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Efficiency clarification on the use of VSDs

Efficiency clarification on the use of VSDs

Efficiency can't be effectively measured for motor specifically designed to operate with a variable speed drive. So should these types of motors be excluded from the regulations, ask the experts at European Automation?

There is some debate as to who originally invented the incandescent light bulb. Some say Thomas Edison whilst others say Sir Joseph Swan. There are also those who claim both of these great minds were merely tweaking existing devices. What is certain is that the incandescent light bulb is going the way of anyone that staked a claim on its invention.

Today, Argentina, Australia, Brazil, Columbia, Cuba and Mexico have already prohibited the use of the highly wasteful bulbs, while Canada, China, the European Union and the United States are in the process of turning out incandescent light bulbs for good because of how inefficient they are.  

In the European Union, we have the Ecodesign Directive to thank for ensuring wasteful electrical products are gradually becoming replaced by more efficient ones. The directive stipulates the ecological requirements of electrical products manufactured and used within the EU. The incandescent light bulb is just one product that doesn't make the grade. In fact, the phasing out of the bulbs is predicted to reduce annual CO2 emissions by 16 million tons in 2020.

A far bigger offender than the infamous incandescent light bulb is the electric motor, accounting for about two thirds of industrial power consumption and about 45% of global power consumption as a whole. Ensuring maximum efficiency from electric motors is a must.

In 2014, the Department of Energy and Climate Change (DECC) released a preparatory study that identified the environmental improvement potential for products outside the scope of Regulation 640/2009 of the Ecodesign Directive. This study is called Lot 30 and refers to special motors and variable speed drives (VSDs).

In September 2014, the Institution of Engineering and Technology (IET) responded to a request for comments regarding Lot 30 and highlighted some interesting points within the draft regulation.

The points that the IET picked up on were in regards to the unclear efficiency regulations concerning VSD and motor combinations. The difficulty in regulating the area stems from the flexibility of the modern general purpose VSDs. Energy losses depend closely on operational settings. For example, if a VSD has a low switching frequency, losses would be much lower than practical operations settings. However, this isn't taken into account by the current framework of the Ecodesign Directive.

A beneficial feature of the modern VSD is that functionality often spans beyond conventional motor control. Sequencing, process control, motion control and system control are associated with using more energy than an average VSD function. These are important elements of drive system design and energy loss from these should be excluded from maximum loss figures so as not to discourage designers.

The main problem is that efficiency can't be effectively measured for motors that are specifically designed to operate only with a VSD. The IET recommends instead that these types of motors be specifically excluded from the regulations. Furthermore, the IET commented that current regulations don't explicitly address the difficulty in calculating the overall efficiency of a motor operating in tandem with a VSD. Its recommendation is for a review of this combination in the next assessment process.

The IET also highlights the increasing sales of VSDs for medium voltage motors (1-35kV) and recommends that this be taken into account in the next assessment process as well.

The final point raised, and one which we here at European Automation agree with unwaveringly, is that there needs to be more onus on the manufacturer to ensure access data for each model and build variant. Countless times we see clients unsure about what part they need once a breakdown has occurred. Who can honestly say they are completely aware of the year of manufacture for every motor in their plant? But if things go wrong, you might well need to know, and quickly.

That's where European Automation comes in. Regardless of whether or not you're running a motor or VSD that is now obsolete thanks to the Ecodesign Directive, we can find and replace those parts, sometimes in as little as nine hours. No incandescent bulbs though. Sorry.

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