VARIABLE FREQUENCY DRIVES: SELECTION AND ACCEPTANCE
Yenra | Updated September 11, 2026
Article: https://yenra.com/variable-frequency-drive/

Purpose: assemble a drive selection brief with the responsible electrical and process engineers.
Use: complete the load and duty fields first; record unknowns as UNKNOWN. Supplier-approved limits and the actual machine documentation govern installation and commissioning.

EQUIPMENT AND LOAD
Asset / location / owner:
Motor model / nameplate photo / rated current A / rated power kW / voltage V / frequency Hz / speed rpm:
Supply phase / voltage V / available electrical design record:
Driven equipment / torque behavior / starting load / overload duration s:
Process output and units / minimum and maximum required service:
Speed range / motor cooling assessment / stopping and braking needs:
Cable length m / route / enclosure / ambient temperature deg C / altitude m:
Drive continuous current and overload rating at this duty / supplier evidence:
Motor insulation, bearing-current and cable mitigation assessment owner:
Command interfaces / loss-of-command response / restart response:

ENERGY COMPARISON (electrical INPUT power at equivalent useful service)
For each operating point: service condition | annual hours h | existing kW | proposed kW | evidence
1.
2.
3.
Sum hours; avoid overlapping operating periods. For each system, sum(kW * hours) = kWh/year.
Fictional check: existing 12 kW * 4,000 h = 48,000 kWh/year.
Proposed: 12.5 kW * 1,000 h + 5 kW * 3,000 h = 27,500 kWh/year.
Difference 20,500 kWh/year. Invented energy-only $0.12/kWh gives $2,460/year.
The full-demand penalty is included. These are teaching inputs, not a performance prediction. Installation, demand charges, taxes, maintenance and process changes are separate.
Your energy-only rate and source / excluded costs / sensitivity to operating hours:

ACCEPTANCE
Operating point | required flow/pressure/other output and units | power measurement method | duration | limits and source | result:
Approved tests for command loss, sensor failure, trip, stopping and restoration:
Reviewer / exceptions / approved parameter file / firmware / drawings / date:
Recheck after motor, cable, load, duty-cycle or process-limit changes.

PRIMARY REFERENCES
part-load efficiency guide
https://www.energy.gov/sites/prod/files/2014/04/f15/motor_tip_sheet11.pdf
motor and drive systems sourcebook
https://www.energy.gov/sites/prod/files/2014/04/f15/amo_motors_sourcebook_web.pdf
motor–drive interaction guide
https://www.energy.gov/sites/prod/files/2014/04/f15/motor_tip_sheet15.pdf