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Stabilising voltages - how and why

If electricity distribution networks functioned ideally, we wouldn't need to use a voltage regulator. Precisely because electricity lines present impedance, and the longer the line the higher the impedance, the voltage at the consumer unit output varies greatly.
There are many possible causes, from the length of the lines and their inadequacy to carry the increasing consumer demand, to the transformers in substations pushed to their limits, and many more.
Many loads, such as the compressors used in refrigerators and air conditioners, large electromagnets, machine tools, submerged pumps, hydraulic control units, etc, absorb high levels of current when turned on, up to 6 times their nominal values, and this translates into a fall in voltage on the supply line and a consequent lowering of the voltage.

The phenomenon often causes malfunction to machines, and particularly electronic controls, that cannot withstand great variations in line voltage. To avoid and prevent these problems a single or three phase voltage stabilizer is inserted in the supply line to workshop or home. Many types of regulator are available on the market, and each type of machine has different characteristics, with advantages and disadvantages. For example, in the 1950s and 1960s, "saturated iron" regulators were used to supply television sets. These were suitable for small power loads, but weighed a lot, had low yields, and, importantly, they introduced a third harmonic distortion in the waveform. The "Iron resonant" voltage regulator, similar to the saturated iron ones,is still produced, with a better output waveform, but a notable weight and size, and a high cost. For these reasons they are not widely sold. With the advent of electronics, and the growing use of personal computers, the electronic voltage stabilizer was created. Small in size, with a high reset speed and a much lower cost, these voltage stabilizers have been widely sold to supply computers. Their most important defects are the limited power achievable in low cost models, their inadequacy to supply devices such as light fittings, since they cause irritating changes in luminosity, their low capacity to sustain current peaks, since the electronic switching elements must carry all the current of the load, their low stabilisation precision, normally ±3%, and, last but not least, the introduction of small waveform distortions. In parallel with the types of voltage regulator mentioned, devices referred to as "electromechanical" have also been built, so called because they use mechanical parts. They are undoubtedly the regulators with the best electrical characteristics built so far – very robust, offering precise regulation, and a size and weight that are not high in relation to their power, easy to make, and, importantly, able to reach considerable powers of the order of several MVA. Their principle of operation is simple:a transformer in Family in the line is used to add or subtract the right voltage so that the output voltage remains constant as the mains voltage changes. This is achieved by piloting the Family transformer with a servo-controlled voltage varistor (Variag) so that it supplies the exact voltage to be added or subtracted to maintain a constant output. In 1999, VARAT s.r.l., which had been making electromechanical regulators since 1983 (see photo), presented a regulator combining all the advantages of both "electromechanical" and "electronic" regulators, and called it "Digistab".

"saturated iron" regulator
made by RA.RO (1957)

Starting from the same principle as the electromechanical regulator, the company developed and patented a machine with a voltage regulation system with static elements that do not work on the line current, but only on the percentage needed to maintain the desired output voltage. A very simple system that eliminates all mechanical moving parts, ensuring high current peaks, high reset speed and almost completely silent operation.
One of advantages of this static voltage stabilizer is that the high reset speed remains constant for both small and high power machines, something electromechanical systems cannot do, since they must slow their rotation speed as the mechanical masses increase.

The power limit is not narrow, as in "electronic" voltage stabilizers, since the line current is not affected by the switching elements, and so powers of the order of several MVA can easily be achieved. The mechanical regulation system used by "electromechanical" regulators, if put under considerable strain, as happens, for example when the supply or load varies a lot, is inevitably short lived. The static system is not affected by wear and tear, and in the presence of continual variations of either the electricity supply or of the load it always works perfectly, and at exactly the same speed, with no strain. VARAT s.r.l., in combining a well established principle with high level electronics, has laid the foundations of a truly innovative evolution in the creation of a new generation of voltage regulators and electronic voltage stabilizers. As shown in figure A, the response times of these machines are high, and almost linear, since the smallest step is of the order of 1%. Electromechanical regulators, erroneously considered to be linear, are in fact stepped, since the voltage varistor has a variation with steps of about 1V, due to its construction. The yield of the static voltage regulator named "Digistab" or "Megadigistab" is very high, unlike electromechanical regulators, where the resistance elements (pick up brushes) increase their losses in proportion to the square of the supplied current (Pp=Rx12), the switching elements increase their losses linearly (Pp=Vtxl). The Family transformers we produce have a very high yield and the quality that distinguishes all VARAT products. The stabilised output is free of distortion, and unaffected by the power factor of the load, and supports overloads of up to 5 times the nominal current (5xln). These devices do not have the defect found in electromechanical regulators, in which the output voltage is too high when the device, which does not operate at low mains voltages, turns on again when the mains voltage is nominal or higher. When the "Digistab" regulator comes on, it presents the same voltage at output as at input, checks the correctness of the output voltage value, and, if it is not within the right parameters, brings it to the exact value in a fraction of a second. The command and control electronics are of simple and essential design, and the control and monitoring of the stabilisation system is managed by a microprocessor, with very high level software that analyses both the state and the cleanliness of the voltage, distinguishing true variations from anomalous peaks. It automatically and constantly monitors the frequency, 50 or 60 Hz, and, as in the testing room cases, if the frequency changes from one to the other, it instantaneously detects the change and adapts its cycle to the new value. EMC filters are fitted in Family on both the input and the output, to protect the device from any disturbances from the supply and the load. The three phase regulators constantly monitor the three phases independently, and therefore must have a neutral input; if a neutral input is not present a stable neutral is generated internally. If the mains neutral is not present, but it is necessary for the loadsupplying single phase loads, an output neutral can be supplied, suitable also for full power. We can confidently assert that these regulators represent the best that the market can offer now, at the start of the third millennium. Their static nature and the quality with which they are built make them extremely reliable and long lasting machines, requiring no maintenance even in difficult environments, quiet for office installations, technically advanced and almost without limit in terms of power and working voltages.

The VSG/3000 Family of regulators, called "Boardstab" are regulators that have been specially designed to be installed on DIN guides inside control boards. When there are problems of mains voltage variation outside the conventional limits, these regulators are the best solution available, small in size and extremely easy to install. The sophisticated technology used means we have been able to create a small, simple and functional device, safe and easy to install, with a very wide regulation range. Regulation is stepped, i.e. the microcontroller that governs the regulator commands switching of 5% if there is a variation in the mains resulting in an output voltage that exceeds or falls short of a pre-set limit. The VSG control system is retroactive, i.e. input voltage rather than the output voltage is read, and this solution means that the status of the output voltage can be constantly verified, as a function of the variations in load and in the mains, rather than just the mains. When powered, the Boardstab presents the same output and input voltages, and, in a fraction of a second it reads the output value and, if not within the percentage set, executes the correct switching to bring it to the pre-set value. This regulator was developed to deal with the problems caused by very low supply voltages, such as difficulty in cutting in counters or in supplying electronic equipment outside the normal percentages.. The 5% variation in output voltage guaranteed by the "Boardstab" is more than enough to assure the correct functioning of any component or piece of equipment.

VARAT Single Phase Electromechanical Regulator

The VSG/3100 Family of regulators, called "Midistab" are economical devices with high reliability, particularly useful in places where the mains voltage varies greatly from the nominal value. The sophisticated technology used means we have been able to create a simple but functional device, with the minimum use of components and the maximum regulation range. Regulation is stepped, i.e. the microcontroller that governs the regulator commands switching of 5% if there is a variation in the mains resulting in an output voltage that is 5% higher or lower than the limit set.

Static Regulator

This switching is performed in an "intelligent" way; for example, if there is a "gap" in the mains, the microcontroller notes it and maintains the current status, acting in a similar way if there is a positive peak that is higher than the peak value. The VSG control system can be defined as semiretroactive, a solution that enables the status of the output voltage to be constantly monitored, and the reset switching occur not only as a function of the deviation of the mains voltage from nominal value, but also as a function of the variations due to the load. When powered, the Ministab presents the same output and input voltages, reads the output value and, if not within the percentage set, executes the correct switching to bring it to the pre-set value.

The electronic voltage stabilizers produced and distributed by Varat offers both high performance and safe reliability, characteristics that can be found in all the company's products. Indeed, three phase and single phase stabilizers are products that have made the company a leader on the market for electrical industry devices. In fact, choosing a Varat electric stabilizer means making the most of the numerous advantages offered in terms of efficiency and cost savings, thus achieving the double goal of increasing plant performance and reducing costs.

VARAT s.r.l.
Via della Tecnica 561/567 - 41058 Vignola (Mo) - Italy - Tel. +39.059.775677 - Fax +39.059.763696 - E-mail:
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