Variable Transformers and Test Sets

Variable Transformers

Staco VT Variable Transformers


Variable Transformer 120-600 VAC, up to 1000 kVA
Continually variable output voltage that can be adjusted from 0 to 117% of the unit’s input.
(1010B rated at 120VAC and 1.56 kVA shown)

Staco Energy Products’ full range of variable transformers offer the exceptional versatility and reliability required for so many of today’s voltage control applications in both industrial and laboratory environments.

Unlike a standard fixed ratio transformer, a Staco variable transformer is designed to provide variable output voltage that can be adjusted from 0 to 117% of the unit’s input voltage.

Staco Energy Products Co. offers a wide range of standard models including the following:
• Panel mount, single phase (fixed and adjustable shaft)
• Enclosed cord and plug
• Metered
• Fully enclosed
• Ganged
• Isolated
• Isolated portable cord and plug models
• “Quick-Step” motorized
• Motor driven
• Cased

A basic Staco variable transformer consists of a copper winding on a toroidal core of laminated, grain-oriented, silicon steel. A carbon brush, connected to an output terminal, is rotated over the length of a precision-ground, precious metal-plated, commutator track to tap off voltage at any turn from zero volts to the maximum output voltage of the winding.

Ganged Variable Transformer Assemblies

High Current Models

By ganging variable transformers with a common rotor shaft wiring the outputs in parallel, the output current can be greatly increased. The models listed here are capable of output currents up to 315 amps. Other models are available in a variety of ranges.

Three Phase Models

All of Staco Energy Products’ variable transformers can be ganged with a common rotor shaft and wired for three phase operation, in either open Delta or Wye configuration. For more information, contact your local sales representative, or call the factory directly.

Accessories and Other Configurations of Standard Models

Cased Models

Transformers of the 1010B through 6011 series are available in either “C” style (featuring protective screening over the coil assembly only) or the “CT” style (which also includes a terminal box cover with knockouts to accept conduit. Example part numbers are “1510C, 2510CT.”

Motor-Driven Models

For applications requiring remote or automatic voltage control, a driving motor can be added to all models of the 501C through 6011 series. Standard motor speeds are: 5, 15, 30 and 60 seconds of travel, and so are designated by the prefix “M.” For example: “30M1510.”


MP Microprocessor Controller

Our MP series of Microprocessor provides for easy interface of computer and process controller to Staco Energy Products’ motor driven variable transformers. It is capable of several operational modes with selectable control ranges – tunable for various motor speeds, output voltage ramping, and feed back voltage. Custom options are available.

The microprocessor can be controlled with the microterminal, process control set point, or a bi-directional communications port such as RS-232 or RS-422. The variable transformer regulation is maintained at +/-0.5 volts. The MP controller is available with one, two or three channels for control of up to three motorized variable transformers or individual phase control of a three phase unit.

FRC-20 Controller

The FRC-20 controller is designed to position and regulate any Staco motor driven variable transformer. It can be controlled with a 0-5 VDC or 4-20 Ma set point, a 1k ohm potentiometer, or a fixed resistor network.

It maintains a full range regulation of 0.5%, and a limited range regulation of 0.25%. This unit is field configurable for feed back voltages up to 600 VAC, full range/limited range, and type of control. Each FRC-20 includes a 1 amp motor supply fuse and a set point supply trim potentiometer. It is a compact package, and can be easily mounted on the motor plate or inside an enclosure. Contact your sales representative or the factory for current and other feed back alternates.

Test Sets

UniStar SB2

Staco PPS

Provider Power System test sets 0-1000 VAC, up to 3500 kVA
Precise variable voltage power supply for all electrical testing application up to 4000amps.

Staco Energy Products Co. has been supporting the power requirements of R&D labs for over 75 years.

Our PPS series provide precise voltage control for any electrical testing application.
Staco Energy Products’ Provider Power Systems are custom engineered test sets offered in a standard, modular format. They can be ordered directly through the standard modules, or can be customized to meet your exacting specifications.

Our Provider Power Systems can be designed to accommodate the most basic or sophisticated test laboratory needs.

We offer a range of testing modules for OEMs, quality control, circuit breaker testing, HVAC, motor test and production, white goods, engineering/quality assurance labs, and product life cycle testing.

• Fast lead times for custom work
• Cost effective method of varying voltage
• Based on mature, Variable Transformer (VT) technology
• Ease of maintenance
• Low cost of ownership

Operating Benefits
• Narrow or full range voltage control (0 – 600Vac)
• Fractional to 1000 Amps
• Motorized voltage control
• Multiple frequency and voltage source
• Contact or controller input and output
• Local or remote control and communications
• Monitoring for all power parameters
• Modular design for complete customization
• Low cost of ownership due to efficiency and virtually maintenance free operation
• No waveform or harmonic distortion added

Standard Construction
• Paralleling choke provides current balancing coils
• Small footprint
• Nickel-plated copper bus bar
• Easy service access
• All copper transformer construction

We offer a range of testing modules for: OEMs, Quality Control, Circuit Breaker Testing, HVAC. Motor Test and Production, White Goods, Engineering/Quality Assurance Labs, Product Life Cycle Testing.

Staco Energy Products are available with a variety of specifications, call eComp at 1-508-881-8399 or email us for information on specific models.