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If you know the total kVA rating of your load it will give you a good indication of desirable UPS sizing, but you need to know more before making a purchasing decision.
Other factors which impact a UPS's ability to perform can and do arise within the load under protection. These include the power factor of the load, whether harmonic distortion is generated and many other issues as described below. Your UPS Ltd Sales Engineer can advise you on how to identify and allow for these. |
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Power Factor of load
Problem Loads
Three phase load distribution
Other electrical factors
Battery Autonomy or back-up time
Physical Appearance
Future proofing |
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Power Factor of load
The power factor of a load expresses the relationship between the power a load draws and the power it actively consumes. Many loads have a 'lagging' power factor of typically 0.8, in which a power consumption of say 400W would equate to a demand of 500VA. However blade servers, which are increasingly popular because of their high density computing power, usually have a 'leading' power factor. Traditional UPSs derate significantly with a leading power factor load. Although modern transformerless UPSs such as the PowerWAVE series have significantly reduced derating, it is still an issue that must be allowed for. |
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Problem loads
Certain loads such as motors and compressors, laser printers and air conditioning equipment can draw high currents during normal operation and particularly during start up. Such load characteristics must be recognised and allowed for in UPS sizing considerations. Alternatively, some of these loads could be powered directly from the mains rather than through the UPS. |
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Three-phase load distribution
When distributing single-phase loads across the output of a three-phase UPS, they should be evenly balanced to utilise the rating of the UPS as fully as possible. |
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Other electrical factors
Computer equipment within an installation can exhibit other behaviour that must be recognised and allowed for, because it can impact the UPS. This could include harmonic distortion, inrush currents and neutral currents on a three-phase supply. Your UPS Ltd engineer can advise on rectifying or allowing for these problems. |
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Battery autonomy or back-up time The battery autonomy describes the time for which the battery can maintain the critical load if the mains power fails. It depends on the battery capacity and the load size. The desired battery autonomy should be specified as part of the UPS sizing exercise. If on site generators are available, an autonomy of 10 - 15 minutes is usually sufficient to allow these to start up and stabilise during a mains failure. Without generators, an autonomy time of 30 minutes is typical. Extra cabinets can be supplied if a significantly extended autonomy is required. |
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Physical Appearance
Today, UPS equipment is frequently designed into data centres alongside the servers it supports, where it is on view to visitors and staff. The PowerWAVE 9000DPAT with an external aesthetic design to complement its advanced internal technology, is ideal for this situation. |
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Future Proofing
After calculating the load requirement for your installation, a contingency capacity of at least 20% should always be provided. Additionally, with inexorably increasing demand for computer processing power, making provision for expected but unknown future growth is advisable.
This can be done easily and efficiently by selecting one of the PowerWAVE modular systems such as the 9000DPAT or 9000T series. An initial capacity close to the actual load can be installed, but as the load grows additional modules can easily be added without even interrupting the supply to the load. Note that the site power infrastructure should be designed from the outset to accommodate any projected growth in load and UPS capacity. |
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