|Despite changes to the UK statutory
supply level there has not been any reduction to our LV supply network levels
and the average incoming voltage still stands at 242V. It is not unusual to see
voltages in excess of 250V and some sites have recorded voltages in excess of
260V. There are many influences on the incoming voltage level of this typical
retail site (Fig. 1 below) most associated with I2R losses, not just this site
own operational characteristics but also those around it. The graph highlights
the differences between day and night levels but also the weekend when other
sites are non-operational. Another aspect worth noting is the imbalance of the
phase voltages another cause of inefficiency.
Fixed Ratio Stepdown Transformer
To correct the situation in Fig.1, it is quite simple to reduce the voltage to a more realistic level. It would seem that most sites are comfortable to initially settle at around 220V phase to neutral. This is achieved by fitting a fixed ratio step-down transformer (Fig.2) with pre-determined tap settings or adjusting the tap setting on their own incoming transformer, if it is not shared. However, the tap setting with the latter are quite course. This method has been general practice within industry for many years but with the low cost of electricity pre 2000 was not considered high priority. The benefits are an immediate reduction in consumption, increased equipment life, low purchase and installation costs giving 12 to 18 months return on investment. The disadvantages are obvious, there is no control, whatever appears on input a fixed percentage drop will occur on the output including voltage fluctuations and sags.
A Voltage Regulator is an active device, fitted at your incoming supply but now with the ability to regulate the output voltages to your site (Fig.3 below). The benefits of this method over the previous are obvious. The output voltages are now controlled to a set level that can be adjusted on-line at site. Each phase has independent control allowing the output voltages to be balanced, thus improving efficiency. This additional saving added to the saving by eliminating fluctuating voltages, out weights any cost advantage of the fixed ratio method. Due to the design of the POWERSAVER it is possible to continually reduce the output voltages to achieve the optimum setting for maximum savings while on-line. A reasonably sized site can expect a return on investment within 18 to 24 months.
Comparison between the two methods
As can be seen from the graph (Fig. 4) there is a substantial difference between the saving using the fixed ratio stepdown transformer and the voltage regulator. Therefore a balance is drawn between the costs of the former against the control of the latter. However, that is not all that should be taken into consideration.
A Final Thought
The existing network infrastructure is close to full capacity and with no new Power Stations on the horizon, against the ever increasing demand, it is possible that in the near future we can no longer rely on the stable supply we have enjoyed in the past.
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