Uninterruptible power supplies (UPS) are big business. According to Frost & Sullivan, the value of the European UPS market alone will grow to reach €733m by 2010. James Hunt looks at UPS, and also gensets for emergency power in this article originally published in Electrical Times magazine:
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| MGE UPS's single-phase Pulsar UPS range. |
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| An MTU standby genset. |
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UPS and
standby gensets both provide emergency power in the event of mains failure, which is not quite as rare as we'd like it to be. For UPS, electrical power is supplied within a few thousandths of a second after mains failure, and - depending upon the autonomy provided - this will continue long enough to allow proper shutdown, or until mains power resumes, so saving data or maintaining safety.
Where almost total supply continuity is essential (up to 99.999999%), the latest digital static transfer systems automatically transfer the load from independent power sources to ensure load continuity - all without disturbing the application.
In the case of standby / emergency gensets, when mains power fails, a warmed diesel engine quickly provides electricity via an alternator until mains power is restored. Compared with a UPS, there is a longer break in the power supply, but emergency power can be maintained at least until fuel runs out. For critical loads (hospitals or airport radars), UPS provide 'no-break' power, but even then they are often backed-up for the longer term by standby gensets - sometimes of the 'short-break' variety. Gensets are supplied by MTU, Rolls-Royce, Aggreko, Energyst Rental Solutions, AEC, Cummins Power Generation, Swan Generators, GE Energy Rentals, Interpower International and Wärtsilä, among many others.
Fear of power outages means that many SMEs, and even some homeowners, are now buying emergency power. There are many small electrical contracting companies carrying out domestic and light commercial work, plus larger companies installing standby sets over 250kVA. About 80% of sector sales fall into the 5.5 - 30kVA bracket.
UPS:
There are two basic types of UPS - dynamic and static:
Static UPS are purely electronic (no moving parts). They provide excellent protection for most applications. There are four main sub-types:
- Offline - Small, inexpensive - ideal for PCs. Power conditioning not usually included.
- Line interactive - Highly reliable. Generally 0.5 - 5kVA to protect rack and distributed server equipment, perhaps in industrial environments. Better protection than offline.
- Double conversion online - Top quality voltage conditioning; easy to parallel, but comparatively low efficiency and expensive. Can interfere with building wiring or cause standby generator problems.
- Delta conversion - From about 5kVA to 1.6MW, providing excellent voltage conditioning, plus high efficiency. Can reduce lifecycle cost of energy in large installations. Harmful harmonics minimised.
Rotary UPS use a heavy flywheel, its high kinetic energy taking ride-through upon mains power failure to several seconds. Another type comprises packaged diesel genset, kinetic energy storage module (or battery) and coupling choke. The diesel starts (almost) instantly if there is a power failure, its driven generator continuously serving the critical load and giving longer-term autonomy, while the other components provide power conditioning and ride through energy.
Rotary system sine wave quality is often better than a static UPS, and harmonics are negligible. Reliability and efficiency are high, as is the fault clearing capability. High inrush loads are easily catered for. Therefore, for certain critical applications, rotary UPS are an attractive option, especially above 400 kVA.
Choice:
Key factors in choosing a UPS include the business type, existing protection, how important to the business the equipment is, the load to be protected, ambient conditions, and likely future requirements. Much of this information can be easily gained using normal mains monitoring instruments.
For emergency gensets, which to use: single- or three-phase power? The former is most common for low-power applications; the latter is preferred for motor starting / running, and most industrial / commercial applications. Proper sizing is essential - identify peak load and control requirements. The diesel engine is the first choice for most applications; petrol sets are limited to domestic applications. Noise, emissions, fuel efficiency and maintenance schedules must all be considered. Gensets for site power applications are limited to 110V output; this can be tapped-off most standard single-phase gensets.
A recent example:
MGE UPS Systems' latest rackable, single-phase UPS (700 VA - 20 kVA) have been designed for IT applications and network infrastructures. The hot-swappable Pulsar, Pulsar M and Pulsar MX feature the ModularEasy technology for dynamically managing single-phase UPS paralleling and power extension. Benefits include increased manageability, flexibility and availability. Until now, the acquisition cost of an upgradeable UPS was about 2.5 times the price of a single unit UPS; these upgradeable units are priced the same as single unit.
Batteries for power back-up:
Industrial batteries are often used to provide a degree of autonomy for UPS and emergency lighting systems while mains power is being restored. Such batteries (in multiple) can be rated to thousands of Ah. This has resulted in demand for powerful yet more compact, totally reliable, low-maintenance battery systems.
Industrial batteries come in sizes and shapes to suit almost any application, and are either of the primary (non-rechargeable, disposable) or secondary (rechargeable) types. These can be further sub-divided into lead acid; nickel cadmium (NiCd), lithium ion (Li-ion), nickel metal hydride (NiMH), and reserve types, but lead acid is still the most commonly used, because this technology offers the best price to power ratio. NiCd cells are more expensive, but work over a very wide temperature range, and are reliable over long and taxing lives. Moreover, they cannot fail in open circuit. The other two hi-tech types have major advantages, but are very expensive in comparison and are not often used for UPS. Very long battery autonomies are ideal for telecomms support.
To take a very recent example, ultra-low maintenance Alcad Vantage NiCd batteries provide lighting autonomy at the CityPoint office development in the City of London. These power three static inverters to provide emergency lighting support. In another example, similar batteries, working in combination with a Benning Thyrotronic power unit, provide between five and 24 hours of backup power for Transco's Scunthorpe gas compressor station.
This article was originally published in Electrical Times magazine by Nexus Media Communications, a Voltimum UK Media Partner. Electrical Times has recently been sold.
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Related contacts
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Contact: Louise Frampton
(Editor - Electrical Times)
Nexus House, Azalea Drive,
Swanley, Kent BR8 8HY
Tel: +44 (0) 01322 660070
E: louise.frampton@nexusmedia.com / www.electricaltimes.com |
Louise Frampton
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