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Voltage optimisation is a term given to the systematic controlled reduction in the voltages received by an energy consumer to reduce energy use, power demand and reactive power demand. While some voltage 'optimisation' devices merely reduce the voltage using a transformer, others give the end-user the ability to control and optimise their electricity supply locally, correcting voltage and power quality problems from the grid, and are designed to do so very efficiently. Voltage optimisation systems are typically installed in series with the mains electrical supply to a building, allowing all its electical equipment to benefit from an optimised supply.

In the UK, where there is a particular problem with over-voltage, voltage optimisation as an energy conservation is growing rapidly in popularity .

Voltage optimisation was originally used in industry to reduce maintenance costs most notably with three phase induction motors. It was found that by reducing the voltage across the motors by about ten volts the carbon brushes in the commutators of the induction motors lasted longer. Hence, the down time on the motors and maintenance costs required to run the motors was reduced. Subsequently, the emphasis has shifted to energy saving and to meet the market voltage optimisation companies have adjusted their sales pitch.

Background

Voltage optimisation is an electrical energy saving technique which is installed in series with the mains electricity supply to give an optimum supply voltage for the site's equipment. Voltage optimisation improves power quality by balancing phase voltages and filtering harmonics and transients from the supply.

Voltage optimisers are essentially electrical transformers - coils of metal that can behave like magnets if an electric charge is passed through them.

Voltage optimisation is an effective means of saving energy, particularly in the UK where some people believe there is a national problem of overvoltage. The technology is being used extensively in Japan and is now being taken up elsewhere in the world.

The declared electricity supply in the United Kingdom is now, as a result of European Harmonisation in 1995, 230V with a tolerance of +10% to -6%. This means that supply voltage can theoretically be anywhere between 216.2V and 253V depending on local conditions. However, the average voltage supplied from the national grid (in mainland UK) is 242V , compared to the nominal European voltage of 230V. (The average supply voltage in Northern Ireland is around 239V, and 235V in the Republic of Ireland .) Older electrical equipment manufactured for the UK was rated at 240V, and older equipment manufactured for Continental Europe was rated at 220V. New equipment should be designed for 230V. A mixture of equipment is likely to be found in older premises. All equipment placed on the market within the E.U. since voltage harmonisation in 1995 should operate satisfactorily at voltages within the range 230V +/-10%. Equipment rated at 220V should operate satisfactorily down to down to 200V . By efficiently bringing supply voltages to the lower end of the statutory voltage range, voltage optimisation technology could yield average energy savings of around 13% .

The higher the voltage the higher the power consumption. In the case of a pure resistance load reducing the voltage by 5% will result in savings of 10%. In addition, higher voltage tends to increase the heat generation in motors, and generally reduces the life expectancy of electrical equipment, including lighting bulbs. Voltage optimisation is effective for almost any site with an electrical load and organisations of all sizes and types have benefited from installing the technology.

However, there are criticisms of aspects of voltage optimisation, particularly its use in a home context. These centre around the issue that variation in voltage does not affect the cost of the power used in many contexts in the home. This is because consumers are charged through the power they use, rather than the voltage they use. For instance, for practical purposes, it costs the same to boil a kettle at 200v as at 240v, and uses same amount of power overall.

In a similar way, devices fitted with a thermostat, such as a fridge, use very similar amounts of power at different voltages. The "electrical" work needed to keep the fridge at a certain temperature is the same - (but it can be delivered more quickly at a higher voltage - the thermostat acts to keep the temperature and hence the power used the same over time however). Modern electronic devices such as PCs also have similar power management.

Therefore the main way that voltage optimisers are able to reduce power consumption and costs in the home seems to be to make lights become dimmer, the electric shower may become slightly less hot at a given setting etc. They may also save money by regulating spikes in the electricity supply which may reduce the life of electrical equipment.

There is suspicion amongst some members of electicians forums in the UK that the problem of "overvoltage" and "voltage optimisation" may be a marketing device in order to sell voltage transformers. See http://www.powerswitch.org.uk/forum/viewtopic.php?t=17893&postdays=0&postorder=asc&start=0 and http://www.electriciansforums.co.uk/electrical-forum-general-electrical-forum/2299-problems-caused-voltage-optimisers.html

Common Power Quality Problems

Overvoltage

Overvoltage refers to voltage higher than the voltage at which equipment is designed to operate most effectively. It causes a reduction in equipment lifetime and increases in energy consumed with no improvement in performance. The 16th edition of the Electricians Guide BS7671 makes the following statements in relation to overvoltage: “A 230V rated lamp used at 240 will achieve only 55% of its rated life” (referring to incandescent lamps) and “A 230V linear appliance used on a 240V supply will take 4.3% more current and will consume almost 9% more energy.” Various technologies can be used to avoid overvoltage, but it must be done so efficiently so that energy savings resulting from using the correct voltage are not offset by energy wasted within the device used to do so. Reliability is also important, and there are potential problems inherent in running full incoming power through electro-mechanical devices such as servo-controlled variable autotransformers.

Harmonics

Harmonics are current and voltage waveforms at multiples of the fundamental frequency of the 50 Hz (or 60 Hz) main supply. Harmonics are caused by non-linear loads, which include power supplies for computer equipment, variable speed drives, and discharge lighting. “Triplen” harmonics (odd multiples of the third harmonic) result when phase voltages are not balanced in a three phase power system and add in the neutral, causing wasteful currents to flow. The possible effects if the level of harmonics, known as total harmonic distortion becomes too high include damage to sensitive electronic equipment and reduction in the efficiency of the HV transformer . The efficiency of electrical loads can be improved by attenuating harmonics at the supply, or by preventing their generation. Some Voltage optimisation devices are able to mitigate harmonics, helping protect the site from harmful grid-borne harmonics, and/or reducing losses associated with harmonic content on the electrical system.

Transients

Transients are large, very brief and potentially destructive increases in voltage. Their causes include lightning strikes, switching of large electrical loads such as motors, transformers and electrical drives, and by switching between power generation sources to balance supply and demand. Although they typically only last thousandths or millionths of a second, transients can devastate sensitive electronic systems causing data loss, degrading equipment components and shortening equipment life. Some Voltage Optimisation devices are able to protect sites against transients.

Phase voltage imbalance

Most medium to large industrial and commercial sites are supplied with 3-phase electricity, which is transmitted from the national grid in 120º phase intervals. Imbalance between the three phases causes problems somewhat similar to those of harmonics, for example heating in motors and existing wiring leading to wasteful energy consumption . Some voltage optimisation devices are able to improve balance on the building's electrical supply, reducing losses and improving the longevity of three phase induction motors.

Power Dips

Power dips are reductions in voltage, mostly of short duration (<300 ms) but sometimes longer. They may cause a number of problems with equipment, for example contactors and relays may drop out causing machinery to stop. There are a number of low voltage ride through techniques including Uninterruptile Power Supplies, the use of capacitors on low voltage DC control circuits, the use of capacitors on the DC bus of Variable Speed Drives. Care must be taken that Voltage Optimisation measures do not reduce the voltage to an extent that equipment is more vulnerable to power dips.

Power factor and reactive power

The power factor of an electrical supply is the ratio of the real power to the apparent power of the supply. It is the useful power used by the site divided by the total power that is drawn. The latter includes power that is unusable, so a power factor of 1 is desirable. A low power factor would mean that the electricity supplier would effectively supply more energy than the consumer’s bill would indicate, and suppliers are allowed to charge for low power factors. Reactive power is the name given to unusable power. It does no work in the electrical system, but is used to charge capacitors or produce a magnetic field around the field of an inductor. Reactive power needs to be generated and distributed through a circuit to provide sufficient real power to enable processes to run. Reactive power increases significantly with increasing voltage as the reactance of equipment increases. Correcting this with voltage optimisation will therefore lead to a reduction in reactive power and improvement in power factor.

Effects on electrical loads

A common misconception as far as Voltage Optimisation is concerned is to assume that a reduction in voltage will result in an increase in current and therefore constant power. Whilst this is true for certain fixed-power loads, most sites have a diversity of loads that will benefit to a greater or lesser extent with energy savings aggregating across a site as a whole. The benefit to typical equipment at three phase sites is discussed below.

Three Phase AC Motors

Three phase AC induction motors are probably the most common type of three phase load and are used in a variety of equipment including refrigeration, pumps, air conditioning, conveyor drives as well as their more obvious applications. The de-rating effects of overvoltage and three phase imbalance on AC motors are well known . Excessive overvoltage results in saturation of the iron core, wasting energy through eddy currents and increased hysteresis losses. Drawing excessive current results in excess heat output due to copper losses. The additional stress of overvoltage on motors will decrease motor lifetime . Avoiding overvoltage high enough to cause saturation does not reduce efficiency so substantial energy savings can be made through reducing iron and copper losses. However, motors designed for the nominal voltage (e.g. 400V) should be able to cope with normal variation in voltage within the supply limits(+/-10%) without saturation, so this is unlikely to be a significant problem.

Reducing voltage to an induction motor will slightly affect the motor speed as slip will increase, but speed is mainly a function of the supply frequency and the number of poles. Motor efficiency is optimum at reasonable load (typically 75%) and at the designed voltage, and will fall off slightly with small variations either side of this voltage. Larger variations affect efficiency more.

Very lightly loaded motors (<25%) and small motors benefit most from reducing voltage..

Motors driven by Variable Speed Drives will use the same power as before, but may draw more current and, with reduced stored energy in the DC Bus capacitors, may be more vulnerable to power dips.

Lighting

When lighting loads are in use for a high proportion of the time, energy savings on lighting equipment are extremely valuable. When voltage is reduced, incandescent lighting will see a large decrease in power drawn, a large decrease in light output and an increase in lifetime, as the previous extracts from the Electricians Guide illustrate.

However, other types of lighting can also benefit from improved power quality, including systems with resistive or reactive ballasts. Fluorescent & discharge lighting is more efficient than incandescent lighting. Fluorescent lighting with conventional magnetic ballasts will see a reduced power consumption, but also a reduced lumen output from the lamp. Fluorescent lamps on modern electronic ballasts will use approximately the same power and give the same light. To provide the same wattage at the reduced voltage will require a greater current and increase cable losses. However, lighting controllers and ballasts are responsible for generating high levels of harmonic distortion, which can be filtered with some types of voltage optimiser, in addition reducing the need for lighting controllers . A common concern is that some lighting will fail to strike at lower voltages. However, this should not occur since the aim of voltage optimisation is not simply to reduce the voltage as far as possible, but to bring it to the service level voltage at which it was designed to operate most efficiently.

Heating

Heaters will consume less power, but give less heat. Thermostatically controlled space or water heaters will consume less power while running, but will have to run for longer in each hour to produce the required output, resulting in no saving.

Switched mode power supplies

Switched mode power supplies will use the same power as before, but will draw a slightly greater current to achieve this, with slightly increased cable losses, and slight risk of the increased current tripping MCBs.

Energy and emissions savings

The energy savings achieved by Voltage Optimisation are an aggregation of the improved efficiency of all equipment across a site in response to the improvements in the power quality problems outlined above. It has been and continues to be a key technique for savings in energy consumption and consequently carbon dioxide emissions.

Research in Taiwan suggested that, for an industrial supply, for voltage reduction upstream of the transformer, there is a 0.241% decrease of energy consumption when the voltage is decreased by 1%, and an increase of 0.297% when the voltage is increased by 1%. This assumed a mixture of loads including 7% fluorescent lighting, 0.5% incandescent lighting, 12.5% single-phase air conditioners, 5% single phase motors, 22.5% small 3-phase motors, 52.5% large 3-phase motors. It is likely that a modern installation would have less opportunity: almost no incandescent lighting, partly high-frequency fluorescent lighting (no saving), some variable speed drives (no saving), higher motor efficiencies (so less waste to save). A northern European installation would not have the large number of small single phase motors for air conditioning.

The best potential for saving is probably with older lighting (incandescent or fluorescent and discharge lighting with conventional control gear. Therefore older commercial and office premises are likely to have a better saving potential than modern buildings or industrial sites.

Conclusion Currently and largely through the rapid increase in fuel prices, voltage optimisation is enjoying increased interest from energy management and procurement professionals and home owners alike. The promise of savings and low cost voltage optimisation units are offset against installation costs and limitations in the product. Most notable limitations include an inability to make a saving with thermostatically controlled electrical loads, as mentioned above. Thermostatically controlled loads are the larger electrically powered loads that are in use on the grid today. E.g. electric ovens, night storage heaters, kettles, immersion heaters and the like. Voltage optimisation equipment is not able to make a saving with such loads. Emerging in the market, however there are newer more robust and powerful products. Energy regulation, for example, is a technology currently making it's way to market. Energy regulation is able to 'recycle' electricity not used by the main load for use or sale (see FIT technology), as outlined above but in such a way that the voltage across the main load is little affected and therefore, energy regulating technology can make a significant saving with thermostatically controlled loads. Also, energy regulation uses solid state technology so that it does not affect the power factor of the electrical installation it is regulating. Mostly voltage optimisation equipment utilises induction (transformer) technology, which has an effect on the overall powerfactor, to reduce the voltage across the load.

See also

• Carbon Reduction Commitment
• Carbon emissions
• Efficient energy use

References

1. The Energy Efficiency Imperative, Verdantix, Dec 2009
2. "Elexon Unmetered Supplies User Group" (PDF). 14 November 2007.
3. "Measured site voltages in Ireland".
4. ^ Chen, M.S. (1981). Effects of Reduced Voltage on the Operation and Efficiency of Electric Loads. EPRI, Arlington, University of Texas. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
5. Hood, G.K. (26 - 29 September). "The effects of voltage variation on the power consumption and energy cost of a domestic household" (PDF). Paper presented to the Australasian Universities' Power Engineering Conference (AUPEC 2004). School of Science and Engineering, University of Ballarat. Retrieved 13 May 2011. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
6. Hood, G.K. (26 - 29 September). "The effects of voltage variation on the power consumption and energy cost of a domestic household" (PDF). Paper presented to the Australasian Universities' Power Engineering Conference (AUPEC 2004). School of Science and Engineering, University of Ballarat. Retrieved 13 May 2011. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
7. "Proceedings of the 8th International Conference on Harmonics and Power Quality". 14 October 1998. {{cite journal}}: Cite journal requires |journal= (help)
8. IEEE recommended practise for establishing transformer capability when supplying nonsinusoidal load currents ANSI/IEEE Standard C57.110–1986, 1986
9. ^ Faiz, J; Ebrahimpour, H (September 2007). "Precise derating of three phase induction motors with unbalanced voltages". Energy Conversion and Management. 48: 2579–2586. doi:10.1016/j.enconman.2007.03.023.
10. "Thirty-Second IAS Annual Meeting". Industry Applications Conference. 1: 196–200. 5 October 1997.
11. ^ IEEE Transactions on Industry Applications. 1A-8, No. 4. 1972-07. {{cite journal}}: Check date values in: |date= (help); Missing or empty |title= (help)
12. Chen, Chao-Shun; Chan, Shun-Yu (1987). "Effects of Voltage Reduction on Distribution Systems". Electric Power Systems Research. 12.

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