Background
Voltage optimisation is an electrical energy saving technique which is mainly installed in series with the mains electricity supply to provide a reduced supply voltage for the site's equipment. Typically, voltage optimisation can improve power quality by balancing phase voltages and filtering harmonics and transients from the supply, although not always. Voltage optimisers are essentiallyUnited Kingdom
The declared low voltage electricity supply in the United Kingdom as per the Electrical Safety, Quality and Continuity Regulations 2002, is now 230 V with a tolerance of +10% to -6%. This means that supply voltage can theoretically be anywhere between 216 V and 253 V depending on local conditions. However, the average voltage supplied from the national grid (in mainland UK) is 242 V, compared to the typical European voltage of 218-222 V. (The average supply voltage in Northern Ireland is around 239 V, and 235 V in the Republic of Ireland.) Older electrical equipment manufactured for the UK was rated at 240 V, and older equipment manufactured for Continental Europe was rated at 220 V (see Worldwide Mains Voltages). New equipment should be designed for 230 V. 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 230 V +/-10%. Equipment rated at 220 V should operate satisfactorily down to 200 V. 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. A reduction in voltage does not affect the energy used by the domestic appliances which use resistive loads except in devices such as kettles and toasters which will take longer to do their job due to atmospheric losses. The main commercial benefit when installing VO units, is on inductive loads, like motors which run pumps, fans and the like. In the home, the potential energy saving can be up to 12% on electricity bills. A VO device will lower the voltage to the most efficient level to maximise the savings on electricity consumption, so you may notice certain things taking a little longer, such as a kettle may take a little longer to boil. It is a common misconception that fridges and freezers do not provide savings through voltage optimisation because they are fitted with a thermostat. Fridges and freezers operate completely differently from resistive heating devices. If a resistive heating device is driven from a higher voltage the result is heat which is helpful in its intended purpose (heating). If a fridge or freezer is driven from a higher voltage the result is also heat however this is not helpful in its intended purpose (cooling). The compressor motor power output is reduced slightly by voltage optimisation so the fridge/freezer thermostat will keep the motor on a little longer however overall the effect is for the motor to run slightly longer at much lower losses. Tests at Manchester university showed a 10 °C reduction in motor temperature under voltage optimisation due to the reduced losses in the motor.Common power quality problems
Overvoltage
Harmonics
Transients
Phase voltage imbalance
Industrial and commercial sites are supplied with 3-phase electricity. Imbalance between the phases causes problems such as 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 Uninterruptible 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 theEffects 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 motors
Three phase 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. 400 V) 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. For the case of motors driven by Variable Speed Drives, when the input voltage is reduced, there will be a proportionate reduction of the output voltage from the VSD and the motor will draw less current and eventually consume less power. However, if the motor is running on high load (>80%), the reduction in voltage will result in reduced torque and motor will end up drawing more current and power.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. Since the decrease in light output will exceed the decrease in power drawn, the energy efficiency -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 savings
The energy savings achieved by Voltage Optimization 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 possible technique for savings in energy consumption in certain circumstances. 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% three phase air conditioners, 5% 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. Energy saving is possible with older lighting, at the expense of lower light output, (e.g. incandescent or fluorescent and discharge lighting with inefficient ballast or control gear). Therefore, older commercial and office premises may save more than modern buildings or industrial sites. However modern lighting systems (typically LED) will save significantly more energy due to higher efficiency than energy saved on older lighting systems following installation of a voltage optimiser. Obtaining energy savings with a voltage optimiser used with modern lighting systems is very questionable. Modern electronic switching controllers for LED or fluorescent lighting systems are designed to run the lights at optimal light output and longevity with high efficiency. Variations in supply voltage will therefore not make any difference to the overall energy use of these types of lights. However, there exist types of low cost LED and fluorescent lamp controllers which reduce the voltage by shedding energy as heat (e.g. multiple LEDs in series with a series resistance). Varying the supply voltage would affect the energy used by these types of lights, but these type of lamps are generally low power and the light output would also be affected.Worked example
A typical 100 watt incandescent lamp has an efficiency of no more than 17.5 lumens per watt (l/W) and will therefore produce 1750 lumens at its rated voltage. A typical modern LED lamp has an efficiency of about 150 lumens per watt, and therefore requires no more than 12 watts for the same light output. According to Lamp rerating formulae, reducing the voltage across an incandescent lamp by 10% reduces the power (and therefore energy) by about 16% and reduces the light output by about 31%. Therefore, a voltage optimiser that reduces the voltage on an incandescent lamp by 10%, will reduce the energy by 16% and light output by 31%, producing only 1210 lumens and consuming 84 watts. Changing the incandescent lamp to an LED lamp with similar light output would have reduce the consumption more effectively, down to 12 watts. Furthermore, since the light output is reduced by so much, higher savings could be made by changing to a 75 watt incandescent lamp without a voltage optimiser (1312.5 lumens assuming 17.5 L/W). The LED lamp could also be reduced in size to 8W, if only 1210 lumens is required.See also
* Energy conservation * Efficient energy use *References
{{DEFAULTSORT:Voltage optimisation Electrical power control Energy conservation Low-energy building