Feature Drives & controls


Going beyond energy saving F


In addition to their well-known uses in saving energy, variable-speed drives are also sophisticated control elements in their own right. Neil Ritchie, from ABB, looks at the functions plant managers are coming to rely on


or a long time, variable-speed drives (VSDs) have been pro- moted for their contributions to energy efficiency and rightly so, as they are among the most effective ways to cut the costs of running elec- tric motors, the largest users of energy in industrial applications. Yet initially, VSDs were mainly valued for their ability to improve process performance and for many users this remains a primary reason for using them on their applications. Many industrial users have come to see VSDs as a pillar of their quality and safety policies, while expecting more support from the VSD vendors.


Cutting wastage An example is The Village Bakery, which is making a 10% saving in tin greasing agent by employing a VSD on its depositing line. The company had problems with its previous drive, which was slow and inaccurate - the machine had to start spraying the greasing agent before it ‘saw’ each tin. With the higher accuracy of the new drive, more of the greasing agent is deposited in the tins, cutting wastage. The VSD also optimises the speed of


The Village Bakery’s conveyor to match the size and throughput of dif- ferent baked products more accurately. In this case, the unit is programmed with four different speeds, leading to savings of around 25% in the running costs for the line.


VSDs have some capabilities that would be hard to replicate any other


way. For example, crane applications might experience conditions where the rotation direction might change, but the torque direction remains the same. The ability to control torque independently of rotation is achieved by the “four quadrant drive”, which means it can drive the motor in for- ward or reverse, with torque direction in forward or reverse for each motor direction.


As VSDs have developed, they have become more user-friendly, giving more detailed and understandable information on their condition and operating parameters. VSD displays can now present information showing, for example, how much energy they are using. These measurements can help ensure that a plant or process is working to its optimum performance, while avoiding the extra cost of exter- nal energy measuring equipment.


The Village Bakery is making a 10% saving in tin greas- ing agent by using a VSD on the depositing line


Within the drive itself, increasing use of software is leading to more intelligent VSDs that can replace many of the functions of traditional PLCs, timers and counters, reducing the complexity of control systems and cut- ting costs. Some drives include a PID controller, so an external PID con- troller is no longer needed for flow or pressure control.


Even the most reli- able of VSDs needs regular mainte- nance to keep it in full working order, and plant managers expecting excellent support from ven- dors are not disap- pointed


A soft approach secures sustainable living


wo Middle Eastern water pumping contracts awarded to Softstart UK mean the company is playing an important role in the region’s long term infrastructure development. Softstart is building 1.3MW softstarts for five giant irrigation pumps being used in a Ministry of Water agricultural development scheme in northern Iraq, and six 3.3MW units for foul water booster pumps in Egypt’s El-Abour Sanitation Project. “Reliable food production and sanitation are absolutely fundamental for large scale economic development,” said


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Stuart Harvey, managing director of Softstart UK. “We are helping put in systems with life expectancies of 25-50 years, from which whole generations of people will benefit enormously...”. The Iraqi units are fitted with load brake disconnects and fuses and line and bypass vacuum contactors, while the Egyptian ones also have load brake earth switches and power factor correction. A soft start briefly reduces the load and torque in an electric motor during


startup. This prevents surges and spikes resonating through the electrical dis- tribution network. It also cuts shock loads in the driven mechanical equipment, while in water distribution pipework, a soft start will reduce pressure surges and air entrapment which in large systems can lead to water hammer effects. Softstart UK T: 01493 660510 www.softstartuk.com Enter 231


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An example of the programmable abilities of VSDs is a control system for a crosslapper, carried out by textile machinery manufacturer Tathams. A crosslapper accepts a light weight fibre web from a carding machine and uses it to build up a heavier web in layers, known as a batt. The crosslapper over- laps the layers by means of a complex arrangement of conveyors and revers- ing mobile carriages that turn the mate- rial through 90˚. Typical end-products include automotive textiles, industry felts and filtration media. Tathams’ TSX control system uses motion con- trol drives and servomotors.


Specialised software can now be added to make a VSD particularly suited to pump and fan applications, including such functions as pump cleaning that keep pumps clear of debris. Diagnostic software can alert operators if the VSD detects set points or other parameters going out of limits. Process information can be checked on line or the drive can send an SMS to a mobile phone to alert an engineer to a problem.


More VSDs are capable of communi- cating over standard communication protocols like Ethernet, allowing easy


SEPTEMBER 2012 Process & Control


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