Variable Frequency Drives

The Blog officially opens doors on December 1, 2016 and we find ourselves under construction. Sorry for the mess. 

We are presenting topics that what you feel is a  ‘Hot Topic’ in your life, at the moment. 

We shall start our blog discussing potential energy savings devices such as VFD drive plant retrofits. Right now, your entire industry is not taking advantage of the benefits and, in some instances, are installing an incomplete system. Come learn and come share.

Variable Frequency Drives have been around for a long time varying the speed of motors. VFDs can save you energy in some instances.

I want to focus on the quick paybacks that are available at the asphalt mix plant in those some instances.

If any of your plants are  running at half the speed most the time and you run about a 1,000 hours a year, you want to read further. At the moment, we are adding three 200 hp vfds and inverter duty motors to replace the two motors at the exhaust fan and the burner fan motor. These loads are centrifugal loads lend themselves to solve a problem the utility companies would like fixed. Most utility companies will chip in a healthy rebate. The utility company is chipping in $60,000 to this project. The customer chips in the balance and finds his Payback is about a year.

The savings projection the utility company is projecting was compared to our calculations and those of other engineers in like applications.

The variable speed fans replace the variable flow dampers and the actuators. The fans begin freewheeling as the damper is being modulated so less air is being pulled through. This lighter load makes the utility company to use more power than normal to get the work done. Consequently, the user gets charged for this.

The VFDs work well with the utility companies and the rest of the equipment on the power grid when properly filtered with reactors.

When you have an application like this, get your utility company and a consulting-contracting company that can work with your utility company to install what is beneficial to both the utility and the customer.

Since you are changing air flows in the combustion process, a consulting-contracting company that can design the electrical retrofit to your application and adjust the air to fuel ratio with a combustion analyzer is important.

So, it was a good idea on commercial power. How good of an idea are VFDs on portable generators? It appears to us, you are probably better off staying with damper control. Contacting your generator service department is a good start when you must add VFDs. They will probably suggest adding a Harmonic Inhibitor besides line and load filter reactors. Now you are loading up a portable plant with a bunch more heavy and big components.  I am not sure you want to go here.

Some people are adding VFDs to adjust the speed of their drum. In most instances, users are just varying the speed 5% to 10% to get the greatest heat recovery from the exhaust gases. This speed reduction is not much, normally does not require changing the motor to an inverter duty motor. The motor shaft does require grounding. A split ring, brush grounding kit must be added to each motor.

Clarence Richard

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