AC Voltage Stabilizer Buying Guide

In power lines, voltage fluctuations are a very common and high phenomenon. Voltage fluctuations can damage household appliances and may even cause permanent damage. A voltage stabilizer solves this problem. It controls voltage fluctuations entering your appliances, saving them from serious damage. Purchasing the right voltage stabilizer for your application is critical and we hope our guide will help you. Here are a few things you should know when you’re buying a voltage stabilizer:

Number of phases

The number of phases of a stabilizer depends on the type of load:

  • Single-phase load: Single-phase stabilizer;
  • Combination of several single-phase loads on the same line: Three-phase stabilizer or a single-phase stabilizer on each load;
  • Three-phase load: Three-phase stabilizer.

Rated voltage

Due to the fact that the nominal voltage varies internationally, establish the rated voltage required at the stabilizer input and output.

In the case of three-phase systems, provide the line-to-line voltage value. The standard voltage stabilizer can operate with nominal voltage 380V-400V-415V (50Hz) or 440V-460V-480V (60Hz).

Different types of voltage stabilizers
Different types of voltage stabilizers for choice

Input variation range

It’s key information for the choice and the design of the voltage stabilizer. Establish the amplitude of the oscillation of the input voltage and always keep a safety margin on such percentage: For example, if the measured fluctuation is ±16%, then choose a stabilizer suitable for ±20% variation. Note: if the input variation exceeds the nominal one, the difference is added to the output precision. For example, if a voltage stabilizer designed for ±15% input variation receives a +20% voltage, the output precision shall not be ±0.5% but ±5.5%.

Type of regulation

The three-phase voltage stabilizers perform an independent regulation on each phase. The connection to the distributing line neutral wire is mandatory. Should the neutral wire not be available, a specific accessory component must be added.

Type of technology

In most applications, the electromechanical voltage stabilizer is a reliable and safe tool. In case of high regulation speed is required (milliseconds), it is better to choose the solution with regulation by means of IGBT static switches.

Rated power

All the stabilizers are designed for the maximum input current, but it is advisable to consider an extra safety margin for possible future expansions. In a voltage stabilizer, the power is expressed in kVA, whilst the load power is usually expressed in kW. Remember that the link between these two measuring units is provided by the power factor (cos φ): kVA = kW / cos φ.

Also, remember that if the power factor and/or the load power in kW cannot be easily established, measure the absorbed currents in order to allow for a correct design of the stabilizer and keep in mind that:

  • kVA (1-ph.) = load voltage x load current.
  • kVA (3-ph.) = root of 3 x phase to phase load voltage x load current.
Different types of voltage stabilizers
Different types of voltage stabilizers for choice


Choose the other parameters of the stabilizer considering the installation conditions. The following aspect must be known:

  • IP protection degree required.
  • Indoor or outdoor installation.
  • Site altitude and climatic characteristics.
  • Ambient temperature.
  • Possible environmental hazards such as aggressive atmosphere, exposure to chemical components and so on.


A standard voltage stabilizer can be enriched with a number of accessories:

  • Interruption and protection devices.
  • Load protection against over/undervoltage.
  • Bypass line.
  • Input isolating transformer.
  • Total protection kit.
  • Surge arrestor (SPD).
  • Integrated automatic power factor correction system.
  • EMI/RFI filter.
  • Neutral point reactor.
  • Up to IP54/55 protection degree for both indoor and outdoor installation.

Special construction

By means of some modifications, it is possible to obtain special stabilizers able to:

  • Deal with asymmetrical input voltage variation different from the standard range (for example, from -55% to +20% of the nominal voltage);
  • Deliver an output voltage different from the input one (for example, Vin = 400V ±15%, Vout = 460V ±0.5%).

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