Understanding Variable Frequency Drives (VFDs) for Energy Efficiency in Industrial Motors ??

[marcellosalas]

Hello everyone,

I am exploring ways to enhance energy efficiency in our industrial motors and came across Variable Frequency Drives (VFDs). I understand they help control motor speed, which can potentially reduce energy consumption. However,, I have a few questions ::-

What is the actual impact of VFDs on energy savings for different motor loads, especially in variable vs. constant torque applications: ??
Are there specific conditions or motor types where VFDs may not provide significant efficiency benefits: ??
How challenging is it to integrate VFDs with existing older motor systems, and what should we consider for a seamless installation: ??

Any insights from those with VFD experience in industrial setups would be very helpful !! Also; if anyone has seen noticeable ROI improvements after VFD implementation, I would love to hear about your results.

Thanks in advance !!

 

With Regards,

Marcelo Salas

[marke]

Hello marcellosalas

Welcome to the forum.

You have asked an interesting and potentially contentious question.

There is a lot of myth and intrigue when it comes to energy saving and the VFD has been promoted very strongly as the means to solve the energy and the carbon crisis of the planet.

I would answer :

1. The VFD increases the losses in the motor by a very small amount due to the frequency components in the waveform. These comprise switching components and harmonics.
   The claims are that the VFD will improve the efficiency of the motor and that is wrong.
    
2. Energy can be saved in some instances by slowing the machine down where full speed is not required, but the work output will drop also and often to achieve the same total work output, you can slow down and run for longer!
   In the case of circulation fans in say a cool store, energy can be saved as less air needs to be moved when product is down to temperature and the store remains sealed.
   Likewise, circulation pumps just circulating water in a pond will reduce energy consumption where less circulation is required.
   Transferring water between sumps can save energy where the maximum capacity (throughput) is not required all the time. Reducing the flow will reduce the frictional losses, but will result in longer pumping times.
    
3. Applications where the motor is oversized, but still needs to run at full speed, will not save energy.
    
4. Applications where the speed is constant and the coupling means has been designed for full motor speed, will not save energy.
    
5. Pumping applications with steep curve pumps and variable flow demands can save energy where they are operating under constant pressure conditions.
    
6. Pumping applications with flat curve pumps with the impellor selected/machined for design pressure at full speed will not save energy under constant pressure control.
    
7. Commonly, the VFD has losses in the order of 2.5 - 3%. If harmonic mitigation is required, you should expect another 3% losses.
   The myth that you can use a high efficiency motor, but must add a VFD to a low efficiency motor to improve the motor efficiency is totally incorrect!