AC Drives

AC drives, also called variable frequency drives (VFDs) or frequency inverters, control the speed and torque of AC motors by varying the frequency and voltage supplied to them. Seven Star LLC supplies industrial AC drives to plants and panel builders in Oman, including Schneider Electric Altivar, ABB ACS355 and ACS580, Danfoss VLT AutomationDrive, Allen-Bradley PowerFlex and Siemens SINAMICS units. Drives from Control Techniques, Yaskawa, LS Electric, WEG and NORD Drivesystems are listed as well.

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Category guide

About AC Drives

34 products 11 brands

Types of AC drive in this category

The listing follows the way manufacturers split their own ranges. Compact machinery drives such as the ABB ACS355 and Schneider Electric Altivar 320 go inside machine panels and run conveyors, mixers and small pumps. General purpose and process drives such as the ABB ACS580, Danfoss VLT AutomationDrive FC 302 and Allen-Bradley PowerFlex 755 cover larger motors and offer more I/O, fieldbus options and control modes. The Siemens SINAMICS G120X is built for pump and fan duty in water and HVAC systems. The NORD NORDAC FLEX is a decentralized inverter mounted on or near the motor. The Schneider Electric Lexium 32 is a servo drive for positioning axes, and the Var-Spe K2 is a hydrostatic speed variator, a hydraulic alternative to an electronic drive.

How to select a variable frequency drive

Size a drive by motor full-load current, not by kilowatts alone, and check the overload class against the load. Pumps and fans have a variable torque characteristic and can use a normal-duty rating. Conveyors, crushers, extruders and hoists need constant torque and a heavy-duty rating. Then confirm the supply voltage and number of phases, the enclosure rating for the location, the EMC filter category, and the ambient temperature, since drives are derated in hot plant rooms, a common condition in the GCC. Long motor cables may call for an output reactor or sine filter, and a motor that was not designed for inverter duty should be checked for winding insulation and bearing currents. Braking resistors, safe torque off (STO) and the fieldbus interface, PROFIBUS, PROFINET, EtherNet/IP or Modbus, are usually options in the type code.

Data needed for a drive quotation

Send the drive type code if you are replacing an existing unit. For a new application send motor nameplate data (power, voltage, full-load current, speed), supply voltage, load type, required enclosure rating, control method, fieldbus, and any options such as a keypad, brake chopper or filter.

What to include in your inquiry

These details let us quote the right item the first time.

Motor power (kW) and rated current
Supply voltage and number of phases
Application (pump, fan, conveyor, compressor)
Communication option
Enclosure rating and ambient temperature

Missing some of them? Send what you have. A nameplate photo or an old part number is enough to start.

Brands in AC Drives

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Guides and articles

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Variable Frequency Drive Selection for Hot Climates: Sizing, Derating, Harmonics and Motor Protection

Request a Quote for AC Drives

Looking for a specific model, part number or brand in AC Drives? Send us your requirements and quantities. Seven Star LLC sources genuine industrial equipment for customers across Oman and the GCC and replies with a formal quotation.

Free, no-obligation quotation · takes about 1 minute

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Frequently Asked Questions

How do I choose between a normal-duty and a heavy-duty rating for a VFD?

It depends on the torque the load needs during starting and overload. Centrifugal pumps and fans need little torque at low speed, so the normal-duty rating with its lower overload allowance is enough. Conveyors, positive displacement pumps, compressors, mixers and cranes need full torque from standstill and short overloads, so select the heavy-duty rating. The same drive frame usually carries both ratings at different current values.

Can I replace an older drive with the current model from the same manufacturer?

Usually yes, but check four things: mounting dimensions and cooling clearances, the control terminal layout, the fieldbus option and its device description file in the PLC, and the parameter set, which rarely transfers directly between generations. Give us the full type code of the old drive and we identify the manufacturer's successor and the matching options from the manufacturer's migration documentation.

What is the difference between an AC drive and a soft starter?

A soft starter reduces voltage during starting and stopping to limit inrush current and mechanical shock, then the motor runs at fixed speed on line voltage. An AC drive controls frequency as well as voltage, so it gives continuous speed control, full torque at low speed and energy savings on variable flow duties. If the process never needs speed variation, a soft starter is the simpler device.

Do I need an output filter or reactor between the drive and the motor?

It depends on cable length and motor insulation. The drive output is a pulsed voltage, and on long cables reflected waves raise the peak voltage at the motor terminals. Each manufacturer publishes maximum cable lengths with and without filters. A dU/dt filter or output reactor reduces the stress, and a sine filter is used for very long cables or older motors not built for inverter supply.

What do you need from me to quote an AC drive?

The drive type code if it is a replacement. Otherwise motor power, voltage and full-load current, the supply voltage and phases, the load type (pump, fan, conveyor, hoist), the enclosure rating, ambient temperature, the fieldbus protocol, and options such as STO, braking chopper, EMC filter or control panel. With these we can check the configuration against the manufacturer's selection data.

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