How much does swapping a 160 kW DC motor for a 90 kW AC motor with VFD save in wire drawing?
About 25,600 kWh a year in BEE's Howrah report. The 160 kW DC motor was drawing only 47.7 kW, 27% loaded, and a 90 kW efficient AC motor with a VFD cuts 6.1 kW of that. Net cost Rs 5.34 lakh after selling the old motor, saving Rs 2.09 lakh, payback 2.56 years.
What the audit found on the DC drives
- DC motors of 100 to 300 kW on drawing machines, mostly imported with little documentation, repaired locally.
- Average loading 27%. Power factor at the drive's AC input about 0.3.
- Harmonic distortion of 13.3% on voltage and 31% on current, against limits of 5% and 8% the report cites from CEA's 2007 regulations.
- Carbon brushes wear fast, and the rectifier and controls lose about 6% before power reaches the motor.
How the 6.1 kW adds up
- Drawn power 47.7 kW at 85.7% efficiency; the new motor runs at 95%: 4.7 kW less.
- DC conversion loss 6% against 3% in the VFD: 1.4 kW less.
- 6.1 kW x 12 hours x 350 days = 25,622 kWh, about 8.7% of the 295,310 kWh a year the report's model unit uses.
- At Rs 8.17 a kWh, the revised rate in the report: Rs 2.09 lakh.
- Cost: Rs 5.66 lakh motor and drive, Rs 1.38 lakh tax and fitting, less Rs 1.70 lakh for the old motor. About a week's downtime.
Size it from your own meter
The whole saving rests on one measured load. Log kW on the machine over full shifts and across the wire sizes you draw before you order. The report warns that an oversized motor stays inefficient and an undersized one burns out. Ask the supplier to state the drive's input power factor and harmonic figures in writing, since those were the faults the audit found.
The CO2 figure
25,622 kWh x 0.675 = 17.3 t of CO2 a year on today's grid. The report's 27 t used 1.05 kg a kWh, an older figure.
One drawing machine, one year
- Power cut: 4.7 + 1.4 = 6.1 kW
- 6.1 kW x 12 h x 350 days = 25,622 kWh
- 25,622 x Rs 8.17 = Rs 2.09 lakh
- Payback: 5.34 / 2.09 = 2.56 years
- CO2: 25,622 x 0.675 = 17.3 t
Grid at CEA's FY 2025-26 factor, an estimate.
What Senseible does here
Senseible reads your electricity bills into monthly kWh and CO2, each linked to its bill, so a drop of about 2,100 kWh a month shows against the same months last year. The green loan check lists what a lender asks for on a motor and drive loan.
- Green loan readiness check
- IE2 to IE4 motor replacement savings
- Target power factor by equipment
- Steel wire drawing footprint per tonne
- Howrah galvanizers and CBAM
Sources: BEE, Detailed project report: replacing 160 kW DC motor with 90 kW AC motor with VFD, Howrah galvanizing and wire drawing cluster (2010, SAMEEEKSHA), CEA, CO2 Baseline Database for the Indian Power Sector, version 22.0 (FY 2025-26 grid factor)
Last reviewed 2026-11-01. Report figures are from a BEE SME programme project report; costs and paybacks are at the report year's prices. Check today's fuel and power prices and a current quote before you rely on the payback.