A VFD or soft starter can reduce some starting stress, but it does not prove generator compatibility. Rectifier type, control, bypass, harmonics and the mechanical process change the duty.
What the project should produce
Teams connecting crushers, conveyors, pumps, fans and process drives.
Avoid treating “VFD fitted” as proof that starting is resolved.
Produce a load data sheet, harmonic and regeneration review, sequence and test procedure.
Obtain motor, drive, process and generation data together and have drive and generator suppliers confirm the boundary. Test approved acceleration, steady operation, deceleration and fault cases.
01
Collect motor, drive and process data
Rated kW alone does not describe the duty. Include torque, ramps, rectifier front end, bypass and coincidence.
- Record drive make, model and input topology
- Provide motor and mechanical torque characteristics
- List acceleration, steady, deceleration and stall cases
02
Review soft-start and VFD input separately
Soft starts can still draw elevated current for a long ramp; VFD demand depends on its input and DC link.
- Confirm current limit, ramp and bypass logic
- Match acceleration time to the process
- Review continuous and low-speed cooling
03
Check harmonics and voltage waveform
Non-linear input can heat the alternator and cables and disturb AVR, protection and sensitive loads.
- Obtain drive harmonic or input-current data
- Review alternator excitation and thermal capability
- Assess filters, reactors and load combinations
04
Identify deceleration and regeneration
Downhill conveyors, hoists and high inertia can return energy to the DC bus; a standard plant cannot absorb sustained reverse power.
- Identify regenerative operating cases
- Confirm braking unit, resistor or energy path
- Define sequencing and reverse-power protection
05
Test the real operating sequence
A single unloaded drive test does not represent several drives, other loads and transfer events.
- Trend voltage, frequency and current through ramps
- Observe waveform, alarms, AVR and protection
- Test bypass, stop, restart and shedding
Project review matrix
| Collect motor, drive and process data | Record drive make, model and input topology；Provide motor and mechanical torque characteristics |
|---|---|
| Review soft-start and VFD input separately | Confirm current limit, ramp and bypass logic；Match acceleration time to the process |
| Check harmonics and voltage waveform | Obtain drive harmonic or input-current data；Review alternator excitation and thermal capability |
| Identify deceleration and regeneration | Identify regenerative operating cases；Confirm braking unit, resistor or energy path |
| Test the real operating sequence | Trend voltage, frequency and current through ramps；Observe waveform, alarms, AVR and protection |
Three common mistakes
Providing motor kW only
Drive input and process behaviour remain unknown.
Assuming a VFD always reduces generator size
Harmonics and coincident operation can introduce new limits.
Testing acceleration but not deceleration
Regeneration often appears during slowing or lowering.
Information to prepare for engineering review
- Motor, drive and process data sheets
- Input topology, bypass and filter configuration
- Torque, ramps and coincidence cases
- Alternator, AVR and protection data
- Regeneration and braking method
- Start, stop and fault test steps