Feature Drives & motors
It’s all about location, location, location!
Selecting the right location to mount a variable speed drive will save time, trouble and money. Stephen Takhar of Vacon UK explains why
W
hile mounting AC VSD’s in a control panel with a PLC was a convenient arrangement for traditional automation systems, it did have its disadvantages. For a start, not only were the cables connecting the drives and motors often ten or more metres long, but screened cables usually have to be used for these connections, and those with a high current rating are expensive and difficult to work with.
Furthermore, VSDs also generate heat. So, if mounted in a control panel, provi- sion has to be made for removing this. A large control panel with several drives can also be hard to accommodate. So what’s the alternative? An option
that’s attractive in many applications is to use drives with a high IP rating and mount them without additional protec- tion on, say, a convenient wall close to the motor. It is, however, important to exercise care when choosing VSDs that will be mounted in this way.
Points to consider
A high IP rating – IP55 or better – is essential, but on its own that may not be enough, especially if the drive is to be mounted outdoors. In these instances, the operating temperature range of the drive must also be considered. Even in the UK in winter, temperatures well below freezing can be encountered; while in direct sunlight in the summer, exposed metal surfaces can easily reach 40˚C. It is therefore important to choose VSDs that, like those in the Vacon 100 MM range, have been designed to withstand these conditions. If their location is chosen carefully, wall mounted drives can do much to reduce installation costs and the amount of costly cable needed to connect the drive to the motor. Another option, however, is to mount the drive directly on the motor. That way, the motor connections are short, the drives are outside the control panel, and the space the drives occupy would usually have otherwise been wasted. The motors can also be delivered to site with the drives already mounted on them, reducing drive installation and wiring time on site to zero.
While the drives are now likely to have longer control connections, this doesn’t tend to be an issue these days, as
nearly all modern automation systems use fieldbus or networked connections.
So, those long control connections are just a few metres of inexpensive network cable. With the benefits being clear, why aren’t more drives mounted on motors? Choice of motor and ease of servicing are among the reasons, and it’s important to note that there’s a big difference between a drive that can be mounted on almost any motor, and a drive that’s integrated with a motor. In the first instance, it’s possible to choose the right motor for the job and source it at the right price. In the second, the range of options is likely to be lim- ited, and prices may be inflated. Further, if the drive is separate from the motor, it can readily be replaced – but this isn’t the case if the motor and drive are integrated. In addition, sitting directly on the
motor, drives are subjected to shock and vibration. Earlier generations of motor-mounted drives were sometimes prone to premature failure under these conditions. The latest products, partic- ularly those in the new Vacon 100 MM range, have, however, been designed to withstand the toughest of operating environments.
Other common concerns are the limited range of power ratings and the lack of functionality in motor mounted drives. But again these concerns have been addressed with the latest products, which are available with ratings up to 30kW, and offer a full range of drive functions comple- mented by integrated PLC functionality.
Mounting solutions Finally, it’s worth mentioning that the wall-mount and motor-mount drives don’t have to be different products. The best drives of this type are equally suitable for both types of application, and you can even mount them in a control panel if you really want.
So, next time you use a VSD, think carefully about where you’ll mount it and remember that the right choice will most certainly save money.
Vacon
www.vacon.com
‘Even in the UK in winter, temperatures well below freezing can be
encountered, while in direct sunlight in the summer, exposed metal surfaces can easily reach 40˚C. It is therefore important to choose VSDs that have been designed to withstand these conditions’
Design Solutions OCTOBER 2013 17 Enter 210
Mounting the drive directly on the motor means the motor connections are short and the drives are outside the control panel
Stephen Takhar
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