What is the
Construction Process?


At the heart of the Voltage Stabiliser are the regulator coils. While some small capacity regulator coils are uncompensated, all larger capacity voltage stabiliser regulator are fully compensated.

Compensation is a method where by the naturally high reactance of long thin coils, used in the construction of the Brentford Regulator coil is limited to a low value across the range of variation.

Limiting the reactance tends to produce a linear variation in the output voltage of the regulator, across the range of operation. Contact pick up tracks are machined onto the faces of the coils. Depending on the required output arrangement there may be tracks on both sides of the coil, or only on one.

The coils are then mounted on a core of grain oriented silicon steel laminations.

The core and coils are mounted in a steel framework that allows roller contacts to be presented to the coil faces at a constant pressure across the range of operation.

To achieve variation in the output voltage the roller contacts are moved along the coil face. Roller contacts are housed within retaining assemblies that are in turn fixed to a carrier board. The carrier board’s position is maintained by a chain drive system that is in turn attached to the drive mechanism, either hand- or motor-driven.


The construction of the Brentford Regulator assembly allows the same basic unit, with only minor changes, to be used either immersed in cooling fluid, or directly air-cooled.

For the larger power ratings of regulator, fluid immersion is used exclusively.

Where fluid immersion is employed secondary cooling can be provided by air natural, forced air, or water-cooling.


Due to the flexibility of the design several arrangements can be provided. These range through single phase or three phase to double output for buck boost arrangements where the output of the regulator starts at a maximum voltage, decreases to zero, and then again increases in voltage but with the polarity reversed.

Buck boost connection is used where the minimum output voltage is above zero volts. Basically the connection comprises of two fixed ratio transformers and a double output voltage regulator.

One fixed ratio transformer (commonly referred to as the Main Transformer) has an output voltage approximating to the mid-point of the range required. The second fixed ratio transformer (commonly referred to as the Buck Boost Transformer) has an output voltage approximating to the difference between mid-point, and minimum / maximum required voltage, and there output windings are connected in series. The input winding of the buck boost transformer is connected across the two outputs of the regulator.

With the roller contacts located at one end of the regulator a maximum voltage at a specific phase relationship to that of the fixed ratio transformers is produced.

The transformers are arranged so that in this condition the output voltage of the buck boost transformer is subtracted from the output voltage of the main transformer.

This provides the minimum output voltage of the arrangement.

As the roller contacts are moved to the centre of the regulator the output voltage of the regulator, and hence the buck boost transformer approximates to zero. The combined output of the arrangement is therefore the output voltage of the main transformer.

Continuing to move the roller contact in the same direction will increase the regulator output voltage. In addition the polarity of the voltage will have reversed so that the output voltage of the buck boost transformer is now added to that of the main transformer. By this means the maximum output voltage of the combination is achieved.


The Brentford Regulator has good short term overload capacities. For some applications we allow a level of de-rating within our design that is invisible to the client.

Almost any duty can be catered for. If you have specific requirements that you wish to discuss please contact our sales force.


All Voltage Stabilisers are supplied with a voltage monitoring relay. In most cases, the voltage monitoring relay monitors the equipment’s output voltage. If the output voltage is low, the relay will instruct the regulator motor to raise, thus raising the roller contacts accordingly. If however, the output voltage is high, then the relay will instruct the motor to rotate in the opposite direction and lower the roller contacts, thus keeping the output stabilised within the given stabilised tolerance. In addition to the motor control we also include an emergency hand-wheel for use if the automatic control is not available, and for maintenance purposes.

End of travel limit switches are provided with motorised systems, and if required, additional interlock / indication contacts can be provided at end of travel.

In addition, if required, an externally adjustable limit switch can be provided for customer setting.

We are also able to offer a potentiometer feedback that is proportional to regulator position, for inclusion into customers’ control schemes.

Contact Us

15-16 Woodbridge Meadows, Guildford, Surrey. GU1 1BJ

Phone: +44 (0)1483 568 281

Fax: +44 (0)1483 504 961

E-mail: sales@transformers.co.uk