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10. Voltage Management – A silver bullet?

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As the cost of electricity has increased, there has been a surge of interest in reducing electrical voltages as a supposedly quick, easy, “guaranteed” energy saving measure. There are a host of voltage reduction solutions being marketed in the form of “secondary transformers” of various types, and with some extravagant claims for their effectiveness. How can you possibly know what, if any, solution is right for you?

In this issue of Intelligent Energy Insights we explain how voltage management can save energy and steps you should take to identify the potential and the best solution for your site.

It covers the following topics:

  • The background to voltage management
  • Will voltage reduction work for you?
  • Assessing the potential
  • Low voltage options
  • High voltage options and excess transformer capacity
  • So, is voltage management a silver bullet?

Click here to see all Intelligent Energy Insight topics

John Treble, Managing Director

The background to voltage management

There3450_insight10-1 - - becky is nothing new about voltage reduction as an energy saving measure – it was widely practiced during the 1970s when industrial action reduced generating capacity and voltage reduction “brown-outs” were frequently implemented. Since then, EU harmonisation has resulted in the nominal UK voltage being reduced from 240 to 230 volts (phase to earth) although in practice this has had virtually no effect on the voltage supplied to an individual site. Sites are mostly still supplied at high-voltage (11,000 volts), to reduce to low voltage via their own transformers, or with low voltage supplies at 230 volts -6%/+10% (216-253 volts). If your supplies are at the top end of this range then the potential for reduction is considerable but the extent of energy savings will depend on the mix of energy consuming equipment that you have.

Will voltage reduction work for you?

Whether a reduction in voltage will result in a reduction in power demands and thus energy consumption depends entirely on the nature of the electrical loads on the site. Some loads are unaffected by variations in voltage, and this includes many power supplies for IT and similar equipment which is often designed to operate across a wide range of voltages. However, these loads are usually a relatively small proportion of the site’s overall load.

Another group of equipment which is unlikely to make any savings is resistance heaters that are thermostatically controlled. For these, there will be a reduction in power demands, but the demand will continue for longer. Whether this results in a saving will depend on the design of the equipment, but it is best to assume that resistance heating will not provide savings through voltage reduction.

Electric3450_insight10-2 - - becky motors will show a reduction in energy use, particularly if they are being used for loads such as fans and circulating pumps where there is a cubic relationship between the speed of the load and the power demand. However If the motor is controlled by an inverter drive, and the inverter is being used to its optimum, the additional savings are likely to be small or non-existent.

Savings on lighting circuits will depend on the type of lighting, but will generally be pro-rata with the voltage for electronic ballasts, and greater than pro-rata for traditional ballasts and for incandescent lights. In general, it is difficult to predict precisely how great an energy saving may be achieved, but for most sites a pro-rata reduction should be anticipated – it could be a bit more. In other words, if your site is currently supplied at 250 volts and this is reduced to 220, a 12% reduction, “all things being equal” the reduction in electricity use for lighting should be about 12% also.

It is also important to consider what changes are likely to occur when you upgrade equipment as there is no point in investing in an expensive solution if changes in load types render it useless before it has paid for itself in energy savings.

Assessing the potential

Before you commit to a particular course of action or a specific piece of kit it is essential to investigate your existing voltage profile to determine what if any savings could be achieved and the most cost effective solution.

Most sites operate at the top-end of the 219-253 volt band, and very occasionally will exceed 253 volts, but usually only for short periods. However, other sites are already at 219 volts or less. If yours is such a site any further reduction is unlikely to be beneficial. Voltage will tend to be higher at night when circuits are lightly loaded, and there will also be a voltage drop across the site from the main incomer to the point that is either the most remote, or has particularly heavy demands.  Both these factors need to be taken into consideration.

Low voltage options

If your supply is low voltage and is greater than 230 volts it is worth considering measures to reduce this. The first option should be to approach your Distribution Network Operator (DNO) and ask for a reduction. If your site is the only one on the supply transformer then this should be feasible, as most transformers can be adjusted by up to 5% from the nominal voltage. Another option might be to request that your DNO transfer you to a high-voltage supply - the charges are lower and you have greater control over your voltage. If neither of these options is available, then the installation of a secondary transformer is likely to be the best option, although, depending on the loads, it might be better to treat individual sub-distribution boards supplying particularly susceptible loads rather than place a big transformer on the entire supply.

High voltage options and excess transformer capacity

A 3450_insight10-3 - - beckymajor cause of energy inefficiency is the oversizing of equipment due to over-specification and/or reduced demand since installation. This is as true of electrical transformers as it is of boilers, chillers or anything else. Such oversizing is endemic and not just marginal but often massive. New oversized transformers are often specified for new buildings ignoring the fact that the site already has substantial overcapacity.

At some high voltage (HV) sites transformer capacity is 300-400% in excess of what is required!  “Standard” transformers are designed to provide 250 volts at “no-load”, and full load on the transformer will reduce this to about 240. If a transformer is only lightly loaded then a voltage drop will not occur.  Transformers are generally fitted with adjustable tappings providing for +/-5% adjustment in 2½% steps. The most cost effective initial measure may be to adjust the tapping to reduce the voltage – from a nominal 250 to 237.5 at no-load (5%). However, the voltage may still be higher than necessary, as the HV supply may exceed the 11,000 volts nominal, resulting in no-load voltages off the transformer in excess of 250. It may be possible to persuade the DNO to reduce this, but this is unlikely.

If 3450_insight10-4 - - beckyan estate has a number of transformers, it may be possible to reduce the number and install appropriately sized replacement “low-loss” units, with additional tappings for low-voltage operation. This will not only result in reduced voltage, but also reduce transformer losses. This measure can be particularly beneficial, especially in comparison with the installation of secondary transformers, a measure that is not only costly but which retains the existing transformers and their losses, as well as doubling the number of transformers on site.

The final option may be to install secondary transformers, but this should only be undertaken once all other possible options have been considered.

So, is voltage management a silver bullet?

Voltage management is an important aspect of a comprehensive approach to managing energy effectively. As always the potential to get it wrong and to spend money and not achieve worthwhile savings is significant. To avoid the pitfalls a systematic and objective approach needs to be taken, as outlined above. If the correct steps are followed then voltage management - not necessarily through using secondary transformers – may be worthwhile. Alternatively, the combination of your voltage range and the mix of equipment that you are using may mean that cost effective energy savings are not possible.

Your Independent RISK FREE Solutions

To determine independently whether or not cost effective energy savings are possible for you, we will be pleased to provide whatever level of Voltage Reduction and Regulation investigation is appropriate for your estate – be it large or small, high or low voltage, multi or single site. For an example please see: University of Portsmouth Case History.

For more information click the above links or call John Treble on 01761 176300, or email John@GreenConsultancy.com

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Voltage Management for University of Portsmouth

“The Green Consultancy’s solution is elegant and maximises energy efficiency at the lowest cost. Salesmen were queuing up to sell us secondary transformers when we already had too many transformers and the result would have been less savings at greater expense.
I have always been impressed with The Green Consultancy’s sound scientific approach to identifying energy reduction opportunities.  I thoroughly recommend them and look forward to the project implementation and further studies by them.”

Ian McCormack, Energy and Environment Manager

See case history of our work for University of Portsmouth

 

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