The old saying ‘biggest is best’ may be true in some instances, but applied to the selection of modern industrial drives it is not necessarily the case says Jonathan Smith from Rockwell Automation.
Back in the early days of industrial automation, customers would often purchase an over-specified industrial drive, so that they could be sure that it would be rugged enough to handle every need. But there was a premium to pay for this excess capacity and, in today’s lean manufacturing environment, paying extra for something you don’t need is a luxury few can afford.
By studying the application and asking a few pertinent questions, the knowledgeable user can precisely match the performance of the drive to the demands of the application. This ensures costs are controlled but performance is not compromised.
How To Analyse Your Application
The sizing of modern drives like the Allen-Bradley PowerFlex range from Rockwell Automation, has been greatly simplified by having both a normal-duty and a heavy-duty rating. By seeking answers to a few basic questions about the application, the user can quickly determine whether a normal, heavy-duty or even a larger drive is required. By abandoning the old ‘one-size-fits-all’ approach, users can save money and reduce panel space requirements.
The selection criteria starts with knowing the load requirements and selecting a drive with enough current to meet that need. Whether you are moving coal, air or boxes, all have varying torque demands, and their characteristics determine the most appropriate drive solutions.
The first question to consider with any application is, “Do I know the torque requirements that will make the process work?” Since this information is required to select an appropriately rated motor, it should be available to properly size the drive.
The Importance Of Load Data
Most loads can be broken into one of three categories:
• Variable torque
Almost all variable torque loads are either centrifugal fans or pumps. These make up nearly 70% of global motor applications. If the application is variable torque, then it almost always requires a normal-duty rated drive. These drives can supply rated torque with some overload (approximately 110%) for up to one minute, providing enough capacity for these types of load.
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