page 2 of 3 2007.12.06

Saving Energy, Improving the Product

These winding machines have 24 heads arranged in a line, each of which produces yarn packages independently.
The fans, as is the case with most evacuation systems, were previously operated at a fixed speed (50 Hz) regardless of the work load.
However, since the number of heads in operation during the working day could vary, the suction capacity (vacuum) of the fans would reflect these variations, the volume of evacuated air being directly proportional to the number of working heads. Transforming the operation of a hydrodynamic machine from a fixed-speed to a variable-speed mode, when the processing conditions allow it, means cutting drastically electrical energy requirement.
To analyse just one machine, an 11 kW Danfoss VLT6000 HVAC converter was introduced to control the evacuation fan of the 24 heads.
The inverter, which has IP54 protection rating, was assembled directly on the machine, therefore without installing dedicated control panels; this solution made it possible to eliminate the problems linked to the dispersion of the heat produced by the drive and to cut the installation costs to a minimum.
The vacuum level in the evacuation pipe (setpoint 40 mbar) is detected by means of a transducer which sends a proportional 4-20 mA signal to the inverter.
Having received this signal, the PID controller integrated in the drive proceeds to vary the motor supply voltage and frequency, keeping the pressure setpoint in the evacuation pipe constant at the level required.
Thus, the fewer the heads running, the slower the fan rpm speed will be.
The installed inverters have RFI filters, in accordance with the EN55011-1A (industrial sector) and EN 55011-1B (civil sector) regulations on radio frequency interference. The use of RFI filters is obligatory in applications where there is electronic equipment sensitive to this kind of interference (PCs, PLCs, sensors, etc.)
Having completed all the installation and the start-up procedures to ensure precise setting of the system parameters, monitoring of electrical consumption levels could begin.
It was immediately apparent that the results were good, with the level of energy consumption cut by half.
Furthermore, the quantity of processing waste also fell dramatically.
Indeed, control and correct “dosing” of vacuum has led to a reduction, in the fault elimination (yarn clearing) stage, of the amount of good yarn discarded; previously, when using a fixed-speed fan, in order to guarantee a correct amount of air even in the heaviest working conditions (all 24 heads in operation), the setpoint selected was 60 mbar. As a result, when fewer heads were in use there was too much vacuum, and thus too much yarn evacuated and discarded.
With variable speed control and a setpoint of 40 mbar, this risk is considerably lessened with the waste being reduced by 24%.
Given the excellent results obtained with the first, pilot machine, this control philosophy was extended to the other 11 machines, producing the same very pleasing results.
The application described here shows how correct management of variable speed systems allows energy to be used strictly in accordance with the actual operating requirements.
It may also be added that collaboration and the ability to exchange information (between the customer and the supplier) are fundamental elements in the effort to obtain a functional and efficient system, integrated into an already operational context, guaranteeing the highest quality levels.