marke

Adding a VFD (Variable Frequency Drive) to a motor running at a fixed speed and continuing to run the motor at that speed, does not make the motor efficiency improve except where:

The motor is very underloaded and a reduction in voltage will reduce the flux in the iron and thereby reduce the iron losses in the motor, BUT

1. The reduction in voltage applied to the motor will :
   1. reduce the magnetising current
   2. reduce the flux in the iron and therebye reduce the inductive current flowing in the motor
   3. Increase the slip in the motor, thereby increasing the slip losses
   4. increase the work component of the current flowing in the motor
       
2. Reducing the flux in the stator can result in an element of energy saving  BUT
   1. Reduced Flux ==> reduced Iron loss
   2. Reduced Flux ==> increase slip loss
   3. Reduced Flux with an open shaft motor ==> reduced line current and reduced copper loss
   4. Reduced Flux in the motor with load current equal to or greater than the magnetising current of the motor ==> increased motor current and increased copper loss.
       
3. At line speed, the potential to save energy by using a VFD is limited by the true losses due to the use of an induction motor. With many modern machines, the efficiency is is typically quite high and until the load is very low and the actual iron loss is commonly less than a few percent of the full load of the induction motor.
    
4. The iron loss is independent of the load, but there will only be a net gain when the load is very low, BUT the addition of a VFD to control the motor can reduce the iron loss by a small amount, but there is an immediate loss of two to three percent due to the the additional losses inherent in the additional losses in the from the use of a VFD.

Definitely still here and I check the forum every day without fail, but everyone has scarpered to facebook et al.

Feel free to post questions, you will get answers, but most discussion forums have died off due to a fascination with the facebook/linkedin social media platforms.

While there is limited posting here at present, there is still a large volume of traffic and it appears to be used as a resource by many, but the focus has shifted to the social media platforms and theyn are slowly dying. LinkedIn had very active groups, but they got hijacked by the advertising Spam people and have essentially died. I am not sure what will be the next platform. In the meantime, come back and ask your questions, you may be surprised who answers!!

Best regards,

Mark.