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Within the scope of an equipment modernization, the decision-makers ofa water supply company were looking for new solutions. On the basis of soft starters, the construction of the pump stations could be improved without additional financial expenditures. After having successfully eliminated pressure hammers, the pipework now only produces “piano”sounds.
The water supply system of Adelsdorf, close to the German city of Erlangen, is based on six wells, from which approx. 700,000m3 water are annually supplied to the connected households. To pump the required volume into the three water towers with a capacity of 800,1,000 and 2,000m3, three jacketed pumps and two centrifugal pumps areemployed. When repair works had to be carried out at parts of the technical equipment, the decision-makers decided to not only replace individual components, but implement comprehensive modernization measures.The responsible managing engineer, Michael Denk, explains: “We went for this modernization step as we must guarantee a 100% security of supply for our citizens.”
With the original construction of the jacketed pump stations, the motors were started via star-delta circuits and operated against a closed valve. When the pumps’ full volume flow was reached, the valve was slowly opened. The shut-off valves and a mechanical check valve prevented a backflow of the water from the ductwork. The worn-out condition of this valve and the constructional arrangementof the components repeatedly led to turbulences in the medium, whichresulted in faults caused by the flow monitors monitoring the pumps’ dry run to protect them against destruction. The plant engineer NorbertLunz reports: “We frequently had to cope with pump failures. The resulting pressure hammers in the pipe work forced us to implement counter-measures.”
Start-up with low material stressing
As a new,state-of-the-art solution, the Sirius 3RW44 soft starters by Siemens now ensure that the jacketed pumps are operated with low material stressing. This multifunction device with Profibus connection can be easilyparameterised and features useful monitoring functions. The pumps benefit from a soft start-up and ramp-down. Usually, particularly the pump shut-down is subject to pressure hammers in the pipework. “This problem is now a thing of the past“, ensures Michael Denk.
Due to the soft start-up and ramp-down, an active shut-off element is no longer required in the water line. The faulty electronic valve therefore did not have to be replaced but could be abandoned without substitution. Only the installed mechanical backflow preventer still prevents backflowwhen the jacketed pump is out of operation. “Due to these external circumstances, the new solution did not incur higher costs than a mere replacement solution”, calculated Michael Denk.
Thanks to the possibility of detecting the motor current in the soft starter and signal itvia Profibus to the superior control system, fault-prone flow monitorsare no longer required. The bus connection now allows for a program-controlled successive start-up of the Adelsdorf pumps to avoid currentpeaks. The visualization is realised via WinCC by Siemens.
The current monitoring concept offers even more advantages. Compared to the starting current of the 15-kW pumps with star-delta-start of approx. 200A, the new soft starter solution only requires 80 A. “Particularly during summer, when two or three pumps start up simultaneously, this full-load reduction has extremely positive effects”, summarises Norbert Lunz. And also for continuous operation, 3RW44 soft starters feature interesting functions. During ramp operation, the current flows throughthe thyristors of the power unit. When the drive is set to nominal speed, an integrated contactor is operated and closes the bypass to the semiconductors. This reduces both power loss and power consumption.
Communication capability as basis for plant optimization
It is getting increasingly important for the water works to provide the power supply company with a highly precise demand forecast to facilitate an optimum drafting of the power supply contract. Consumers who frequentlyexceed the agreed upper limit have to pay disproportionately high costs for extra kilowatt hours. This was also the case in Adelsdorf. The use of communication-capable 3RW44 soft starters lays the foundation for a future energy management with further improvement potentials in terms of consumption values – and consequently with regard to the entirecost situation. Consistent data recording forms a pre-requisite for this approach.
If several similar drives in a plant are equippedwith soft starters, the parameterization can be realised via Profibus. To be able to easily and rapidly integrate the 3RW44 soft starters into superior controls – even without Profibus – the devices are fittedwith control inputs and programmable relay outputs. For operation andmonitoring, the 3RW44 devices feature an illuminated LCD display withplain text.
Prior to the use of the new soft starters, the Adelsdorf water supply system did not offer such differentiated current valuedetection. Since the end of 2006, the first devices have been in operation and simplified the entire plant transparency and control. As this retrofitting measure in Adelsdorf was virtually a “pilot project”, the plant engineers received technical support by the Siemens device manufacturer. Michael Denk recalls: “Siemens assumed the responsibilityfor the configuration and redrew the plans of the previous electricalsystem to adjust them to the new requirements. This support made it easier for us to move towards modernization.”
The new plant construction included further positive aspects. The bearings of jacketed pumpsare rapidly subject to damage when they are exposed to axial pressuretoo long. This is the case if the temporal coordination between the star-delta-start and the opening of the pipeline valve gate is poor. Thenew solution prevents such critical situations as the pump start-up and ramp-down follows a settable ramp function and the backflow preventer is sensitively matched to the volume flow.
Transparency leads to process optimization
The example of the retrofit project of the Adelsdorf water supply system demonstrates that thinking about new concepts is worth its while. Modern technology not only serves plant modernization, but also lays the foundation for future-proof investments. As was proven by the decision-makers in Adelsdorf, such a solution can be even more cost-effective than mere “spare parts business”. A newinstallation would offer even greater financial benefits as the present calculation was only based on a comparison of the components to bereplaced and the investments for the additional functions were not included.
With the 3RW44 soft starters, the most powerful device typeby Siemens, even further process optimizations can be realised thanksto the possible Profibus communication. Michael Denk confirms: “Everyadditional drive retrofitted for communication-capable low-voltage controls & distribution increases the transparency of our systems. We gradually create further improvement potentials.”
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