Variable Frequency Drives (VFDs) cut energy bills dramatically on variable-flow systems — a 30% speed reduction on a pump is roughly a 65% power reduction. But the wrong VFD class for the load will trip out or shorten its life. Heres how to specify correctly.
Load category first
Two main load types VFDs are rated for:
- Variable Torque (VT): Pumps, fans, blowers — torque rises with the square of speed. Use a “Heavy-Duty / VT” rated drive at the motors rated kW.
- Constant Torque (CT) / Heavy Duty (HD): Conveyors, compressors, mixers, hoists. Torque is roughly constant across speed. You must select a drive ONE SIZE LARGER than the motors nameplate kW for the VT-only model, or use the HD rating directly.
Sizing rule of thumb
VFD model nameplates always show two power ratings:
- Normal Duty (ND) / VT: The higher figure. Use for fans/pumps.
- Heavy Duty (HD) / CT: The lower figure. Use for conveyors/compressors.
Example: ABB ACS580-01-018A-4 is rated 11 kW ND or 7.5 kW HD. For a 7.5 kW conveyor motor, this is the right size at HD rating.
Required accessories
- Input choke (line reactor): Recommended for drives ≥ 15 kW to reduce harmonics back to the supply. Required by some UAE utilities.
- EMC filter: Built-in on most modern drives; check if your drive is C1, C2, or C3 class. Industrial enclosed panels usually accept C3.
- Output reactor / dV/dt filter: For motor cable runs > 50 m, prevents voltage spikes from damaging motor windings.
- Brake chopper + resistor: For overhauling loads (descending hoists, decelerating high-inertia fans) — drive needs to dump regenerated energy.
Brand cross-reference
| Motor kW (4-pole, 400V) | VFD VT (ND) rating | ABB ACS580 | Schneider ATV320 / 71 | Inovance MD500 |
|---|---|---|---|---|
| 2.2 | 3 kW ND | ACS580-01-04A1-4 | ATV320U30N4 | MD500-4T3.7 g |
| 5.5 | 7.5 kW ND | ACS580-01-012A-4 | ATV320U75N4 | MD500-4T7.5 g |
| 11 | 15 kW ND | ACS580-01-025A-4 | ATV71HD15N4 | MD500-4T15 g |
| 22 | 30 kW ND | ACS580-01-046A-4 | ATV71HD30N4 | MD500-4T30 g |
| 45 | 55 kW ND | ACS580-01-088A-4 | ATV71HD55N4 | MD500-4T55 g |
UAE-specific considerations
DEWA, ADDC, and SEWA have published preferred-supplier lists for utility-feed installations. ABB, Schneider, Danfoss, and (recently) Inovance are routinely on those lists. We confirm utility approval at quote stage.
Sourcing
EPFINDER stocks ABB ACS, Schneider ATV, Danfoss FC, and Inovance MD-series VFDs in Dubai. Common ratings are on the shelf; specialised options (high-output choke, IP66 enclosure, Profibus card) are typically 1-3 weeks from manufacturer. Request a VFD project quote.
