

increasingly is), rotary UPS are less affected. Therefore, they may be more suitable for very large multiple megawatt data centres. In such applications, rotary UPS tend to be more suited for a centralised architecture, while static UPS are more flexible, so can accommodate distributed UPS solutions.

The increasing numbers of UPS can also provide major business opportunities for electrical contractors

...and finally The multiple impacts of changing power supplies and demands, our increasing dependence on electricity, the changing nature of digital communications, plus climate change mean that the market for UPS is certain to grow, and that the technologies will improve still further. ‘With that,’ says Giuliano Digilio, ‘will come many challenges and benefits for electrical designers, engineers and specifiers, as well as big opportunities for electrical contractors.’

n If you want to know more about UPS, please call Giuliano Digilio at the ECA on 020 7313 4825.

Eaton’s compact Ellipse ECO UPS for office equipment power protection provides energy savings of up to 25 per cent, achieved by automatically disabling peripherals when the master device is turned off

September 2011 ECA Today 31

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