Existing Starting Method Star Delta to be Replaced with VFD

Are any of these motors rated for use and installed in Zone 2 or Zone 1 hazardous areas?

If so, then a certified combination of Ex-rated VFD and Ex-rated motor must be selected for those ones. Otherwise, no problem.

VFD need not be of same hazardous class as motor. It may be located in safe area say electrical room.

Not in the European Union. It is a requirement that the VFD and motor be certified in combination for use in Zone 1 or Zone 2. Usually, the motor required comes out a frame-size larger than the safe area motor for the same duty, though it is best to check on the individual certification before placing a purchase order.

no they are not installed in zone 1 or zone 2.they are install in open area near the cooling tower.and no hazardous area exist in the plant

hello dear

i see any induction motor squireel cage can be controlled by VFD inverter .the more imoprtant to sett its paramater proerly .

Maher

Aside from the hazardous area issue, you can get 3 engineers in a room to discuss the need for VFD rated motors and end up with 5 opinions.

There are very good reasons for selecting motors that are designed to be used on inverters. They are too numerous for me to go into again, but this has been discussed in here ad nauseum, do your homework with the search function. But there are also very good arguments to be made against justifying the cost of prophylactic* replacement of perfectly good motors. If you are concerned and on a tight budget, there are perfectly good solutions that can mitigate the problems associated with running non-inverter duty motors from VFDs, most will cost less than replacing the motors. Some inverters now come with some of these mitigating capabilities built-in, but there are myriad side issues that must be considered, many will be specific to your installation and power system. This is something you need to discuss in detail with your VFD suppliers before you buy anything.

*(Word of the Day, please try to use it in as many posts as you can today.)

All valid points.

The Bakelite and grounding methods on a motor designed to run with a VFD are Superior to an inverter rated, high efficiency motor. Usually on braking the drives dump their back feed through the stator and its bearings to the casing for grounding. this causes premature bearing wear.

A simple motor brush kit or even ceramic bearings are the simplest solution to having a motor last longer though not designed for a VFD.

If you are talking about starting method, my company is considering the replacement of the standard Y/D starter with a soft starter due to the fact that it is mounted in the pump head. The soft start is much less complex and is very compact. The drawback at this point is cost.

Again this only involves starting method.

thanks for the reply .starting is not the case its the speed control that is they want to control the flow of water

If they will be slowing the motors down in a pump application then the motors may well need to be modified to incorporate external cooling fans - not shaft driven.

Yes i agree with your comments external cooling fan will be needed because when speed of the motor will be reduced ( motors can get hot if they run slower than their rated speed if motor overheats, bearing and insulation life will be reduced) it will affect the motor cooling system as well .S o inverter duty motors have that in mind.It is recommended that when the turn down ratio is 5:1 than a motor with separately powered cooling fan is used so that the fan runs at full speed regardless of the motor speed .this is what your answer mean

Please let me know that the motor used with inverters has spike resistant insulation on the magnet wire because the fast rise time and steep wave from the PWM output will create what are called standing waves in the conductors.these waves travel up and down the conductors and can be additive/ cumulative to the point of reaching voltage levels far exceeding what is used on standard insulation.what happens is a turn to turn short in the first turns of the motors..

this information was passed to me by my friend but he insists that i should clear this point. i hope some one help me out and obviously with some more points thanks.will it be possible to point out pay back period by replacing D.O.L. with VFD

Dear Mr. Salahuddin,

The Answer is NO, because the Motor design for VFD application is different in terms cooling, insulated bearings or provide insulation for the conventional bearings.

For cooling it may be possible to provide external cooling, but bearings should be insulated bearings or provide insulation for the conventional bearings and this may pose problem.

Some times you may have to provide a dedicated earth flat to the Motor from the VFD drive Panel directly and this is NOT REQUIRED for Conventional Motor.

Thanks,

DHAYANANDHAN.S, INDIA.

DEar DHAYANANDHAN.

Thanks for your reply will follow your instruction and will inform the client accordingly.

In the meantime can you please pass on some details on 1) what are insulated bearing and what you mean by 2) " earth flat to the motor" thanks

Zia

Dear Mr. Salahuddun zia,

Sorry for the delay in replying to your query.

NEED FOR INSULATED BEARING OR PROVIDING INSULATION FOR THE BEARING of the VFD MOTOR:

The CIRCULATION of Shaft Current in the V.F.D DUTY MOTOR will pose a SERIOUS PROBLEM hence to avoid the current circulation in the rotor shaft- INSULATED BEARING IS TO BE PROVIDED in the Non-Drive End of the Motor (OR) provide conventional Bearing with Insulation to the Outer Race of the Bearing.

2nd Part of your Quiery - The Conventional Motor body will be earthed with 6 or 8 Swg. wire. this is not Sufficient for V.F.D Motor.

A DEDICATED EARTH FLAT for the Motor should be provided with Half the cross sectional area of the Neutral - to take care of or NULLIFY Hormonics Effect.

Thanks.

DHAYANANDHAN.S

Dear dhayanandhan

Solution in time or late is always welcomed.A very special thank-you dhayanandha for your answers. can you please let me know why it is recommended to place the insulated bearing in the Non-Drive end of the motor.regards