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Variable Frequency Drives

Variable frequency drives control AC motor speed and torque by varying the frequency and voltage of the power supplied to the motor, enabling energy-efficient speed regulation across a wide range of industrial applications. PLC Direct supplies VFDs from leading automation manufacturers as surplus sealed, refurbished, and used hardware, supporting replacement and maintenance of installed variable frequency drive systems across manufacturing, process, utilities, and infrastructure environments.

Where Are Variable Frequency Drives Used in Industrial Environments?

Variable frequency drives are used wherever an AC induction motor requires speed control, soft starting, or torque regulation rather than running at fixed mains frequency. They are one of the most widely installed drive types in industrial facilities and are present across virtually every sector that runs pump, fan, conveyor, compressor, or mixer equipment.

Facilities and operations that depend on variable frequency drives include:

Water and wastewater treatment facilities using industrial VFDs on pump and blower motors to match output to demand and reduce energy consumption across distributed sites.

Mining and mineral processing operations running variable speed drives on conveyor drives, crusher motors, and slurry pump systems, where starting torque and speed control are critical.

HVAC and building services installations where VFDs on air handling unit fans and chilled water pumps deliver energy savings through variable speed operation matched to load.

Food and beverage processing plants using AC drives on mixer, conveyor, and filling line motors, where sanitary operation and precise speed control govern product quality.

Oil and gas and petrochemical facilities running variable frequency drives on compressor and pump motors in process-critical applications, where controlled starting and speed regulation reduce mechanical stress.

When a VFD fails on an installed motor circuit, sourcing a matched replacement by part number is the fastest way to restore motor control and resume normal operations.

Which Brands of Variable Frequency Drives Does PLC Direct Stock?

PLC Direct stocks variable frequency drives from major industrial automation manufacturers.

Siemens SINAMICS G120C and MICROMASTER 440: The SINAMICS G120C compact VFD family is available across power ratings from 0.55 kW to 75 kW with PROFINET and PROFIBUS variants; legacy MICROMASTER 440 AC drives are also available for maintaining older installed Siemens drive systems.

Schneider Electric Altivar 61 and Altivar 71: The Altivar 61 variable frequency drive is optimized for pump and fan applications; the Altivar 71 covers high-power machine and complex load applications, both available across multiple power ratings.

ABB ACS550: The ACS550 industrial VFD family covers general-purpose motor control applications with 3-phase 380-480 V input and NEMA 1 and NEMA 12 enclosure options.

Yaskawa GA800, GA500, V1000, and A1000 Series: Current-generation GA800 and GA500 variable speed drives, and legacy V1000 and A1000 VFDs, are available across a wide range of power ratings and enclosure types for general-purpose and application-specific motor control.

All variable frequency drives at PLC Direct are available as surplus sealed, refurbished, and used, depending on current inventory.

What Should You Know Before Ordering Variable Frequency Drives?

Hardware condition options: PLC Direct supplies variable frequency drives as surplus sealed, refurbished, and used hardware. Surplus sealed units are factory-sealed stock in original packaging; refurbished units have been tested and restored to operational condition. Used hardware has been previously installed and carries the same 1-year PLC Direct warranty as all other condition grades.

Compatibility and part identification: A replacement VFD must match the installed unit's input voltage, output current rating, enclosure type, and communication interface, all of which are encoded in the part number. Motor nameplate data, specifically the full-load current and voltage ratings, provides the primary reference for sizing; the installed drive's part number is the most reliable basis for sourcing a like-for-like replacement that matches the existing control wiring and fieldbus configuration without modification.

Warranty: All variable frequency drives hardware purchased from PLC Direct carries a standard 1-year warranty covering defects and functionality, applicable to surplus sealed, refurbished, and used products.

PLC Direct supplies variable frequency drive hardware for replacement and maintenance, and does not provide system design, programming, or integration services.

Frequently Asked Questions

A variable frequency drive controls motor speed continuously across its full operating range by varying both frequency and voltage, and can run the motor at any speed between zero and maximum. A soft starter only controls the starting and stopping ramp; it does not provide variable speed during running, making it suited to applications that only need to limit inrush current and mechanical shock on start, not continuous speed control.

Overcurrent trips during normal operation are most commonly caused by mechanical overload on the motor, a winding fault, or drive current limit parameters set below the motor's actual load requirement. A drive that trips only during acceleration typically indicates the acceleration ramp is too short for the connected load inertia; extending the ramp time is usually the first corrective step.

Safe Torque Off is a functional safety function that prevents the drive from generating torque without removing mains power, enabling a controlled, safe stop without a full power cycle. If the installed VFD used STO as part of a machine safety circuit, the replacement must also include STO and must be wired to the same safety relay or safety PLC; confirm the original drive's safety function before ordering a replacement.

IP20 and NEMA 1 enclosures are rated for installation inside a control panel in a clean, dry environment and are not suitable for direct exposure to dust or moisture. NEMA 12 and IP54 or higher enclosures allow the variable frequency drive to be mounted in more exposed locations, and applications in food processing, washdown environments, or outdoor enclosures require confirming the installed drive's enclosure rating before ordering a replacement.

A line reactor reduces harmonic distortion fed back to the mains supply and provides some protection to the VFD from voltage spikes on the incoming supply. An EMC filter limits high-frequency conducted emissions from the drive to meet regulatory limits; if the original installation included either of these components, they are part of the system design and should remain in place when replacing the drive.