Column-type & Toroidal Voltage Regulators

Solutions for all applications

We offer an extensive line of voltage regulators to accommodate the enormous variety of electrical equipment in use today. Variable transformers provide an adjustable output voltage whenever a continuous regulation of AC voltages with load is necessary. With standard input voltages and different transformer designs to choose from, we are sure to have a regulator that meets your specific application.

Toroidal Variable Transformers (TOVT)

  • Continuously adjustable output voltage for inputs ranging from 120 to 600 Volts AC
  • Provides output voltage as a percentage of the input voltage over a range of either 0-100% or 0-117%
  • Applications include test equipment and lab instruments, as well as an enormous variety of power supplies


TOVTs are a simple and efficient auto-transformer distinguished by their unique shape. Copper windings encompass a toroidal, or “doughnut” shaped core, to form a toroidal helix. The outer face of the windings is exposed to provide a path for current collection. A carbon brush traverses the windings by means of an output voltage selector, or “swinger”. The swinger originates at the center of the toroid and rotates a maximum of 318 degrees about the face of the transformer. The result is an output voltage that varies linearly in proportion to the angle of rotation of the swinger. By stacking multiple transformers on a common shaft and wiring them in series and/or parallel, the line voltage may be doubled and the current and kVA rating increased accordingly

Mechanical Features

  • Single and three-phase configurations
  • Motorized and manual units available
  • Standard rise time for AC units is 60 seconds, DC units is 15 seconds
  • Stackable design for wide KVA range
  • The precise assembly provides longer life with minimal maintenance
  • Individual cooling fans

Electrical Features

  • Line voltage inputs from 120 to 600 Volts AC
  • Output voltage from 0 to 17% above line voltage
  • Parallel configurations include current chokes
  • 250% overload capability for 2 minutes
  • Wiring diagram conveniently located on terminal plate

Column-Type Variable Transformers (CTVT)

  • Regulate large throughput power with fewer components
  • Single and three phase units available providing a continuously adjustable output voltage for inputs from 240 to 600 Volts


The CTVT is constructed of an outer copper coil, as well as a series of internal compensation coils, both encompassing a laminated steel core. The coils are encapsulated using a process known as vacuum pressure impregnation (VPI) to strengthen the column and provide uniform heat transfer. A contact face of the windings is exposed to reveal the individual turns. The face is then nickel-plated to provide a wear-resistant and corrosion-free path for current collection. A combination of aluminum and steel structures support the columns providing a heavy-duty and structurally dependable unit.

Mechanical Features

  • Single and three-phase configurations
  • Nickel-plated commutator path
  • Rolling carbon current collectors
  • Unique plus/minus design available
  • Motorized ball-screw drive
  • Fixed or variable rate or rise
  • Heavy-duty construction
  • Continuous duty to 40 degrees C ambient
  • Upper and lower limit micro switches
  • Modular design for extensive kVA capacity

Electrical Features

  • Low turn-to-turn voltage difference (.7 volts max)
  • Quasi-stepless regulation from 0-100%
  • Compensation winding on all columns
  • Step-up output available for 0-115% rated input voltage
  • Delta and wye auto-winding standard
  • Operating frequency range from 50-60 Hz
  • Minimal output distortion
  • Roller Holder Assembly


The most important feature of the CTVT is the low turn-to-turn voltage difference across the transformer windings, (designed to never exceed .7 volts per turn). In order for a variable transformer to yield continuous, uninterrupted output voltage, the current collector must touch the next turn before leaving the previous one. The potential difference across the collector results in current flow, which results in heat dissipation. CTVTs use 35mm diameter carbon rollers as the collector device. In addition to eliminating mechanical problems associated with sliding contacts, the rollers endure greater cycles due to decreased friction. The carbon offers excellent electrical conductivity as well as exceptional thermal withstand capabilities. When the rollers bridge two turns, a combination of the low potential difference and the resistance characteristics of the contact devices limit current flow throughout the roller. These properties make the CTVT ideal for applications in which the rollers are stationary or do not experience frequent movement.

Controls & Movement

Optional controls and metering are available to accommodate a voltage regulator. Each assembly can be custom designed to best match your equipment capabilities and your metering requirements. Optional components include digital voltmeter and ammeter, on/off controls with “zero-start” interlock, raise/lower controls, input circuit breaker, and main contactor.


Each CTVT unit is equipped with lifting points for movement by forklift or crane. Also available are IP21 enclosures, as detailed in the Toroidal Variable Transformer section. The structurally solid frame has removable panels for easy access to columns. Cabinets may also include fan assemblies to provide forced-air cooling.

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For any information you can contact us by phone or e-mail:
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