A Surge of Interest
How to avoid common mistakes and get the best from power conditioning, by Rob Morris, UK Country Manager, Powervar Ltd.
Power quality problems frequently affect sensitive electronic systems in both industrial and commercial installations. Facilities with a great many traditional power loads often experience power disturbances. This is one result of a ‘low technology’ power supply having to support increasingly ‘high technology’ systems.
Experience shows that users often fail to get the benefits they should from their investments in power protection systems. This is because of errors are made in the selection, application, and installation of
the devices concerned. This is a result of misunderstanding the basic power quality needs of modern computer technology.
The most common protection technologies include transient voltage surge suppressors, transformer based
power conditioners, and uninterruptible power supplies.
Most TVSS (Transient voltage surge suppressor) manufacturers use standard ratings and this can lead to a
misunderstanding. Ratings of 330 volts LN (line to neutral) and 330 volts N-G (neutral to ground) are common specifications. These state the lowest, not the highest, voltage level, to which the device clamps high voltage impulses. If low voltage impulses or high frequency noise are the cause of system malfunction, then TVSS technology is not the right solution.
Incorrect installation of TVSS products can be a problem since users often install them at the computer itself, which may frequently cause system lockups, no-fault-found service calls. TVSS products are best used at the distribution panel or electrical service entrance to the building.
A power conditioner should incorporate an isolation transformer and be installed close to the equipment it is
protecting.
For today’s technology, the transformer should be low impedance – of the order of 2%. Higher impedance
transformers cannot faithfully accommodate non-linear current requirements and to avoid starving the power supply, they must frequently be oversized to handle modern computer loads. Low impedance designs, while slightly more expensive, avoid the need to oversize, which saves money and provides the customer with higher efficiency and a solution with a smaller physical footprint..
The best place to start is with the design of the UPS inverter. High quality UPS inverters will convert stored DC energy into a low distortion sine-wave ideal for powering a computer. In order to get the price down some manufacturers offer small UPS products with modified sine-wave inverters.
Larger UPS sizes (above 2 kVA) are generally sine-wave designs, but the rest of the UPS topology may still require some research to ensure proper selection. As with power conditioners, a properly selected UPS should also contain a low impedance isolation transformer.
Most common power quality mistakes are the result of not realising that today’s electronic computer systems have different power protection requirements from their predecessors.
Power supply topology has changed, microprocessors are much faster, and today’s technology is more sophisticated than ever. All too often, the first power protection tactic that is tried is the one that worked 20 years ago.
Dedicated/isolated electrical circuits are of limited usefulness in networked computing environments, and the design of switched mode power supplies makes the use of voltage regulators unnecessary.
Proper selection and application of power quality solutions begins with an understanding of the technology that is being protected. Only after you understand what the system needs in the way of power quality can you select the best solution and design the best implementation.
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