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Industry 4.0, the 4th industrial revolution, smart manufacturing, digital factories…these are (more)
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Drives are far greener than most people realise
We're all aware of the energy saving potential of variable speed drives. But the experts at Mitsubishi Electric say there's a bigger picture, and controlling the power consumption of motors is only the first of inverters' many environmental credentials.
We've heard the figures many times: motors account for 65% of all industrial power consumption, and yet only 25% of motors are fitted with variable speed drives. But use a variable speed drive to control a motor with an appropriate speed profile for the task in hand, and you can slash that motor's energy usage. Last year the government woke up to the fact that use of variable speed drives represents one of the best ways to reduce the UK's carbon footprint, bettered only by a wholesale switch to LED lighting and thermal insulation in commercial buildings.
But, as the world economy recovers from its battering of the last couple of years, a more sophisticated definition of green manufacturing is emerging. And this time it makes even better business sense, because best practice environmental measures can actually boost productivity. As ever, it is variable speed drives that can really make the difference.
Consider, for example, the stopping of large machines, or indeed any shaft driving a load that needs to be brought to a controlled stop. Traditionally, this would be achieved with some sort of mechanical brake. But these work by clamping the shaft and using friction to bring it to a stop - an inherent by-product of which is of course heat, or wasted energy. But a key feature of many modern variable speed drives is regenerative braking, which converts braking energy back into electrical energy. This energy can then be fed back into the main supply or shared with other drives by connecting their power reserves together. Not only does this save energy in its own right, but the regeneration function also makes it possible to achieve smaller, less expensive drive systems and simpler, more compact switchgear layouts.
It seems obvious, but better control of a motor on any machine or process, optimising speed and torque, means better controllability. When you apply that tighter control to the whole production line, what you immediately see is significantly increased useful output, with far fewer reject products, and a dramatically reduced need for any product rework. How many products, for example, are thrown away at the start of the production cycle as the machinery is tuned and optimised? How many more are rejected as processes drift out of tolerance? Variable speed drives can help in optimising machinery and processes from the minute they are turned on, and in keeping them at optimum efficiency throughout the production cycle. If a process is making greater numbers of useful products for a higher proportion of time, that makes you more competitive and better able to meet customer requirements. But it also means that you're using less energy per finished product.
We can apply the same thinking to the wider production cycle, which more and more today is characterised by frequent line changeovers that cater for short runs of many different products. In machinery and processes without inherent flexibility, there are significant costs in product changeovers, in terms of manpower and lost production. But once we have tighter control of those processes, changeovers from one product run to another become recipe based, with complete lines reset at the touch of a button. What would have required time-consuming retuning of motor speeds and profiles can now benefit from automatic adjustment. This optimisation of the production cycle can mean the difference between having to manufacture for stock (representing some degree of wasted energy) and being able to manufacture to order - or at the very least to a more optimised inventory schedule.
We can look at the wider plant environment, too, because every motor - regardless of its efficiency rating - generates heat. In some controlled environments, that can be critical, so if one process is generating excess heat, then another process has to be introduced to bring the temperature down - and this, of course, is using energy. Much more efficient would be to reduce the heat signature of the motors themselves - or even capturing that energy - and here again variable speed drives come into their own. The variable speed drive more closely matches the motor to the load, and so the motor generates less heat. Not only is the motor being run more efficiently, less work has to be done to compensate for the heat generated.
It is clear, then, that variable speed drives are making an even greater contribution to energy efficiency than might first be considered.
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