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Understanding Voltage Optimisation

Voltage Optimisation (VO) is being offered as an energy efficiency option by a wide variety of companies for domestic, commercial and industrial customers. Although VO can give significant energy and cost savings, care is required to ensure that appropriate VO equipment is targeted at the most cost effective applications, particularly with regard to the changing nature of electrical loads. The two most important facts concerning VO are:

-

In most cases the majority of energy savings from VO are due to reduced services such as less light output
- The minority of energy savings from VO are due to reduced losses in energy consuming equipment
If this is news to you, read on...

What is Voltage Optimisation and how does it work?

Electricity customers around the world receive a supply voltage within regulatory defined limits; for example in the UK the limits are currently 230/400V +10/-6%, whereas most of Europe operates on 230/400V +/-10%. Power consuming equipment will usually operate across a range of different voltages, but is designed for a nominal or 'nameplate' voltage, at which it will deliver the specified service, such as X Lumens for a light or Y kW of shaft power for a motor. When equipment is supplied with a higher voltage than the design voltage it may produce more 'service' (greater light output for example) or may deliver the same service at a lower efficiency (greater loss), or a combination of both, and vice versa if supplied at a lower voltage than its design voltage.

Apart from the difficulty of choosing the 'right' VO equipment, potential users face a baffling set of claims for the benefits of VO, with many equipment suppliers making claims such as, "...can save you up to 26% of your total electricity...". The reality is complicated, specific to the types of load a premises has, depends on the effect the user expects, and should take account of the risks involved for sensitive loads.
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Example showing how energy savings are clearly achieved through VO applied to fluorescent lighting, but also showing how illumination is reduced.


Few people truly understand the most important reality of VO as defined by the bulleted points at the head of the page; the majority of energy savings result from reduced 'service', whereas the minority of energy savings result from reduced losses. This needn't necessarily be a barrier to applying VO to make energy and cost savings, but customers particularly need to be aware that large energy savings are usually associated with lost lighting output - in some circumstances the loss of illumination (in percentage terms) can be greater than the energy savings, particularly with regard to gas discharge lighting - see the chart above for an example of the energy saving and loss of illumination associated with fluorescent tube lighting. However, it is equally important to realise that a workplace designed to have sufficient illumination according to the nameplate specification will be over-lit if the supply voltage is higher than the nameplate voltage.

Some of the many considerations with VO:

- Electronically interfaced loads may have little or no sensitivity to supply voltage - inverters, most new consumer electronics, computers, LED lighting, ErP compliant circulators, etc.
- Reducing supply voltage to the 'norm' may increase the life of some devices
- Stabilised VO may add failure risk for some critical loads - hospitals
- Supply and wiring impedance must be assessed before applying VO - care required for rural applications
- Lightly loaded or idling induction motors are likely to save energy and run cooler at lower voltages, but heavily loaded motors may increase consumption and run hotter
- Secondary effects of VO need to be accounted - for example shaded-pole induction motors run slower at lower voltages
- In some areas supply voltage is rising
- Not all supply voltages are too high
- In some sectors average demand is falling and benefits from VO are reducing - particularly domestic
- Electricity costs are rising, so benefits from VO may increase
- ...and many more factors ....
The situation with motor loads can be even more confusing. A lightly-loaded induction motor will deliver essentially the same service at the lower end of the statutory voltage range but consume less power, whereas a motor loaded to near its rated output will consume more power at the lower end of the voltage range. This effect may be magnified in the case of refrigeration, air conditioning and heat-pump equipment where the compressor motor is often sized for starting torque, but runs the majority of the time at a relatively light load. However, an increasing amount of equipment, particularly air conditioning and heat-pumps, utilise inverters which usually have little or no sensitivity to the supply voltage.

Voltage Optimisation for all but the largest customers (with their own supply transformer) usually involves the addition of one of a variety of forms of subtractive transformers that 'trim' the supply voltage to either reduce the supply voltage by a pre-defined ratio or may also include mechanisms to vary the voltage reduction ratio to give a stabilised, lower voltage for loads. There are many subtle variations of transformer types to achieve VO, but essentially they all work on the principle of transforming only a limited proportion of the supply voltage so that less iron and copper is required than normally associated with an isolating transformer. The choice of VO can be daunting; each manufcaturer makes claims for the advantage of their technology over their competitors' and the overall benefits of VO are presented with various degrees of hyperbole.

Many factors are driving change in the types of load connected to the mains supply. The Eco Design Directive for example has resulted in the rapid phase-out of tungsten filament lighting and will soon eliminate the magnetic ballast for fluorescent lighting. Most small power loads are now supplied by Switched Mode Power Supplies, such that small transformers are rarely found. In the future it is likely that more and more loads will be electronically interfaced to the supply, often resulting in little or no sensitivity to supply voltage. Although some applications may still benefit from VO, care needs to be taken to ensure that the benefits calculated today persist into the future.

In general, the use of VO can be a far more complicated subject than some suppliers indicate. Just a few of the issues are outlined in the bulleted points to the left. KinXerG Limited can help your organisation understand where VO is likely to provide the maximum benefit, what equipment is likely to be suitable for your application, and how the benefits may change over time as equipment is replaced.

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