Installation of Inverter Instead of Star Delta Operation

At least one of the pulleys must be replaced, because the drive ratio will be different.

Thanks for the prompt reply you will recommend to replace the fan pulley?

It might depend on the sizes of the existing pulleys. If the motor pulley is now small in relation to suitable belt bending radius, I would opt for increasing it rather than reducing the fan pulley. This will also reduce overhung bearing loads.

i m not expert but u should change pully of fan side & fit same pully as 22kw motor side pully. In short u should maintan both pully of same OD.

What if motor rpm of 1000 is to match fan rpm of 750, and motor rpm of 750 is to match fan rpm of ~560?

some one out of cr4 forum is advising not to replace the existing pulley of motor and fan.any comments thanks

Is this advice on another thread about the same topic?

no got this information on phone

Why not control the motor speed between 1450 and say 1000 rpm? No need to change the pulleys then.

in case we maintain the speed of motor between 1450 and 1000 rpm and retain the same pulleys as suggested by you than what will be the rpm of fan

Some one alerady asked

The fan rpm required is 750

But you want the motor RPM between 1000 to 750 RPM? ie you want a VFD drive and that means the fan RPM will also change (Repat from the previous query not answered yet)

One interesting part (I am not sure that I am right though) is that the motor power is a bit derated at lower frequencies (VFDs are supposed to be constant torque fellows so power will go down with the speed. The 22KW motor at 1000 RPM will not give the same power. But the fan (still at 750 RPM as earlier) will demand the same.

Question - if your motor speed is 750-1000 RPM why didn't you go for a 6 pole (Synch speed 1000 RPM) with a VFD to bring it down upto 750?

thanks for the guideline but the client wants to retain the existing siemens motor 22kw, 1450 rpm.client intrest is to go for vfd to control the rpm of the motor say from 1450 to 850 and wants the fan rpm to be 750-800.please dont mind my question in case it has simple solution.

On the theoritical front -

The VFDs work on constant V/f ratio (to maintain the designed flux density in the iron)

So the 1450 KW motor 22KW you want to run at 1000 /850/750 RPM. A simple calculation

V_vfd = Voltage to Keep the V/f constant

New Power = V_Vfd I Cos φ = (V_Vfd/V).V.I Cos φ = (V_Vfd/V). P_{rated freq}

Since the VFDs normally keep the current constant. And that is not usually increased either due to the copper constraint.

RPM Equiv Freq V_vfd P_newfreq Power (Derating to)

1450 50 Hz 415 V 22 KW 100%

1000 34.5 286 15.2 69%

850 29.3 243.3 12.9 59%

750 25.86 214.7 11.4 51%

Usually it wont matter since the fan load would have gone down with RPM and the usual motor would have been sufficient. But now you want to use a normal 22KW/50Hz motor at 34.5Hz and that means its rated power output will be 15KW and not 22KW. If it can withstand that derating then of course the RPM will later go down and derating will be taken care of by the reduced load demand.

Look from this aspect and then only go about with your pully/ any ther drive train modification. The pulley is simple

It will be the new RPM (1000) Vs Fan (750) now instead of the earlier 2:1

Depending upon your belt section (A,B,C..) there will be recommended diameter of the pulley. If both the new pulleys are in the range of the specific belt, then go for it. Any way if well selected in the previous system the smaller belt (motor) would have been in the range so the fan can be changed to the new.

thanks for the detail solution. will request the client to work on the basis you have suggested.they have now installed inverter which is suitable for 18.5kw motor instead of 22kw motor. .one drawback with the client maintenance department is that they are doing experiment on pulleys.first they changed the fan pulley than they changed the existing 22kw motor pulley and brought down the rpm of the motor to 600rpm and of the fan to 750-850 rpm.but the result that is energy saving is not according to their requirement in terms of kwh . hope you will update me when needed thanks

Kids riddle?

You must Change 1 Pulley at least.

Now that you are changing to VFD motor - better to change the new motor's pulley.

If as you say your fan rpm "required is 750" you cannot have any pulley--you need direct coupling.And VFD is a waste- because you need to have 750rpm out of motor.

So help you God.

I agree with @MUKULMAHANT.

This is simple really. If you opt to calculate by pulley ratios, then, you can play around with the size of the pulleys. calculate by simple math, and get the ratios, assumingly that the motor rpm wont drop not even 0.5% (if its that critical - but for a fan/blower, should be ok). Most customers nowadays, they will prefer using VFD or Inverter if they need to pre-program them, let say, at certain time the speed run at 1000rpm, and other times remain 'jog' at 750rpm etc.

And to change to pulley into a same size, is a no-no. because, might as well, just use a direct coupling. unless, you are unsure wether one day the customer will come back to you asking to change back to pulley system or not.

thanks for the guidance.but the client wants to retain the existing siemens motor of 22kw he is only intrested to install inverter so that it has final effect on his energy consumption(kwh). as replied earlier the maintenance dept is carrying different options i.e changing of pulleys of motor and fan.the manegement wants to keep the motor pulley and if necessary replace the fan pulley.will highly appreciate any further suggestion from your side

What does the centrifugal fan supply that is attached to the motor?

it supply fresh air to the plant

I would assume that it is set up as CV to the plant. In that case I would agree with all the previous advise, you will need to change one of the pulleys to maintain proper air flow on the forward curve fan when reducing hertz to the motor.

What may be a better option and less expensive than the VFD would be to (though the owner does not want to change the motor) replace the motor with a premium efficient motor. The are designed to provide energy savings at full amperage draws all based on their power factor curves.