The future of Variable Speed Drives in the water industry.

In a recent article, Oliver Endres, European Variable Speed Drive (VSD) Product Manager at Mitsubishi Electric Europe considers the future of Variable Speed Drives in response to the many challenges facing the water industry at a time when scientists are predicting that unstable weather patterns affecting rainfall

In many countries we have taken water for granted and the structure of the industry meant it was often left to run aging and inefficient distribution networks. However, as urban populations are increasing there is a mounting need to provide clean fresh drinking water and process more waste water.

Need to address water and wastewater

In addition to improving collection, and reducing leakage new methods for the treatment of sewage that use less water need to be developed. One starting point to this is sewage waste being used to generate energy, and if this can be done relatively locally, then less input energy will be required.

Variable speed drives (VSDsS), or inverters, are seen as a key technology for helping the industry address some of these issues. Originally developed to bring more control to industrial processes, VSDs can also reduce electric motor energy consumption significantly. Both of these characteristics are very attractive to the water industry.

One of the most important attributes water engineers look for when specifying equipment is long design life, and VSD’s are not exempt from this. Therefore, a robust design and reliable components are essential. Additionally, water engineers will need their VSDs to be adaptable, because they may want to redeploy them to a different duty in five, ten or even fifteen years’ time.

An important advantage of VSD’s is that when they are running equipment at less than full speed, there is a consequent reduction in wear and tear. This can lead to reduced service and maintenance requirements, which in the case of remote and hard to access pumping stations can represent a significant cost saving in logistics alone.  The electronic intelligence of a VSD can also be put to use for issues that are specific to the water industry, such as controlling water hammer and ‘deragging’.

Water hammer

Water hammer is induced when there is a sudden load within the distribution network, such as may be caused by the closure of a valve, an impact from an external source, a sudden increase or decrease in demand or a pump suddenly coming on line. The shock load can reverberate repeatedly through the pipework, reflect off hard surfaces and even feed off itself. This can lead to temporary or permanent leakage and even catastrophic failure of pipes.

Deragging

Deragging is the water industry term for unjamming the impeller of a pump, which is often caused by a build-up of rags or other fibrous debris in the pipework. The problem is almost inevitable, even though screens and filters are fitted throughout water plant facilities and the wider distribution network. Clearing a blocked pump can be very disruptive and very expensive because it may involve closing a part of the distribution network, craning out the affected pump and dismantling.

In response, VSD makers have developed self-deragging drives that detect any increase in local pressure and trigger a self-clearing sequence that will consist of increasing power and/or cycling the pump back and forward to see if the blockage can be dislodged and dispersed.

Variable Speed Drives like Mitsubishi Electric’s new Freqrol FR-F800 intelligent VSDs are now one of the key technologies for ensuring success. The drive of the future then, to a certain extent, is here now. They can communicate wirelessly, an operator can visualise them within a system, monitor and control them securely via a mobile device, they will sort problems out on their own, work incredibly efficiently at different speeds and loads, reduce maintenance costs and burdens as well as being easier to set-up as they are self-calibrating.

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