By Jorma Mannerkoski, 
Product Marketing Director, Powerware EMEA

Aug 29 - Sep 04, 2005


The primary task of a UPS system is to protect the load from down time caused by potential power problems. A UPS must be able to cope with all the power problems which exist in the utility power.

However, when choosing any type of electrical equipment it is important that operational costs are taken into account. Operational costs consist of electrical, operations staff and maintenance costs. In UPSs the electrical costs are closely linked to the efficiency of the UPS equipment.

The efficiency of a UPS system needs to be measured in an actual installed environment. The type of load, stability of the utility power and the effect of partial loads are all factors which need to be taken into account.

There are many competing claims about the relative efficiencies of different types of UPS topologies. When tested in laboratory conditions the efficiency ratings for various types of UPS can be misleading. The reason for this is that the parameters of utility power input and the load can be precisely controlled and optimized to produce the highest efficiency levels. When the UPS is used in real life situations the results can be radically different.

In a normal operating environment the most important elements, as far as factors for efficiency, are: input voltage fluctuations, load level of the UPS and the type of load.

Voltage fluctuations are present in just about all utility systems. Most UPS are able to correct them, but some designs, for example line-interactive UPSs, have low efficiency when they are forced to regulate voltage.

Partial loads are very common as UPSs are hardly ever 100% loaded in real-life situations. In most installations some allowance for load expansion is made. Single UPS units are typically 60-80% loaded. When two or more units are run in parallel (redundancy), it automatically means that the UPSs are not fully loaded under normal conditions. For example when a 200kVA load is fed through two 250kVA units the load for each UPS is only 40% of the full capacity. It is important therefore to consider whether the UPS you choose will offer high efficiency under low or partial load conditions

IT equipment, including computers, are typically powered by what is called Switch Mode Power Supplies (SMPS). These power supplies are small and cost-effective, but have a special characteristic in that they draw electrical current from the mains in bursts which gives a non-linear waveform. Therefore, when protecting computers, the efficiency of a UPS needs to be determined under computer (non-linear) load conditions.

A double conversion on-line UPS regenerates power continuously regardless of the input voltage and load waveform. Therefore because the rectifier and inverter are used continuously any change in the input voltage or load conditions has very little effect on the operation and efficiency of the UPS. Double conversion not only offers the highest level of protection available but also, through the use of advanced IGBT and DSP electronic circuitry can offer the highest levels of efficiency as well (up to 94%). Use of these technologies means there are less components in the UPS, which in turn means less energy is consumed.

Line interactive (including Delta Conversion) UPSs compensate for the deficiencies of the utility power and distortions caused by the load. This means that if the load and utility power are set to optimal levels, the UPS does not need to compensate for any deficiencies (in effect does not need to do anything) and therefore high efficiency levels can be achieved under laboratory conditions. In contrast when this type of UPS is used in real life situations there are inevitably going to be voltage fluctuations which will cause the output converter to be employed and typical computer loads will create waveform distortion which means the input converter also needs to be used. These converters consume power, which means the overall efficiency of this type of UPS can in fact be much lower in a normal operating environment compared to 'ideal' laboratory conditions. When combined with the fact that these units do not operate very efficiently under partial loads, it is apparent that the real life efficiency is typically lower than in a modern double conversion UPS.

In conclusion, as the performance of a modern double conversion UPS is not dependent on the utility or load conditions it offers the highest efficiency in real world installations. Not forgetting that it also offers best power protection available.


A globally recognized industry leader for more than 40 years, Powerware designs and manufactures a full line of Uninterruptible Power Systems (UPS), DC power systems, power management software/connectivity products. Powerware products are typically used in networking, PC, financial, medical, industrial, voice and data communications, military and aerospace applications - wherever continuous power is essential to daily operations. Powerware is headquartered in Raleigh, NC, and is part of Eaton Corporation.

The company offers a full range of UPSs ranging in size from 300 volt-amperes (VA) for personal computers to greater than 1,000 kilovolt-amperes (kVA) for mission-critical applications including data centers, Internet service providers, and server farms. Network-connectivity devices, extended battery cabinets, power distribution modules and other power-related devices further enhance Powerware UPS hardware offerings. The Powerware product portfolio also includes a full line of DC Power Systems ranging in size from mini systems for roadside cabinets or customer premises equipment to large systems for major switching installations. Power management software and IT infrastructure management software complete the company's product line. Basic power management software provides industry-standard monitoring, alarm and shutdown capabilities. More advanced software packages offer expansive data archiving, trending and regression analysis tools with predictive capabilities. With innovative software that can predict the type and timing of possible future events, Powerware is leading an industry shift from reactive power protection to proactive power management.


Eaton Corporation is a diversified industrial manufacturer with 2003 sales of $8.1 billion. Eaton is a global leader in fluid power systems and services for industrial, mobile and aircraft equipment; electrical systems and components for power quality, distribution and control; automotive engine air management systems and powertrain controls for fuel economy; and intelligent drivetrain systems for fuel economy and safety in trucks. Today, the company classifies its business into four distinct segments, which are, by size: Fluid Power, Electrical, Automotive and Truck. Eaton has 51,000 employees, 207 manufacturing sites and sells products to customers in more than 100 countries.


GemNet is a power solutions company, providing quality power products and services. Our philosophy has always been to combine its local expertise and commitment with quality products, technical competence and the support of its principal. Since inception, it has been our goal to build deep and long lasting relationships with our customers and alliance partners by providing them top-quality power products and services. This has been the single most important success factor for GemNet, earning it the reputation as one of the leading and most professional power products and solutions companies. Today, GemNet enjoys an established track record of excellence with its customers in Pakistan and the United Arab Emirates. GemNet is the authorized distributor for Eaton Powerware's range of AC and DC Uninterruptible Power Systems, and offers a large range of specialized power related products and services. The company has local offices in Karachi, Lahore and Islamabad (GemNet Pvt. Limited) and Dubai, United Arab Emirates (GemNet Gulf).


* Service plans to fit the clients needs, including plans that cover the client's existing Power Systems and UPSs.

* Services also include: Needs Analysis, Comparative Product Analysis, Cost Justification, End-User Training, Maintenance, After Sales Support, Data/telecom center, electrical contracting and site preparation.

* Power Consulting & Critical Environment Site Audit (CESA): Audit of existing UPS and recommendation of a power solution. Analysis of the quality of power feeding the systems. Facility/Site inspection, identification and correction of the problem.