|
In the section on "load linearity", I introduced the humble diode. Here, I continue the journey with regards its implementation in modern society. What does surprise me is that 'technology' is blamed for producing and adding to power problems, especially the rectifiers found in switch mode power supplies (SMPS). Some thought needs to go into just how long rectifiers have been in existence. Furthermore, railways have also been using DC for quite some time and they draw loads of power, up to 1MW per small passenger train, all needing to be rectified. However, it will be agreed that what has changed is the diversity of technology and the amount of implementation. Just look at a modern work desk. It is not uncommon to find a PC, monitor, and printer all fitted with SMPSs each having diodes up front. The desk lamp is likely to be a modern 'energy saving' type (as the heat output is low) with a current curve far from a sine wave. And so on..... The attention given to reducing energy requirements and increasing efficiency factors has somehow led to less attention being given to the junk such measures cause on the network. It's all fair and well when the average household has a PC and all its bits, a TV, Hi-Fi, and other 'techy' things as the major consumption is made up of resistive loads such as lights (incandesent), electric cookers, and hot water heaters. In the grander scheme of things the 'techy' bits do not account for much of the household usage. The workplace, however, has a far greater ratio of tech to resistive loads, especially as most lighting is florecent, low energy, or low voltage (with SMPS 'transformer' units, sometimes one per lamp!), all this ading to each work desk brimming with technology in the stive for the 'paperless' business world. There are also businesses whose only purpose in life is to offer technology backbones (computer centres, Internet service providers, etc.) where the ratio of tech to resistive can be measured in factors instead of percent. In the interests of power quality there are two issues that are of concern when powering technology being the rectification of AC to DC which causes very non-linear current curves and raises the harmonic content, and high frequencies fed back onto the network owing to the operation of the power supplies. A further, less important factor (as this can be planned for) is the leakage caused by the filters of modern power supplies. This is dealt with next.
© 09.06.01 / 14.10.04 |
CAUSES: