VFD Control and Blower Life

It's very unlikely.

Two things to think about-

If the motor is "VFD rated"- meaning that it has higher cooling capacity than "standard" motors, it will not be affected by the VFD speed changes. If it is a standard motor retrofit with a VFD, its live will be lowered due to heat increase degrading insulation, causing drying and cracking and ultimately an internal short.

The "life" of the motor (assuming it is a rated unit) will INCREASE because wear on bearings is directly related to the inverse square of the speed ratio- a motor running at 50% speed will last 4 times as long (look up formulae for sizing bearings). Also- the power consumed by the motor is the inverse cube of the speed ratio- 70% speed will only draw about 35% (0.7x0.7x0.7) of full load power (while it does 70% of the work) and the motor will last nearly twice as long (1 / (0.7x0.7)).

The other issue is that the rate of speed change is likely relatively slow as it tracks the loads which normally do not change drastically.

Besides, if you are increasing the speed beyond rated speed of moter, it will fail as the insulation is not designed for the certifugal forces.

thanks for the info.....ur info is more to motor....i want info regarding blower .....will the blower impeller get affected due to this speed change frequently....

If the speed changes are not sudden, it should not affect the life of blower. Sudden changes means high accelaration, decellaration means higher forces.

Sudden changes may creat fatigue and lead to failure.

the life time of your blower will not be affected by the change of VFD motor speed in conclusion.

First, you can not increase the speed too much since motor will trip. this means that increasing the head by increasing the speed will have very apparent limitation.

You may decrease the speed and lower speed will not badly affect the life time. You can but will not decrease the speed too much since head will not be sufficient. This means you also have the limitation on decreaing the speed.

Sudden change in speed sufficiently rapid to affect the life time of motor and blower can not be achievable since converter(and motor) can not generate the rapid change in torque in a really short time.

your bearings must be anti-friction based on my experience.

don't worry. they can withstand much lower and higher speed and frequently change also as long as the lubrication oil is always nice.

I forgot to log in before reply to your question.

Reply one more time

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the life time of your blower will not be affected by the change of VFD motor speed in conclusion.

First, you can not increase the speed too much since motor will trip. this means that increasing the head by increasing the speed will have very apparent limitation.

You may decrease the speed and lower speed will not badly affect the life time. You can but will not decrease the speed too much since head will not be sufficient. This means you also have the limitation on decreaing the speed.

Sudden change in speed sufficiently rapid to affect the life time of motor and blower can not be achievable since converter(and motor) can not generate the rapid change in torque in a really short time.

your bearings must be anti-friction based on my experience.

don't worry. they can withstand much lower and higher speed and frequently change also as long as the lubrication oil is always nice.

If you are varying the flow by reducing speed, the resultant blower life will be greatly increased since you are doing less work at lower speeds. Ensure that all lubrication is OK at lower speeds which it normally is.

Changing the speed will have very little impact since you should do this within normal torque availability at the motor, stresses and strains are generally much lower using VFD when applied correctly so you can change speed as often as you like in my opinion and experience.

If the motor is a standard motor it should be suitable for VFD, if its an integrated unit in the blower, check with manufacturer / supplier. The motor should also be more optimised and run cool at lower speed and, therefore, lighter loads. Fit the VFD within 20m of cable to the motor (closer is better) to avoid any transmission line issues and you should have a hassle free long life.