In reality, very often the devices have to face more problematic conditions such as:
— Not sinusoidal supply voltage due to harmonics in the mains caused by non-linear loads (inverters, drives, welders, discharge lamps, etc.).
— Supply voltage ﬂuctuating in relation to the nominal value. Said variations can be “fast” and waste themselves away in a few milliseconds (for example, distribution lines hit by lightning) or “slow,” with duration that can last several seconds, minutes or
even hours depending on the cause.
Slow ﬂuctuations can increase the voltage level (“surges” generated, for example, by poor MV regulation at distribution, disconnection of large loads, overvoltage at generators output) or — more frequently — decrease the nominal voltage (“sags” generated, for example, by connection of large loads, motor startup, undersized distribution lines, faults to ground, poor MV voltage regulation).
Although specific means for each of the issues listed above are available, the voltage stabiliser is the solution with the best cost/beneﬁt ratio.
The availability of high-quality voltage supply independently from input fluctuation is very often a key feature to ensure efﬁciency and reliability for the User.
Reduced productivity, data loss, security failure, machine faults, inaccurate information and domestic inconveniences are only a few examples of potential problems caused by unsteady supply. Obviously, all that results in higher managing costs.
The voltage stabiliser has proven to be an effective solution able to prevent potentially dangerous situations created by input voltage instability.
A list of possible fields and applications where devices sensitive to voltage variations can be used is given below:
— Public Sector:
Telecommunication/telephoning, hospitals, public ofﬁces, radar installations, military industry.
— Food & Beverage:
Bottling, packaging, food processing industry, intensive breeding.
— Private Sector:
Banks, factories, laboratories, small businesses, fun parks and fairs.
— lndustrial Sector:
Laser cutting, water shearing, electronic drives, tobacco industry, machinery in general.
In all these applications, voltage fluctuation, even though within the tolerance admitted by the Standards, can generate operating issues. In that case, devices particularly sensitive can show errors or malfunctions beyond the acceptable limit.
Typical situations where voltage can be subject to fluctuation beyond the admitted threshold even in standard equipment, are:
— Loads supplied by weak or undersized distributing lines. This happens in rural area or where the distributing line is long (breeding farms, tourist FQSOITS, hotels).
— Private houses with high power installations (swimming pool pumps, big chillers, special lighting systems) and/or particularly sensitive (high power consumer
— Loads located near large industrial plants where individual high power devices (MV motors) can induce voltage reduction at startup.
— Island operating loads (ships, offshore rigs, loads not connected to the mains).
In all the above mentioned examples, the choice of a voltage stabiliser instead of an Uninterruptible Power Supply (UPS) system is the optimum solution:
— Considerably lower cost at the same power.
— High output voltage stability guaranteed even tor input ﬂuctuation not manageable by a UPS.
— Given the same performance, absence of introduced harmonic distortion.
— More robust and reliable construction, allowing tor use in hard environments.
— Overload capability up to twice the rated current (max 2 mins).
— No concerns in terms of storage, transportation, maintenance and disposal due to the tact that batteries are not used.
— Smooth and reliable regulation of the load voltage ensuring a ±0.5% accuracy even with important input voltage variation.
— High efﬁciency.
— High inrush current withstand ability.
A voltage stabiliser is a power device destined to be positioned between the mains and the User. The purpose is to ensure that the User is fed a voltage subject to a variation much lower (±O.5% with regards to the nominal value) that the one guaranteed by the distributing system.
The stabilization is performed on the “true ms” voltage and it is not affected by harmonics in the mains.
Due to the fact that the regulation does not involve any sine wave slicing (which is what happens in power electronic converters such as inverters and UPSs), neither an appreciable harmonic distortion nor a phase displacement is introduced on the downstream line.
The stabiliser is not affected by the load power factor (cos θ) and can operate with a load percentage varying between 0% and 100% on each phase.
Regulation speed depends on the input voltage variation percentage and the type of construction. Indicatively, said speed ranges between 8 and 30 millisec/V.
Basically, a voltage stabiliser is made of a buck/boost transformer, a voltage regulator, and an electronic control. Based on a microprocessor that samples at high frequency the output voltage, the control system
drives the regulator gearmotor.
By doing so, the regulator rollers change their position and therefore the voltage drawn and supplied to the buck/boost transformer primary winding. Being the secondary voltage of the buck/boost transformer in phase or in opposition to the supply, the voltage drawn from the regulator is added or subtracted to the mains voltage, thus compensating its variations.
The voltage regulator is nothing but an autotransformer with continuously variable transformer ratio. Depending on the stabiliser power, the regulator can be either toroidal or columnar.
The stabilisers are designed and built in compliance with the European Directives concerning CE marking 2006/95/EEO (Low Voltage Directive) and 2004/EEO (Electromagnetic Compatibility Directive).
Standard units are housed in an IP21 metallic enclosure RAL?085 painted. Cooling is guaranteed by natural air circulation aided by extracting tans over a certain temperature.