Saturday, May 10, 2014

Power Saving by Using Variable frequency drives (VFD'S)

As VFD’S are used for speed control specially in Fans, Centrifugal pumps, compressors etc. In that cases flow is proportional to current so whenever flow to be reduced it will leads to lower power drawn by induction motor which leads to lower power consumption depending upon the flow requirement.

There are some facts which you must know:-
According to Laws of Affinity:-
1. Speed is proportional to current flow.
2. Torque is proportional to the square of the speed change
3. Horsepower is proportional to the cube of the speed change.

VFD’S will be power savings upto 33% below that we can’t achieve power saving by reducing the speed. VFD’s speed can be either controlled by either connecting Potentiometer or directly from VFD.
Also it should be noted that if you don’t require speed control or flow control means induction motor will always run at full load then there is no use of connecting VFD as that will not leads to any power saving at all.

Mostly everyone got confused that VFD’S will always lead to power saving even sellers misguide consumers about VFD’S.
But Just think that if VFD’S will always saves power then everyone will install VFD’S and save power.


No Power Factor correction required:-

There is another advantage of VFD is that there is no need of capacitor bank for induction motors if VFD’S are installed as VFD’S has inbuilt capacitor . So no need of power factor correction required. This is leads to savings leading to installation and maintenance of capacitor bank.

Lower load applications:-
There are certain cases where load is lower and needed to de-rate the motor so as to keep MDI in limits than in such cases VFD's are best to be used. In such cases frequency is reduced so this will leads to lower power requirement of motor. This is also lower rpm of motors .