Design Topology Overview

Design TopologyNot all Voltage Stabiliser solutions are designed or built the same!

For the lay person, differentiating between the numerous suppliers and various design technologies utilised to deliver voltage stabilisation can often be a daunting task and it is not always clear as to which technology is best for a particular application.

As one of the world’s leading specialist ‘Quality’ manufacturers and suppliers of Voltage Stabilisers and associated Power Line Conditioning solutions we offer probably the widest choice and cross section of alternative design types and models.

Below we discuss the various design topologies available in today’s market and highlight the advantages, disadvantages and most appropriate application for each topology

Servo Electronic

Servo ElectronicDesign Overview

Being able to accommodate an input voltage swing of in excess of 40%, whilst still capable of delivering accuracy on the output of 1% or better, the Servo Electronic design principle comprises a transformer having its secondary winding connected between the mains supply and the load. The primary voltage is automatically controlled through a servo motor driven variable transformer, thereby ensuring a continuous, smooth and very stable output voltage.

A solid state Servo-Amplifier continuously monitors the output voltage of the stabiliser. Should, due to an incoming voltage or load current change, the output voltage deviate from the required value, the Amplifier sensor instructs the servo motor to rotate the brush-gear on the variable transformer to correct the output for the deviation. The speed of detection and actions of the servo system are exceptionally fast, with controlled motor deceleration to minimise any possibility of overshoot.


Design Advantages

  • Size and weight advantages over other methods of stabilisation
  • Fast speed of response to voltage changes – ideal for 95% of all applications
  • Very competitively priced
  • Negligible output waveform distortion
  • Not Frequency dependent
  • Will attenuate voltage spikes (if required)
  • Unaffected by load or power factor changes
  • Low cost of ownership with ease of serviceability
  • Endurable with long life expectancy

Design Disadvantages

  • Moving parts requiring a certain amount of limited maintenance
  • Lower speed of response in comparison to the more costly solid state design topology solutions



By far our most popular offering, being an ideal cost efficient design solution for 95% of all applications.

Over the last 25 years our Servo Electronic ranges have been tried, tested and extensively proven in all corners of the world – including some of the harshest and most remote power environments on this planet.

In recent times with advances in semi-conductor, motor and digital technologies, our development engineers have considerably enhanced the performance of the basic design principle. Our latest Servo Electronic generation of solutions deliver the most reliable, fastest acting, highly stable and most energy efficient operation seen in the market today.

Magnetic Induction

Magnetic InductionDesign Overview

Magnetic Induction based solutions, utilise a simple, yet highly reliable, rotor and stator design principle to increase or reduce the magnitude of the voltage in a series transformer winding, thereby delivering and maintaining a constant output voltage. The arrangement is similar to a motor, except that the rotor does not rotate continuously. Its maximum rotation is only 130 degrees.

The magnetic coupling between the rotor (the shunt winding) and stator (series winding) will cause the magnitude of the voltage in the series winding to increase or decrease, depending on the angle or position of the rotor to the stator. For example, when the input voltage drops, the rotor will rotate clockwise to such an angle to make up for the drop in voltage, rotating anti-clockwise to correct for a high voltage.


Design Advantages

  • Brushless – virtually Maintenance Free with no contact wear or requirement for carbon brush replacement.
  • Highly reliable, efficient and robust design – ideal for the tougher style industrial applications
  • Oil Cooling Option - delivers smaller physical size and makes the topology ideal for applications in more humid environments

Design Disadvantages

  • Usually less price competitive when compared to servo electronic design based systems



Being brushless in nature, the design principle is highly robust and virtually maintenance free making it ideal for more demanding higher rated three phase industrial applications.

Ashley-Edison Three Phase Magnetic Induction based Solutions


Ferro-Resonant / Constant Voltage Transformer

Ferro-Resonant / Constant Voltage TransformerDesign Overview

Ferro-Resonant / Constant Voltage Transformer (CVT) based solutions, utilise a tank circuit composed of a high-voltage resonant winding and a capacitor to produce a constant output voltage whilst supporting a varying load current - even in situations where the input voltage varies widely.

The circuit has a primary on one side of a magnet shunt and tuned circuit coil and a secondary on the other side.  Voltage regulation is achieved through the magnetic saturation in the section around the secondary. 

The design offers excellent isolation – delivering exceptional transient voltage surge suppression and short-circuit protection.



Design Advantages

  • High speed of response to voltage changes
  • Highly dependable Output voltage - voltage does not collapse on high overload or severe input voltage drop
  • Solid State – No moving parts and virtually maintenance free.
  • Competitively priced – especially for ratings of 5 kVA or below, where the nominal input voltage can vary widely
  • Inherent ride-through capability – ensuring that in the event of a short break of up to 3 milli-seconds in duration output is maintained.
  • Highly reliable – with extremely high MTBF performance

Design Disadvantages

  • Not generally price competitive in ratings above 10 kVA
  • High weight to kVA ratio compared to servo electronic designs
  • Frequency Dependent – not ideal for applications where severe frequency variations are an issue
  • Not the quietest – due to magnetostriction there is a tendency for slight transformer hum and a result it is normally best practice not to install too close an employee’s workstation or audio recording equipment



Highly reliable and endurable. Ideal ‘install and forget’ solution for severe environments where the input voltage varies widely.

Ashley-Edison Saturable Reactor based Solutions


Saturable Reactor

Saturable ReactorDesign Overview

An ‘Aiding’ and ‘Opposing’ Magnetic Amplifier is connected across the main transformer to either increase or reduce the input voltage should it go high or low. This is achieved by increasing or reducing the magnetic inductance in the two cores. The Control Amplifier Sensor will detect the input fluctuations and then inject a DC current into the two respective amplifiers to either increase or reduce its inductance.

Reducing the inductance will increase or reduce the output voltage and vice versa. The Sensing Amplifier monitors the output voltage continuously and automatically adjusts the DC currents through the control coils, thereby ensuring that the output voltage is kept constant.

The Filter, in conjunction with the inductance of the magnetic core, forms an extremely effective means of suppressing high energy spikes and other mains borne noise.


Design Advantages

  • Solid State – with no moving parts – virtually Maintenance Free
  • Ultra-fast speed of response to voltage changes
  • Extremely accurate output voltage - accuracy better than 1%, typically 0.5%

Design Disadvantages

  • Less price competitive when compared to servo electronic design based systems
  • High weight to kVA ratio compared to servo electronic designs



Being a considerably more pricey design topology when compared to our more popular ranges of Servo Electronic and Magnetic Induction based solutions, Saturable Reactor based systems are primarily intended for truly ‘Mission Critical’ applications where a solid state solution is required and the load equipment is ultra-sensitive to the vagaries of the incoming mains supply and demands a highly stable and clean supply voltage - eg. Laboratory and testing equipment and ‘High-Tech’ manufacturing processes.

Ashley-Edison Saturable Reactor based Solutions

Please contact us for details on our PEN & PCEN ranges of Solid State AC Voltage Stabilisers and Power Conditioners



Solid State Electronic Tap Changer

Solid State Electronic Tap ChangerDesign Overview

Using triacs in series with a tapped auto transformer, regulation is achieved by electronically selecting the most appropriate output tap (from typically 8+) on the transformer.

As a stepped regulation solution with a limited number of taps being available they generally offer a poor level of output voltage accuracy (typically ±5% or worse!)

Historically the topology has proven to be highly unreliable with the triacs being prone to firing simultaneously when being subjected to spurious transients, or failing under over voltage or current situations





Design Advantages

  • Low Cost  – most competitive in price for “Plug N Play” and smaller single & three phase solutions
  • Solid State – with no moving parts – virtually Maintenance Free
  • High Efficiency
  • Negligible Output Waveform Distortion

Design Disadvantages

  • Extremely Poor Output Voltage Accuracy when compared to other topologies
  • Unreliable – historically being prone to triac failure or miss-operation



Historically an unreliable design which is usually the choice of customers where a low price is the overriding factor in the buying process. Tend to be the domain of our more “bargain basement” competitors. Gives adage to the saying “You get what you pay for!”

Ashley-Edison Tap Changer based Solutions

NONE – topology considered to be unreliable


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