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Last issue, we discussed several factors which can influence the decision regarding the type of VSD – stand-alone module or packaged drive – to utilize for your application. These factors included the configuration of the drive you are seeking to replace (if this is not a new application); available space; ambient conditions in/around the installation site; and peripheral equipment to be connected to the drive.

Other factors can play important roles as well. For instance, safety and code compliance can heavily impact the VSD configuration to choose. For instance, packaged drives which are UL labeled provide assurances that the assembly is properly built, tested, and suitable for its rated output. While not all installations require UL labeling, the assurances it provides can more than offset the nominal cost for obtaining it. And while many stand-alone drives are UL labeled, a packaged unit ensures that the upstream disconnecting means, overcurrent protection, and any associated peripherals are specified and installed in compliance with applicable codes – which can translate to less work by field engineering and installation personnel.

The installation of any VSD requires properly rated disconnecting means and over-current protection installed in conjunction with the drive. (A basic VFD power wiring installation is shown in Fig. 1 below.) […]

There are a number of things to consider before deciding if a variable speed drive (VSD) is right for your application. These considerations can be roughly assigned to one of three groups: energy usage, process/application, and hardware.

Energy Usage:

 With the rising cost of electricity and increasing demands on aging power grids, there are large incentives to reduce power consumption wherever possible. According to US Department of Energy statistics, electric motors consume approximately 68% of industrial energy usage, and a significant majority of these could see energy reductions when controlled by VSDs. Couple this with the fact that nearly 96% of the total lifecycle cost of motor ownership is electricity consumed, and you can see that there can be real cost benefits to VSD use.

There are numerous sources online to assess VSD energy savings. For tools to estimate the energy savings your application might realize, go here or here.

Process/Application:

If the process or application you are considering uses a motor to drive a variable torque load (also referred to as a quadratic torque […]

January 14, 2015

Welcome to the new and improved Joliet Technologies website. This is the look of our new site.

We have converted it to a responsive site design, which means it will be viewable on all devices and the functionality and content will remain the same whatever device you are viewing it on.
It has always been our goal to have the user experience be the best possible on our website and hopefully this new design will do just that. Our new user interface allows you, in most cases and on most devices, to navigate to any page on our site with just one click.

Also we have increased the security of our site by switching to https, so whenever you are on our site anything you do is encrypted. Your connection to https://joliettech.com is encrypted with 256-bit encryption & the identity has been verified by COMODO RSA Domain Validation Secure Server CA.

All the content on our site […]

January 14, 2015

We have completed the process of re-designing our website. This will be the new look of our new site.

We have converted it to a responsive site, which means it will be viewable on all devices and the functionality will remain the same whatever device you are viewing it on.

Also we have increased the security of our site by switching to https, so whenever you are on our site anything you do is encrypted.

All the content on our site should remain the same, some pages may be updated to reflect the current status of our company and our products and services.

If you have any questions and/or comments, please feel free to contact us directly at info@joliettech.com.

The causes and effects of VFD-supplied motor shaft and bearing currents, as well as measures to counteract them, have been exhaustively covered in literature. However, as a drive and motor supplier, we frequently receive requests for information on this topic. So a summary seems in order…

Basically, shaft currents are induced because of the high frequency of the voltage pulses sent to the motor from the VFD. Recall that a pulse-width modulated VFD creates a synthesized sine wave by firing its output transistors many thousands of times per second. These pulses form high-frequency waves sent along the motor cable to the motor. Since impedance is inversely proportional to frequency, the capacitances of the cable and motor present little or no impedance to these high-frequency pulses. As a result, circulating currents can readily flow in the motor shaft. With sufficient magnitude,  and in the absence of corrective measures, these shaft currents can pass through the bearings and races to the motor frame, causing bearing pitting or “fluting” – regular, tightly spaced grooves on the bearing races – via a process referred to as Electric Discharge Machining (EDM). Ultimately, these irregularities will cause bearing failure.

Cable length and characteristics are often important factors in ensuring a high quality, dependable drive installation. Certain applications simply require a long motor lead length; moving the motors and/or drives closer to one another may be too costly or space constraints may prevent it. There are the normal cable capacitance, high-frequency pulse, and voltage drop issues, of course, but what if additional motors are added to the mix? Let’s look at one reader’s question:

Q: I intend to connect 6 fans each 1.5 kW to a single VFD unit. The largest distance between the VFD unit and a fan is 25m. However, the total length of cables connected to the 6 fans is about 120m. Is the distance from the drive unit to the most remote fan the significant parameter or is it the total length of cables that is connected to the unit?

A: The most important consideration in the case of multiple motors connected to a single drive is the length of the leads between the VFD and the point of common connection of the […]

Those of us who’ve experienced unexpected failure of variable speed drives may be interested in an analysis of the following problem:

Problem: A plant operating a large number of VFD’s is facing the problem of  spikes resulting in damaging of  the drives. Can you please suggest some means to overcome this serious problem? The plant has its own generation through its gas-operated engines and during gas shutdown the plant is supplied power through furnance oil engines. Power is generated at 11Kv and is stepped down to 400 volts through step-down transformers.

Analysis: It’s almost always advantageous in cases like this to take the “top down” approach; that is, start by investigating system elements common to all of the components being affected. If you find a problem, it may just be that correcting it will resolve all of your downstream issues. Power supply stability/quality should be checked first. If incoming sources are surging/sagging, why?  Are the power supplies stable under conditions of varying load? If not, it pays to understand whether the generators are sized properly and the controls/monitoring equipment are in good working condition. Keep in mind also that it is possible […]