VFD Drive Parameter

Dear Mr.sriram1988,

Normally the Speed of the Motor to be specified by the Buyer. The range will be 10% as Min. and 90% of the specified speed by the Buyer of the Motor will be the Range.

DHAYANANDHAN.S

Thanks for your valuable comment Sir dhayanandhan

Motor speed is 1485 rpm used as primary air fan for small boiler.

Is there is any rule that motor more than 20kw should not be run less than 20Hz (just to avoid lesser audible frequency) or any specific reasons.

Regards sriram.

If the motor is self-fan-cooled, too low of a speed may result in insufficient cooling. Each installation needs to be considered separately.

There may also need to be one or more skipped-over frequency ranges, to avoid resonances of the driven equipment.

Thanks for your reply Tornado

1) Motor has got separate cooling fan

2) Motor spec:

Power : 315 Kw ; V: 380 V ; A: 596 A

P.F: 0.85 ; Eff: 0.90 ; speed: 1485 rpm

Delta connection

class : F insulation

3) VFD now we are planning to connect was manufactured by ABB stromberg Oy (Finish). ABB announced this product as oboslete.

Sorry to hear about the inconvenience of an obsoleted product.

Another item you should check is that the motor is rated for VFD operation, which affects the insulation of the windings.

Dear sriram1988

You have referred that the Motor Speed is 1485 RPM. You can run 150 RPM approx. and above (10% of 1485 is 148.5) provided

1.The Motor is SUITABLE for VFD OPERATION, which should have external Fan, Insulated Bearing, or Bearing Insulation.

2. Earhting provided is minimum 2.5 times more than the Normal/Conventional size as that of the Conventional Motor,

3.The Cable to the Motor from VFD is less than 15 Metres.

4. Earthing of Cable Armor should be ON ONE END ONLY.

Pl. check up why the VFD purchased from China has failed and verify whether the above details are satisfied with the actual Installation.

Pl. check up the Effectiveness of HARMONIC FILTER and its level.

Pl. post the information - what was the problem,observed and reason for the failure.

DHAYANANDHAN.S

Thanks for the detailed explanation sir. dhayanandhan

Soon i will post the problem observed in the VFD.

Sriram1988

Have your company purchased motor or VFD or both together from China. You have given the kW capacity of the motor but what is the other details of the name plate like voltage , phase, frequency ,RPM etc. VFD has to be purchased to suit the motor . So your question is not clear please explain clearly so that a proper reply can be given.

Thank for your interest V.I.Abraham

1) Motor spec:

Power : 315 Kw ; V: 380 V ; A: 596 A

P.F: 0.85 ; Eff: 0.90 ; speed: 1485 rpm

Delta connection

class : F insulation

2) Motor & VFD are manufactured in china. due to heat sink problem in VFD ( trips often), we decided to replace the VFD with avaliable VFD in plant .

3) VFD we are planning to install is ABB ACS 503 model.

Dear sriram1988,

You have referred "due to heat sink problem in VFD ( trips often),..."

The above point posted by you, makes to me to conclude

1. That the Heat Generated, due to Harmonic Effect is more than the Permissible Limit or the Ventilation in the VFD.

2. The Cooling Effect for the Heat Sink is NOT SUFFICIENT.

3. Harmonic Filter is NOT properly sized.

In my earlier reply, to you, I have raised these point.

To avoid this, HARMONIC FILTER is to be properly sized. Ventilation/air circulation to cool the Heat sink should be taken CARE. If AC is provided for the VFD Panel Room, pl. ensure the Temp.is just 24 deg.C and below.

DHAYANANDHAN.S

1) yes i agree with you dhayanandhan We talked to the supplier , they informed us there is no problem with VFD . Real problem is ambient temperature ( 35 c) , suggested us to install chiller unit for the MCC room to bring down the temp to 25 C.This seem to be an expensive option for management on long run.

chiller unit installation+ running cost >= VFD energy saving

2) So we decided to replace VFD unit with ABB ACS -503. ABB unit works very well under harsh conidition.

3) We couldnt able to get any data from the VFD ,since parameter settings are locked (Password protected). Supplier are not helpful.

4) now we are using soft starter for motor.

1) Thanks for your reply.JRaef

2) Yes i am inexperienced in VFD or Field of engineering . i am not the one who is going to install that VFD .

3) I posting here ,because others (experts) can give some ideas , so that i can gain knowledge .vendors and plant engineers not so helpful..

4) sorry for my poor presentation (english skill).VFD i am talking was made in china, plant engineers are planning to replace the chinese VFD with ABB (ACS 503).

chinese VFD are vendor locked /password protected .

5) I already have the ACS 503 manual .we also had a chat with ABB .

My primary question

how to calculate minimum and maximum frequency for motor to operate safely.

Regard,

Sriram

The minimum speed for a motor to operate safely is 0Hz.

The maximum speed depends upon the load. In the case of a fan, the power varies with something like the cube of the speed, so increasing the speed by 10% over its nameplate figure will lead to an increase in current of aroound 33%. Now, if the motor is oversized for the job, it may cope. If it is correctly sized for the job then increasing its speed may result in trips on overcurrent, indicating that if more forced ventilation is required, additional equpiment would be needed.

Without visibility of the installation it is difficult to comment further.

The Maximm Frequency for the Fan Motor will be the Nameplate value, which is 50 Hz as long as this is the original manufaturer equipment and it was not modified.

if you increase the frequency above that value, you will be overloading the motor since the Power requirement for the fan is proportional to the cube of the rpm( if from 50 to 55 Hz, 55/50=1.1 => (1.1)³=1.331 ==> 1.331 * 315 = 419 kW). Therefore, the maximum limit will depend on the motor, the Fan+Ducting etc Curve Chart, and the VFD size. Most VFD can handle frequencies above the normal 50 , 60 Hz up to 100 Hz or up to 400 Hz.

As the Lower limit, below the Motor rated 50Hz (your motor), the limit will be dependent on the Boiler minimum requirement at the minimum firing load, and on the overall design.Also, on the cooling method of the Motor. Preferably, not less than 40% of the rated motor rpm, if there is no independent cooling fan(20 Hz).

You can run the Fan Motor at higher than 20Hz and close the inlet damper more to control the air volume while keeping the rpm high enough to keep cooling the motor at the low firing positions.

I hope that I understood your installation ...

Thanks for the wonderful explanation . LAA_Lucke

1) Motor has got independent cooling fan.

2) Can you explain a bit more for " if there is no independent cooling fan(20 Hz)" .why 20 Hz why not 15 Hz or other frequencies. ( any association with audible frequency range.)

Regards,

Sriram.

If the motor is cooled by an external fan, fixed on its own shaft, the cooling air volume will be reduced as the motor speed is reduced. The motor windings will not be cooled properly as designed by the manufacturer if this self cooling fan speed is reduced too much. Usually, the heating will start to increase the internal temperature if run too long at very low speed. How long and at what speed this will happen is dependent on ambient temperature and designs ...

An independent cooling Fan is driven by an independent electric motor, at a constant speed not dependent on the speed of the Motor it is cooling. This will allow lower speeds if necessary, but try not to go too low for long periods unless the motor maker is consulted.

Thanks for detailed information. LAA_Lucke

regards

Sriram.