Variable Speed Drives 3

[lindalee]

I have an existing 4000-cfm belt-driven process roof exhaust fan with a 3/4-hp electric motor. I am considering to install a VFD to control the spped of this motor.

Will this cause an undue hardship opn the motor?

 

[friartuck]

Probably not. Just check that the motor and VSD are compatible. The inverter manufacturer will tell you.

Also, the drives usually come with a set up manual..(Usually about a foot thick). Either read it from front to back, or get an expert to set it up for you.

If set up properly, your motor will run ok and save you lots in energy. It will also provide good overload protection.

If set up badly, you may get noise and weird harmonics. Also get a reputable inverter drive such as Danfoss or ABB. Dont go for cheap.

The drive can also be set up to start very slowly which will reduce slippage of the belt.

Friar Tuck of Sherwood

 

[ClydeMule]

We have had problems with 3 phase motors with internal overload protection. At low requencies the protector trips erroneously.

Also make sure the insulation can handle the VFD, that is the biggest problem. That is why there are now "Inverter Duty" motors.

Clyde

 

[pennpoint]

lindalee
Also, be aware of the changes to your fan performance (fan laws) when increasing/decreasing motor speed and how it effects the motor hp.

Regeards
pennpoint

 

[friartuck]

One last tip

Don't fit an isolator AFTER the inverter, i.e. most people would install the cable, then the inverter (in some convenient position) and then to comply with regs, an isolator at the motor. If you isolate the motor this way, you might not have an inverter..but just a pile of useless electronics.

The way we do it is take the cable to the motor.Fit an isolator. Then take the cable back to where you want to fit the inverter. Then go from the inverter to feed the motor. Its a bit snaky but you isolate the power upstream of the inverter which stops it going bang.

Also, dont exceed the maximum distance between the inverter and the motor. It varys between makers.
Excessive lengths cause interference.

In the UK we fit filters to cut out the 'noise' generated by the inverter.

Friar Tuck of Sherwood

 

[lindalee]

Thanks, everyone, for your kind inputs.

Lindalee

 

[lilliput1]

Does it pay back to control the speed? What control scheme wil you use to control the fan speed? Will you make the process take longer if you reduce the fan speed, therby penalize productivity?

 

[lindalee]

Lilliput1,
What we plan to control is cooling air, which is 100% outside air in an industrial facility. A space thermostat will dictate fan speed, in wintertime, to save on heating bill. Process is not affected.
Thanks for comments.