1. Actual situation
The transition to digital era
For little more than a decade, the growth in the use of digital technologies, in order to improve the performances of systems used to carry out the most important technological functions, has produced a proper revolution in every field of human life. By now, the use of computers are available mostly at every place and area, from households to complex industrial activities, for entertainment or to perform specific tasks. Digital computerized systems control and manage all machines commonly used in every day life. Not only, new tools, unknown a couple of years ago, have appeared in our life such as tablet, smartphone, etc. Additionally, some basic concepts like lighting, heating, air-conditioning are being digitalized especially thanks to the coming of LED and heat pumps with inverter system. Later, in the essay we will consider the consequences of this phenomenon in energy field and on the efficient management of it, now we will take into account how the biggest developments of digital technologies generate the presence in our electrical grids of non-linear loads.
In the last few years, above all in Europe, but in the whole world, electricity generation has been changing deeply. Twenty years ago, electricity distribution was centralized mainly due to the exploitation of atomic power which gave the possibility to establish large power stations at the service of a wider and wider end users. But, recently, we have assisted to a revolution in the production of electricity with new policies for the development of new forms of sustainable energy using sun, wind and water power. The purpose of this essay is not to explain the consequences of distributed generation on end users, but, we think, it can be interesting to analyze as a starting point the main differences between the two approaches. For the sake of simplicity, two images below will show the transmission of electricity in the two approaches, in order to assess qualitatively the impact of the change on end users. As it can be seen from the two images above the main difference concerns topology. In particular, in the case of centralized generation the power of electricity is shipped through central distribution systems to the end consumers, while in the distributed generation is different, electricity is produced next to its point of use, in fact there can be exchanges of energy directly from generators to consumers. This phenomenon has a significant impact on the quality of electricity power supplied by generators, because of the absence of intermediate steps, the power of energy supplied by distributed generators is more efficient than that of centralized ones. Recently, there is a talk on Power Quality referring to the quality of transmission power from grid to end users.
Overvoltage or undervoltage
Overvoltage is a phenomenon for which voltage in a circuit is raised above its designed limit. It can be temporary or steady. In the first case the overvoltage is carried out within few seconds or few cycles with peak amplitude of few Volts to hundreds of Volts, it is often caused by the switching of inductive loads or transformers under load, etc. Overvoltage can disturb electrical installations and causes energy inefficiencies, but the real problem linked to this phenomenon is the possibility to injury devices connected to plants. In the second case, the phenomenon can be considered steady when the voltage is constantly over the rated voltage which in Italy is of 230 Volts for single-phase installations in low voltage, and of 400 Volts for three-phase installations with low voltage. Also in this case the phenomenon could injury devices directly connected to plants, even if it can also depends of the design of the equipment itself, usually designed to have a tolerance of +- 10%. But, the problem can be in terms of energy efficiency. In particular for most linear loads connected to electrical grids an increase of the voltage cause a decrease of useful life of device, and the increase of the use of energy with low performances. At the same time, undervoltage in a steady state can cause problems during the distribution requiring higher functioning current.
The transmission of power on electrical grid should occur through a sine wave at a frequency of 50 Hz (in Italy) with a rated voltage of 230V. Moreover, this wave passing on linear loads should generate sinusoidal current with a frequency of 50 Hz and with an amplitude depending on the Ohmic part of the impedance and on a phase shift of an imaginary voltage wave of the impedance itself. We have used the word “should” for both the voltage input and current output because the probability that are both sinusoidal waves is low. From a mathematical point of view, this wave represents periodic oscillations and therefore can be developed in Fourier series, defined as the sum of infinite sinusoidal waves with frequency, amplitude and phase different among them. Technically every single component of the series is defined as harmonic, in particular, even the sinusoidal at a fundamental frequency is an harmonic. In any electric circuit powered by a sine wave on linear loads, the current output wave will have only one component at the input frequency and will not have any harmonic different component from the fundamental one. While in the case in which at least one of the load is not linear, it will be possible to obtain current harmonics at a frequency different from the fundamental one. Taking apart for the moment the phenomenon of interharmonics, for electrical loads the current output components are that with multiple frequencies from the fundamental, so harmonics that are produced can be sorted numerically referring to the multiple of the frequency of interest, that is, for example for a fundamental frequency of 50 Hz the second harmonic is at 100 Hz. In addition, to most of non-linear loads connected to electricity power networks (eg. Switching power supplies) harmonics with a greater amplitude have an odd order: the third, fifth, seventh, etc. Furthermore, in real cases, the harmonics have an amplitude greater in lower ordinal numbers and are decreasing, in general the third harmonic has an amplitude higher than the fifth, the fifth than the seventh and so on. It is obvious that should be analyze every single case because different no-linear loads connected to the grid can generate a different harmonic distortion and for this reason even the sum could be different. Referring to the current output wave, the harmonic distortion can be defined as follow:
lt is the whole current
lf is the current of fundamental frequency
It is the same for the voltage wave:
And more in detail for the transmitted power:
The index gives information about the total amount of distortion in the waves. The more the value is greater than 0 the more the form of wave moves away from the hypothetical case. The presence of harmonic distortions cause energetic problems in the electrical grid. It is possible to demonstrate that current distortion cause effects on the form of voltage wave which supplies loads, and for this reason cause consequences on linear loads connected to plants as well as it cause losses in the system resulting from the dissipation of power on line impedance and on internal impedance of the generator. In general, a linear load has an almost infinite bandwidth, for example an incandescent light bulb transforms into heat energy all the electrical power of an infinite bandwidth, this means that supplying the light bulb at a 5 V with a frequency of 400 Hz the filament in it will heat and for the Joule effect it will generate heat. But the problem is that it will not be generated light emissions detectable to human eye, or rather it will generate a minimum quantity of light emissions detectable, for eg. Ultraviolet or infrared, this occurs because the filament is conceived to work at defined frequency. This has three important implications: The use of equipment outside nominal parameters can lead to a premature rupture of it. The produced light energy has an unwanted component, so the extra energy is just a noise. Radiations not detectable to humans could be harmful. If we consider other kind of loads such as electric motors, pumps or whenever else, consequences could be even worse. Distortions transfer power to loads which use it both for the work they are conceived to and to generate inefficiencies which increase the possibility of breakage of the loads themselves. In addition to economic damage resulting from the increased use of energy, there is a reduction of the useful life of equipment.
2. Answer of loads
In this section, with the help of some simulations, will be analyzed how the loads face the noises listed above. For simplicity’s sake it has been used a domestic type circuit with a contractual power of 3k W, which can be presented as follow: For simulations a lumped parameter model will be used.
Rg is the internal resistance of the generator.
RLinea is the capacitive and inductive effects of impedance itself will be ignored. The resistance value is set at 3 Ohms which suits with 350 meters cable of 2 sqmm resistance of the line of electrical grid;
Z Load is the impedance of load, as the equivalent impedance of generator;
The circuit can be divided in two parts one refers to input and the other refers to loads. In order to evaluate energy balance will be considered a number of factors, in particular: the real power supplied by generator and the real power absorbed by load, in such a way to assess the efficiency of the power during transmission in different situations.
Stationary overvoltage on linear load
Considering as a first example a pure Ohmic load and its effects when is supplied by a voltage higher than the optimal one on the system. The optimal voltage assumed is of 220 V:
Real power supplied by the generator: 1785W
Real power drown by the load: 1322W
Real power supplied by the generator: 2124W
Real power drown by the load: 1573W
In conclusion, for the case analyzed, with an optimal source the total power used by generator is about 16% lower. Consequently, even the power supplied to the load is lower than about 16% because of the linearity of the circuit, but as we have assessed dealing about the effects of high voltage on loads, it does not always produce an increase of load efficiency. For example, if a load is represented by one or more incandescent bulbs connected in parallel, surely, supplying them with an higher voltage at a fundamental frequency there will be a greater light energy in the visible band and also in the other source bands of equipment, so the overall light power detectable by human eye will not rise the 16% but a lower percentage. Moreover, the life span of the equipment would be shortened of more than 16%. Some case studies of Omran on incandescent light bulbs have demonstrated that in comparison with the nominal operating voltage the useful life of a light bulbs is reduced when it is supplied at a power of 240 V. Another factor to consider is the loss of Ohmic energy through the electrical grid. In the case of optimal input there is a loss of (1785- 1322) W= 463W, while in the case of an input with a higher voltage there is (2124-1173)W= 551 W, so, from a relative point of view the percentage loss is the same, but considering it in absolute value the loss of power is higher in the case of input with higher voltage, because there is 100 W in more dissipation on electrical grid, that is more energy recorded at counter, more heating and inefficiencies of electrical cables.
Low power factor
Let’s consider now the presence of an Ohmic- inductive load in the circuit:
Power supplied by generator: 632 W
Power drown by load: 561 W
In parallel we introduce a capacitive impedance to load in order to obtain from the same circuit an equivalent Ohmic impedance:
Power supplied by generator: 758 W
Power drown by load: 573 W
For the present case study, two important reflections can be made:
A generator with an ohmic inductive load produces power 18% higher than an ohmic equivalent one.
The real power used on load is about of 3% higher.
So, considering the first statement: the improvement of the power factor reduces the total power used, therefore, in this case study, the energetic balance is positive and even the load has benefits because the power that it uses is lightly higher than the previous case study. Of course, this is possible with an input voltage of 220 V, for higher voltage the problem is more complex. The inclusion of inductive loads produces a phase shift and a loss of voltage on the loads themselves due to the effect of line impedance. Naturally, by performing correction on the system, the situation improves from the point of view of energy, but it also turn back to the above condition of overvoltage steady load, therefore the dissipation on the load has to be reformulated in order to make it work in its optimum operating conditions, this last factor produces greater energetic savings and therefore is a desirable element, but it will be discussed below.
Now let’s consider the presence of linear and not linear
mixed loads in the circuit:
Power supplied by the generator: 654 W
Power absorbed by the load: 592 W
Power supplied by the generator: 656 W
Power absorbed by the load: 586 W
About the case under review, we can notice 3 observations:
The power supplied by the generator in the case of a no linear circuit, with reference to the case of its ohmic equivalent is greater than the 0,4% approximately.
The power overall transmitted to the load is about upper of the 1%.
The power transmitted to the load at the frequency of Hz is fall short of 3,5%, this power’s percent has transmitted out of band.
In this case, the no linear load generates a circulation of a flux with another harmonic content out of band, this flux doesn’t generate problems to others loads because flows only between the generator and the involved load. The problem is that the variation of power on the impedance of line has a high harmonic content and then the total supply power of the loads is suffer from harmonic distortion, which depends on, as said, the power of the ohmic loads and transformed in heat, probably without profit from the point of view of the efficiency, rather with detriment sometimes considerable about the duration of the system. Therefore we can say that, although in the first instance from a point of view of the energy balance it would seem that there are not considerable variations (1%), from the point of view of the loads’efficiency there are considerable variations (3- 4%),so, the absorbed total power is virtually fall short of about 5% if consider the useful power to the work (that supplied at 50 Hz).
The present technologies
The optimization of voltage
The optimization of voltage is a technique of energy saving that has adopted installing in series to the transmission line a transformer in order to reduce or increase the voltage available to the load. The optimization can occur in static or dynamic way according as the voltage has reduced in fixed way by some percentage or has changed in dynamic way during the normal function of the circuit. Generally you have a energy saving, as we have appreciated in the previous simulation, before mostly ohmic loads with problems of static overvoltage, or anyway linear, in the case of particular no linear loads (for example the switching feeders) the drop of voltage can completely lead increases of consumption, indeed, that loads works with regular power, that is they always absorb the same amount of power even against variations of voltage, therefore a variation of voltage in decline induces to an increase of current in the node, and then in the line, that current, obviously increases the loss on the cable of transmission.
Power factor correction
It defines power factor correction any taken steps to increase (or how usually it says to improve) the power factor (cos φ) of a specific load, in order to reduce at identical active power absorbed, the value of the current flowing through the plant. The purpose of the power factor variation is especially to reduce the electricity loss and decrease the apparent power’s absorption proportionally to the machinery and the existing lines in an industrial area. The power factor variation of the installations has taken importance because the electricity authority has enforced contractual clauses through the CIP’s pricing measures (n 12/1984 e n 26/1989) which bind the user to vary the power factor their own plant, punishment the payment of a penalty. In the circuits with a particular electric appliance such as filament lamps, the water heater, some kinds of furnace, the apparent absorbed power is all active power. In the circuits with electric appliance which have within them winding such as the motors, welding machine, stoker of the fluorescent lamp, transformers, a piece of apparent absorbed power has applied to excite the magnetic circuits and it is not used as active power but a power generally known as reactive power. From the perspective of the global energy balance the power factor variation reduces the quantity of reactive energy absorbed by the circuit, but not reduce straight the used active energy, or better the lowering of active energy is generally a consequence of the fact that lower the loss on the conductive because the series impedance of the same conductive is crossed by a lower overall power, actually not the whole active energy is saved, because the lesser dissipation on the conductive lead to a lower voltage drop on the load, and in the case of ohmic loads this means most dissipation of energy. It is clear that in this case that excess of energy is positive to the load, unless we are in the case of stationary overvoltage.The power factor variation of the loads could be centralized, placed or mixed. In the first case has varied the power factor the whole plant upstream of the load and downstream of the generator, therefore at the way out of the generator the alternating-current power factor improves but does not mean that there is an improvement in any square of the load. In the second case, the loads are singularly varied the power factor, and the effect is an improvement of the alternating-current power factor at the downstream of the generator, in the third case, there is a mixed solution between the first two.Ordinarily the power factor variation of the loads occurs putting at the same time to the same loads a generator with a reactive power push-pull in regard to the reactive power of the loads, in a way to destroy the reactive outgoing power. The simplest generator of the reactive power in the sinusoidal loads is the condenser, then are included one or more condensers in parallel to the loads with the aim of achieving an improvement of the alternating-current power factor. However there are other technique for example the static trimmers or active circuits.
The filtration of the harmonics in the systems of power, normally occurs putting in electronics in the circuits qualified to reduce the total harmonic distortion generally in current, with the aim of improve the effects of the distortion on the voltage. There are 2 primary categories of filters suitable to this purpose:
In the first case there in another difference between harmonised filters and inductive filters. The harmonised filters are peculiar rlc filters harmonized on a specific frequency and usually electrical grounded, in some cases can also be used plus band or plus high filters to create for the troubles at that frequencies a way with a lower impedance toward a mass to delete the trouble to the origin. However in the case of the inductances of line the principle is that of LR lowplus filters, indeed the inductance of line forms with the ohmico circuit downstream a lowplus filter that will not let power to the far frequencies from the 50 Hz. This kind of solutions, obviously improve the situation to the load placating the factor of the total harmonic distortion, but from the perspective of the energy balance the situation is the same, so the troubles are convoyed electrically grounded, after the crossing of the counter and then the energy that has departed electrically grounded is however recorded (even if the dissolute part on the load is anyway saved). The active filters are from the perspective of the generators’load at the same time pump an equal and opposite current to that distorted load out of band and so they delete the harmonic current generated by the same load. They work toward the modulation of the voltage line, do an analysis of the net’s situation, and pump the compensation currents, obviously to pump in a right way this current need of an extremely high switching frequency to more than double of the highest harmonic of compensation, consequently they need of inner electronics especially in working order and quick, usually it has used the IGBT to work at the wished switching frequency. Naturally, this makes that electronics more expensive. Also from the perspective of the energetic balance, the situation is the same to the passive filters, because according to the filters’efficiency for the compensation of the trouble an equivalent quantity of power has absorbed. The interesting thing is that the active filters could improve also the alternating-current power function of the system because they work as a generator of reactive power. Another very interesting aspect is that the deliveries filters also different from each other could be introduced in parallel and do not cause trouble to the circuit or resonance risks.
The EMI’s filter is a passive filter that is present in the most area of the electronic equipment, to allow that electronics to react at the rules of electromagnetic compatibility, especially to that concerning to the managed releases. In essence, the EMI’s filter is a lowplus filter that it connected as last stage between the equipment and the alimentation’s net, so as mitigate the trouble’s component that any electronics tend to release. Obviously, the filter must be transparent to the alimentation frequency (50-60 Hz) to allow the right working of the electronics, while must work in the range of frequencies established by the normative (150kHz-30MHz).
There are a series of electronics on offer that allow profiling the users’consumptions, or better to understand how the users make use the electric power during a given period of interest. Naturally, that system does not produce an improvement on the use of the power from the user, but they have 2 important implications that allow optimizing the consumptions:
The awareness of the consumptions to the users can cause a most attention and a saving.
The implementation of a competent system that analyse the data in question and rework them can cause to a most efficiency management of the power and to a substantial saving , without changing the consumption’s habits.
The mIO – minimum Impedance Optimizer born to answer to an increasing necessity to optimize the transfer of power between any kind of electric generator and a net’s loads connected with it. In this area on interest, to optimize we mean a series of measures to improve the incoming power quality to the installation and balance out the negative effects caused by the insertion of the loads, as we have appreciated from the previous analyzed simulations. Adaption’s system of the independent electric circuits to the impedance of the generator, for the improvement of the efficiency of the equipment, the safety of the systems and the eco-save. The product envisages the basic variation named mIO edition 2.1, the TG variation that involves the features of telemanagement of the system, as before specified and the TL variation that involves the features of telereading as before specified. The system should be link to the equipment, both domestic and business, downline of the meter and in input to the primary distribution line. Once connected with the circuit is able to calculate the impedance seen by the meter towards the circuit and optimize this impedance in order to improve the transfer of power between the meter and the system, reducing power dissipation from the system for the factors not linked to the use of the same systems. Moreover, the system works as optimizer of the Power Quality concerning to the line in input. The Power Quality is the peculiarity of the electricity grid to move the power in functional way to the consumption and as much as possible deleting the squandering.
The tele-managed system involves all the basic features with the possibility to manage from remote all the installed devices. The tele-management of the systems is more important to the improvement of the operation’s parameters of the system, because there is the possibility to set up from remote each system depending on the situation of standard operation of the efficiently period. Moreover through the tele-management is possible to have in any moment from office profile the overall picture of the functional situation of the systems and eventually and attending from own office is possible bypassing each system disconnecting the same system from the equipment at that is was linked. There is the possibility in case of anomaly on the system to have a notification about the kind of anomaly that happened and eventually on which component was on it.
Naturally, the product has sold with a net of inner sensors that confirms the operation of every single inner component, in order to control all the parameters of operation of the system, and is also allowed to understand very quickly if there are anomalies or some malfunctioning in the system and specify to assistance service the problem observed and the possible solutions to apply for solving promptly the problem.
The tele-managed’s product from the architectonic point of view is made up by a central and dedicated server that provided for communicate with all system for having the clear situation and the parameters of operations of all the connected devices. Also from the company is expected the possibility to access to a software and confirm in each moment the condition of any systems, is possible, towards the same software change the configuration of any system and eventually disconnect it from the equipment, all of this in an easy and fast way. Moreover is expected the possibility to procure a dedicated software to other users that take up the assistance on the small areas, in way to give them a possibility to manage all the system in their own areas. Obviously both the company that do assistance receive notification about possible malfunctioning of the systems, and eventually the assistant’s tickets to manage.
The tele-readed product involves all the features of the tele-managed product, with the possibility to have available all the element concerning to the user’s consumptions, all of this on the one platform, easy and operational. The features of the tele-reading are accessible to the company, and can at company’s discretion be make available for each users, owner of the system. The users can easily enter to their own usage profiles towards web on the company’s website and towards smartphone and tablet, with one easy and intuitive interface. The great innovation is that thanks to the system is possible manage not only the electricity consumption but also of water and gas, and even is possible manage the data of production of possible equipment a renewable sources that are in the property, for example photovoltaic system, mini aeolian, solar thermic and other.
Data of project and simulations
Let’s see now how the system interacts with the electrical system, simulating a real situation, where are present events of stationary overvoltage, state of being out of phase and existence of not linear loads:
Power supplied by the generator: 1094 W
Power absorbed by the load: 738 W
Power supplied by the generator: 843 W
Power absorbed by the load: 756 W