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One factor that if over-looked can cause significant equipment issues is proper environmental protection of variable speed drives (VSD’s) and other electronic equipment. We are often requested to install VSD’s and other control components in custom enclosures which will be installed under a wide variety of ambient conditions, including high temperature and/or high humidity environments. The drive electronics are rated for operation within given temperature and humidity ranges in order to ensure longevity and proper current output, so there are real risks and cost impacts associated with ignoring environmental constraints.

Temperature:

Although there is some variability from manufacturer to manufacturer, VSD’s are generally de-rated – that is, their rated amperage output is reduced – for operation between 40°C and 50°C. F0r instance, ABB specifies that output current is to be reduced by 1% for each 1°C above 40°, and the units are not rated at all for operation above 50°. This is to accommodate the rise in resistance under higher temperatures and to protect sensitive electronics from being over-stressed. Sometimes the 50°C maximum rating will be shown in manufacturers’ information as intended for “heavy duty” or “overload” use. This should not be […]

Variable frequency drives (VFD’s) can provide significant energy savings and increases overall process/system efficiency by effectively matching the power applied to the level the process requires. By controlling motor speed, changes in load demands can be adjusted for quickly and automatically to maintain optimum process conditions. Also, the energy the driving motor needs to begin rotating, manifested as a high amperage commonly referred to as “in-rush” current, can be slowly increased to ramp up the motor while minimizing current draw. The VFD shares this soft-start functionality with the reduced voltage starter, often referred to as a soft-starter, but goes beyond this by allowing adjustable speed control. Let’s examine these two characteristics of the VFD – speed control and controlled starting and stopping – to understand how energy savings and other cost benefits are achieved.

VFD controls motor speed by comparing a reference signal to a pre-set value. The reference signal can be generated externally, for example via a process setpoint, or internally by the VFD using software to model motor parameters. The latter is accomplished by most VFD’s through the auto-tuning process during initial drive setup. It then adjusts the frequency and voltage to match the reference signal, which in […]

Last week in Part II, we discussed several electrical line-side issues which should be factored in when selecting a drive. Life would be too easy if this were the whole story. There are several critical load-side (i.e. from the drive output to the motor) concerns which should be examined carefully because they can impact equipment life and your prime mover’s ability to perform the work necessary for the process.

Load Side Considerations:

• Motor amperage: Drives are properly sized by amperage, not horsepower. In order to ensure proper output capacity, the driven motor nameplate full load amperage (FLA) should be known. It is important to note that sizing the drive based on FLA is not merely being conservative. Under the working assumption that the motor is sized correctly for the load torque needed, sizing a drive for only what the motor draws under “normal” (i.e. non-peak) load conditions may not provide sufficient torque to drive the process under heavy load conditions. Also, sizing a drive by horsepower alone ignores the amount of overload the drive can provide. For example, a 460-volt drive suited for a 75hp motor under variable torque conditions may be […]

As we discussed last week in Part I, defining your application and its specific characteristics is critical to ensuring a cost-effective and successful drive installation. In addition to the mechanical considerations we discussed in Part I, there are several electrical line and load-side issues which should be factored in when deciding on the right drive (or no drive) for your process. Because there are many factors involved we will cover supply side issues for AC drives this week, and load side next week. Future posts will discuss DC drive applications in detail.

Line (Supply) Side Considerations:

• Voltage: Modern variable frequency drives (for AC motor applications) are rated to accept a nominal voltage with a typical +10/-10% tolerance. Outside of this range, the drives will usually trip out to protect themselves. In the case of an over-voltage condition, the risk is to the DC bus, which typically runs at about 1.2x the incoming voltage level. Once that level exceeds about 1.4x of the upper end of the incoming voltage range, the drive will trip out on OV. (Note that unlike AC drives,  due to the nature of their output electronics DC drives up […]

Variable speed drives (VSD’s) are considered state-of-the-art in controlling driven processes, but it is important to realize they may not be the answer to every process control problem. End users need to understand their application requirements and mechanical and electrical system constraints in order to ensure that a VSD is the right solution, and to specify it correctly. In the first part of this series, we’ll summarize some of the main process and load characteristics which should be taken into account before specifying a VSD:

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Process Factors:

• The need for speed (…control, that is)

Many processes can benefit from the ability to periodically or continuously reduce output by reducing the speed of driven equipment. For example, piping systems are often “over-designed” to accommodate future expansion or simply provide some operating headroom. If driving the motor at full speed results in output that must be “turned down”, via control valves for instance, there is a potential to increase overall system efficiency and reduce energy consumption using a VSD. Bearing in mind that capital costs tend to be higher for VSD use, it is important […]

At Joliet Technologies, it is our business to keep pace with the advance of variable speed drive and motor technology and effectively apply that knowledge to your application. To help you help us, one of the most valuable resources we can supply is information. The old adage is true…an educated consumer is our best customer. Toward that end, we are pleased to announce this inaugural issue of our blog, “blog.joliettech.com”.

Upcoming issues will discuss topics such as:

• Variable Speed Drive (VSD) technology – the basics of form and function
• VSD’s and energy savings
• Proper VSD application and installation
• Drive-generated harmonics – their impact and mitigation
• Motor selection and protection
• VSD’s and “Soft-starters” – and when to use each
• And many more…

The format will be varied and interactive – we invite you to comment, ask questions, and provide your own perspectives and experiences. The knowledge you share will enhance the value of this forum for everyone. We will respond to inquiries as time permits, with highest priority placed on those concerns shared by the greatest number of readers. And of course we will always provide other means to contact us should you wish.

This blog is being presented by Joliet Technologies, L.L.C..

In addition to our regular website, we felt we needed a more casual place to air our views and feelings about what we do and the industry we are in. As you can see this is a very simple website.

If you have done any research at all into variable speed drives and variable frequency drives and controls, you probably have come across our website. It is our goal to provide the information you need to make intelligent decisions regarding variable speed drives and controls you use in your facilities.

It is our plan to post to this blog at least twice a month. The posts will be on a wide range of subjects. From information about our company and people that work here, to posts regarding our products and services.

Regards,
John Gierich
Owner/Administrator