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Voltage variations issue

Electrical equipment is designed to function in power supply systems characterised by rated voltage values (e.g. 400V) and frequency values (e.g. 50Hz).

In reality, the distribution of electricity can be such that it does not ensure the stability of these parameters. In particular, the supply voltage may undergo variations, even significant ones, compared to the rated value that may cause undesired situations that are potentially very damaging for users.

These voltage variations may be “fast” and end in just a few milliseconds (for example, as a result of lightning hitting the lines) or “slow”, lasting several seconds, minutes, or even hours, depending on the cause. The “slow” variations may be caused both by rises (poor MV regulation by the power distributor, detachment of large loads from the mains, output overvoltage from generators, etc.) and, more frequently, by drops (connection of large loads, starting up of motors, undersized power lines, ground faults, poor regulation of MT voltage).

The stabilizer is the solution that ensures the best cost/benefit ratio for voltage variations. The continuous availability of stably supplied voltage, independent of input fluctuations, is the key for ensuring efficiency and reliability for the final user.

Reduced productivity, data loss, security loss, equipment failures, inaccurate information and domestic disturbances are just some examples of potential issues caused by unstable supply. All this translates into an increase in management costs for the user.

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The solution: voltage stabiliser

The voltage stabiliser is an effective solution for preventing potentially damaging situations caused by input voltage instability.

Typical plant situations where the voltage can undergo fluctuations beyond the allowed values include:

  • users powered by “weak” or undersized power lines, as happens in rural areas or those very distant from distribution centres (farms, tourist resorts, hotels)
  • users situated near distribution centres and, thus, subject to voltage rises
  • private residences equipped with high-power equipment (pool pumps, large air conditioners, special lighting fixtures, lifts) or specifically sensitive to voltage variations
  • users situated near large industrial plants, sources of voltage drops
  • users that operate in isolation (ships, offshore platforms, users not connected to the mains)

Compared with other types of equipment, the voltage stabiliser has a series of advantages that often make it the optimal solution. The cost is generally lower and provides the following benefits:

The voltage stabilizer operates without the aid of batteries and, therefore, does not have storage, transport, maintenance, and disposal issues. The gradual and reliable regulation of the supply voltage to loads ensures, at output, a precision of ±0.5% of the rated voltage, including when faced with significant variations in the input voltage.

The voltage stabilizers are simple to use, have a very high yield, are small in size, and have a reduced sensitivity to inrush currents.


Number of phases

The number of phases of a stabiliser depends on the nature of the loads:

Rated voltage

Since, internationally, rated voltages vary, it is important to measure the input and output rated voltages of the stabilizer. In three-phase systems, provide the concatenated value of the voltages. The standard three-phase models can operate with a rated voltage of 380V-400V-415V (50Hz) or 440V-460V-480V (60Hz).

Input variation amplitude

This is a key piece of data for choosing and sizing the stabilizer. The amount of input voltage oscillation needs to be identified, keeping a safety margin on this percentage. If, for example, voltage variations of ±16% on the rated voltage are measured, a stabilizer sized for ±20% variations should be chosen. Attention to the following rule: if the input variation exceeds the pre-established one, the difference in excess is added to the output precision. For example, if a stabilizer sized for ±15% receives a variation of +20%, the precision of the output voltage will no longer be ±0.5% but ±5.5%.

Type of adjustment

The standard three-phase voltage stabilisers are produced with independent phase control. The stabilizer must be connected to the neutral of the power line. In the absence of a line neutral, it is possible, upon request, to equip the machine with a special accessory.


In the majority of applications, the electro-mechanical voltage stabiliser is a reliable and safe tool. If high intervention speed is requested (in the order of milliseconds), it is better to choose the solution with adjustment via IGBT static circuit breakers.

Rated power

All the stabilisers are sized for the maximum input current. We advise, in any case, to keep a safety margin for any future increases. The power of the stabiliser is expressed in kVA, while the power of the load is normally expressed in kW.

Please take into account that the link between these two measurement units is provided by the power factor (cosφ): kVA = kW / cos φ.

If the power factor and/or the kW power are not easy to determine, measure the absorbed currents and, taking into account the following formulas, correctly size the stabiliser.


The additional features of the stabiliser can be defined based on the type of installation.
In particular, the following factors need to be taken into account:

  • required IP protection rating
  • internal or external installation site
  • site’s altitude and climate characteristics
  • ambient temperature
  • presence of hazardous environmental situations: corrosive atmosphere, exposure to chemical substances, etc.


It is possible to enhance the stabiliser with different types of accessories:

  • interruption and protection devices
  • over/undervoltage load protection
  • bypass line
  • total protection kit
  • input isolating transformer
  • automatic, integrated power factor correction system
  • SPD overvoltage dischargers
  • anti-disturbance EMI/RFI filters
  • neutral point reactance
  • protection rating available up to IP54/55 indoor/outdoor
  • Ortea Cloud
  • Ortea Monitored Rollers

Special production

Thanks to solution customisation, through suitable variants, it is possible to obtain “special” stabilisers capable of:

  • managing asymmetrical variations of the input voltage that differ from the standard range (for example, from Vn -55% a Vn +20%)
  • provide, at output, a different voltage to the input one (for example, Vin = 400V ±15%, Vout = 460V ±0.5%)