Sensitive electronic equipment frequently suffers as a result of power quality problems. Facilities with numerous traditional power loads often generate power disturbances that result in a ‘low technology’ environment supporting ‘high technology’ systems. Power conditioning is the answer, says Bob Morris, who offers some advice about its implementation
Experience shows that users often fail to fully realize the full benefit of their investment in power protection equipment because it is not selected, applied or installed correctly. This stems from a misunderstanding of the basic power quality needs of modern computer technology. The most common protection technologies include transient voltage surge suppressors (TVSS), uninterruptible power supplies (UPS), and transformer based power conditioners. So, where and when is it appropriate to implement these technologies?
The standard ratings used by many TVSS manufacturers can lead to a misunderstanding. Ratings of 330V line to neutral (L-N) and 330V neutral to ground (N-G) 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 causes of system malfunction, then TVSS technology is not the right solution.
Incorrect installation of TVSS products can raise problems since users often install them at the computer itself, which may frequently cause system lockup, resulting in no-fault-found service calls. TVSS products are best used at the distribution panel or electrical service entrance to the building.
Where the UPS is concerned, the key factor is the design of its inverter. High quality UPS inverters will convert stored dc energy into a low distortion sine-wave ideal for powering a computer. In order to meet a low price point some manufacturers offer small UPS products with modified sine-wave inverters.
Larger UPS sizes (above 2kVA) 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, which I will come on to next, a properly selected UPS should also contain a low impedance isolation transformer.
A power conditioner should incorporate an isolation transformer and be installed close to the equipment it is protecting. For modern 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 both higher efficiency and a smaller physical footprint.
To make sure that the power conditioner is more than just an isolation transformer in a box, its design should also incorporate a surge diverter (TVSS) and a high frequency noise filter. These components will turn an ordinary isolation transformer into a bi-directional power conditioner capable of addressing power disturbances regardless of their origin - line or load.
New approach needed
Power supply topology has changed, microprocessors are much faster, and today’s technology is more sophisticated than ever. So the latest electronic systems need a new approach towards their power quality needs. Yet, all too often, the first power protection option is the one that worked 20 years ago.
Dedicated/isolated electrical circuits are of limited use to 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 systems 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 specify the correct method.
Rob Morris is UK country manager, Powervar