Existing Application
A food packaging company in the Manchester area called upon us to find out if there were any saving to be made from converting their old DC motor on their plastic extruding machine, to a Brook Crompton World series AC equivalent.
They already had an energy survey compiled for them which stated a 6 month payback period on the investment. They found this hard to believe and wanted a second opinion.
DC electric motor: 132kw 2080rpm foot mounted.
Gearbox specifications: 63/1 @ 8 and 25rpm output running speeds.
Suggested Solution
Firstly we suggested that they log the power on a full production cycle to collect data to compare. This was done and the average power consumed was 85kw, peaking at 98kw. The motor was in use for 6000 hours per year at a cost of 9pence per KWr. Taking the average of 85kw we deduce that the machine was costing £45,900 per year in electricity costs.
There was an additional cost of approximately £3000 per year for the on going maintenance of their motor and the cost of buying a spare motor to compensate when the original went for refurbishment.
We calculated that a 1450rpm motor through the 63/1 gearbox would achieve a running speed of 23rpm at 50hz. Therefore we could obtain full motor power at 50hz (123Kw), more inportantly obtain 30kw of power at the 8rpm idling speed. For this we offered a 110kw motor.
Calculated Savings
The extruder DC-AC conversion calculation is not an exact science but from past experience we could confidently quote between 20-30% savings. this would mean between £9,180 – £13,770 saving per year on electricity costs alone.
Against the cost of the inverter and motor this payback would be longer than the 6 month stated by others. This as stated earlier is based on past experience and the calculations shown.
Installation go ahead
We were given the go ahead to supply a Brook Crompton world series IE2 motor and a Danfoss FC302 variable speed controller. we also supplied the engineers to install and commission.
Whilst installing a new motor drive solution, legislation allows the use of an IE2 motor if installed with a Inverter drive.
IE3 motors are mandatory on all applications if they are controlled DOL.
Once the conversion had been completed we logged the motor again to ascertain the actual saving.
Total Savings
The savings were excellent. The average power consumed was 56kw and as a result reduced the annual running costs to £30,240. This was an electrical saving of £15,660 per year which equates to a 34% saving. Adding to the approximate £3,000 maintenance saving totals £18,660.
We offer surveys and honest experienced advice for your DC motor conversions. Contact our office for more details.
