Voltage optimisation
Encyclopedia
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 use a specialised transformer based electronic circuit to automatically regulate the electricity supply locally, and are designed to work 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.
s used to deliver power at a different voltage from the supply.
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 (see Worldwide Mains Voltages). 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. Higher current levels, however, which result from undervoltage, will cause serious damage to a motor as well since resistive heat losses go like I^2*R; this reduces motor life.
However, there are criticisms of voltage optimisation, particularly in a home context. These centre around the issue that variation in voltage does not greatly affect the power used by many domestic appliances. 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, because the same amount of energy is used 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 that 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
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.
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 systems
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.
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.
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.
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.
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.
- of the lighting will drop.
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.
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.
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.
Voltage reduction
In a simple resistive circuit, a reduction in the voltage across the resistance will result in a reduction in the power dissipated by the circuit.-Electric utilities:...
using a transformer, others use a specialised transformer based electronic circuit to automatically regulate the electricity supply locally, and are designed to work 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.
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 transformerTransformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s used to deliver power at a different voltage from the supply.
Voltage optimisation is an effective means of saving energy, particularly in the UK where some people believe there is a national problem of overvoltage
Overvoltage
When the voltage in a circuit or part of it is raised above its upper design limit, this is known as overvoltage. The conditions may be hazardous...
. 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 (see Worldwide Mains Voltages). 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. Higher current levels, however, which result from undervoltage, will cause serious damage to a motor as well since resistive heat losses go like I^2*R; this reduces motor life.
However, there are criticisms of voltage optimisation, particularly in a home context. These centre around the issue that variation in voltage does not greatly affect the power used by many domestic appliances. 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, because the same amount of energy is used 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 that 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
Overvoltage
OvervoltageOvervoltage
When the voltage in a circuit or part of it is raised above its upper design limit, this is known as overvoltage. The conditions may be hazardous...
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
HarmonicsHarmonics (electrical power)
Harmonics are electric voltages and currents that appear on the electric power system as a result of certain kinds of electric loads. Harmonic frequencies in the power grid are a frequent cause of power quality problems.-Causes:...
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
Three-phase
In electrical engineering, three-phase electric power systems have at least three conductors carrying voltage waveforms that are radians offset in time...
power systems
Electric power system
An electric power system is a network of electrical components used to supply, transmit and use electric power. An example of an electric power system is the network that supplies a region's homes and industry with power - for sizable regions, this power system is known as the grid and can be...
and add in the neutral, causing wasteful currents to flow. The possible effects if the level of harmonics, known as total harmonic distortion
Total harmonic distortion
The total harmonic distortion, or THD, of a signal is a measurement of the harmonic distortion present and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency...
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
TransientsTransient (oscillation)
A transient event is a short-lived burst of energy in a system caused by a sudden change of state.The source of the transient energy may be an internal event or a nearby event...
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 dipsPower dips
A power dip is a very short drop in voltage in a system . It is most commonly observed when a high-current device is switched on and lights in the same system will dim momentarily...
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
Low voltage ride through
In electricity supply and generation,low voltage ride through , or fault ride through , is what an electric device, especially wind generator, may be required to be capable of when the voltage in the grid is temporarily reduced due to a fault or load change in the grid. The voltage may be reduced...
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 factorPower factor
The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load over the apparent power in the circuit, and is a dimensionless number between 0 and 1 . Real power is the capacity of the circuit for performing work in a particular time...
of an electrical supply is the ratio of the real power
AC power
Power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow...
to the apparent power
AC power
Power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow...
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
AC power
Power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow...
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. Since the decrease in light output will exceed the decrease in power drawn, the energy efficiency - luminous efficacyLuminous efficacy
Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power. Depending on context, the power can be either the radiant flux of the source's output, or it can be the total electric power consumed by the source.Which sense of the term is...
- of the lighting will drop.
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% 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.
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.